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Environmental Science River Pollution
Ellen Wohl
  • LAST REVIEWED: 10 May 2017
  • LAST MODIFIED: 29 September 2014
  • DOI: 10.1093/obo/9780199363445-0003


People who are not researchers are most likely to intersect environmental science in the context of protecting or restoring a place or species about which they are concerned, or in the context of pollution—trying to understand the sources and effects of contaminants, or trying to prevent or remediate environmental contamination. The works in this entry address pollutants affecting river ecosystems, including the people who live within or use resources from those ecosystems. Pollution is commonly subdivided based on the primary medium affected by contamination, creating categories such as air pollution, soil pollution, freshwater pollution, groundwater pollution, or marine pollution. In reality, of course, all of these media are intimately connected. Atmospheric deposition of contaminants pollutes soil and water bodies. Contaminated groundwater seeps into rivers, and contaminated rivers recharge groundwater aquifers. Fluxes of water, sediment, solutes, and even organisms carrying contaminants within their tissues create vectors to disperse pollutants. This is one of the great challenges to understanding and mitigating pollution: the contaminant is seldom an inert substance that stays in one place. Another great challenge is that there are many different types of contaminants, including human and animal wastes such as sewage or intestinal bacteria, excess nutrients, heavy metals, petroleum products, radioactive isotopes, and an enormous array of synthetic chemicals such as pesticides and personal care products. Each type of contaminant can disperse through environmental media, combining with other chemical compounds to form metabolites that may have different levels of toxicity for organisms or different dispersal mechanisms than the original contaminant. Yet another challenge in understanding and managing pollutants is that a substance that is harmful to one type of organism may not cause harm to another type of organism, but detailed knowledge of how individual pollutants affect the spectrum of living organisms is almost never available. Consequently, the environmental standards set by government agencies for maximum permissible levels of contaminants are based on very limited knowledge and are likely to be inadequate. Most of the standards are also based on acute effects that show up very quickly. Contaminant levels below permissible standards can cause chronic effects—subtle but pervasive changes that eventually degrade the health of individual organisms and populations. Some chronic effects result from bioaccumulation, as an organism accumulates contaminants within its tissues over the course of its life, and biomagnification, as organisms pass on their accumulated doses to predators or scavengers.

General Overviews

The works cited in this section provide broad overviews of topics, including the diverse types of contaminants that can be present in river environments, as well as the physical and chemical properties and environmental toxicity of these contaminants; methods of sampling contaminants in water, sediment, and biota; regulatory standards for contaminants and how these standards are established and enforced; and methods of mitigating or remediating river pollution. Edzwald 2011 focuses on these issues in the context of drinking-water quality, whereas Haslam 1994 focuses more on the effects of pollutants on river plants and animals. Steingraber 1998 provides a highly readable account of the sources of environmental contamination, including rivers, and the effects on human health. Wohl 2004 examines diverse sources of river pollution across the continental United States in the context of historical developments in technology that result in pollution. Gallo and Ferrari 2008 includes treatments of these issues in several countries, facilitating comparisons between countries and regions. Both Smol 2008 and Heim and Schwarzbauer 2013 provide a good introduction to using river sediments to understand the contemporary distribution and historical dissemination of pollutants. Jain 2009 exemplifies book-length treatments of pollution in individual rivers, in this case the Yamuna River of India.

  • Edzwald, J. K., ed. 2011. Water quality and treatment: A handbook on drinking water. 6th ed. New York: McGraw-Hill.

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    This book provides an overview of diverse sources and types of water pollution, and of drinking water standards and regulations, but primarily focuses on treatments to improve water quality. Individual chapters cover both theory and practice with respect to specific water treatments.

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  • Gallo, M. N., and M. H. Ferrari, eds. 2008. River pollution research progress. New York: Nova Science.

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    This edited volume includes twelve chapters summarizing diverse aspects of the state of the science as of 2009. These include case studies from Russia, the United States, Greece, Brazil, and Zimbabwe, as well as overviews of processes, modeling, human perceptions, and different types of river pollution.

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  • Haslam, S. M. 1994. River pollution: An ecological perspective. Chichester, UK: Wiley.

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    This book provides an overview of different types of river pollution and how pollution affects river biota. The writing is readily accessible to nonspecialists, but includes extensive referencing for research uses. Although now more than twenty years old, this text is a good introduction to the topic of river pollution.

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  • Heim, S., and J. Schwarzbauer. 2013. Pollution history revealed by sedimentary records: A review. Environmental Chemistry Letters 11:255–270.

    DOI: 10.1007/s10311-013-0409-3Save Citation »Export Citation »E-mail Citation »

    A useful and thorough review of how sediments can be used to evaluate distribution and concentration of persistent pollutants within rivers through time and across space. The paper describes different types of contaminants, including heavy metals, PCBs, PAHs, pesticides, and pharmaceuticals; contamination sources and pathways; and numerous case studies.

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  • Jain, A. K. 2009. River pollution: Regeneration and cleaning. New Delhi: A. P. H. Publishing Corporation.

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    This book is a comprehensive case study of a single large river in India, the Yamuna, and of the large cities, including Delhi, that pollute the river. Following an introduction to the river’s ecology, geomorphology, and flow regime, the book focuses on pollutants and remediation of pollution in the river.

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  • Smol, J. P. 2008. Pollution of lakes and rivers: A paleoenvironmental perspective. 2d ed. Malden, MA: Blackwell.

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    This book covers diverse types of pollutants from the perspective of sedimentary records of changing types and concentrations of pollutants through time. Because river channels, floodplains, alluvial fans, and deltas preserve thousands of years of river sediments, these depositional environments provide a unique perspective on river pollution over long time spans. First published in 2002 (London: Arnold).

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  • Steingraber, S. 1998. Living downstream: A scientist’s personal investigation of cancer and the environment. New York: Vintage.

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    Written for nonspecialist readers, this highly readable book provides an overview and in-depth introduction to river pollution and other forms of environmental contamination, and reviews a wide array of studies documenting the resulting impairment of human and animal health.

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  • Wohl, E. 2004. Disconnected rivers: Linking rivers to landscapes. New Haven, CT: Yale Univ. Press.

    DOI: 10.12987/yale/9780300103328.001.0001Save Citation »Export Citation »E-mail Citation »

    This book examines human effects on rivers throughout the continental United States, and includes an extensive discussion of diverse types, sources, and effects of river pollution. The book discusses specific examples of river pollution from the Great Lakes region and provides an overview of riverine water quality throughout the country.

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The works cited in this section are designed as textbooks. Each work has a very systematic and logically organized presentation of material suitable for a textbook, but can also be read as a source of information. Goel 2006 examines river pollution in the context of India, although most of the topics addressed within the text also apply to other geographic regions. Laws 2000 addresses a broad suite of aquatic environments, including rivers. Between these two textbooks, a reader can quickly gain an appreciation for the ubiquity of river pollution, and for the diversity of contaminants in river environments.

  • Goel, P. K. 2006. Water pollution: Causes, effects and control. Rev. 2d ed. New Delhi: New Age International.

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    Focuses on water pollution in India, but provides a nice example of integrated understanding by relating river pollution to population and economic levels and pollution legislation, as well as discussing riverine physical and ecological properties, types of pollution, effects of pollution on rivers, and remediation strategies.

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  • Laws, E. A. 2000. Aquatic pollution: An introductory text. 3d ed. New York: Wiley.

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    Provides a comprehensive introduction to how contaminants enter and alter aquatic biological communities, as well as sources and effects of diverse types of contaminants. Discussion of lake, groundwater, and marine pollutants connects rivers to other aquatic environments. Aimed at university undergraduates, so the technical content of this book is readily accessible.

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The works cited in this section are mostly journals that deal with diverse types of pollution and environmental contamination, including pollution in rivers. Some of the journals focus particularly on pollutants in various environments, including Clean: Soil, Air, Water, Environmental Pollution, and Water, Air, & Soil Pollution. Aquatic Toxicology focuses on biological and ecological responses to pollutants in aquatic systems. Other journals, particularly Environmental Science & Technology, Journal of the American Water Resources Association, Science of the Total Environment, and Water and Environment Journal, are much broader in scope, but they do include many articles on river pollution.

Types of Pollutants

The entries that follow are organized with respect to type of pollutant, and thus overlap with the case studies of specific river basins. The ten categories of pollutants treated here represent major types of pollutants, rather than a complete list of all riverine contaminants. Among these categories, Heavy Metals, Mercury, Nitrates, Phosphorus, Pathogens, and Sediment are all naturally occurring chemicals, but human activities can concentrate these chemicals and significantly increase the quantities entering rivers from point and nonpoint sources. Polynuclear Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs), Pesticides, and Persistent Organic Pollutants (POPs) are all categories of synthetic chemicals. By 2000, about 60,000 known synthetic chemicals were used in manufacturing, along with more than 10,000 pesticides, with over 250 active ingredients. Only a fraction of these synthetic chemicals have been tested for their behavior in water, sediment, and the tissues of diverse living organisms, so we know very little about how these chemicals break down, persist, or react with one another in environmental media. The works cited here provide an introduction to each of these major categories of pollutants. Many of the works provide examples rather than definitive treatments summarizing what is known of each type of pollutant.

Heavy Metals

Heavy metals are a persistent and toxic form of river pollution. Their occurrence reflects natural and anthropogenic sources. Their availability and toxicity to aquatic life depend on speciation, which is governed by the physicochemical conditions at each site. Major anthropogenic sources of heavy metals include mining chemical industries, fossil fuel combustion, pesticides and fertilizer application, sewage waters, urban pollution and runoff, and outdated drinking water systems. Heavy metals entering rivers can sorb onto fine-grained sediments, suspended material, and the biofilm of microorganisms covering mineral surfaces. Sorption depends on factors such as the particular metal, the ion-exchange properties of the sediment, the physical and chemical characteristics of the pore water in the sediment, and the concentration of dissolved organic chelators. Heavy metals can be released to river water, transported, and redistributed in complex manners that reflect changes in stream flow and the factors governing sorption. Sorption can also be used to remove metals from riverine environments, however, by sequestering the metals in plant tissues, as reviewed in Adams, et al. 2013, or in spent coffee grounds, as explained in Dávila-Guzmán, et al. 2013. A first step in dealing with heavy metal pollution is to identify point and nonpoint sources and determine how metals disperse from these sources with time, as discussed in relation to fluctuating discharge from an abandoned metal mine in Wales in Byrne, et al. 2013. A second step is to characterize distribution and concentration in riverine systems, particularly sediments, as discussed in a case study of Danube River tributaries in Bednarova, et al. 2013, and for industrial and urban sites across China in Zhang and Shao 2013. Heavy metals in riverine environments are a concern because they can be toxic when ingested or absorbed by living organisms, including humans. Examples include the effects of copper on rainbow trout, discussed in Heydarnejad, et al. 2013; the effects of diverse heavy metals on two fish species and the people who consume the fish, discussed in Yehia and Sebaee 2012; and for invertebrates and fish across the Elbe estuary, discussed in Wetzel, et al. 2013. Together, the works cited here provide an overview of the types of heavy metal contamination in river environments, the sources of these contaminants, the dispersal of the contaminants with time and across space, the manner in which the contaminants are concentrated in river sediments and enter the body of riverine organisms, and potential for removing heavy metals from sediment or from aqueous solutions.

  • Adams, A., A. Raman, and D. Hodgkins. 2013. How do the plants used in phytoremediation in constructed wetlands, a sustainable remediation strategy, perform in heavy-metal-contaminated mine sites? Water and Environment Journal 27:373–386.

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    A review of phytoremediation techniques utilizing selected plant species in constructed wetlands at sites where ground and surface waters are contaminated by mine waste rock dumps and tailings. Phytoremediation uses plants to remove or sequester hazardous substances via uptake from water and assimilation in plant tissues.

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  • Bednarova, Z., J. Kuta, L. Kohut, et al. 2013. Spatial patterns and temporal changes of heavy metal distributions in river sediments in a region with multiple pollution sources. Journal of Soils and Sediments 13:1257–1269.

    DOI: 10.1007/s11368-013-0706-2Save Citation »Export Citation »E-mail Citation »

    This case study of Danube River tributaries in the Czech Republic assessed nine heavy metals in streambed sediments. Greater enrichment occurs at locally polluted sites, but the widespread influence of diffuse sources, including traffic, agriculture, and urban wastes, appears in elevated concentrations of Pb, Cu, and Zn at all sites.

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  • Byrne, P., I. Reid, and P. J. Wood. 2013. Stormflow hydrochemistry of a river draining an abandoned metal mine: The Afon Twymyn, central Wales. Environmental Monitoring and Assessment 185:2817–2832.

    DOI: 10.1007/s10661-012-2751-5Save Citation »Export Citation »E-mail Citation »

    Most measurements of mine drainage occur during baseflow. This case study indicates that significant quantities of metals are flushed during stormflow, in part because of oxidation of metal compounds during dry periods, which can facilitate dissolution and transport during wetter periods.

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  • Dávila-Guzmán, N. E., F. de J. Cerino-Córdova, E. Soto-Regalado, et al. 2013. Copper biosorption by spent coffee ground: Equilibrium, kinetics, and mechanism. Clean: Soil, Air, Water 41:557–564.

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    A beneficial use for all those spent coffee grounds! Coffee grounds can take up copper from aqueous solutions via ion-exchange mechanisms with calcium and hydrogen, and the biosorption capacity exceeds that of activated carbons. Solid coffee wastes are readily available from global coffee production of seven trillion kg per year.

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  • Heydarnejad, M. S., M. Khosravian-hemami, A. Nematollahi, and S. Rahnama. 2013. Effects of copper at sublethal concentrations on growth and biochemical parameters in rainbow trout (Oncorhynchus mykiss). International Review of Hydrobiology 98:71–79.

    DOI: 10.1002/iroh.201201443Save Citation »Export Citation »E-mail Citation »

    The effects of sublethal concentrations of heavy metals on fish are poorly known. Sublethal copper concentrations decreased growth rates in rainbow trout and produced characteristic changes in serum enzymes that can be used as biomarkers in ecotoxicological studies.

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  • Wetzel, M. A., D. S. Wahrendorf, and P. C. von der Ohe. 2013. Sediment pollution in the Elbe estuary and its potential toxicity at different trophic levels. Science of the Total Environment 449:199–207.

    DOI: 10.1016/j.scitotenv.2013.01.016Save Citation »Export Citation »E-mail Citation »

    Diverse contaminants (including eighty heavy metals) in sediments across the Elbe estuary decreased in concentration with distance from the port of Hamburg toward the open sea. Concentrations exceeded acute-effect thresholds for invertebrates and fish at a majority of the sites, which explains the absence of pollution-sensitive species.

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  • Yehia, H. M., and E. S. Sebaee. 2012. Bioaccumulation of heavy metals in water, sediment and fish (Oreochromis niloticus and Clarias anguillaris), in Rosetta branch of the River Nile, Egypt. African Journal of Biotechnology 11:14204–14216.

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    One of the fish species assessed in this Nile River study showed higher levels of bioaccumulation, and both showed differential accumulation in diverse tissues. Heavy metals also accumulated differentially in water and sediment relative to fish tissues. Levels of accumulation in fish tissue pose a risk for human consumption.

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  • Zhang, L., and H. Shao. 2013. Heavy metal pollution in sediments from aquatic ecosystems in China. Clean: Soil, Air, Water 41:878–882.

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    Synthesis and overview of heavy metal pollution and potential ecological risk at sites across China. Cadmium, mercury, and arsenic tend to be particularly prevalent and concentrated in riverine sediments, and river sediments are more contaminated than sediments in other aquatic environments.

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Mercury is now ubiquitous in the environment, largely as a result of atmospheric emissions of inorganic mercury from coal combustion, waste incineration, and wildfire. Mercury also enters rivers from discharge of industrial and municipal wastes. Inorganic mercury entering rivers can be biologically transformed to methylmercury, which is environmentally persistent and capable of bioaccumulation and biomagnification. Methylmercury is a potent neurotoxicant that especially affects the developing brain of human fetuses, but mercury can also detrimentally affect the health of adults. People typically absorb mercury from the riverine environment by eating mercury-contaminated fish. Consequently, a great deal of effort is devoted to quantifying the concentration of mercury in the tissues of different fish species, and to determining the risks these concentrations pose to humans who eat fish, as described in Alvarez, et al. 2012 and Marrugo-Negrete, et al. 2013 for rivers in Colombia, and in Miller 1989 for a river in Canada. Many of the assessments of mercury concentrations within fish require killing individual fish to obtain tissues for analyses. Hopkins, et al. 2012 describes a nonlethal method of assessing mercury bioaccumulation in freshwater turtles. Jardine, et al. 2012 examines lower trophic levels to assess how mercury enters and moves through riverine trophic chains. Sherman and Blum 2013 provides an example of how long it can take riverine biota to recover after a source of mercury is removed—on the order of decades to centuries—because of persistence of mercury in streambed sediment and other riverine storage zones. Tong, et al. 2013 describes bioaccumulation of mercury in riverine plants, which results in mercury concentrations higher than background levels despite the absence of a mercury point source within the river basin. Fisher, et al. 2012 examines how the warming climate is changing mercury loading in Arctic rivers and the Arctic Ocean.

  • Alvarez, S., A. S. Kolok, L. F. Jimenez, C. Granados, and J. A. Palacio. 2012. Mercury concentrations in muscle and liver tissue of fish from marshes along the Magdalena River, Colombia. Bulletin of Environmental Contamination and Toxicology 89:836–840.

    DOI: 10.1007/s00128-012-0782-9Save Citation »Export Citation »E-mail Citation »

    Samples of fish tissue from the Magdalena River watershed, which contains gold mines, indicate high mercury concentrations in carnivorous fish species. Some noncarnivorous species also had high concentrations. Despite levels below World Health Organization limits for human consumption, prolonged low-level exposure to mercury may affect frequent consumers of fish.

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  • Fisher, J. A., D. J. Jacob, A. L. Soerensen, H. M. Amos, A. Steffen, and E. M. Sunderland. 2012. Riverine source of Arctic Ocean mercury inferred from atmospheric observations. Nature Geoscience 5:499–504.

    DOI: 10.1038/ngeo1478Save Citation »Export Citation »E-mail Citation »

    Rivers transport large quantities of mercury during summer peak flows. Rivers are the dominant source of mercury to the Arctic Ocean, from which the mercury enters the atmosphere. Increased mobilization of mercury from thawing permafrost and wildfires, along with greater Arctic river discharge, could increase mercury fluxes as climate warms.

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  • Hopkins, W. A., C. Bodinof, S. Budischak, and C. Perkins. 2012. Nondestructive indices of mercury exposure in three species of turtles occupying different trophic niches downstream from a former chloralkali facility. Ecotoxicology 22:22–32.

    DOI: 10.1007/s10646-012-0999-8Save Citation »Export Citation »E-mail Citation »

    Turtles have long life spans and feed at trophic levels that create high exposure to anthropogenic chemicals. Sampling mercury in blood and toenails allows assessment of spatial distributions of mercury concentration without killing the animals. Extremely high concentrations near a former industrial site persisted for 130 km downstream.

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  • Jardine, T. D., K. A. Kidd, and J. B. Rasmussen. 2012. Aquatic and terrestrial organic matter in the diet of stream consumers: Implications for mercury bioaccumulation. Ecological Applications 22:843–855.

    DOI: 10.1890/11-0874.1Save Citation »Export Citation »E-mail Citation »

    Mercury concentrations are higher in aquatic insects and fish that feed primarily on aquatic sources than in species that also feed on riparian sources. These differences have implications for understanding how contaminants move through ecosystems and for choosing species to sample for contaminant monitoring.

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  • Marrugo-Negrete, J. L., J. A. Ruiz-Guzmán, and S. Díez. 2013. Relationship between mercury levels in hair and fish consumption in a population living near a hydroelectric tropical dam. Biological Trace Elements Research 151:187–194.

    DOI: 10.1007/s12011-012-9561-zSave Citation »Export Citation »E-mail Citation »

    Case study of mercury concentrations in fish and people at a dam on a river in Colombia. Among fish, mercury concentrations were highest in carnivorous species. Among people, mercury correlated with frequency of fish consumption, and was highest in children 2–15 years of age and in women of childbearing age.

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  • Miller, D. R. 1989. Mercury in Canadian rivers. In Ecotoxicology and climate. Edited by P. Bourdeau, J. A. Haines, W. Klein, and C. R. Krishna Murti, 373–381. Chichester, UK: Wiley.

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    Case study of mercury from industrial manufacturing entering rivers in northwestern Ontario. The mercury bioaccumulated and biomagnified, creating dangerously high concentrations in game fish. The game fish formed a large part of the diet of local indigenous people, whose society was severely impacted by the inability to consume these fish.

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  • Sherman, L. S., and J. D. Blum. 2013. Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA. Science of the Total Environment 448:163–175.

    DOI: 10.1016/j.scitotenv.2012.09.038Save Citation »Export Citation »E-mail Citation »

    This case study from aquatic environments near a coal-fired power plant on the Crystal River in Florida provides a cautionary note in that recovery of some freshwater fish populations to baseline methylmercury concentrations may take decades to centuries after atmospheric mercury deposition is reduced at a site.

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  • Tong, Y., W. Zhang, D. Hu, et al. 2013. Behavior of mercury in an urban river and its accumulation in aquatic plants. Environmental Earth Science 68:1089–1097.

    DOI: 10.1007/s12665-012-1810-0Save Citation »Export Citation »E-mail Citation »

    This paper examines mercury pollution in an urban area with no mercury point source. Mercury concentrations in river water of this Chinese city were lower than concentrations in mining areas, but higher than concentrations in rural areas or global background levels. Riverine plants bioaccumulated mercury from both water and sediment.

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Nitrogen is a naturally occurring nutrient that is critical at some level for many living organisms. Nitrogen becomes a river pollutant at concentrations exceeding those of natural or background levels because it facilitates growth of cyanobacteria, algae, and other plants. Nuisance algal blooms can limit dissolved oxygen necessary for other organisms such as fish when dead cells decompose. Some types of algae, such as cyanobacterial, can also produce compounds that are toxic to other organisms, including humans. Nitrogen can occur in several different forms, some of which are reactive. Reactive nitrogen is organic nitrogen and biologically and chemically active forms of inorganic nitrogen. Biogeochemical reactions exert an important control on transformations of nitrogen between different forms. Thouvenot-Korppoo, et al. 2009 illustrates how understanding nitrogen reactions can be used to develop strategies to reduce downstream nitrogen fluxes. Anthropogenic sources of reactive nitrogen (the nitrogen molecules that can be metabolized by plants and animals) to the environment have increased substantially since the mid-20th century, as reviewed in Galloway, et al. 2004. Riverine fluxes of nitrogen have also increased, as reviewed in Green, et al. 2004. Although riverine fluxes vary substantially among continents, as discussed in Boyer, et al. 2006, rivers and nearshore areas around the world now show adverse effects from excess nitrogen, primarily derived from agricultural and urban runoff. One of the best studied examples is the Mississippi River and the Gulf of Mexico, as described in Swarzenski, et al. 2008 and Turner, et al. 2008. Mitsch, et al. 2001 reviews techniques that can be used to reduce nitrogen inputs to the river. The US Environmental Protection Agency estimates that almost one-third of the nation’s river miles and one-fifth of its lakes contain high total nitrogen concentrations, making nitrogen reduction a national water-quality priority. Hey, et al. 2012 describes one approach to reducing nitrogen, by using wetland creation and restoration to store nitrogen.

  • Boyer, E. W., R. W. Howarth, J. N. Galloway, F. J. Dentener, P. A. Green, and C. J. Vörösmarty. 2006. Riverine nitrogen export from the continents to the coast. Global Biogeochemical Cycles 20:GB1S91.

    DOI: 10.1029/2005GB002537Save Citation »Export Citation »E-mail Citation »

    This paper provides a global summary of contemporary anthropogenic and natural inputs of reactive nitrogen to terrestrial landscapes, as well as resulting riverine nitrogen fluxes. Rates of riverine nitrogen export vary substantially among the continents as a result of differences in population and anthropogenic nitrogen inputs.

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  • Galloway, J. N., F. J. Dentener, D. G. Capone, et al. 2004. Nitrogen cycles: Past and present. Biogeochemistry 70:152–226.

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    This paper thoroughly reviews the basic components of the nitrogen cycle, the global terrestrial nitrogen budget in 1860 and in the early 1990s, including riverine export, regional nitrogen budgets for the major continents, marine nitrogen budgets, and projects future trends in nitrogen budgets.

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  • Green, P. A., C. J. Vörösmarty, M. Meybeck, J. N. Galloway, B. J. Peterson, and E. W. Boyer. 2004. Pre-industrial and contemporary fluxes of nitrogen through rivers: A global assessment based on typology. Biogeochemistry 68:71–105.

    DOI: 10.1023/B:BIOG.0000025742.82155.92Save Citation »Export Citation »E-mail Citation »

    This paper reviews historical changes in nitrogen budgets, summarizing the evidence that nitrogen loading to terrestrial environments has doubled globally from the preindustrial condition, and increased six-fold in many industrialized areas. Riverine nitrogen fluxes also reflect climate and hydraulic residence times.

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  • Hey, D. L., J. A. Kostel, W. G. Crumpton, W. J. Mitsch, and B. Scott. 2012. The roles and benefits of wetlands in managing reactive nitrogen. Journal of Soil and Water Conservation 67:47A–53A.

    DOI: 10.2489/jswc.67.2.47ASave Citation »Export Citation »E-mail Citation »

    Paper develops an argument for strategic wetland creation and restoration as an efficient means to reduce the deleterious effects of reactive nitrogen. After reviewing the nitrogen cycle and the role of wetlands in storing nitrogen, the authors use the Mississippi River basin as a case study.

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  • Mitsch, W. J., J. W. Day, J. W. Gilliam, et al. 2001. Reducing nitrogen loading to the Gulf of Mexico from the Mississippi River basin: Strategies to counter a persistent ecological problem. BioScience 51:373–388.

    DOI: 10.1641/0006-3568(2001)051[0373:RNLTTG]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    This paper reviews hypoxia in the Gulf of Mexico resulting from excess nitrogen inputs and transport along the Mississippi River, but focuses on means to reduce nitrogen reaching the Gulf. Suggested techniques include modifying agricultural and urban practices, and using riparian zones and wetlands to trap and store nitrogen.

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  • Swarzenski, P. W., P. L. Campbell, L. E. Osterman, and R. Z. Poore. 2008. A 1000-year sediment record of recurring hypoxia off the Mississippi River: The potential role of terrestrially-derived organic matter inputs. Marine Chemistry 109:130–142.

    DOI: 10.1016/j.marchem.2008.01.003Save Citation »Export Citation »E-mail Citation »

    Sediment cores from the coastal shelf adjacent to the Mississippi River delta indicate periodic occurrence of hypoxia in the Gulf of Mexico for 1,000 years. Past hypoxic events reflect increased river discharge and associated wetland export of nitrogen, likely as a result of climate fluctuations and increased tropical storm activity.

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  • Thouvenot-Korppoo, M., G. Billen, and J. Garnier. 2009. Modelling benthic denitrification processes over a whole drainage network. Journal of Hydrology 379:239–250.

    DOI: 10.1016/j.jhydrol.2009.10.005Save Citation »Export Citation »E-mail Citation »

    Denitrification occurs when bacteria remove nitrogen from a river ecosystem. This paper models denitrification throughout a river network by simulating hydrological and biogeochemical processes. This type of model identifies places of low and high denitrification along a river and facilitates management strategies to reduce nitrogen fluxes through the river network.

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  • Turner, R. E., N. N. Rabalais, and D. Justic. 2008. Gulf of Mexico hypoxia: Alternate states and a legacy. Environmental Science & Technology 42:2323–2327.

    DOI: 10.1021/es071617kSave Citation »Export Citation »E-mail Citation »

    Summer variation in the size of the hypoxic zone in the Gulf of Mexico reflects surface water phytoplankton production and associated sediment oxygen demand. The potential size of a hypoxic zone for a given nitrogen load doubled during 1980–2000. This nonlinear response suggests a shift to an alternate ecosystem state.

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Phosphorus concentrations and fluxes exert an important influence on biological activity in rivers. Davies and Bothwell 2012 provides an example of how riverine organisms respond to increased inputs of phosphorus. As with nitrogen, excess phosphorus can lead to eutrophication. Excess phosphorus can enter rivers from many sources, including urban runoff (wastewater effluent, runoff from pavement, septic tanks) and agricultural runoff (crop lands, pastures, farmyards). Merrikhpour and Jalali 2013, for example, discusses how deicing salt used on roads can increase phosphorus in urban runoff. Increasing land use has led to widespread phosphorus-enrichment of rivers and this has caused problems for human health (related to algal toxins), species abundance and diversity, and amenity values and costs of drinking water treatment. Phosphorus concentrations and fluxes within rivers reflect numerous factors beyond phosphorus source to the river, including flow regime, hydraulics, water chemistry, and streambed substrate and floodplain soils. Noe, et al. 2013 provides an example of a study examining how differences in river and floodplain characteristics influence phosphorus fluxes. Phosphorus is retained within rivers via biogeochemical and physical processes, including deposition of phosphorus-rich particles attached to suspended solids, uptake by algae, and diffusion into pore water within the streambed. Pan, et al. 2013 provides an example from the Yellow River of China illustrating how high levels of suspended sediment can limit phosphorus concentrations in river water because of deposition of phosphorus attached to sediment particles. Withers and Jarvie 2008 provides a comprehensive overview of phosphorus sources to, and dynamics within, rivers, and is a good starting point for understanding phosphorus pollution. Smith and Schindler 2009 also provides a useful overview of eutrophication caused by excess nutrients, including needs for research and management of phosphorus. Withers, et al. 2009 provides an example of identifying and monitoring sources of excess phosphorus inputs to rivers as a first step in reducing these inputs. However, Jarvie, et al. 2013 provides a useful, if sobering, exploration of why simply reducing a pollutant may not be enough to ensure river recovery.

  • Davies, J.-M., and M. L. Bothwell. 2012. Responses of lotic periphyton to pulses of phosphorus: P-flux controlled growth rate. Freshwater Biology 57:2602–2612.

    DOI: 10.1111/fwb.12032Save Citation »Export Citation »E-mail Citation »

    Numerous studies address how stream organisms respond to the addition of limiting nutrients such as phosphorus. This paper provides an example that illustrates how the hourly average phosphate concentration to which periphyton communities are exposed is critical in determining phosphorus-limited growth dynamics.

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  • Jarvie, H. P., A. N. Sharpley, P. J. A. Withers, J. T. Scott, B. E. Haggard, and C. Neal. 2013. Phosphorus mitigation to control river eutrophication: Murky waters, inconvenient truths, and “postnormal” science. Journal of Environmental Quality 42:295–304.

    DOI: 10.2134/jeq2012.0085Save Citation »Export Citation »E-mail Citation »

    This commentary examines why, despite two decades or more of reduced phosphorus inputs, water quality and aquatic ecology have not recovered in many rivers. The reasons are complex, particularly because of recovery trajectories that include thresholds and alternative stable states.

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  • Merrikhpour, H., and M. Jalali. 2013. The effects of road salt application on the accumulation and speciation of cations and anions in an urban environment. Water and Environment Journal 27:524–534.

    DOI: 10.1111/j.1747-6593.2012.00371.xSave Citation »Export Citation »E-mail Citation »

    An interesting case study from Iran of how use of deicing salts on roads can increase phosphorus levels in urban runoff, which then enters rivers. The runoff from impervious urban surfaces also contained other contaminants, including sulfate and lead.

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  • Noe, G. B., C. R. Hupp, and N. B. Rybicki. 2013. Hydrogeomorphology influences soil nitrogen and phosphorus mineralization in floodplain wetlands. Ecosystems 16:75–94.

    DOI: 10.1007/s10021-012-9597-0Save Citation »Export Citation »E-mail Citation »

    A good example of a case study, here from Virginia, USA, of how factors such as hydrologic connectivity, soil characteristics, and vegetation communities influence phosphorus uptake and retention in floodplain environments.

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  • Pan, G., M. D. Krom, M. Zhang, et al. 2013. Impact of suspended inorganic particles on phosphorus cycling in the Yellow River (China). Environmental Science & Technology 47:9685–9692.

    DOI: 10.1021/es4005619Save Citation »Export Citation »E-mail Citation »

    Despite high nutrient inputs to the Yellow River, average dissolved phosphorus concentrations remain below global averages. The authors attribute this to attachment to suspended sediment, which is present at high concentrations. Interesting case study in the complex physical and biogeochemical interactions within a river that influence phosphorus dynamics.

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  • Smith, V. H., and D. W. Schindler. 2009. Eutrophication science: Where do we go from here? Trends in Ecology and Evolution 24:201–207.

    DOI: 10.1016/j.tree.2008.11.009Save Citation »Export Citation »E-mail Citation »

    A useful overview of why eutrophication is a major water-quality issue for rivers around the world. The paper also discusses how levels of nitrogen and phosphorus influence the fate and effects of other river pollutants, including pathogens.

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  • Withers, P. J. A., and H. P. Jarvie. 2008. Delivery and cycling of phosphorus in rivers: A review. Science of the Total Environment 400:379–395.

    DOI: 10.1016/j.scitotenv.2008.08.002Save Citation »Export Citation »E-mail Citation »

    An excellent overview of sources of phosphorus to rivers, instream processes that influence phosphorus dynamics, and the ability of rivers to retain and process phosphorus inputs. River retention and processing depend on factors such as flow regime and water chemistry.

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  • Withers, P. J. A., H. P. Jarvie, R. A. Hodgkinson, et al. 2009. Characterization of phosphorus sources in rural watersheds. Journal of Environmental Quality 38:1998–2011.

    DOI: 10.2134/jeq2008.0096Save Citation »Export Citation »E-mail Citation »

    Discusses use of weekly monitoring of water quality in various urban and agricultural storm runoff to identify runoff from farmyards, roads, and septic tanks as having higher concentrations of phosphorus than runoff from croplands and pastures.

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Pathogens, as the term is used here, include any microbial organism that can impair the health of humans or other organisms. Pathogens are a distinct class of river pollutant that can come from the same sources as many other types of pollutants, including wastewater treatment effluent, sewage tanks, and agricultural operations, particularly those involving animals. Poorly treated or untreated wastewater is a major source of pathogens, particularly in developing countries, as illustrated in Robles-Marua, et al. 2012. Even in high-income countries, sewage-associated bacteria and antibiotic-resistant bacteria increase in abundance downstream from wastewater sources, particularly following precipitation, as discussed for the Hudson River in Young and Juhl 2013. Korzekwa, et al. 2012 discusses the use of genetic markers in bacteria to evaluate the type and number of pollutant sources upstream. One of the difficulties of wastewater treatment is that bacteria are necessary to promote biochemical reactions critical to this treatment, but these bacteria can also be pathogens harmful to human health, as reviewed in Varela and Manaia 2013. In addition, not all sources of the same pathogen are created equal. Williams, et al. 2012 illustrates how pathogen activity in a receiving river differs significantly in relation to land use type and consequent source of the pathogen, as well as nutrients and microbial communities in the river. The works cited here reflect the diversity of sources and types of pathogens, as well as methods used to detect the presence of pathogens in river water, the sources of pathogens to river water, and the effects of river-borne pathogens on humans and other organisms. Brinkman, et al. 2013 provides an example of a technique for detecting pathogens in river water. Hurst, et al. 2012 illustrates how river management (here, dam removal) can introduce pathogens to previously isolated aquatic communities. Jagai, et al. 2012 provides an example of the complex relationships between river-borne pathogens, human health, and processes that introduce pathogens to rivers.

  • Brinkman, N. E., R. Francisco, T. L. Nichols, et al. 2013. Detection of multiple waterborne pathogens using microsequencing arrays. Journal of Applied Microbiology 114:564–573.

    DOI: 10.1111/jam.12073Save Citation »Export Citation »E-mail Citation »

    Indicator organisms are commonly used to monitor water quality, but these organisms do not always correlate well with the presence of microbial pathogens. Microsequencing arrays can directly detect DNA from multiple pathogens within a sample.

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  • Hurst, C. N., R. A. Holt, and J. L. Bartholomew. 2012. Dam removal and implications for fish health: Ceratomyxa shasta in the Williamson River, Oregon, USA. North American Journal of Fisheries Management 32:14–23.

    DOI: 10.1080/02755947.2012.655843Save Citation »Export Citation »E-mail Citation »

    Dam removal can result in the introduction of pathogens to previously isolated aquatic communities. In this example, the risk that dam removal can facilitate dispersal of an endemic salmonid pathogen is evaluated.

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  • Jagai, J. S., J. K. Griffiths, P. K. Kirshen, P. Webb, and E. N. Naumova. 2012. Seasonal patterns of gastrointestinal illness and streamflow along the Ohio River. International Journal of Environmental Research and Public Health 9:1771–1790.

    DOI: 10.3390/ijerph9051771Save Citation »Export Citation »E-mail Citation »

    Incidence of waterborne gastrointestinal illnesses among elderly people along the Ohio River peaks just before streamflow peaks, for reasons that remain unknown. Paper illustrates the complexities of relations between river pollution by pathogens and potential controlling factors.

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  • Korzekwa, K., I. Golas, and M. Harnisz. 2012. Evaluation of anthropogenic pollution in river water based on the genetic diversity of Aeromonas hydrophila. Archives of Environmental Protection 38:41–50.

    DOI: 10.2478/v10265-012-0032-6Save Citation »Export Citation »E-mail Citation »

    Study uses DNA markers to assess genetic diversity of a bacterium that causes disease in fish and humans and is an indicator of water quality. Greater genetic diversity indicates multiple pollutant sources, and drug resistance reflects the presence of intensive fish cultivation in the river system.

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  • Robles-Marua, A., A. S. Mayer, M. T. Auer, and E. R. Vivoni. 2012. Modeling riverine pathogen fate and transport in Mexican rural communities and associated public health implications. Journal of Environmental Management 113:61–70.

    DOI: 10.1016/j.jenvman.2012.08.035Save Citation »Export Citation »E-mail Citation »

    Discharge of untreated or poorly treated wastewater to rivers is a major source of pathogens and other pollutants. This study uses Escherichia coli as an indicator of surface water quality. Modeling indicates which regions along the river are in noncompliance with water quality.

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  • Varela, A. R., and C. M. Manaia. 2013. Human health implications of clinically relevant bacteria in wastewater habitats. Environmental Science and Pollution Research International 20:3550–3569.

    DOI: 10.1007/s11356-013-1594-0Save Citation »Export Citation »E-mail Citation »

    Indigenous bacteria promote biochemical reactions necessary to wastewater treatment, but can also be pathogenic or harbor antibiotic resistance harmful to humans. This paper reviews the potential of bacteria in wastewater habitats to harm human health and the potential for receiving rivers to be polluted.

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  • Williams, A. P., R. S. Quilliam, C. E. Thorn, D. Cooper, B. Reynolds, and D. L. Jones. 2012. Influence of land use and nutrient flux on metabolic activity of E. coli O157 in river water. Water, Air, & Soil Pollution 223:3077–3083.

    DOI: 10.1007/s11270-012-1090-zSave Citation »Export Citation »E-mail Citation »

    Land use and existing microbial communities in rivers influence the activity of waterborne Escherichia coli O157, a pathogen to humans. Expanding populations, intensified agriculture and climate change are all predicted to amplify risks from E. coli O157.

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  • Young, S., and A. Juhl. 2013. Antibiotic-resistant bacteria in the Hudson River estuary linked to wet weather sewage contamination. Journal of Water and Health 11:297–310.

    DOI: 10.2166/wh.2013.131Save Citation »Export Citation »E-mail Citation »

    Documents a link between the abundance of antibiotic-resistant bacteria and levels of sewage-associated bacteria, both of which increased following precipitation, suggesting a shared sewage-associated source.

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Polynuclear Aromatic Hydrocarbons (PAHs)

Polynuclear aromatic hydrocarbons (PAHs) are a group of diverse compounds containing two or more fused rings of carbon and hydrogen atoms; they are products of coal, tar, and oil, and their combustion. Anthropogenic PAHs formed from the combustion of fossil fuels can be pyrolitic compounds formed from incomplete combustion or petrogenic compounds derived from crude oil or unburned fuel and its refined products. Both types of PAHs are lipophilic (fat-loving) chemicals that are widespread pollutants of water and sediments. PAHs can accumulate in fatty tissues of animals, and PAHs with four or more condensed benzene rings are commonly mutagenic and/or carcinogenic to diverse organisms, including aquatic species. The ecotoxicology of PAHs largely depends on the metabolic fate of the compounds once they enter an organism. PAHs taken up by fish, for example, are rapidly metabolized to compounds in the liver that are secreted into bile. Consequently, the level of biliary PAH metabolites has been used as an indicator of PAH exposure in several studies, including that of Yang, et al. 2003 for the Cuyahoga River basin of Ohio, USA. Mermillod-Blondin, et al. 2013 describes the sometimes subtle effects of PAHs, which may not kill aquatic organisms outright but can modify the activity of the organisms in a manner that exacerbates river pollution. Milani, et al. 2013 illustrates the importance of selecting the correct organisms when assessing the environmental effects of PAHs: benthic macroinvertebrate communities in a contaminated stream are not directly affected by PAH exposure, but the macroinvertebrates contain high concentrations of PAHs, which can be passed to higher trophic levels in the stream. Schäfer, et al. 2011 provides an example of the difficulties in regulating pollutant concentrations because the compounds most responsible for creating potential acute effects on aquatic organisms are not currently priority substances in the study area. El Bouraie, et al. 2012 and Chung, et al. 2013 provide examples of the type of basic field measurements that are necessary to quantify the distribution and concentration of PAHs in river water and sediment. Heimann, et al. 2011 documents one method by which PAHs can be concentrated in specific sediment deposits within rivers. Wu, et al. 2011 illustrates procedures used to assess health risks for humans created by PAHs in drinking water supplies.

  • Chung, C.-Y., W.-L. Lai, H.-S. Gau, and S.-W. Liao. 2013. Interpretation and apportionment source of polycyclic aromatic hydrocarbons from neighboring rivers in Dapeng Bay (Taiwan). Water Environment Research 85:308–317.

    DOI: 10.2175/106143012X13503213812526Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of the spatially detailed sampling of surface sediment necessary to understand the potential sources and distribution of PAHs. Concentrations of the sixteen PAHs analyzed differed spatially in response to locations of distinct contaminant sources. This type of contaminant mapping facilitates containment and remediation.

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  • El Bouraie, M. M., A. A. El Barbary, and M. M. Yehia. 2012. Distributions of polycyclic aromatic hydrocarbons in surface water and bed sediments of El Rahawy area, Egypt. Journal of International Environmental Application and Science 7:76–87.

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    PAH concentrations are higher in streambed sediment than in river water. PAHs in bed sediments have increased during the past twenty years. Lack of correlation between PAH concentrations in water and sediment suggests that absorption of PAHs from the air is a more important source to water than industrial discharges.

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  • Heimann, W., M. Sylvester, T.-B. Seiler, H. Hollert, and R. Schulz. 2011. Sediment toxicity in a connected oxbow lake of the Upper Rhine (Germany): EROD induction in fish cells. Journal of Soils and Sediments 11:1279–1291.

    DOI: 10.1007/s11368-011-0416-6Save Citation »Export Citation »E-mail Citation »

    Despite improved water quality, contaminated sediments continue to pose risks for riverine biota. Partially cutoff meander bends that store contaminated sediments can be hydrologically reconnected to the main channel during floods. Contaminants enter cutoffs during floods, posing risks for fish using the cutoffs for spawning and rearing habitat.

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  • Mermillod-Blondin, F., A. Foulquier, F. Gilbert, et al. 2013. Benzo(a)pyrene inhibits the role of the bioturbator Tubifex tubifex in river sediment biogeochemistry. Science of the Total Environment 450–451:230–241.

    DOI: 10.1016/j.scitotenv.2013.02.013Save Citation »Export Citation »E-mail Citation »

    This paper addresses the effects of a specific PAH on the interactions between microorganisms and a worm that bioturbates river sediment. Lower PAH concentrations do not limit worm survival, but they inhibit worm activity and the associated effects on microbial processes that reduce pollutant concentrations.

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  • Milani, D., L. Grapentine, and R. Fletcher. 2013. Sediment contamination in Lyons Creek East, a tributary of the Niagara River: Part 1. Assessment of benthic macroinvertebrates. Archives of Environmental Contamination and Toxicology 64:65–86.

    DOI: 10.1007/s00244-012-9817-9Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of a river in which severe toxicity from PAHs, PCBs, DDT metabolites, and zinc appears to have only minimal effects on benthic macroinvertebrate communities. Contaminant concentrations in macroinvertebrates are two orders of magnitude higher than reference sites, however, posing a risk of biomagnification.

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  • Schäfer, R. B., P. C. von der Ohe, R. Kühne, G. Schüürmann, and M. Liess. 2011. Occurrence and toxicity of 331 organic pollutants in large rivers of north Germany over a decade (1994 to 2004). Environmental Science & Technology 45:6167–6174.

    DOI: 10.1021/es2013006Save Citation »Export Citation »E-mail Citation »

    Paper illustrates the complexities of pollutant regulation. PAHs were the most frequently detected pollutants. Although detection frequency decreased from 1994 to 2004, toxicity for crustaceans remained acute in 2004. Most of the compounds creating potential acute effects on aquatic organisms are not currently priority substances in the European Union.

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  • Wu, B., Y. Zhang, X.-X. Zhang, and S.-P. Cheng. 2011. Health risk assessment of polycyclic aromatic hydrocarbons in the source water and drinking water of China: Quantitative analysis based on published monitoring data. Science of the Total Environment 410:112–118.

    DOI: 10.1016/j.scitotenv.2011.09.046Save Citation »Export Citation »E-mail Citation »

    In this paper, published monitoring data of PAHs are used in a carcinogenic risk assessment for different age groups and exposure pathways. In general, risk values for children and teens are lower than accepted values, with slightly higher values for adults, but specific regions have higher risks.

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  • Yang, X., D. S. Peterson, P. C. Baumann, and E. L. C. Lin. 2003. Fish biliary PAH metabolites estimated by fixed-wavelength fluorescence as an indicator of environmental exposure and effects. Journal of Great Lakes Research 29:116–123.

    DOI: 10.1016/S0380-1330(03)70420-1Save Citation »Export Citation »E-mail Citation »

    Levels of biliary PAH metabolites in brown bullhead fish collected throughout the Cuyahoga River basin were related to PAH sediment contamination and to abnormalities and tumors on the fish. Even sites without known industrial discharges contained some PAH contamination near road and railroad bridges.

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Polychlorinated Biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) are a type of persistent organic pollutant (POP) targeted for elimination by the United Nations Environment Programme as one of the “dirty dozen” POPs. Commercial PCBs were widely used as additives in oils, industrial fluids, and products as diverse as pesticides, paints, copying paper, adhesives, sealants, and plastics. Despite their versatility and usefulness, production and use in commerce of PCBs have been banned in the United States since 1973 because they bioaccumulate, resulting in much higher concentrations in biota than in the surrounding environment, and because they are toxic to a variety of living organisms. The US Clean Water Act requires that rivers in which PCBs exceed water quality standards must be subjected to a process in which a total maximum daily load (TMDL) is calculated and implemented, providing some means for regulating inadvertent production of PCBs. Rodenburg, et al. 2010 describes one form of inadvertent production of PCBs and explains why this production is likely to create a significant obstacle to achieving water quality standards for PCBs throughout the United States. Velinsky, et al. 2011 illustrates the detailed sampling needed to understand spatial distribution and temporal trends in PCB concentrations in river sediments. Barnthouse, et al. 2009, Eqani, et al. 2013, and Maes, et al. 2013 provide examples of the difficulties of interpreting the environmental effects of contaminant exposure. Babut, et al. 2012 illustrates how individual fish species can show different bioaccumulation levels of PCBs, which may not correspond to levels expected based on knowledge of the fish’s food sources. Consequently, a tiered monitoring strategy that combines sediments and biota may be more effective than sampling only one component of a river environment when assessing whether the river meets regulatory guidelines for a contaminant. Morrissey, et al. 2013 exemplifies studies that record the persistence of PCBs in river organisms. Johnson, et al. 2013 is an example of a study that demonstrates the consistent presence of PCBs in a threatened fish species, although the threat to species survival posed by these pollutants relative to threats posed by issues such as habitat loss remains unclear.

  • Babut, M., C. Lopes, S. Pradelle, H. Persat, and P.-M. Badot. 2012. BSAFs for freshwater fish and derivation of a sediment quality guideline for PCBs in the Rhone basin, France. Journal of Soils and Sediments 12:241–251.

    DOI: 10.1007/s11368-011-0448-ySave Citation »Export Citation »E-mail Citation »

    This paper uses several years of data on fish contamination by PCBs throughout a large river basin to assess the distribution of biota-to-sediment accumulation factors (BSAFs) of PCBs, with the intent to determine a sediment quality guideline corresponding to the regulatory fish consumption limit.

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  • Barnthouse, L. W., D. Glaser, and L. DeSantis. 2009. Polychlorinated biphenyls and Hudson River white perch: Implications for population-level ecological risk assessment and risk management. Integrated Environmental Assessment and Management 5:435–444.

    DOI: 10.1897/IEAM_2008-080.1Save Citation »Export Citation »E-mail Citation »

    PCB concentrations in sediment and fish tissue and fish abundance and reproduction have been measured for thirty years in the Hudson River. These long-term data indicate no correlation between maternal PCB tissue concentration and reproductive success, suggesting that adaptation and other ecological processes influence population-level response to PCB exposure.

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  • Eqani, S. A.-M.-A.-S., R. N. Malik, A. Cincinelli, et al. 2013. Uptake of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) by river water fish: The case of River Chenab. Science of the Total Environment 450–451:83–91.

    DOI: 10.1016/j.scitotenv.2013.01.052Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of the detailed sampling and analysis necessary to understand dissemination of PCBs throughout a river environment. Pesticide and PCB concentrations were higher in carnivorous fish than in herbivorous fish, and higher in all fish collected near industrial areas, followed by urban and agricultural areas.

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  • Johnson, L., B. Anulacion, M. Arkoosh, et al. 2013. Persistent organic pollutants in juvenile Chinook salmon in the Columbia River basin: Implications for stock recovery. Transactions of the American Fisheries Society 142:21–40.

    DOI: 10.1080/00028487.2012.720627Save Citation »Export Citation »E-mail Citation »

    This paper describes frequent detection of PCBs in juvenile fish of a threatened species, including PCB concentrations above estimated thresholds for levels that affect fish growth and survival. Tidal freshwater portions of estuaries in which fish are exposed to pollutants from urban and industrial activities are important sources of PCBs.

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  • Maes, G. E., J. A. M. Raeymaekers, B. Hellemans, et al. 2013. Gene transcription reflects poor health status of resident European eel chronically exposed to environmental pollutants. Aquatic Toxicology 126:242–255.

    DOI: 10.1016/j.aquatox.2012.11.006Save Citation »Export Citation »E-mail Citation »

    Paper illustrates the difficulties of documenting and understanding the effects of chronic pollutant exposure. Populations of European eels have declined for three decades. Bioaccumulation levels of PCBs and other contaminants show strong inverse correlations with health status, including dysfunctional gene transcription, but long-term consequences for the entire species remain unclear.

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  • Morrissey, C. A., D. W. G. Stanton, M. G. Pereira, et al. 2013. Eurasian dipper eggs indicate elevated organohalogenated contaminants in urban rivers. Environmental Science & Technology 47:8931–8939.

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    Paper provides an example of the persistence of PCBs in river environments. Analyses of the eggs of Eurasian dippers, a bird that preys on aquatic macroinvertebrates, indicate that concentrations of PCBs and organochlorine pesticides have remained stable or increased during the past twenty years, despite discontinued use during the 1980s.

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  • Rodenburg, L. A., J. Guo, S. Du, and G. J. Cavallo. 2010. Evidence for unique and ubiquitous environmental sources of 3,3’-Dichlorobiphenyl (PCB 11). Environmental Science & Technology 44:2816–2821.

    DOI: 10.1021/es901155hSave Citation »Export Citation »E-mail Citation »

    PCB 11 is created during production of diarylide yellow pigments used in newspapers, food packaging cardboard boxes, and plastics. Disposal of these materials introduces PCB 11 to wastewater treatment plants and storm sewers. Consequently, PCB 11 in the Delaware River exceeds TMDL (total maximum daily load) by a factor of two.

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  • Velinsky, D. J., G. F. Riedel, J. T. F. Ashley, and J. C. Cornwell. 2011. Historical contamination of the Anacostia River, Washington, D.C. Environmental Monitoring and Assessment 183:307–328.

    DOI: 10.1007/s10661-011-1923-zSave Citation »Export Citation »E-mail Citation »

    Paper provides an example of spatially and temporally intensive analysis of river-bed sediment cores. Using isotopic dating to establish ages of sediment at different depths, this study evaluates changes in the concentration of various contaminants through time and relates these changes to contaminant inputs. Recent declines in PCBs reflect discontinued use.

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As with some of the other types of pollutants covered here, a search for river pollution and pesticides in the Water Resources Abstracts database results in hundreds of hits. This reflects the enormous number of papers written on this type of river pollution, including case studies of transport, dispersal, deposition, and concentration of pollutants, of biotic effects, of human health hazards, of remediation, and of pollution in nearshore, estuary, and delta environments that integrate one or more rivers. The works cited here provide a starting point for understanding this diversity. Given the huge number of chemicals released into the environment (more than 14 million), chemicals must be prioritized for risk assessment and monitoring. Von der Ohe, et al. 2011 provides an example of such prioritizing in the context of the European Water Framework Directive, which mandates achievement of good water quality for surface and ground waters, and prevention of further deterioration, by 2015. Barzman and Dachbrodt-Saaydeh 2011 is related in that it does not discuss details of pesticide reduction plans, but rather explores common aspects of approaches that engage stakeholders in several European countries. In contrast, Plant, et al. 2012 explores how, in an Australian case study, small-scale vegetable horticulturists with minimal oversight or access to information on pesticide use are creating ongoing river pollution. As this paper concludes, standard practices of risk management are unable to adequately control pesticide pollution in rivers. With respect to the science underlying attempts to understand and control pesticide contamination in rivers, Damasio, et al. 2011, Christin, et al. 2013, and Blazer, et al. 2012 provide examples of documenting biological responses to the presence of pesticides in river water with respect to invertebrates, frogs, and fish, respectively. One of the challenges to testing for pesticide exposure in people, particularly in young children, is to find a simple, easily collected bodily fluid or tissue, such as the saliva used in biomonitoring in Bulgaroni, et al. 2012. Tien, et al. 2011 assesses the potential of river biofilms to reduce concentrations of pesticides in river water. River biofilms are communities of bacteria, algae, fungi, and micrometazoa that develop on submerged surfaces in rivers. Algae in biofilms take up nutrients and produce oxygen, while bacteria release carbon dioxide. The symbiotic association between algae and bacteria makes biofilms a form of river self-purification and helps to remove organic matter and other contaminants from wastewater entering rivers.

  • Barzman, M., and S. Dachbrodt-Saaydeh. 2011. Comparative analysis of pesticide action plants in five European countries. Pest Management Science 67:1481–1485.

    DOI: 10.1002/ps.2283Save Citation »Export Citation »E-mail Citation »

    Five European countries have started national initiatives to reduce pesticide use or risk. Rather than creating targets for reducing pesticide volume, these initiatives focus on reducing impacts and risk based on a single, objectively verifiable target, which can mobilize a variety of stakeholders to work toward a common goal.

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  • Blazer, V. S., L. R. Iwanowicz, H. Henderson, et al. 2012. Reproductive endocrine disruption in smallmouth bass (Micropterus dolomieu) in the Potomac River basin: Spatial and temporal comparisons of biological effects. Environmental Monitoring and Assessment 184:4309–4334.

    DOI: 10.1007/s10661-011-2266-5Save Citation »Export Citation »E-mail Citation »

    The severity of gonadal abnormalities in male fish correlates with the proportion of upstream sources of endocrine-disrupting chemicals from wastewater treatment plants, crop agriculture, animal feeding operations, and poultry houses. This raises concerns about water quality in the Potomac, which is a source of drinking water for over five million people.

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  • Bulgaroni, V., M. G. Rovedatti, G. Sabino, and G. Magnarelli. 2012. Organophosphate pesticide environmental exposure: Analysis of salivary cholinesterase and carboxilesterase activities in preschool children and their mothers. Environmental Monitoring and Assessment 184:3307–3314.

    DOI: 10.1007/s10661-011-2190-8Save Citation »Export Citation »E-mail Citation »

    Saliva samples from women and children living near an agricultural area in Argentina were used to assess exposure to organophosphate pesticides. Enzymes inhibited by exposure to pesticides decreased significantly in saliva during the growing season, demonstrating the usefulness of this simple, noninvasive test for biomonitoring.

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  • Christin, M. S., L. Menard, I. Giroux, et al. 2013. Effects of agricultural pesticides on the health of Rana pipiens frogs sampled from the field. Environmental Science and Pollution Research International 20:601–611.

    DOI: 10.1007/s11356-012-1160-1Save Citation »Export Citation »E-mail Citation »

    As part of ongoing efforts to explain massive, widespread declines in amphibian populations during the past thirty years, this paper examines influences of pesticide exposure on frogs in Canada’s St. Lawrence River. Frogs in agricultural regions are smaller in size and weight and likely have lower immunity to diseases and infections.

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  • Damasio, J., D. A. Barcelo, R. Brix, et al. 2011. Are pharmaceuticals more harmful than other pollutants to aquatic invertebrate species: A hypothesis tested using multi-biomarker and multi-species responses in field collected and transplanted organisms. Chemosphere 85:1548–1554.

    DOI: 10.1016/j.chemosphere.2011.07.058Save Citation »Export Citation »E-mail Citation »

    This study used river invertebrates exposed to sewage-treated effluents to assess the primary causes of observed biochemical responses to toxic substances. Pesticides and heavy metals accounted for most of the predicted toxicity, with inhibition of enzyme activity correlating strongly with level of the pesticide diazinon.

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  • Plant, R., J. Walker, S. Rayburg, J. Gothe, and T. Leung. 2012. The wild life of pesticides: Urban agriculture, institutional responsibility, and the future of biodiversity in Sydney’s Hawkesbury-Nepean River. Australian Geographer 43:75–91.

    DOI: 10.1080/00049182.2012.649520Save Citation »Export Citation »E-mail Citation »

    This paper presents a useful “reality check” in the form of a case study from southeastern Australia demonstrating that riverine pesticide pollution is rarely measured or monitored, and that it is not a priority of any particular government agency. The authors characterize the present system as “organised irresponsibility” and recommend specific improvements.

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  • Tien, C.-J., T.-L. Chuang, and C. Chen. 2011. The role of naturally occurring river biofilms on the degradation kinetics of diazinon. Clean: Soil, Air, Water 39:931–938.

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    River biofilms can remove the pesticide diazinon from river water, particularly during the spring, when bacterial and algal biomass is higher. Experiments in a river in Taiwan indicated that biofilms promoted degradation of diazinon, with nearly all of the pesticide removed during spring.

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  • Von der Ohe, P. C., V. Dulio, J. Slobodnik, et al. 2011. A new risk assessment approach for the prioritization of 500 classical and emerging organic microcontaminants as potential river basin specific pollutants under the European Water Framework Directive. Science of the Total Environment 409:2064–2077.

    DOI: 10.1016/j.scitotenv.2011.01.054Save Citation »Export Citation »E-mail Citation »

    Paper uses data from European rivers to assess risk from five hundred synthetic chemicals. Chemicals are categorized based on knowledge of ecotoxicity, then prioritized based on frequency and extent of exceedance of predicted no-effect concentrations (PNECs). PNECs were available for 56 percent of the compounds. About 75 percent of priority compounds were pesticides.

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Persistent Organic Pollutants (POPs)

The works cited here discuss types of POPs beyond those treated as separate categories in this entry. POPs include deliberately produced compounds such as pesticides, PCBs, polychlorinated naphthalenes (PCNs), polychlorinated n-alkanes (PCAs), and brominated flame retardants. POPs also include compounds accidentally formed or released as a by-product of activities such as industrial or combustion processes (e.g., polychlorinated dibenzo-p-dioxins [PCDDs] or polychlorinated dibenzofurans [PCDFs]). All of these compounds are harmful to living organisms, environmentally persistent, lipophilic, able to bioaccumulate, and semivolatile. The international community has been working to eliminate POPs since 1995, but only a few forms have been banned to date, even as new forms of POPs continue to be created. Eljarrat and Barceló 2009 summarizes the history and properties of different types of POPs, and reviews the history of attempts to regulate POPs. Bogdal, et al. 2009 provides an intriguing example of geological recycling of stored POPs that continue to enter rivers, despite reduced direct POP production. Sediments are the primary abiotic reservoirs in which POPs from diverse emission sources accumulate. In an overview of POPs, Langenbach 2013 notes that application of pesticides and other POPs over large areas can only be sustainable if the molecules biodegrade naturally, because remediation can only be applied to accidents in restricted areas and is not feasible over large areas. Consequently, the only efficient policy for molecules that do not biodegrade is to restrict their use or ban them completely. Polybrominated diphenyl ethers (PBDEs) are one type of brominated flame retardant that has been widely used worldwide, despite being known endocrine disrupters and neurotoxicants for developing organisms, as discussed in Hooper and McDonald 2000 and Eriksson, et al. 2001. PBDE manufacture in the United States was phased out starting in 2005, but a large number of products containing these compounds remain in use, resulting in continued release of the compounds into the environment. Concentrations of total PBDEs in marine mammals, birds, and humans have doubled approximately every four to seven years between 1970 and 2000, as detailed in de Wit 2002. Most investigations of PBDEs in relation to aquatic biota come from the North Atlantic Ocean and Europe, although several studies focus on freshwater fishes in North America, as exemplified by Xia, et al. 2008. Reiner and Kannan 2011 provides a case study of yet another type of POPs: synthetic or polycyclic musks used in clothes for their pleasant odor and binding affinity for fabrics.

  • Bogdal, C., P. Schmid, M. Zennegg, F. S. Anselmetti, M. Scheringer, and K. Hungerbhler. 2009. Blast from the past: Melting glaciers as a relevant source for persistent organic pollutants. Environmental Science & Technology 43:8173–8177.

    DOI: 10.1021/es901628xSave Citation »Export Citation »E-mail Citation »

    Despite decreases in production of several forms of POPs during the 1980s and 1990s, input into a high alpine lake in Switzerland has increased sharply since the late 1990s. This reflects storage in and release from glacial ice with ongoing global warming. Mountain rivers fed by glacial meltwater can thus be contaminated.

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  • de Wit, C. A. 2002. An overview of brominated flame retardants in the environment. Chemosphere 46:583–624.

    DOI: 10.1016/S0045-6535(01)00225-9Save Citation »Export Citation »E-mail Citation »

    Brominated flame retardant chemicals, including polybrominated diphenyl ethers (PBDEs), are now ubiquitous in sediment and biota across Europe, Japan, and North America. Levels of PBDEs are increasing rapidly, including in humans. Knowledge of PBDEs is limited, but high concentrations can adversely affect wildlife and humans, particularly children and fish consumers.

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  • Eljarrat, E., and D. Barceló. 2009. Chlorinated and brominated organic pollutants in contaminated river sediments. In Contaminated sediments. Edited by T. A. Kassim, and D. Barceló, 21–56. Berlin: Springer-Verlag.

    DOI: 10.1007/978-3-540-88014-1Save Citation »Export Citation »E-mail Citation »

    This useful overview distinguishes classical POPs such as PCBs, PCDDs, and PCDFs from emerging POPs such as PCAs and brominated POPs. Emerging POPs can bioaccumulate and are toxic, but they continue to have widespread and unrestricted use. This paper includes a review of data on chlorinated and brominated POPs in sediments.

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  • Eriksson, P., E. Jakobsson, and A. Fredriksson. 2001. Brominated flame retardants: A novel class of developmental neurotoxicants in our environment. Environmental Health Perspectives 109:903–908.

    DOI: 10.1289/ehp.01109903Save Citation »Export Citation »E-mail Citation »

    PBDEs disperse in the environment similarly to PCBs and DDT. PBDE concentrations are increasing in human milk. Studies with mice indicate that neonatal exposure to common PBDEs can cause permanent aberrations in spontaneous behavior and affect learning and memory in adult animals, similar to the developmental defects caused by PCBs.

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  • Hooper, K., and T. A. McDonald. 2000. The PBDEs: An emerging environmental challenge and another reason for breast-milk monitoring programs. Environmental Health Perspectives 108:387–392.

    DOI: 10.1289/ehp.00108387Save Citation »Export Citation »E-mail Citation »

    Because of the rapid rise of PBDEs concentrations in human tissues, the authors urge continued monitoring of human breast milk to identify important emerging pollutants. The paper also reviews the use, occurrence, and toxicity of PBDEs, and their similarities to PCBs and other POPs.

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  • Langenbach, T. 2013. Persistence and bioaccumulation of persistent organic pollutants (POPs). In Applied bioremediation: Active and passive approaches. Edited by Y. B. Patil and P. Rao, 307–331. Rijeka, Croatia: InTech.

    DOI: 10.5772/50859Save Citation »Export Citation »E-mail Citation »

    Focused mainly on pesticides and on POPs that contaminate large areas, this book chapter is a useful review of the chemical characteristics and environmental dynamics of these POPs. Whether a molecule is adsorbed to sediment is critical to the molecule’s bioavailability, partly because adsorption limits environmental degradation of the molecule.

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  • Reiner, J. L., and K. Kannan. 2011. Polycyclic musks in water, sediment and fishes from the Upper Hudson River, New York, USA. Water, Air, & Soil Pollution 214:335–342.

    DOI: 10.1007/s11270-010-0427-8Save Citation »Export Citation »E-mail Citation »

    Samples indicate that musks are present in water, sediment, fish, and mussels in the Hudson River, with bioaccumulation in fish. Although concentrations tend to be lower than those reported from Europe, the environmental effects of these concentrations remain unknown, but are potentially of concern.

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  • Xia, K., M. B. Luo, C. Lusk, K. Armbrust, L. Skinner, and R. Sloan. 2008. Polybrominated diphenyl ethers (PBDEs) in biota representing different trophic levels of the Hudson River, New York: From 1999 to 2005. Environmental Science & Technology 42:4331–4337.

    DOI: 10.1021/es703049gSave Citation »Export Citation »E-mail Citation »

    Sampling along the Hudson River indicated highest PBDE concentrations in large carnivorous fishes and lowest concentrations in insects. Measurable PBDEs were found in 98 percent of samples. Variations in food preferences, metabolism, and location along the river result in different concentrations among fish species.

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Sediment of sand size or smaller can be of concern as a pollutant in rivers because the sediment carries adsorbed contaminants, or because the sediment creates adverse impacts on water and channel properties. Adverse impacts include turbidity; filling of interstitial spaces between coarser streambed sediment that provides habitat for microorganisms, aquatic insects, and fish eggs, as well as facilitating hyporheic exchange, as described in Huang and Garcia 2000; increased costs of drinking water treatment; clogging fish gills; stimulating growth of cyanobacteria that can produce chemicals toxic to other organisms; altering ecosystem processes such as breakdown of organic matter, as discussed in Magbanua, et al. 2013; bed abrasion and loss of benthic algae, as illustrated by Luce, et al. 2013; increased methane emissions from sediment deposited in ponded areas, as discussed in Maeck, et al. 2013 for dammed rivers; reducing flow depth when sediment accumulates on the streambed; and reducing pool volume and associated aquatic habitat when sediment preferentially accumulates in pools. The US Environmental Protection Agency lists sediment as the most common river pollutant. Excess sediment enters rivers from agricultural lands, construction sites, and places where vegetation cover is being cleared, such as for timber harvest. Sediment can enter streams from point or nonpoint sources, and as sustained or episodic events associated with rainfall, snowmelt, or floods. Chiu, et al. 2013 provides an example of an episodic sediment point source associated with the removal of a dam. Fine sediments require relatively little flow energy to mobilize and transport. Consequently, understanding the dynamics of sediments in a riverine environment requires data of high temporal resolution for both water and sediment discharge, as described in Legout, et al. 2013. Lisle and Hilton 1992 describes a relatively easily measured and consistent index of fine sediment supply to a channel based on surveys of the proportion of pool volume occupied by fine sediment. Ideally, one needs to know the origin of sediments creating pollution; the pathways, magnitude, duration, and frequency of transport; and the environments in which sediments are deposited, as well as retention time, chemical transformations, and biological availability within the sediment storage areas.

  • Chiu, M.-C., C.-H. Yeh, Y.-H. Sun, and M.-H. Kuo. 2013. Short-term effects of dam removal on macroinvertebrates in a Taiwan stream. Aquatic Ecology 47:245–252.

    DOI: 10.1007/s10452-013-9439-ySave Citation »Export Citation »E-mail Citation »

    Removal of a dam on a Taiwanese mountain stream caused immediate decrease in density and taxonomic richness of downstream macroinvertebrates because of scouring or burial by sediment. Macroinvertebrates are likely to recover with time, however, and the abundance of dippers, a very mobile avian insect predator, was not affected.

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  • Huang, X., and M. H. Garcia. 2000. Pollution of gravel spawning grounds by deposition of suspended sediment. Journal of Environmental Engineering 126:963–968.

    DOI: 10.1061/(ASCE)0733-9372(2000)126:10(963)Save Citation »Export Citation »E-mail Citation »

    Rates of fine sediment deposition in spawning gravels are linked to the concentration of fines suspended in the water column. This paper describes a method to numerically predict concentration and transport of fine suspended sediment, which can be used to estimate deposition in gravel beds.

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  • Legout, C., J. Poulenard, J. Nemery, et al. 2013. Quantifying suspended sediment sources during runoff events in headwater catchments using spectrocolorimetry. Journal of Soils and Sediments 13:1478–1492.

    DOI: 10.1007/s11368-013-0728-9Save Citation »Export Citation »E-mail Citation »

    Paper applies rapid and inexpensive methods of identifying sediment sources based on spectroscopy to predicting proportion of various source materials in suspended sediments in a French river. Half of the twenty-three streamflow events analyzed had large variations in the source proportions between sediment samples.

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  • Lisle, T. E., and S. Hilton. 1992. The volume of fine sediment in pools: An index of sediment supply in gravel-bed streams. Water Resources Bulletin 28:371–383.

    DOI: 10.1111/j.1752-1688.1992.tb04003.xSave Citation »Export Citation »E-mail Citation »

    This paper introduces a technique now widely used to assess the supply and deposition of fine sediment in gravel-bed streams. Measuring the relative volume of fine sediment stored in pools can help to assess changes in sediment supply and associated effects on aquatic habitat.

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  • Luce, J. J., M. F. Lapointe, A. G. Roy, and D. B. Ketterling. 2013. The effects of sand abrasion of a predominantly stable stream bed on periphyton biomass losses. Ecohydrology 6:689–699.

    DOI: 10.1002/eco.1332Save Citation »Export Citation »E-mail Citation »

    An example of the effects of mobile sand-sized sediment on riverine ecology. Periphytic algae are an important food source for diverse stream biota, but they can be removed through abrasion by mobile sediments. There is a negative relationship between sand transport rate and biomass after the flow.

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  • Maeck, A., T. DelSontro, D. F. McGinnis, et al. 2013. Sediment trapping by dams creates methane emission hot spots. Environmental Science & Technology 47:8130–8137.

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    Using the Saar River in central Europe as an example, this paper infers that decay of organic matter stored in sediments of dammed reservoirs is the major source of riverine methane emissions, which account for 18 percent of total global emissions. Sediment accumulation correlates with methane production and emission.

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  • Magbanua, F. S., C. R. Townsend, K. J. Hageman, and C. Matthaei. 2013. Individual and combined effects of fine sediment and the herbicide glyphosphate on benthic macroinvertebrates and stream ecosystem function. Freshwater Biology 58:1729–1744.

    DOI: 10.1111/fwb.12163Save Citation »Export Citation »E-mail Citation »

    Paper examines interactions in agricultural streams between fine sediment and a widely used herbicide as these affect leaf breakdown (here, a representative ecosystem function). Sediment accelerated leaf breakdown and affected greater numbers of taxa than the herbicide. The two stressors acted without interaction.

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  • Wagenhoff, A., K. Lange, C. R. Townsend, and C. Matthaei. 2013. Patterns of benthic algae and cyanobacteria along twin-stressor gradients of nutrients and fine sediment: A stream mesocosm experiment. Freshwater Biology 58:1849–1863.

    DOI: 10.1111/fwb.12174Save Citation »Export Citation »E-mail Citation »

    Authors evaluated the interactions between inorganic dissolved nutrients and deposited fine sediment as they influence benthic algae and bacteria in agricultural streams. The two stressors mainly acted in a simple, additive way, with sediment increasing motile organisms, although thresholds existed at which community variables changed abruptly.

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Contaminant Dynamics

Contaminant dynamics here includes processes of physical dispersal in rivers; biological uptake, concentration, and dispersal of contaminants; storage of contaminants in river sediments and biota; chemical transformations of contaminants that create metabolites; and aqueous and particulate (sediment-adsorbed) forms of contaminants. The typically complex dynamics of various forms of river pollution create challenges to measuring and monitoring the spatial and temporal distribution and concentration of contaminants, as well as predicting contaminant response to diverse natural processes (e.g., floods) and remediation strategies. The works cited here are categorized with respect to the role of specific influences on contaminant dynamics, including Contaminant Source, Role of Flow Regime (hydrology), Role of River Geometry, Role of Biota and Role of Chemistry of the river environment. A final category covers Temporal and Spatial Scales of contaminant dynamics by including works that address contaminant persistence and/or transport rates in rivers. In most examples of river pollution, hydrology, river geometry, biota, and chemical influences on contaminant dynamics are so closely intertwined that the designation of individual works as representing specific categories is to some extent artificial. The distinction of works with respect to the categories in the following subsections is useful, however, to emphasize the presence of these diverse influences on contaminant dynamics.

Contaminant Source

Contaminants can originate from diverse sources. Basic categories include point and nonpoint sources. Point sources are typically associated with a single entry point to a river, such as the outflow from a wastewater treatment plant or the confluence of a tributary contaminated by mining sediment. Nonpoint sources are more diffuse, such as widespread runoff that carries nitrates from agricultural lands. Contaminant sources can also be categorized in terms of land cover or land use, such as urban, agriculture, industrial, or mining. The types of contaminants present and the manner in which they are delivered to rivers are influenced by land use. Urban areas typically release heavy metals and synthetic chemicals, including POPs, PCBs, PAHs, and insecticides, to rivers via wastewater treatment plants, storm sewers, and other runoff. Agricultural lands are more likely to release herbicides and excess nutrients to rivers via diffuse runoff, although highly concentrated agricultural operations, such as confined animal feeding operations, can release diverse contaminants, including hormones, antibiotics, manure, and excess nutrients. The type of contaminant and manner of release from industrial sources vary widely, depending on the specific industry. Electroplating facilities can release heavy metals, for example, and pulp and paper mills release a variety of synthetic chemicals. Similarly, mining can release heavy metals, mercury, cyanide, or excess sediments via widespread runoff or point sources, depending on the specific material being mined and the techniques being used for mining and for waste disposal. Arroyo, et al. 2013 provides an example of how the chemistry of receiving river waters influences the fate of these mining pollutants. Hopkins and Roush 2013 illustrates how the spatial distribution of sediment introduced by mining influences fish response. Although many of the works cited in other subheadings within this entry include some aspect of contaminant sources, the works cited here illustrate the diversity of contaminant sources and the methods used to identify these sources. Bende-Michl, et al. 2013 uses modeling to identify nutrient sources. Liang, et al. 2013 uses dual isotopes to identify nitrate sources. Comber, et al. 2013 uses existing national-scale water quality with a decision support system to identify sources and magnitudes of river contaminants.

  • Arroyo, Y. R. R., A. H. S. Munoz, E. Y. Barrientos, I. R. Huerta, K. Wrobel, and K. Wrobel. 2013. Natural decrease of dissolved arsenic in a small stream receiving drainages of abandoned silver mines in Guanajuato, Mexico. Bulletin of Environmental Contamination and Toxicology 91:539–544.

    DOI: 10.1007/s00128-013-1091-7Save Citation »Export Citation »E-mail Citation »

    Example of abandoned mines as a contaminant source, and of how characteristics of the receiving river, such as water chemistry, influence contaminant concentration and dispersal.

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  • Bende-Michl, U., K. Verburg, and H. P. Cresswell. 2013. High-frequency monitoring to infer seasonal patterns in catchment source availability, mobilisation, and delivery. Environmental Monitoring and Assessment 185:9191–9219.

    DOI: 10.1007/s10661-013-3246-8Save Citation »Export Citation »E-mail Citation »

    Develops conceptual model of nutrient sources and transport for an Australian river in which nutrients build up during dry periods, are flushed downstream during the start of high flow, and then become limited unless increasing hydrologic connectivity accesses new nutrient sources.

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  • Comber, S. D. W., R. Smith, P. Daldorph, M. J. Gardner, C. Constantino, and B. Ellor. 2013. Development of a chemical source apportionment decision support framework for catchment management. Environmental Science & Technology 47:9824–9832.

    DOI: 10.1021/es401793eSave Citation »Export Citation »E-mail Citation »

    EU legislation mandating strict water quality standards encourages identifying and quantifying the sources of river pollution. Paper illustrates the application of decision support tools to these tasks, using available national data sets on nutrients, metals, and synthetic chemicals.

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  • Hopkins, R. L., and J. C. Roush. 2013. Effects of mountaintop mining on fish distributions in central Appalachia. Ecology of Freshwater Fish 22:578–586.

    DOI: 10.1111/eff.12061Save Citation »Export Citation »E-mail Citation »

    A nice example of why details matter. Here, the effects of sediment pollution depend strongly on the spatial pattern of sediment introduction—specifically, patch size matters more to fish response than overall proportion of watershed affected.

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  • Liang, X. Q., Z. Y. Nie, M. M. He, et al. 2013. Application of 15N-18O double stable isotope tracer technique in an agricultural nonpoint polluted river of the Yangtze Delta region. Environmental Science and Pollution Research International 20:6972–6979.

    DOI: 10.1007/s11356-012-1352-8Save Citation »Export Citation »E-mail Citation »

    Uses dual isotopes to trace nitrates to specific tributary sources along the Yangtze River. This information can be used to target areas for nitrate mitigation.

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Role of Flow Regime

Flow regime refers to the spatial and temporal characteristics of river discharge, and includes magnitude, duration, frequency, and seasonality of flow. Variations in discharge through time and space influence the physical transport and dispersal of pollutants from point and nonpoint sources, commonly in a nonlinear manner. Kocman, et al. 2011 provides an example of contaminant transport that occurs primarily during short, high-magnitude floods when streambed sediments with adsorbed mercury are mobilized and carried downstream in suspension. Similarly, Bushey, et al. 2008 documents increases in concentrations and fluxes of mercury during storm runoff, although the increases are not linear because of interactions between mercury and other solutes and suspended material in transport. Reid, et al. 2013 illustrates some of the nonlinearities associated with interactions between flow regime and biogeochemical processing by documenting the importance of seasonal high flows on macroinvertebrate communities within intermittent streams. Smith, et al. 2013 discusses how seasonal differences in hydrological connectivity between uplands and rivers influence surface versus subsurface flow paths and associated nutrient transport to rivers. Human alteration of hydrologic pathways and fluxes can also influence river pollution, as illustrated by Buchanan, et al. 2013. As climate and land use change in the future, studies such as Baron, et al. 2013 suggest that hydrologic changes are likely to have the greatest effect on river pollution, in part because measures such as soil conservation practices can be implemented to reduce pollutant inputs, whereas runoff and river discharge may be harder to control. Alam and Dutta 2013 provides another example of assessing the potential impacts of climate change on hydrology and river pollution using a distributed hydrological model. Models can also be used to evaluate the effect on river pollution of different hydrologic scenarios associated with dam operation, as illustrated by Nikoo, et al. 2013 in a case study from Iran.

  • Alam, M. J., and D. Dutta. 2013. Predicting climate change impact on nutrient pollution in waterways: A case study in the upper catchment of the Latrobe River, Australia. Ecohydrology 6:73–82.

    DOI: 10.1002/eco.282Save Citation »Export Citation »E-mail Citation »

    Modeling results suggest that rising temperature increases nutrient-transformation processes and release into rivers. This offsets projected reductions in flow, with the end result that riverine nitrate concentrations increase. This paper illustrates interactions between hydrology and other influences on river pollution.

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  • Baron, J. S., E. K. Hall, B. T. Nolan, et al. 2013. The interactive effects of excess reactive nitrogen and climate change on aquatic ecosystems and water resources of the United States. Biogeochemistry 114:71–92.

    DOI: 10.1007/s10533-012-9788-ySave Citation »Export Citation »E-mail Citation »

    Useful overview of how climate change may influence nitrogen dynamics in rivers and lakes in the United States. The primary effect of climate change will be alteration of the hydrologic cycle, which is more difficult to control than nitrogen inputs to freshwaters.

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  • Buchanan, B., Z. M. Easton, R. L. Schneider, and M. T. Walter. 2013. Modeling the hydrologic effects of roadside ditch networks on receiving waters. Journal of Hydrology 486:293–305.

    DOI: 10.1016/j.jhydrol.2013.01.040Save Citation »Export Citation »E-mail Citation »

    Paper illustrates one form of human alteration of hydrology and river pollution. Roadside drainage ditches in agricultural areas increase peak and total storm runoff discharge. By expediting the transport of agricultural pollutants, ditches limit natural degradation processes that would reduce these pollutants.

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  • Bushey, J. T., C. T. Driscoll, M. J. Mitchell, P. Selvendiran, and M. R. Montesdeoca. 2008. Mercury transport in response to storm events from a northern forest landscape. Hydrological Processes 22:4813–4826.

    DOI: 10.1002/hyp.7091Save Citation »Export Citation »E-mail Citation »

    The complicated patterns of changes in mercury concentration during storm runoff documented in this paper for forested watersheds provide insight into the influences of upland versus floodplain wetland runoff, surface versus subsurface runoff, and dissolved organic carbon concentrations as these influence mobility of mercury.

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  • Kocman, D., T. Kanduc, N. Ogrinc, and M. Horvat. 2011. Distribution and partitioning of mercury in a river catchment impacted by former mercury mining activity. Biogeochemistry 104:183–201.

    DOI: 10.1007/s10533-010-9495-5Save Citation »Export Citation »E-mail Citation »

    This paper illustrates the importance of river discharge not only in transporting dissolved and particulate mercury, but also in mobilizing bed sediments with adsorbed mercury during short but high magnitude floods. Higher discharges also correspond to changing levels of dissolved organic carbon, which reacts with mercury.

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  • Nikoo, M. R., A. Karimi, and R. Kerachian. 2013. Optimal long-term operation of reservoir-river systems under hydrologic uncertainties: Application of interval programming. Water Resources Management 27:3865–3883.

    DOI: 10.1007/s11269-013-0384-2Save Citation »Export Citation »E-mail Citation »

    Paper uses an integrated water quantity-quality model to optimize water allocation and meet water quantity and quality targets. Dilution during wet years satisfies water quality standards. Total dissolved solids can be reduced during dry years through combined changes in water use and storage as influenced by reservoir operations.

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  • Reid, D. J., P. S. Lake, and G. P. Quinn. 2013. Influences of agricultural landuse and seasonal changes in abiotic conditions on invertebrate colonisation of riparian leaf detritus in intermittent streams. Aquatic Science 75:285–297.

    DOI: 10.1007/s00027-012-0273-4Save Citation »Export Citation »E-mail Citation »

    Macroinvertebrates colonize riparian leaf detritus within intermittent rivers in patterns that reflect primarily spatial and temporal variations in flow, rather than adjacent land use. Abundance and species composition of macroinvertebrates are important, as these influence the river’s ability to process nutrients and facilitate biogeochemical reactions that break down contaminants.

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  • Smith, A. P., A. W. Western, and M. C. Hannah. 2013. Linking water quality trends with land use intensification in dairy farming catchments. Journal of Hydrology 476:1–12.

    DOI: 10.1016/j.jhydrol.2012.08.057Save Citation »Export Citation »E-mail Citation »

    Paper illustrates how effects of intensified dairy farming on river water quality differ between catchments because of differing hydrology and dominant hydrological pathways. Seasonal drying of catchments can influence the relative importance of surface and subsurface flow from uplands to rivers, with surface flow carrying greater N and P concentrations.

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  • Wu, L., T.-Y. Long, X. Liu, and J.-S. Guo. 2012. Impacts of climate and land-use changes on the migration of non-point source nitrogen and phosphorus during rainfall-runoff in the Jialing River Watershed, China. Journal of Hydrology 475:26–41.

    DOI: 10.1016/j.jhydrol.2012.08.022Save Citation »Export Citation »E-mail Citation »

    Paper evaluates potential impacts of climate and land-use changes on hydrology and nonpoint sources of nitrogen and phosphorus to a river by using an integrated model of climate, runoff, and nutrient transport. Modeling results suggest that increased runoff will be the greatest cause of increased nutrient concentrations in future.

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Role of River Geometry

River geometry includes the planform and cross-sectional shape of river channels, the presence of a floodplain, and the grain-size distribution of the streambed and banks. As a simple generalization, greater physical complexity of a channel equates to greater potential for areas of flow separation and associated retention of fine sediments and solutes, as well as greater habitat diversity and abundance that promote biological uptake or degradation of pollutants. Physical complexity can occur in the planform of a channel that has multiple branches, sinuosity, or a floodplain connected to the channel. James, et al. 2008 discusses the potential for using this type of physical complexity to reduce nitrogen concentrations in river water. Physical complexity can also occur at the cross-sectional scale in the form of downstream variations in channel width or flow depth. Hydraulic mixing associated with cross-sectional variations can be used to enhance diffusion and dispersion of pollution point sources, as explained in Boxall, et al. 2002. Physical complexity can also take the form of lateral or longitudinal variations in the grain size of sediment forming the channel boundaries; these variations create spatial differences in porosity and permeability that influence hyporheic and groundwater exchange, and create habitat for benthic organisms such as algae and macroinvertebrates. Rates and spatial variations in hyporheic exchange influence nitrogen dynamics, as discussed in Carleton and Mohamoud 2013 and Maazouzi, et al. 2013. Fitzgerald, et al. 2012 demonstrates that rivers with limited physical complexity and retention are likely to be most sensitive to land use changes and pollutant inputs. Where rivers have been artificially simplified through dredging, channelization, or flow regulation, restoration of some level of physical complexity can enhance the diversity and abundance of aquatic biota and reduce pollutant loads, as in the example from an agricultural landscape presented in Evans, et al. 2007. Knowledge of how spatial variations in channel geometry influence the deposition and concentration of pollutants is also necessary when stabilizing or removing pollutants, as discussed for mercury-contaminated river sediments in Blum, et al. 2001.

  • Blum, M., M. S. Gustin, S. Swanson, and S. G. Donaldson. 2001. Mercury in water and sediment of Steamboat Creek, Nevada: Implications for stream restoration. Journal of the American Water Resources Association 37:795–804.

    DOI: 10.1111/j.1752-1688.2001.tb05512.xSave Citation »Export Citation »E-mail Citation »

    Paper describes how mercury-contaminated sediments from historical headwater mining are dispersed along the streambed and banks, from which they can be remobilized during erosion of channel boundaries. Characterizing the spatial distribution of contaminant concentrations in different portions of the channel is used to guide channel stabilization.

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  • Boxall, J. B., I. Guymer, and A. Marion. 2002. Locating outfalls on meandering channels to optimise transverse mixing. Water and Environment Journal 16:194–198.

    DOI: 10.1111/j.1747-6593.2002.tb00394.xSave Citation »Export Citation »E-mail Citation »

    When pollutant sources approximate steady-state conditions, as in the flow from industrial outfalls, the rate of transverse mixing determines whether the pollutant is effectively dispersed or concentrated. This paper demonstrates how outfalls can be located to take advantage of spatial variations in transverse mixing associated with variations in channel geometry.

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  • Carleton, J. N., and Y. M. Mohamoud. 2013. Effect of flow depth and velocity on nitrate loss rates in natural channels. Journal of the American Water Resources Association 49:205–216.

    DOI: 10.1111/jawr.12007Save Citation »Export Citation »E-mail Citation »

    This paper explores how the loss rates of pollutants such as nitrate reflect the movement of pollutant ions from the river water column to anoxic sediments in the streambed. Channel geometry and the resulting distribution of hydraulic forces influence rates of mass transfer between water and bed sediment.

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  • Evans, R. O., K. L. Bass, M. R. Burchell, R. D. Hinson, R. Johnson, and M. Doxey. 2007. Management alternatives to enhance water quality and ecological function of channelized streams and drainage canals. Journal of Soil and Water Conservation 62:308–320.

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    Agricultural drainage straightened and deepened natural channels, disconnecting channels from floodplains and limiting instream processing of nutrients. Restoration designed to reconnect channels with floodplain wetlands and to increase physical channel complexity and retention of solutes and particulates results in reduced nitrogen concentrations and transport.

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  • Fitzgerald, E. P., W. B. Bowden, S. P. Parker, and M. L. Kline. 2012. Urban impacts on streams are scale-dependent with nonlinear influences on their physical and biotic recovery in Vermont, United States. Journal of the American Water Resources Association 48:679–697.

    DOI: 10.1111/j.1752-1688.2012.00639.xSave Citation »Export Citation »E-mail Citation »

    Paper provides an example of threshold effects associated with channel geometry. The effect of urbanization on channel stability and macroinvertebrate diversity interacted significantly with drainage area and channel slope. Small drainage areas and steep channel gradients equate to greater urbanization impacts.

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  • James, W. F., W. B. Richardson, and D. M. Soballe. 2008. Contribution of sediment fluxes and transformations to the summer nitrogen budget of an Upper Mississippi River backwater system. Hydrobiologia 598:95–107.

    DOI: 10.1007/s10750-007-9142-xSave Citation »Export Citation »E-mail Citation »

    This paper addresses altering flow on regulated rivers to take advantage of natural channel geometry as a means to enhance nitrogen retention. Flow regulation limits flooding of backwater areas, but routing water through these floodplain areas can increase nitrate diffusion, denitrification in sediments, and uptake by biota.

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  • Maazouzi, C., C. Claret, M.-J. Dole-Olivier, and P. Marmonier. 2013. Nutrient dynamics in river bed sediments: Effects of hydrological disturbances using experimental flow manipulations. Journal of Soils and Sediments 13:207–219.

    DOI: 10.1007/s11368-012-0622-xSave Citation »Export Citation »E-mail Citation »

    Paper illustrates the effects on nutrient dynamics of river discharge, channel geometry, and vertical hyporheic exchanges between the water column and pore water in the streambed. The hyporheic zone is a source for nitrates and nitrites. Pool-riffle sequences, gravel bars, and grain-size distribution of bed sediments influence hyporheic flow paths.

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Role of Biota

Plants and animals in aquatic and riparian environments both influence and reflect the dispersal and concentration of pollutants. Mobile organisms such as fish and birds influence pollutant dispersal by carrying pollutants in their bodies and introducing the pollutants to new environments when they die. This is exemplified by Ewald, et al. 1998, a study of the Copper River of Alaska, where contaminants are introduced only by global atmospheric transport or in the tissues of migratory salmon. Mobile and sessile organisms can concentrate pollutants through bioaccumulation within an organism and biomagnification within a trophic cascade. Molina, et al. 2010 documents how differences in the food source among diverse invertebrate trophic chains in a floodplain lake in the Amazon result in very different levels of biomagnification of mercury. Hinck, et al. 2009 examines the risk to piscivorous wildlife created by bioaccumulation of diverse contaminants in fish tissues. Some organisms, particularly microbes and plants, can sequester or metabolize pollutants, and thus be used for remediation. Adams, et al. 2013 reviews the use of plants to remove or sequester heavy metals produced by mining. Tyler, et al. 2012 is an example of directly assessing the nitrogen-removal potential of individual plant species as a means of managing vegetation communities to promote nitrogen reduction in receiving waters. Xu, et al. 2012 describes experiments designed to enhance the ability of biofilms of attached algae and bacteria to remove pollutants such as nitrogen from agricultural effluent. Plants that sequester pollutants can also create concentrated contamination that poses problems if the plants are mechanically disturbed by human activities, or if the plants are eaten by other organisms, as in the case study discussed in Hua, et al. 2008. Other organisms, particularly those with short life spans that reflect contemporary and recent water or sediment quality, can be used as bioindicators of the presence and biological availability of pollutants. Arini, et al. 2012 provides an example in which periphytic biofilms are used as bioindicators of heavy metals.

  • Adams, A., A. Raman, and D. Hodgkins. 2013. How do the plants used in phytoremediation in constructed wetlands, a sustainable remediation strategy, perform in heavy-metal-contaminated mine sites? Water and Environment Journal 27:373–386.

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    This paper provides a nice overview of the strengths (low cost, sustainable) and weaknesses (operates only to the depth of plant roots, relatively slow) of phytoremediation. The paper also explains the functional mechanisms of plant species able to tolerate and sequester heavy metals in constructed wetlands at a mining site.

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  • Arini, A., A. Feurtet-Mazel, S. Morin, R. Maury-Brachet, M. Coste, and F. Delmas. 2012. Remediation of a watershed contaminated by heavy metals: A 2-yr field biomonitoring of periphytic biofilms. Science of the Total Environment 425:242–253.

    DOI: 10.1016/j.scitotenv.2012.02.067Save Citation »Export Citation »E-mail Citation »

    Biofilms of attached algae and bacteria that adhere to substrates in water have a short life cycle that facilitates a rapid response to environmental changes. This paper assesses the effects of remediation on an industrially contaminated site by measuring Cd and Zn concentrations and species diversity in biofilm communities.

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  • Ewald, G., P. Larsson, H. Linge, L. Okla, and N. Szarzi. 1998. Biotransport of organic pollutants to an inland Alaska lake by migrating sockeye salmon (Oncorhynchus nerka). Arctic 51:40–47.

    DOI: 10.14430/arctic1043Save Citation »Export Citation »E-mail Citation »

    Paper provides a fascinating example of biotransport of PCBs and DDT. Grayling in a lake used by spawning salmon that had bioaccumulated pollutants during the marine stage of their life cycle had pollutant concentrations more than twice as great as grayling in a lake without migratory salmon.

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  • Hinck, J. E., C. J. Schmitt, K. A. Chojnacki, and D. E. Tillitt. 2009. Environmental contaminants in freshwater fish and their risk to piscivorous wildlife based on a national monitoring program. Environmental Monitoring and Assessment 152:469–494.

    DOI: 10.1007/s10661-008-0331-5Save Citation »Export Citation »E-mail Citation »

    Paper describes concentrations of diverse organochlorine chemicals in fish tissues at sites across the United States. Concentrations in fish from the Mississippi River basin exceed the greatest number of toxicity thresholds. Risk to wildlife consuming fish differs among species and sites, but mainly comes from DDT, PCBs, mercury, and selenium.

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  • Hua, M., J. Darrow, B. K. Greenfield, et al. 2008. HgL3 XANES study of mercury methylation in shredded Eichhornia crassipes. Environmental Science & Technology 42:5568–5573.

    DOI: 10.1021/es800284vSave Citation »Export Citation »E-mail Citation »

    Nonnative water hyacinth in the Sacramento-San Joaquin River delta accumulates mercury and clogs rivers and wetlands. Shredding of plants using specialized boats in order to clear waterways increases mercury methylation. Although mechanical removal of the entire plant is more expensive, it may be necessary to avoid biomagnification of mercury.

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  • Molina, C. I., F.-M. Gibon, J.-L. Duprey, E. Dominguez, J.-R. D. Guimaraes, and M. Roulet. 2010. Transfer of mercury and methylmercury along macroinvertebrate food chains in a floodplain lake of the Beni River, Bolivian Amazonia. Science of the Total Environment 408:3382–3391.

    DOI: 10.1016/j.scitotenv.2010.04.019Save Citation »Export Citation »E-mail Citation »

    Stable isotope tracers indicate multiple trophic chains in a floodplain lake. Biomagnification of methylmercury through these invertebrate trophic chains reflects the source and length of each chain. Biomagnification is virtually absent in the sediment-based chain, but very effective in the periphyton-based chain, which offers the highest rate of source contamination.

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  • Tyler, H. L., M. T. Moore, and M. A. Locke. 2012. Influence of three aquatic macrophytes on mitigation of nitrogen species from agricultural runoff. Water, Air, & Soil Pollution 223:3227–3236.

    DOI: 10.1007/s11270-012-1104-xSave Citation »Export Citation »E-mail Citation »

    Allowing vegetation to grow in agricultural drainage ditches can decrease nitrogen inputs to rivers, but the efficiency of nitrogen removal varies between species. This paper describes experiments designed to measure efficiency of nitrogen removal by individual species, developing knowledge that can be used to manage vegetation communities in ditches.

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  • Xu, X.-Y., L.-J. Feng, L. Zhu, J. Xu, W. Ding, and H.-Y. Qi. 2012. Biofilm formation and microbial community analysis of the simulated river bioreactor for contaminated source water remediation. Environmental Science and Pollution Research 19:1584–1593.

    DOI: 10.1007/s11356-011-0649-3Save Citation »Export Citation »E-mail Citation »

    This paper describes laboratory experiments to determine the optimal combination of suspended sediment and flow velocity for creating biofilms that optimize removal of manganese and ammonia nitrogen from agricultural waters. Experimental results can be used to enhance biofilm formation and pollutant sequestration in natural environments.

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Role of Chemistry

Pollutants can disperse through a river environment in solution, as particulate matter moving alone or adsorbed to sediment, or within the tissues of organisms. In each of these scenarios, the characteristics of the pollutant and how it reacts with water, sediment, and air are influenced by environmental chemistry. Many pollutants break down into metabolites, which may also be toxic to living organisms and persistent in the environment. Understanding the distribution, persistence, and toxicity of pollutants, and how these characteristics change through time, requires information on local chemistry. The works cited in this section reflect the range of influences exerted by environmental chemistry. Anning 2011 compares natural and anthropogenic sources of solutes in rivers in the southwestern United States. Pan, et al. 2013 describes how the removal of phosphorus by adsorption to suspended particulate matter may be reduced as a result of lower particulate matter in water released from dams. Prokes, et al. 2012 discusses different chemical reaction and transport pathways for diverse PAHs, PCBs, and pesticides in relation to factors such as water temperature and concentration of suspended particles. Higashino and Stefan 2011 models the transfer of solutes from stream flow into a porous stream bed, which influences rates of pollutant dispersal and potential biogeochemical reactions in the bed. Wang, et al. 2013 illustrates the influence of ambient chemistry on the retention or release of arsenic adsorbed on river sediments. Xiao, et al. 2013 describes the effect of sediment particle size on phosphorus adsorption in river sediments. Worrall, et al. 2013 describes how solute concentrations vary diurnally and seasonally in relation to changing rates of biogeochemical reactions in a river.

  • Anning, D. W. 2011. Modeled sources, transport, and accumulation of dissolved solids in water resources of the southwestern United States. Journal of the American Water Resources Association 47:1087–1109.

    DOI: 10.1111/j.1752-1688.2011.00579.xSave Citation »Export Citation »E-mail Citation »

    Paper illustrates statistical modeling of solute dynamics based on delivery of solutes from natural and human sources. Solutes accumulate as precipitated salts in sediments and/or dissolved salts in sediment pore water. In the southwestern United States, 56 percent of solutes come from irrigated lands, which make up 2.5 percent of the land area.

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  • Higashino, M., and H. Stefan. 2011. Non-linear effects of solute transfer between flowing water and a sediment bed. Water Research 45:6074–6086.

    DOI: 10.1016/j.watres.2011.09.004Save Citation »Export Citation »E-mail Citation »

    Paper describes a numerical model of solute transfer between stream flow and pore water in the stream bed. Turbulence, standing surface waves, and bedforms each enhance solute transfer into the bed. This is an example of how bed grain-size distribution, geometry, and hydraulics influence contaminant dispersal and chemical reactions.

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  • Pan, G., M. D. Krom, M. Zhang, et al. 2013. Impact of suspended inorganic particles on phosphorus cycling in the Yellow River (China). Environmental Science & Technology 47:9685–9692.

    DOI: 10.1021/es4005619Save Citation »Export Citation »E-mail Citation »

    Much of the phosphorus input to the Yellow River is removed by adsorption because of high total particulate matter, creating phosphorus levels lower than world averages despite high nutrient inputs. Water storage behind dams has substantially reduced particulate matter. Eutrophication can occur if particulate matter falls below a critical threshold.

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  • Prokes, R., B. Vrana, and J. Klanova. 2012. Levels and distribution of dissolved hydrophobic organic contaminants in the Morava River in Zlin district, Czech Republic as derived from their accumulation in silicone rubber passive samplers. Environmental Pollution 166:157–166.

    DOI: 10.1016/j.envpol.2012.02.022Save Citation »Export Citation »E-mail Citation »

    This paper illustrates different chemical reaction pathways for diverse pollutants. Concentrations of volatile PAHs decrease with increasing water temperature, which reflects seasonality in atmospheric deposition. Concentrations of more hydrophobic PAHs, PCBs, and pesticides reflect desorption from suspended particles. Dissolved and particle-bound concentrations of DDT metabolites correlate with each other.

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  • Wang, S., C. Lin, M. He, X. Liu, and S. Liu. 2013. Arsenic distribution and adsorption behavior in the sediments of the Daliao River system in China. Water Environment Research 85:687–695.

    DOI: 10.2175/106143012X13560205144894Save Citation »Export Citation »E-mail Citation »

    This investigation of arsenic distribution and adsorption in river sediments indicates that arsenic adsorbs on sediment within a certain pH range, and is then retained or released from sediments primarily as a function of the presence of other compounds, such as calcium, phosphate, or iron oxyhydroxides.

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  • Worrall, F., N. J. K. Howden, C. S. Moody, and T. P. Burt. 2013. Correction of fluvial fluxes of chemical species for diurnal variation. Journal of Hydrology 481:1–11.

    DOI: 10.1016/j.jhydrol.2012.11.037Save Citation »Export Citation »E-mail Citation »

    This paper describes how river solute concentrations fluctuate diurnally and seasonally as a result of diurnal differences in rates of biogeochemical processes. Dissolved organic carbon concentrations (DOC), for example, are highest during short winter days. Neglecting such effects can cause overestimation of DOC fluxes by up to 19 percent.

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  • Xiao, Y., X.-L. Zhu, H.-K. Cheng, K.-J. Li, Q. Lu, and D.-F. Liang. 2013. Characteristics of phosphorus adsorption by sediment mineral matrices with different particle sizes. Water Science and Engineering 6:262–271.

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    Paper describes the influence of sediment particle size on physical adsorption of phosphorus. Fine sediment has a larger specific surface area and pore volume than coarse sediment, so phosphorus adsorption capacity decreases as particle size increases. Consequently, adequate prediction of phosphorus distribution in river sediments requires knowledge of grain-size distribution.

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Temporal and Spatial Scales

Documenting temporal and spatial scales of river pollution involves quantifying factors such as spatial distribution, spatial and temporal variation in contaminant concentration, persistence of contaminants in diverse media (water, sediment, biota), transport rate of contaminants in solution, adsorbed to sediment, or incorporated into organisms, and sources of pollution. The works cited here provide a few examples of studies targeting some aspect of temporal and spatial scales of river pollution. Ballesté and Blanch 2010 uses survival of sensitive microbial species as an indirect indicator of persistence of fecal pollution. Huang, et al. 2012 is an example of a data-rich situation in which pollution is assessed based on fifteen years of sediment samples from diverse locations along a river. A more common scenario is to have limited data on spatial and temporal trends in pollutants. Cabanillas, et al. 2012 applies fuzzy logic to the problem of assessing risk associated with presence and concentration of diverse pollutants in rivers with limited water-quality data. Ricart, et al. 2010 examines the persistence of a particular pollutant under different scenarios of wastewater treatment, as well as the effect of the pollutant on river biota. Smit, et al. 2010 uses experimental data on desorption of the pesticide dieldrin from contaminated sediment suspended in the water column during floods to model river pollution under scenarios of changing discharge. Solecki, et al. 2011 is an example of developing specific markers to identify pollution sources—in this case, identifying biochemical, bacterial, and genetic indicators of pig manure as a source of fecal pollution.

  • Ballesté, E., and A. R. Blanch. 2010. Persistence of Bacteroides species populations in a river as measured by molecular and culture techniques. Applied and Environmental Microbiology 76:7608–7616.

    DOI: 10.1128/AEM.00883-10Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of using a biomarker to assess persistence of fecal pollution in rivers. The study measured the survival of two microbial species sensitive to low levels of dissolved oxygen and fecal pollution as a means of detecting continuing fecal contamination of water.

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  • Cabanillas, J., A. Ginebreda, D. Guillén, et al. 2012. Fuzzy logic based risk assessment of effluents from waste-water treatment plants. Science of the Total Environment 439:202–210.

    DOI: 10.1016/j.scitotenv.2012.09.008Save Citation »Export Citation »E-mail Citation »

    Limited data on pollutant distribution and persistence create uncertainty in pollution control or remediation strategies. This paper applies fuzzy logic to the problem of assessing risk from wastewater treatment plants. Using data from treatment plants in Spain, the approach identifies four pollutants as being of greatest concern.

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  • Huang, Y., W. Zhu, M. Le, and X. Lu. 2012. Temporal and spatial variations of heavy metals in urban riverine sediment: An example of Shenzhen River, Pearl River Delta, China. Quaternary International 282:145–151.

    DOI: 10.1016/j.quaint.2011.05.026Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of a labor-intensive field campaign to measure the spatial and temporal distribution of heavy metals in river sediments by collecting sediment cores at numerous locations along the river over a period of fifteen years. Cd and Hg create the greatest risk.

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  • Ricart, M., H. Guasch, M. Alberch, et al. 2010. Triclosan persistence through wastewater treatment plants and its potential toxic effects on river biofilms. Aquatic Toxicology 100:346–353.

    DOI: 10.1016/j.aquatox.2010.08.010Save Citation »Export Citation »E-mail Citation »

    Triclosan is an antiseptic common in personal care products, cleansers, and textiles. It is not removed by wastewater treatment and, in dry regions with limited dilution, can become concentrated in rivers. This paper describes the use of experiments to examine the persistence of triclosan and its effects on river biofilms.

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  • Smit, M. P. J., T. Grotenhuis, H. Bruning, and W. H. Rulkens. 2010. Modeling desorption kinetics of a persistent organic pollutant from field aged sediment using a bi-disperse particle size distribution. Journal of Soils and Sediments 10:119–126.

    DOI: 10.1007/s11368-009-0144-3Save Citation »Export Citation »E-mail Citation »

    This paper describes a numerical simulation designed to assess how dieldrin is desorbed, or released, from contaminated sediment into the water column during flooding that erodes the sediment particles and carries them suspended in the water. Modeling was based on desorption kinetics of dieldrin measured using experiments with contaminated sediment.

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  • Solecki, O., L. Jeanneau, E. Jardé, M. Gourmelon, C. Melon, and A. M. Pourcher. 2011. Persistence of microbial and chemical pig manure markers as compared to faecal indicator bacteria survival in freshwater and seawater microcosms. Water Research 45:4623–4633.

    DOI: 10.1016/j.watres.2011.06.012Save Citation »Export Citation »E-mail Citation »

    This paper describes the evaluation of several potential indicators of fecal pollution in river water. European water directives require identification of fecal pollution sources, so this study focused on identifying animal-specific markers for pig manure.

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Remediation removes a pollutant source or mitigates the effects of pollutants dispersed through a river. Remediation can occur outside the channel: a source of pollutants such as mine tailings can be contained or isolated from the stream; wastewater treatment can be improved to prevent pollutants from entering a river; reduction of urban stormwater runoff from impervious surfaces can improve water quality; or wetlands or riparian zones can be used to filter pollutants transported by surface runoff or groundwater. Remediation can also occur within a river, as when contaminated sediments are dredged from a channel or floodplain, clean water is added to dilute a contaminant, or crushed limestone is added to neutralize the effects of acid rain or acid mine drainage. Wetlands within a watershed provide pollutant mitigation, as demonstrated by Pound, et al. 2013 for river recovery from acidification. Plants within a river can also be effective in remediation. Phytoremediation is remediation of polluted water via sorption and degradation of pollutants by plants. Xiao, et al. 2013 describes the use of aquatic plants able to survive in nutrient-laden waters in a constructed tank through which polluted water was run. Many remediation activities target mining pollutants. Associated studies focus on assessing water quality and biological communities along a contamination gradient. The remote location of some mines can make monitoring very difficult, and Chapin and Todd 2012 describes an automated water sampler that collects samples at regular temporal intervals over periods of several months. Myers 2013 numerically simulates contaminant transport in order to prioritize individual mines within a watershed for remediation. Hadley and Newell 2012 provides a comprehensive overview of the importance of conceptual models, in this case of groundwater dynamics, in remediation technologies. Strawn, et al. 2012 provides an example of understanding the spatial complexities of contaminant distribution within soils in a watershed when containing or removing contaminated soils. Davis and Kidd 2012 illustrates the importance of understanding sources of water quality degradation in order to design remediation strategies targeting these sources. The Clean Water Act stipulates that impaired rivers must have total maximum daily loads (TMDLs) formulated for the river that indicate the amount of contaminant the river can receive and still meet water quality standards. Walton-Day, et al. 2012 provides an example of using spatially detailed water quality data and numerical simulation to develop TMDLs for a river with mining sources of heavy metals.

  • Chapin, T. P., and A. S. Todd. 2012. MiniSipper: A new in situ water sampler for high-resolution, long-duration acid mine drainage monitoring. Science of the Total Environment 439:343–353.

    DOI: 10.1016/j.scitotenv.2012.07.083Save Citation »Export Citation »E-mail Citation »

    A pilot study demonstrating the effectiveness of automated water sampling during a period of more than eight months at a high-elevation abandoned mine in Colorado. The temporally detailed samples collected in this manner illustrate correlations between climatic and hydrologic variations and metal loading to the Snake River.

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  • Davis, J., and I. M. Kidd. 2012. Identifying major stressors: The essential precursor to restoring cultural ecosystem services in a degraded estuary. Estuaries and Coasts 35:1007–1017.

    DOI: 10.1007/s12237-012-9498-7Save Citation »Export Citation »E-mail Citation »

    Paper uses an Australian estuary to illustrate the importance of identifying contemporary and historical sources of river degradation, here by sediment, in order to design effective remediation strategies that target the sources of degradation.

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  • Hadley, P. W., and C. J. Newell. 2012. Groundwater remediation: The next 30 years. Ground Water 50:669–678.

    DOI: 10.1111/j.1745-6584.2012.00942.xSave Citation »Export Citation »E-mail Citation »

    Uses groundwater remediation to discuss how conceptual models influence remediation, and how conceptual models can change in response to new information. Although groundwater processes differ from those in rivers, contaminated groundwater can be a source of river pollution.

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  • Myers, T. 2013. Remediation scenarios for selenium contamination, Blackfoot watershed, southeast Idaho, USA. Hydrogeology Journal 21:655–671.

    DOI: 10.1007/s10040-013-0953-8Save Citation »Export Citation »E-mail Citation »

    Paper illustrates the complexities of prioritizing remediation. Phosphate mining in the Blackfoot watershed concentrated naturally occurring selenium, resulting in river pollution via ground and surface pathways. Remediation of mines in different locations within the watershed can reduce selenium discharge to the river, or reduce the size of groundwater contaminant plumes.

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  • Pound, K. L., G. B. Lawrence, and S. I. Passy. 2013. Wetlands serve as natural sources for improvement of stream ecosystem health in regions affected by acid deposition. Global Change Biology 19:2720–2728.

    DOI: 10.1111/gcb.12265Save Citation »Export Citation »E-mail Citation »

    Example of how wetlands influence watershed-scale recovery from atmospheric deposition of pollutants. This large, regional-scale study in the Adirondack Mountains of New York demonstrates that greater wetland area correlates with higher organic content and lower concentrations of acidic anions, both of which are beneficial for diatom biodiversity.

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  • Strawn, D. G., P. J. Hickey, P. A. McDaniel, and L. L. Baker. 2012. Distribution of As, Cd, Pb, and Zn in redox features of mine-waste impacted wetland soils. Journal of Soils and Sediments 12:1100–1110.

    DOI: 10.1007/s11368-012-0543-8Save Citation »Export Citation »E-mail Citation »

    Mining contaminants concentrate within surface soil horizons, suggesting that soil-forming processes create an upward-flux of contaminants. The details of contaminant distribution reflect landscape position and water table history: As and Zn preferentially associate with Fe-rich soil features, for example, whereas Pb and Cd associate with Mn-enriched soil aggregates.

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  • Walton-Day, K., R. L. Runkel, and B. A. Kimball. 2012. Using spatially detailed water-quality data and solute-transport modeling to support total maximum daily load development. Journal of the American Water Resources Association 48:949–969.

    DOI: 10.1111/j.1752-1688.2012.00662.xSave Citation »Export Citation »E-mail Citation »

    Paper illustrates an approach to developing guidelines for total maximum daily loads (TMDLs) using a solute transport model to simulate attenuation from instream reactions and inputs from groundwater and surface sources. This case study illustrates spatial and temporal variations in contaminant inputs and within-watershed reactions that make TMDL development difficult.

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  • Xiao, J., H. Wang, S. Chu, and M.-H. Wong. 2013. Dynamic remediation test of polluted river water by Eco-tank system. Environmental Technology 34:553–558.

    DOI: 10.1080/09593330.2012.704405Save Citation »Export Citation »E-mail Citation »

    Paper provides an example of using aquatic plants to remediate river water polluted by domestic sewage. Different plant species took up ammonium nitrogen and phosphorus and increased dissolved oxygen levels in an experimental tank through which polluted water was run, indicating potential for in situ remediation of nutrient-laden river water.

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Case Studies of River Basins

The case studies that follow represent geographic diversity, with at least one case study from each continent, and diverse forms of river pollution. Pollution can come from point sources such as a tributary discharging contaminants into a larger river, or a mine, factory, or sewage treatment plant along a river that discharges wastes directly into the river. Nonpoint sources of pollution are more widespread and diffuse, and typically harder to control, such as when agriculture across the uplands of a river catchment creates excess nutrient fluxes into the river, or numerous urban areas in a developing country that lacks sewage treatment release raw sewage and other wastes into a river. Within a riverine environment, river dynamics strongly control pollutant transport and dispersal. Contaminants can concentrate in floodplain sediments over time, or be diluted and dispersed widely downstream by stream flow. Assessment of pollutant levels or sources is not straightforward, as demonstrated by the case studies that follow. Papers written about the same river catchment can contradict each other regarding whether a particular contaminant is or is not a problem, sometimes because of spatial or temporal discontinuities in distribution of the contaminant relative to the sampling program designed to assess the contaminant. Demonstrating cause and effect between contaminant levels and resulting declines in health can also be difficult, because people and other animals are commonly mobile during the course of their lives, limiting exposure to contaminants in one particular environment.

Clark Fork River, Montana, USA

Mining and processing of metal ores began in the 1850s in the upper Clark Fork River. An estimated 100 million tons of tailings rich in heavy metals were dumped into the river between 1880 and 1982. Riverine processes dispersed contaminated material over 400 kilometers downstream, with the highest concentrations in the upper 45 kilometers. The area was declared a US Environmental Protection Agency Superfund site in 1989. Remediation efforts in the upper 45 kilometers include construction of berms, in situ treatment of riparian soils, and bank stabilization. Tributary inputs dilute metal concentrations downstream, but the Milltown Reservoir, constructed in 1906, has trapped metal-contaminated sediment. Periodic ice-jam flooding causes scouring and mobilizes contaminated sediment from the reservoir, as documented in Moore and Landrigan 1999. Most monitoring studies cover less than five years and focus on indirect measures that may not reflect metal exposure and bioavailability. Hornberger, et al. 2009 is unusual in that it includes a much longer monitoring time period and directly measures metal concentrations in streambed surface sediments and in aquatic insects. A key component of understanding river pollution is the physical processes that transport and redistribute contaminants, as illustrated by Moore and Landrigan 1999, Davis and Atkins 2001, and Lauer and Parker 2008. Numerical modeling undertaken by Lauer and Parker 2008 suggests that natural removal of tailings from the Clark Fork River floodplain could take thousands of years. Another key component is to decipher the complex biogeochemical reactions that influence contaminant concentration, as illustrated by Gammons, et al. 2007. Isolating the effect of individual contaminants can be difficult. Erickson, et al. 2010 provides an example of a study that examines the effects on juvenile fish growth rate of several contaminants. Aquatic organisms can be exposed to heavy metals through their diet or through the water. Waterborne metals exposure has been considered more important, but Meyer, et al. 2006 suggests that this reflects laboratory diets of fish that do not simulate metal-laden prey such as aquatic insects in contaminated river sites. Biological transformations significantly influence mobility of aqueous metal ions. Such transformations include bacterial respiration of minerals, which facilitates dissolution, desorption, and release of metal ions, and redox reactions of nonessential metals taken up by bacteria. By altering metal speciation, these bacterial transformations affect metal bioavailability to higher organisms. Bouskill, et al. 2007 uses readily assessed microbial biomarkers to examine metal bioavailability at sites along the Clark Fork River.

  • Bouskill, N. J., E. P. Barnhart, T. S. Galloway, R. D. Handy, and T. E. Ford. 2007. Quantification of changing Pseudomonas aeruginosa sodA, htpX and mt gene abundance in response to trace metal toxicity: A potential in situ biomarker of environmental health. FEMS Microbiological Ecology 60:276–286.

    DOI: 10.1111/j.1574-6941.2007.00296.xSave Citation »Export Citation »E-mail Citation »

    Paper illustrates microbiological and genetic assessment of metal detoxification and general stress genes in sediment-dwelling prokaryotic bacteria as a measure of severity of metal contamination. The highest incidence of bacterial stress genes correlate with most severe pollution, demonstrating the usefulness of microbial biomarker tools to monitor and predict metal bioavailability.

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  • Davis, A., and D. Atkins. 2001. Metal distribution in Clark Fork River sediments. Environmental Science & Technology 35:3501–3506.

    DOI: 10.1021/es001881cSave Citation »Export Citation »E-mail Citation »

    Accurately sampling pore water and streambed sediment can be difficult in cobble-bed rivers that limit coring. This paper describes the use of frozen cores that allow intact samples to be extracted for analysis. The small proportion of samples composed by the clay/silt fraction contained higher metal concentrations than the sand.

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  • Erickson, R. J., D. R. Mount, T. L. Highland, et al. 2010. Effects of copper, cadmium, lead, and arsenic in a live diet on juvenile fish growth. Canadian Journal of Fisheries and Aquatic Sciences 67:1816–1826.

    DOI: 10.1139/F10-098Save Citation »Export Citation »E-mail Citation »

    This paper provides an example of assessing the effects of individual contaminants. Juvenile fish fed invertebrates contaminated with heavy metals over a period of thirty days had no change in growth and survival, but arsenic in the food reduced trout growth rates in a dose-dependent manner.

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  • Gammons, C. H., T. M. Grant, D. A. Nimick, S. R. Parker, and M. D. DeGrandpre. 2007. Diel changes in water chemistry in an arsenic-rich stream and treatment-pond system. Science of the Total Environment 384:433–451.

    DOI: 10.1016/j.scitotenv.2007.06.029Save Citation »Export Citation »E-mail Citation »

    This paper illustrates the complexities of biogeochemical reactions that influence contaminant dynamics in rivers. Dissolved arsenic concentrations in river water increased up to 51 percent during the day relative to nighttime levels because of pH- and temperature-dependent sorption of arsenic onto hydrous metal oxides or biofilms on the streambed.

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  • Hornberger, M. I., S. N. Luoma, M. L. Johnson, and M. Holyoak. 2009. Influence of remediation in a mine-impacted river: Metal trends over large spatial and temporal scales. Ecological Applications 19:1522–1535.

    DOI: 10.1890/08-1529.1Save Citation »Export Citation »E-mail Citation »

    Examining metal concentrations in aquatic insects and bed sediment over nineteen years after the start of remediation, this paper demonstrates the complexities of remediation. Although heavy metal concentrations declined, remediation mobilized arsenic, causing increasing concentrations of this highly toxic element. High flows redistributed the newly mobilized contaminants throughout the river.

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  • Lauer, J. W. and G. Parker. 2008. Modeling framework for sediment deposition, storage, and evacuation in the floodplain of a meandering river: Application to the Clark Fork River, Montana. Water Resources Research 44:W08404.

    DOI: 10.1029/2006WR005529Save Citation »Export Citation »E-mail Citation »

    An example of using numerical modeling of physical processes to predict contaminant dispersal with time as a function of flow regime, sediment supply, and channel geometry. The model reproduces observed processes such as floodplain aggradation during mining and subsequent net supply of sediment from the floodplain to the channel.

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  • Meyer, J. S., M. J. Suedkamp, J. M. Morris, and A. M. Farag. 2006. Leachability of protein and metals incorporated into aquatic invertebrates: Are species and metals-exposure history important? Archives of Environmental Contamination and Toxicology 50:79–87.

    DOI: 10.1007/s00244-005-7005-xSave Citation »Export Citation »E-mail Citation »

    The experiments reported in this paper reveal that leachability of metals and protein differ considerably among invertebrate species. Consequently, different invertebrates and different histories of metals exposure might create different availability of metals and protein to predators.

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  • Moore, J. N., and E. M. Landrigan. 1999. Mobilization of metal-contaminated sediment by ice-jam floods. Environmental Geology 37:96–101.

    DOI: 10.1007/s002540050365Save Citation »Export Citation »E-mail Citation »

    A large jam formed by river ice caused flooding and mobilized substantial amounts of fine-grained, metal-contaminated sediment from a reservoir. Metal concentrations were enriched downstream from the reservoir after the flood, whereas metal concentrations upstream were diluted by the flood.

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Chang Jiang (Yangtze River), China

Several of China’s major rivers are characterized by naturally high concentrations of suspended sediment as a result of erodible soils, relatively dry climate, and steep topography. The Huang He, or Yellow River, was so-named because of its yellowish hue resulting from suspended sediment. Agricultural and industrial land uses have exacerbated sediment inputs to rivers, and sediment has long been viewed as a source of pollution in Chinese rivers. Human and animal wastes have also been traditional river pollutants in China, but dilution and biological breakdown of these materials have limited their effects on riverine communities and human consumptive uses of river water. Increasing population and concentration of population in larger urban centers now creates health risks from intestinal protozoan pathogens, however, as discussed in Xiao, et al. 2013. As China has rapidly industrialized during the late 20th and early 21st centuries, numerous additional types of pollutants have entered rivers. Gui, et al. 2013 discusses excess nutrient inputs from upland sources. Development and enforcement of environmental regulations have not kept pace with the introduction of new sources of river pollution, and water quality in China is now widely perceived as a major problem. Contaminants from the river also affect deltaic and nearshore sediments and biota, as documented in Shi, et al. 2013 and Yu, et al. 2013. In the works cited here, the Chang Jiang is used to represent the condition of rivers throughout China. Attention has been focused on this river partly because of the construction of Three Gorges Dam, and partly because the river supplies drinking water to major urban centers, including Beijing. Papers about river pollution in the Chang Jiang only recently began to appear in international English-language journals, so all of the works cited here were published in 2013. Floehr, et al. 2013 provides a comprehensive overview of the pollution status of the river by reviewing twenty years of published research from sites along the entire length of the river. Maloney and Hutchins 2013 also provide an effective overview of the history and contemporary status of land use and associated river pollution in the Chang Jiang drainage basin.

  • Floehr, T., H. Xiao, B. Scholz-Starke, et al. 2013. Solution by dilution?—A review on the pollution status of the Yangtze River. Environmental Science and Pollution Research 20:6934–6971.

    DOI: 10.1007/s11356-013-1666-1Save Citation »Export Citation »E-mail Citation »

    Huge amounts of urban sewage, agricultural effluents, industrial wastewater, and ship wastes enter the Chang Jiang. Twenty years of research indicate contamination of water, sediment, and aquatic organisms with PAHs, PCBs, pesticides, PBDEs, PFCs, and other compounds. Dilution reduces ecotoxicological risk in the river, but does not eliminate it.

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  • Gui, Z.-F., B. Xue, S.-C. Yao, W.-J. Wei, and S. Yi. 2013. Organic carbon burial in lake sediments in the middle and lower reaches of the Yangtze River basin, China. Hydrobiologia 710:143–156.

    DOI: 10.1007/s10750-012-1365-9Save Citation »Export Citation »E-mail Citation »

    Cores from five floodplain lakes along the Yangtze record one hundred years of sedimentation. Total organic carbon in the cores increased significantly during the mid- to late 20th century in response to changing lake organic productivity as a result of increased nutrient inputs from upland sources.

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  • Maloney, T. B., and B. R. Hutchins, eds. 2013. Yangtze River: Geography, pollution and environmental implications. Hauppauge, NY: Nova Science.

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    This book covers the long history of land use in the Yangtze, including recent changes associated with China’s rapid economic development. The book also addresses some of the river contamination associated with land use. Individual chapters focus on sediment and chlorinated organic contaminants.

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  • Shi, H., J. Yuan, Z. Dai, and H. Yao. 2013. The teratogenic effects of sediments from the Yangtze Estuary and adjacent bay, China, on frog embryos. Environmental Earth Sciences 68:2385–2391.

    DOI: 10.1007/s12665-012-1922-6Save Citation »Export Citation »E-mail Citation »

    Extracts from sediments in the Chang Jiang estuary induced multiple malformations in frog embryos. Nearshore sediments induced malformations in a greater percentage of embryos than did offshore sediments, suggesting a spatial gradient in ecotoxicity of sediments with distance from the river mouth.

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  • Xiao, G., Z. Qiu, J. Qi, et al. 2013. Occurrence and potential health risk of Cryptosporidium and Giardia in the Three Gorges Reservoir, China. Water Research 47:2431–2445.

    DOI: 10.1016/j.watres.2013.02.019Save Citation »Export Citation »E-mail Citation »

    The reservoir formed by Three Gorges Dam is the largest lake in the world and a major source of water for consumptive human use in China. A majority of water samples from monitoring sites and wastewater-treated effluent within the reservoir contained high concentrations of intestinal protozoan pathogens.

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  • Yu, Y., J. Song, X. Li, H. Yuan, and N. Li. 2013. Fractionate, sources, and budgets of potential harmful elements in surface sediments of the East China Sea. Marine Pollution Bulletin 68:157–167.

    DOI: 10.1016/j.marpolbul.2012.11.043Save Citation »Export Citation »E-mail Citation »

    Spatial distributions of nine potential harmful elements (V, Cr, Co, Ni, Cu, Zn, Mo, Cd, and Pb) in surface sediments of the East China Sea indicate that the Chang Jiang is a major source (82–90%) of these contaminants to the nearshore environment.

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Cuyahoga River, Ohio, USA

The Cuyahoga River of northern Ohio is famous as the river that was so polluted that the water surface caught on fire during the 1960s. Although this was not the first time the river had caught fire, and although the Cuyahoga was not the only river to burn, the highly publicized 1960s fire helped to raise awareness of river pollution and contributed to later passage of the Clean Water Act in the United States. A variety of contaminants pollute the Cuyahoga River, which flows into Lake Erie. By the late 1960s, Lake Erie was suffering from eutrophication and hypoxia because of the fluxes of nutrients entering the lake from numerous tributary rivers. Other contaminants became concentrated in riverine and nearshore sediments, as discussed in Arbuckle, et al. 1995. Richards, et al. 1996 documents how concentrations of herbicides entering Lake Erie from different tributaries correlate with the proportion of each tributary’s drainage area in row crops, and Richards, et al. 2008 describes how amounts of suspended sediments, and adsorbed contaminants, have increased with development in the region. Some of the effects of these contaminants on riverine biota are discussed in Smith, et al. 1994; Lesko, et al. 1996; and Mitchelmore and Rice 2006. A section of the Clean Water Act addresses total maximum daily loads (TMDLs), which specify the amount of a specific pollutant that is allowable within a watershed. The Clean Water Act includes provisions for developing TMDLs to restore impaired water bodies where controls on point sources alone are insufficient to meet Clean Water Act goals. TMDLs can be met via actions such as increasing flow to increase dissolved oxygen or decrease nutrient concentration. Tuckerman and Zawiski 2007 describes the removal of dams as part of a strategy to meet TMDLs for dissolved oxygen.

  • Arbuckle, W. B., J. H. Olive, and S. Tuckerman. 1995. Toxicity of Cuyahoga River and nearshore Lake Erie sediments to Photobacterium phosphoreum. Journal of Great Lakes Research 21:64–70.

    DOI: 10.1016/S0380-1330(95)71021-8Save Citation »Export Citation »E-mail Citation »

    Despite improved treatment of sewage and industrial waste, and improvements in water quality, riverine and nearshore sediments remain a potential reservoir of pollution. Ninety-three percent of sediment samples from the lower Cuyahoga River and Lake Erie were toxic to a common aquatic bacterial species.

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  • Hartig, J. H. 2010. Burning rivers: Revival of four urban-industrial rivers that caught on fire. Essex, UK: Multi-Science.

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    The Cuyahoga is one of four rivers profiled in this well-written book by a limnologist. The book is designed for a nonspecialist audience; it explores the condition of each river at the time it burned, as well as the river’s subsequent restoration and ecological revival.

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  • Lesko, L. T., S. B. Smith, and M. A. Blouin. 1996. The effect of contaminated sediments on fecundity of the brown bullhead in three Lake Erie tributaries. Journal of Great Lakes Research 22:830–837.

    DOI: 10.1016/S0380-1330(96)71004-3Save Citation »Export Citation »E-mail Citation »

    Comparison of fecundity and condition of female brown bullhead from the Cuyahoga River and unpolluted sites indicates that, despite a high frequency of external abnormalities on Cuyahoga fish, fecundity was not adversely affected by contaminated sediments. This may reflect reduced predation and competition from sensitive fishes absent from the Cuyahoga.

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  • Mitchelmore, C. L., and C. P. Rice. 2006. Correlations of nonylphenol-ethoxylates and nonylphenol with biomarkers of reproductive function in carp (Cyprinus carpio) from the Cuyahoga River. Science of the Total Environment 371:391–401.

    DOI: 10.1016/j.scitotenv.2006.08.049Save Citation »Export Citation »E-mail Citation »

    Carp sampled at seven sites from the relatively pristine headwaters to downstream river segments heavily polluted by industrial and urban sources show increasing effects downstream from hormone-mimicking pollutant sources. Surfactants used in industrial processes and household products impact fish reproductive processes. These compounds are abundant downstream from wastewater treatment plants.

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  • Richards, R. P., D. B. Baker, J. P. Crumrine, J. W. Kramer, D. E. Ewing, and B. J. Merryfield. 2008. Thirty year trends in suspended sediment in seven Lake Erie tributaries. Journal of Environmental Quality 37:1894–1908.

    DOI: 10.2134/jeq2007.0590Save Citation »Export Citation »E-mail Citation »

    Sediment entering Lake Erie is a direct pollutant and a carrier of other pollutants adsorbed to the sediment. Daily suspended sediment measurements from 1975 to 2005 indicate increasing suspended sediment discharge from the Cuyahoga River since 2000, which may reflect increased development of the watershed.

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  • Richards, R. P., D. B. Baker, J. W. Kramer, and D. E. Ewing. 1996. Annual loads of herbicides in Lake Erie tributaries of Michigan and Ohio. Journal of Great Lakes Research 22:414–428.

    DOI: 10.1016/S0380-1330(96)70966-8Save Citation »Export Citation »E-mail Citation »

    Riverine loading of several herbicides correlates with proportion of the drainage area in row crop agriculture, but exhibits substantial interannual variability as result of fluctuations in precipitation and discharge. The lowest loads occur during drought years, and the highest loads exceed the lowest by up to sixtyfold.

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  • Smith, S. B., M. A. Blouin, and M. J. Mac. 1994. Ecological comparisons of Lake Erie tributaries with elevated incidence of fish tumors. Journal of Great Lakes Research 20:701–716.

    DOI: 10.1016/S0380-1330(94)71188-6Save Citation »Export Citation »E-mail Citation »

    Comparing the Cuyahoga and other polluted rivers tributary to Lake Erie with unpolluted tributaries, this paper demonstrates lower species diversity of benthic invertebrates and fish and much greater incidence of fish tumors in the polluted rivers.

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  • Tuckerman, S., and B. Zawiski. 2007. Case studies of dam removal and TMDLs: Process and results. Journal of Great Lakes Research 33:103–116.

    DOI: 10.3394/0380-1330(2007)33[103:CSODRA]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    This paper describes modification of one dam and removal of another along the Cuyahoga in order to restore habitat and meet water quality objectives of increasing dissolved oxygen (DO). Changes to the dams resulted in marked improvements in fish communities and increased DO levels within a year.

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Danube River, Europe

As with all of the river basin case studies in this entry, the Danube River is polluted by a wide variety of contaminants from diverse sources. The Danube River basin spans a large part of Europe, from headwaters in Germany to the delta in Romania. The basin includes the territories of twelve countries and collects some discharge from an additional four countries. The river network illustrates geographic differences between western Europe, where water quality has improved substantially in recent decades as a result of strict environmental standards and enforcement, and eastern Europe, where water quality remains highly compromised because of limited environmental regulation and enforcement. Nachtnebel 2000 describes some of the challenges in coordinating water quality policies among such a large group of diverse nations. Particular pollution problems include mining wastes from mountainous headwaters in Romania, as described in Lucas 2001 and Servida, et al. 2013; high nitrogen and phosphorus loads from agricultural runoff and insufficient urban sewage treatment or aging/failing sewage infrastructure; changes in water and sediment transport that result from intensive flow regulation and influence pollutant transport and storage; and contamination from various hydrocarbons and synthetic chemicals. Some of the works cited here provide examples of characterizing specific types of pollution in limited geographic areas, such as Famera, et al. 2013 for heavy metals in a Danube tributary within the Czech Republic. Others provide an integrative view of the combined effects of multiple stressors on river biota, such as Steffen, et al. 2013 for riverine plants, and Subotić, et al. 2013 for fish. Ulniković, et al. 2013 discusses wastes released by cruise ships, a source of pollution for which there may not be as much awareness as there is for the “traditional” pollutant sources such as mining or industry. Mousing, et al. 2013 describes the cumulative effects of Danube River pollution on downstream ecosystems in the Black Sea.

  • Famera, M., O. Babek, T. M. Grygar, and T. Novakova. 2013. Distribution of heavy-metal contamination in regulated river-channel deposits: A magnetic susceptibility and grain-size approach; River Morava, Czech Republic. Water, Air, & Soil Pollution 224:1525 (18 pp).

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    Heavy metals in riverine environments typically bind to fine-grained sediments such as clay, but sampling in this Danube tributary indicates that heavy metals in the form of fly-ash spherules can concentrate in sands within the river channel. Local point sources are fly-ash deposit spills from industrial and power plants.

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  • Lucas, C. 2001. The Baia Mare and Baia Borsa accidents: Cases of severe transboundary water pollution. Environmental Policy and Law 31:106–111.

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    Detailed description of two tailings dam failures at gold mines in the Romanian headwaters of the Danube during 2000. Hundreds of thousands of cubic meters of water and sediment contaminated with cyanide spread over tens of kilometers downstream. The resulting acute transboundary pollution killed river biota and affected drinking-water supplies.

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  • Mousing, E. A., T. J. Andersen, and M. Ellegaard. 2013. Changes in the abundance and species composition of phytoplankton in the last 150 years in the southern Black Sea. Estuaries and Coasts 36:1206–1218.

    DOI: 10.1007/s12237-013-9623-2Save Citation »Export Citation »E-mail Citation »

    Paper summarizes a paleoecological study of fossils contained in two sediment cores from the southern Black Sea. Changes in species composition and a marked increase in the abundance of siliceous protists after around 1960 reflect increased nutrient loading from the Danube River, providing a nice example of downstream effects of river pollution.

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  • Nachtnebel, H.-P. 2000. The Danube River Basin Environmental Programme: Plans and actions for a basin wide approach. Water Policy 2:113–129.

    DOI: 10.1016/S1366-7017(99)00025-2Save Citation »Export Citation »E-mail Citation »

    Cooperation among countries within the river basin has mainly occurred as bilateral agreements, except for a basin-wide navigation agreement established after World War II. National economic and political differences limited more comprehensive agreements, but a basin-wide environmental program established in 1992 created a strategic action plan, which this paper discusses.

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  • Servida, D., S. Comero, M. D. Santo, et al. 2013. Waste rock dump investigation at Roşia Montană gold mine (Romania): A geostatistical approach. Environmental Earth Sciences 70:13–31.

    DOI: 10.1007/s12665-012-2100-6Save Citation »Export Citation »E-mail Citation »

    The largest European gold mine, located in a Danube tributary within Romania, is a source for heavy metals from abandoned underground workings and piles of waste rock. This paper reviews geochemical techniques for identifying sources, distribution, and environmental effects of individual toxic elements.

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  • Steffen, K., T. Becker, W. Herr, and C. Leuschner. 2013. Diversity loss in the macrophyte vegetation of northwest German streams and rivers between the 1950s and 2010. Hydrobiologia 713:1–17.

    DOI: 10.1007/s10750-013-1472-2Save Citation »Export Citation »E-mail Citation »

    Resampling of 338 plots to assess changes in river macrophyte diversity in seventy rivers indicates a 28 percent decrease in the total macrophyte species pool, as well as a shift toward species with higher tolerance of mechanical stress. Changes reflect continued nutrient inputs, and channel maintenance that reduced low-velocity and undisturbed river habitats.

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  • Subotić, S., Ž. Višnjić Jeftić, S. Spasić, A. Hegediš, J. Krpo-Ćetković, and M. Lenhardt. 2013. Distribution and accumulation of elements (As, Cu, Fe, Hg, Mn, and Zn) in tissues of fish species from different trophic levels in the Danube River at the confluence with the Sava River (Serbia). Environmental Science and Pollution Research 20:5309–5317.

    DOI: 10.1007/s11356-013-1522-3Save Citation »Export Citation »E-mail Citation »

    Analyses of six fish species indicated concentrations of contaminants in liver tissue and higher concentrations of Hg in predators than in prey species. Contaminants come from untreated municipal and industrial wastewaters. Hg and Zn concentrations exceed maximum acceptable concentrations and thus pose a risk for human consumption of these fish.

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  • Ulniković, V. P., M. Vukić, and A. Milutinović-Nikolić. 2013. Analysis of solid waste from ships and modeling of its generation on river Danube in Serbia. Waste Management and Research 31:618–624.

    DOI: 10.1177/0734242X13477716Save Citation »Export Citation »E-mail Citation »

    At present, there is no control system for solid waste or wastewater generated by cruise and cargo ships passing through river ports on the Danube in Serbia. This paper provides data on quantities and distribution of solid waste as a first step toward developing management guidelines for this waste.

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Gold Mining, South America

Many rivers in Brazil, Guyana, Peru, and Venezuela are affected by artisanal and industrial gold and silver mining. Artisanal mining dates to the late 16th century, as reviewed in Nriagu 1994. Artisanal mining is conducted by individuals or small groups rather than commercial operations, but thousands of miners can operate in an area with no environmental regulations. Ore produced in gold mines is concentrated by gravimetric means, mixed with metallic mercury inside barrels for amalgamation, and then transferred to pans in which the gold is washed. Burning of the mercury-gold amalgam is usually done in the open air and the waste from the amalgamation is directly discharged into rivers. Numerous papers now document the riverine pollution and other environmental effects of these practices, and the works cited here provide a sampling of these studies. Miller, et al. 2003 demonstrates that mercury concentrates in riverine sediments downstream from mining sites, although the exact processes responsible for this concentration remain uncertain, as discussed in Roulet, et al. 1999. The difficulties in directly correlating pollutant source with dispersal and the resulting environmental hazards are also illustrated by Gammons, et al. 2006. Regardless of the specific mechanisms of mercury dispersal, Pfeiffer, et al. 1993 demonstrates that mercury contamination of riverine sediments, river water, carnivorous fishes, and fish-eating human populations is widespread. Many studies assessing animal contamination by mercury require killing the animals and assaying specific tissues, but Gutleb, et al. 1997, a study of otters, provides an example of assessing organismal contamination without killing the subject animals, in this case by using otter scat. Studies of human mercury contamination use hair, blood, and urine, as illustrated by Akagi, et al. 1995 and Barbosa, et al. 1997. These studies indicate high mercury levels in fish-eating populations downstream from mining-related sources of mercury.

  • Akagi, H., O. Malm, F. J. P. Branches, et al. 1995. Tapajos River basin, Amazon, Brazil: Speciation of mercury in human hair, blood and urine. Water, Air, & Soil Pollution 80:85–94.

    DOI: 10.1007/BF01189656Save Citation »Export Citation »E-mail Citation »

    Tissue samples collected from people living in gold mining areas and fishing villages in upstream portions of this Amazon River tributary indicate that residents of fishing villages harbor abnormally high levels of mercury as a result of consuming fish contaminated with mercury released from mining areas.

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  • Barbosa, A. C., A. M. Garcia, and J. R. de Souza. 1997. Mercury contamination in hair of riverine populations of Apiacás Reserve in the Brazilian Amazon. Water, Air, & Soil Pollution 97:1–8.

    DOI: 10.1007/BF02409639Save Citation »Export Citation »E-mail Citation »

    This study of the environmental distribution of mercury found that mercury concentrations are highest in piscivorous fish. In people who eat fish several times a week, mercury concentrations increase with age and tend to be greater in women of childbearing age than in similarly aged men.

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  • Gammons, C. H., D. G. Slotton, B. Gerbrandt, et al. 2006. Mercury concentrations of fish, river water, and sediment in the Río Ramis–Lake Titicaca watershed, Peru. Science of the Total Environment 368:637–648.

    DOI: 10.1016/j.scitotenv.2005.09.076Save Citation »Export Citation »E-mail Citation »

    Mercury concentrations in fish tissues in Lake Titicaca exceed US EPA water quality criteria, suggesting health hazards to local people consuming fish. However, although elevated concentrations of Hg occur in headwater streams near mining centers, the quantity of Hg entering the lake from these streams is below detection limits.

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  • Gutleb, A. C., C. Schenck, and E. Staib. 1997. Giant otter (Pteronura brasiliensis) at risk? Total mercury and methylmercury levels in fish and otter scats, Peru. Ambio 26:511–514.

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    Mercury levels in scats of otters in Manu National Park exceed maximum tolerable levels for European otter. Giant otter are now rare, but little is known about their contaminant tolerance. Extrapolation from European otters suggests severe risk to giant otter populations from gold mining on the borders of the park.

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  • Miller, J. R., P. J. Lechler, and G. Bridge. 2003. Mercury contamination of alluvial sediments within the Essequibo and Mazaruni river basins, Guyana. Water, Air, & Soil Pollution 148:139–166.

    DOI: 10.1023/A:1025465800121Save Citation »Export Citation »E-mail Citation »

    Significant increases in mining since the late 1980s correspond to recent increases in mercury concentration in floodplain sediments. Locally high concentrations result from junctions of mining-impacted tributaries and mining sites along the mainstem rivers, but it remains unclear whether the mercury comes primarily from direct inputs or soil erosion.

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  • Nriagu, J. O. 1994. Mercury pollution from the past mining of gold and silver in the Americas. Science of the Total Environment 149:167–181.

    DOI: 10.1016/0048-9697(94)90177-5Save Citation »Export Citation »E-mail Citation »

    This useful, comprehensive overview of mercury released to the environment during mining estimates that annual loss of mercury in mines of Spanish America averaged 612 tons per year between 1580 and 1900. Continuing recycling of this mercury may explain high background levels and fluxes of mercury in some areas.

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  • Pfeiffer, W. C., L. D. Lacerda, W. Salomons, and O. Malm. 1993. Environmental fate of mercury from gold mining in the Brazilian Amazon. Environmental Reviews 1:26–37.

    DOI: 10.1139/a93-004Save Citation »Export Citation »E-mail Citation »

    Mercury contamination is widespread in the Amazon as a result of burning gold-mercury amalgam and discharge of metallic mercury into rivers during amalgamation. River water is also contaminated. Local carnivorous fishes show high mercury concentrations, as do fish-eating human populations.

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  • Roulet, M., M. Lucotte, N. Farella, et al. 1999. Effects of recent human colonization on the presence of mercury in Amazonian ecosystems. Water, Air, & Soil Pollution 112:297–313.

    DOI: 10.1023/A:1005073432015Save Citation »Export Citation »E-mail Citation »

    Atmospheric deposition of mercury from gold mining sources accounts for only a small amount of mercury in soils of the Amazon. Erosion of deforested soils, however, allows runoff to carry mercury into streams, accounting for increased mercury levels in streams of newly colonized watersheds.

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Hudson River, New York, USA

Like most rivers in the world today, the Hudson River contains a variety of pollutants from diverse sources. The Hudson River exemplifies contamination associated with industrial wastes, however: in this case, polychlorinated biphenyls (PCBs) associated with General Electric Company capacitor manufacturing facilities in Hudson Falls and Fort Edward. Contamination was so severe that portions of the Hudson River were designated a US Environmental Protection Agency Superfund site in 1984. Thirty-two years after the last PCBs were discharged into the river, dredging was undertaken starting in 2009 to remove an estimated 400,000 tons of contaminated sediments along a 10-kilometer stretch of the river, with additional dredging planned in future for a much longer section of the river downstream. Suszkowski and D’Elia 2006 provides a historical overview of contaminant production, dispersal, and mitigation along the river. Many studies document the dispersal of PCBs and other contaminants along the river corridor. The example cited is Palmer, et al. 2011, which details the occurrence of PCBs in drinking water supplies along the river. Even more studies examine dispersal of PCBs through the food web. The examples cited here are Baldigo, et al. 2006, which documents PCBs in Hudson River fish; Custer, et al. 2010, which discusses PCB contamination in the eggs of birds that consume insects and fish; and Fitzgerald, et al. 2008, which documents PCB exposure and health effects on older people living along the Hudson River. Other industrial contaminants in the Hudson River include mercury, nickel, and cadmium. Gobeille, et al. 2006 documents mercury concentration in fishermen along the river. Levinton, et al. 2006 examines how 1994–1995 dredging of nickel- and cadmium-contaminated sediments from a battery factory at Foundry Cove influenced levels of these heavy metals in the riverine environment. Asher, et al. 2007 provides an example of studies examining dispersal of contaminants downstream to nearshore environments.

  • Asher, B. J., C. S. Wong, and L. A. Rodenburg. 2007. Chiral source apportionment of polychlorinated biphenyls to the Hudson River estuary atmosphere and food web. Environmental Science & Technology 41:6163–6169.

    DOI: 10.1021/es070763nSave Citation »Export Citation »E-mail Citation »

    The authors used chiral signatures of PCBs to determine that about half the PCB loadings to estuarine water are from river inputs, but 73 to 86 percent of the PCBs taken up by phytoplankton and introduced into the food web are from contaminated river sediments.

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  • Baldigo, B. P., R. J. Sloan, S. B. Smith, N. D. Denslow, V. S. Blazer, and T. S. Gross. 2006. Polychlorinated biphenyls, mercury, and potential endocrine disruption in fish from the Hudson River, New York, USA. Aquatic Sciences 68:206–228.

    DOI: 10.1007/s00027-006-0831-8Save Citation »Export Citation »E-mail Citation »

    Sampling of fish tissues at eight sites across the Hudson River basin revealed correlations between PCBs in streambed sediments and fish tissues. Endocrine biomarkers also revealed disruption by mercury and PCBs of normal endocrine function in Hudson River fish of diverse species and both sexes.

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  • Custer, C. M., T. W. Custer, and P. M. Dummer. 2010. Patterns of organic contaminants in eggs of an insectivorous, an omnivorous, and a piscivorous bird nesting on the Hudson River, New York, USA. Environmental Toxicology and Chemistry 29:2286–2296.

    DOI: 10.1002/etc.276Save Citation »Export Citation »E-mail Citation »

    PCB concentrations in eggs of birds along the upper Hudson River were highest in piscivorous kingfishers, lowest in insectivorous swallows, and intermediate in omnivorous sandpipers, indicating the expected food chain biomagnification. Adult swallows had higher PCB concentrations, however, because of differences in how their prey species accumulate toxins.

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  • Fitzgerald, E. F., E. E. Belanger, M. I. Gomez, et al. 2008. Polychlorinated biphenyl exposure and neuropsychological status among older residents of upper Hudson River communities. Environmental Health Perspectives 116:209–215.

    DOI: 10.1289/ehp.10432Save Citation »Export Citation »E-mail Citation »

    PCBs can accelerate the cognitive and motor dysfunction found in normal aging. This study of 253 individuals of 55–74 years in age living along the upper Hudson found that higher blood serum PCB concentrations correlated with decreased verbal learning and increased depressive symptoms.

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  • Gobeille, A. K., K. B. Morland, R. F. Bopp, J. H. Godbold, and P. J. Landrigan. 2006. Body burdens of mercury in lower Hudson River area anglers. Environmental Research 101:205–212.

    DOI: 10.1016/j.envres.2005.08.017Save Citation »Export Citation »E-mail Citation »

    Despite state health advisories, many local anglers consume fish caught from the river. This study of 191 anglers found that those eating locally caught fish have significantly higher levels of mercury in their blood than those not eating local fish. Mercury concentration increases with frequency of eating locally caught fish.

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  • Levinton, J. S., S. T. Pochron, and M. W. Kane. 2006. Superfund dredging restoration results in widespread regional reduction in cadmium in blue crabs. Environmental Science & Technology 40:7597–7601.

    DOI: 10.1021/es0614058Save Citation »Export Citation »E-mail Citation »

    A 1994–1995 Superfund dredging cleanup of sediment contaminated by Ni and Cd from a battery factory resulted in reduced tissue concentrations of Cd in blue crab, an important fishery species. Cd sediment concentrations and export from the tidal estuary into the Hudson River were also substantially reduced after dredging.

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  • Palmer, P. M., L. R. Wilson, A. C. Casey, and R. E. Wagner. 2011. Occurrence of PCBs in raw and finished drinking water at seven public water systems along the Hudson River. Environmental Monitoring and Assessment 175:487–499.

    DOI: 10.1007/s10661-010-1546-9Save Citation »Export Citation »E-mail Citation »

    Baseline monitoring undertaken prior to sediment dredging indicated similar ranges of PCB concentration in raw and finished drinking water and in locations at varying distances downstream from the contaminant source. All samples were below drinking water maximum contaminant levels for PCBs.

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  • Suszkowski, D. J., and C. F. D’Elia. 2006. The history and science of managing the Hudson River. In The Hudson River estuary. Edited by J. S. Levinton and J. R. Waldman, 313–334. New York: Cambridge Univ. Press.

    DOI: 10.1017/CBO9780511550539Save Citation »Export Citation »E-mail Citation »

    This chapter provides a historical overview and context for understanding sources, dispersal, mitigation, and effects of various pollutants in the Hudson River. The book that includes this chapter also has several other chapters relevant to pollution in the Hudson River.

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Illinois River, Illinois, USA

The Illinois River basin of the north-central United States provides a particularly well-documented example of a long history of diverse sources of pollution and of the effects of these contaminants on the river ecosystem. Some of the earliest documentation of the biological effects of pollution comes from pioneering studies of the effects of sewage on invertebrates and fish in the river, as illustrated by an early study of fish deformities in Thompson 1928, and as summarized in an overview in Colten 1992. Sewage introduced into the river from the Chicago metropolitan area starting in the early decades of the 20th century was joined in subsequent decades by a broader array of pollutants from urban and agricultural sources. Lead came from spent shotgun pellets, as first documented in Bellrose 1959. Excess nitrates came from fertilizer applications in croplands, as discussed in Panno, et al. 2008. Pesticides and other synthetic chemicals became increasingly widespread in the latter half of the 20th century, as documented in Sullivan, et al. 1998. The Illinois River basin was one of the original fifty-nine drainage basins throughout the United States chosen for detailed sampling and analyses as part of the US Geological Survey’s National Water-Quality Assessment (NAWQA) Program during the latter half of the 1990s. Sullivan, et al. 1998 also provides an example of the type of synthesis that resulted from the NAWQA Program. Active remediation of various types is now being undertaken throughout the Illinois River drainage basin, as summarized in Lemke, et al. 2010 for agricultural land uses designed to reduce sediment and nutrient yields to the river, and in Prato and Hey 2006 for wetland restoration designed to reduce nutrient yields. Wohl 2013 provides a thorough overview of the history, contemporary status, and mitigation of river pollution in the Illinois River drainage basin.

  • Bellrose, F. C. 1959. Lead poisoning as a mortality factor in waterfowl populations. Illinois Natural History Bulletin 27:235–288.

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    Pioneering study of the effects of spent lead shot ingested by waterfowl in the riverine corridor. In this and subsequent publications, Bellrose estimated that up to 40 percent of the waterfowl population ingested lead shot, resulting in acute poisoning and death, as well as chronic poisoning and gradually increased mortality.

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  • Colten, C. E. 1992. Illinois River pollution control 1900–1970. In The American environment: Interpretations of past geographies. Edited by L. M. Disalver and C. E. Colten, 193–214. Lanham, MD: Rowman and Littlefield.

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    Nice description of a case study involving organic (sewage, feedlot, and slaughterhouse wastes) pollution. After Chicago’s sewage and urban wastes were diverted into the upper Illinois River in 1900, a front of pollution and reduced numbers of insects, mussel, and fish species moved downstream during the next several decades.

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  • Lemke, A. M., T. T. Lindenbaum, W. L. Perry, M. E. Herbert, T. H. Tear, and J. R. Herkert. 2010. Effects of outreach on the awareness and adoption of conservation practices by farmers in two agricultural watersheds of the Mackinaw River, Illinois. Journal of Soil and Water Conservation 65:304–315.

    DOI: 10.2489/jswc.65.5.304Save Citation »Export Citation »E-mail Citation »

    Intensive outreach that does not interfere with planting and harvesting increases farmers’ use of conservation practices designed to limit nonpoint source runoff to this Illinois River tributary. Programmatic changes and complex application processes decrease adoption of conservation practices.

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  • Panno, S. V., W. R. Kelly, K. C. Hackley, H.-H. Hwang, and A. T. Martinsek. 2008. Sources and fate of nitrate in the Illinois River basin, Illinois. Journal of Hydrology 359:174–188.

    DOI: 10.1016/j.jhydrol.2008.06.027Save Citation »Export Citation »E-mail Citation »

    The primary source of nitrate varies with land use, from treated wastewater in urban areas to tiles draining row crops in farmlands. Concentrations decrease with distance from urban areas, although wastewater influence is greatest during river low flow, whereas fertilizer nitrate from croplands is greatest during high flow.

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  • Prato, T., and D. Hey. 2006. Economic analysis of wetland restoration along the Illinois River. Journal of the American Water Resources Association 42:125–131.

    DOI: 10.1111/j.1752-1688.2006.tb03828.xSave Citation »Export Citation »E-mail Citation »

    A floodplain restoration project that converted 999 ha of cropland to forests and wetlands along the Illinois River created a net benefit of US$1,827 per ha of restored floodplain. This value reflects reduced nitrogen loads to the river and increased local benefits from recreation, wildlife habitat, and water quality.

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  • Sullivan, D. J., T. W. Swinson, J. K. Crawford, and A. R. Schmidt. 1998. Surface-water quality assessment of the Upper Illinois River basin in Illinois, Indiana, and Wisconsin: Pesticides and other synthetic organic compounds in the water, sediment, and biota, 1975–90. Water-Resources Investigations Report 96–4135. Urbana, IL: US Geological Survey.

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    Comprehensive overview of distribution, concentration, and types of synthetic chemicals in the river environment. Despite large quantities of pesticide use in agriculture, much greater concentrations of pesticides are applied in urban areas. Drinking-water standards exist for only four of the seventeen pesticides detected, but each standard was exceeded somewhere.

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  • Thompson, D. H. 1928. The “knothead” carp of the Illinois River. Bulletin, State of Illinois, Division of the Natural History Survey 17.8: 285–320.

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    Pioneering study of the effects of river pollution on animal health that linked deformities in carp to lack of vitamin D in the diet. Sewage inputs to the river caused rooted aquatic plants to be replaced by non-chlorophyll-bearing plankton lacking vitamins. The changing flood supply caused vitamin deficiencies in carp.

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  • Wohl, E. 2013. Wide rivers crossed: The South Platte and the Illinois of the American prairie. Boulder: Univ. Press of Colorado.

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    This book examines environmental change throughout the Illinois River basin, including different forms of river pollution. Although written for a general audience, the book presents a comprehensive overview of pollution in the basin and includes numerous primary, scholarly references.

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Mississippi River, United States

The extensive Mississippi River basin integrates water and sediment yields from across much of the continental United States. The river basin also integrates a diverse array of pollutants associated with industrial, agricultural, and municipal activities. Recognition of the effects of pollution on human and animal health goes back decades, as illustrated by Gottlieb and Carr 1982, a study of increased cancer risk in people along the lower Mississippi River who use the river for drinking water. Increased use of organochlorine pesticides has resulted in contamination of riverine organisms and health risks for people consuming these organisms, as discussed in Watanabe, et al. 2003 and Blocksom, et al. 2010. In recent decades, however, increased nutrient fluxes from the river basin have received more attention. Excess nutrients, and particularly nitrate, are exported to the Gulf of Mexico by the river. Nitrate concentrations have increased substantially since the 1970s, as reviewed in Goolsby and Battaglin 2001. Increased nitrate fluxes have contributed to extensive hypoxia in the Gulf. David, et al. 2010 discusses how most of the nitrates come from fertilizer inputs to crop fields in the Upper Mississippi basin. Large floods create periods of particularly high nitrate inputs to the Gulf, as documented in Goolsby, et al. 1993 for the historic 1993 flood from the upper basin. The need to reduce nutrient inputs to the Gulf is being addressed using a variety of strategies, as reviewed in Kröger, et al. 2012, but Bianchi, et al. 2010 explains the complexities of controls on hypoxia in the Gulf.

  • Bianchi, T. S., S. F. DiMarco, J. H. Cowan, et al. 2010. The science of hypoxia in the northern Gulf of Mexico: A review. Science of the Total Environment 408:1471–1484.

    DOI: 10.1016/j.scitotenv.2009.11.047Save Citation »Export Citation »E-mail Citation »

    Hypoxia in the northern Gulf of Mexico is caused primarily by algal production stimulated by excess nitrogen delivered from Mississippi River basin, but the controls on hypoxia are complex and reflect processes such as seasonal vertical stratification of incoming stream flow and Gulf waters, non-riverine organic matter inputs, and mobile muds.

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  • Blocksom, K. A., D. M. Walters, T. M. Jicha, J. M. Lazorchak, T. R. Angradi, and D. W. Bolgrien. 2010. Persistent organic pollutants in fish tissue in the mid-continental great rivers of the United States. Science of the Total Environment 408:1180–1189.

    DOI: 10.1016/j.scitotenv.2009.11.040Save Citation »Export Citation »E-mail Citation »

    This study measured pesticides, PCBs, and PBDEs in fishes of the Upper Mississippi River and its primary tributaries. PCBs, PBDEs, chlordane, dieldrin, and DDT were detected in most samples across all rivers. Many sites exceeded risk values for wildlife and humans, although exposure risk is localized and limited in scope.

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  • David, M. B., L. E. Drinkwater, and G. F. McIsaac. 2010. Sources of nitrate yields in the Mississippi River basin. Journal of Environmental Quality 39:1657–1667.

    DOI: 10.2134/jeq2010.0115Save Citation »Export Citation »E-mail Citation »

    River runoff times fertilizer N input is the best predictive term for winter-spring riverine nitrate yields from 153 watersheds within the Mississippi River basin. Fertilizer inputs correlate strongly with the fraction of land area in row crops. Greatest N yields correspond to the tile-drained Corn Belt in the Upper Mississippi basin.

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  • Goolsby, D. A., and W. A. Battaglin. 2001. Long-term changes in concentrations and flux of nitrogen in the Mississippi River basin, USA. Hydrological Processes 15:1209–1226.

    DOI: 10.1002/hyp.210Save Citation »Export Citation »E-mail Citation »

    Nitrogen concentrations and flux in the river have increased significantly during the past century, particularly since the early 1970s, largely due to increased nitrate resulting from increased fertilizer use, annual variability in precipitation and increased streamflow, and interannual variability in N available in soils and groundwater for leaching to streams.

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  • Goolsby, D. A., W. A. Battaglin, and E. M. Thurman. 1993. Occurrence and transport of agricultural chemicals in the Mississippi River, July through August 1993. US Geological Survey Circular 1120-C. Denver, CO: US Geological Survey.

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    A case study of the effects of a very large flood on pollutant transport. Widespread rainfall flushed contaminants from uplands and limited dilution, so concentrations of nitrate and individual pesticides during summer 1993 flooding were similar to maximum concentrations during previous years. Total daily loads were higher during 1993.

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  • Gottlieb, M. S. and J. K. Carr. 1982. Case-control cancer mortality study and chlorination of drinking water in Louisiana. Environmental Health Perspectives 46:169–177.

    DOI: 10.1289/ehp.8246169Save Citation »Export Citation »E-mail Citation »

    Several areas of Louisiana using the Mississippi River for their drinking-water source have the highest mortality rates in the United States for several forms of cancer. Increased risk for rectal, brain, breast, and multiple myeloma forms of cancer is associated with chlorinated ground- or surface water.

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  • Kröger, R., M. T. Moore, K. W. Thornton, J. L. Farris, J. D. Prevost, and S. C. Pierce. 2012. Tiered on-the-ground implementation projects for Gulf of Mexico water quality improvements. Journal of Soil and Water Conservation 67:94A–99A.

    DOI: 10.2489/jswc.67.4.94ASave Citation »Export Citation »E-mail Citation »

    Nutrient reduction strategies rely on input management of nutrient application and controlling and trapping nutrient runoff at the edge of the field or in the primary river associated with the system. Controlling and trapping strategies include riparian buffer strips, riparian corridors, and drop pipe structures.

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  • Watanabe, K. H., F. W. Desimone, A. Thiyagarajah, W. R. Hartley, and A. E. Hindrichs. 2003. Fish tissue quality in the lower Mississippi River and health risks from fish consumption. Science of the Total Environment 302:109–126.

    DOI: 10.1016/S0048-9697(02)00396-0Save Citation »Export Citation »E-mail Citation »

    Organic compound and heavy metal concentrations in tissues from three shellfish and sixteen fish species suggest nine species of concern for increased cancer risk by humans consuming the species. Compounds primarily responsible for elevated risks were the pesticides aldrin, dieldrin, lindane, and heptachlor epoxide, as well as arsenic and mercury.

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Murray-Darling River, Australia

The primary water pollution issues in the Murray-Darling River basin of southeastern Australia are salinization and blooms of cyanobacteria. Salinization first became an issue of widespread concern in the basin during the 1980s. Increasing salinization results from several historical changes in the basin. Clearing of perennial native vegetation and replacement with annual crops and pasture plants reduced evapotranspiration and increased groundwater recharge. The groundwater is naturally saline, so a rising water table allowed saline water to enter soils and streams. Saline irrigation return flows, combined with diversions for irrigation that reduced stream flow, further increased the salinity of the river water. Under these circumstances, one of the first tasks is to map the spatial extent of salinization and examine potential causal processes based on correlations between spatial extent and environmental variables, as described in Jolly, et al. 2001. Subsequent tasks include documenting the effects of salinization on biotic communities and ecosystem processes, as illustrated in Baldwin, et al. 2006, and developing strategies to mitigate or reduce salinization, as discussed in Khan, et al. 2008. Cyanobacterial blooms are a more recent but equally serious threat. More than twenty-five species of freshwater cyanobacteria can be toxic to humans and other animals. Cyanobacterial blooms can consist of one or more species that can produce neurotoxic alkaloids and hepatotoxic peptides. The toxicity of individual species is confirmed by isolation in a laboratory culture and testing on mice, as described in Baker and Humpage 1994 and Humpage, et al. 1994. Cyanobacterial blooms in the Murray-Darling River are commonly associated with nutrient-rich water that results from widespread agriculture and substantial off-channel consumptive water use for irrigated agriculture. Such blooms are becoming more widespread and frequent with time, causing animal deaths and human illness. In 1991, Australia experienced the world’s worst cyanobacterial bloom thus far, an event that affected more than 1,000 kilometers of the Darling River, threatening several rural water supplies. The state of South Australia takes about half of its domestic water supply from the Murray River downstream from the area affected by the 1991 cyanobacterial bloom. This and other sources of contamination led to the arguments in favor of mandatory drinking water standards in Australia, which are discussed in McKay and Moeller 2001. Manipulation of river flow to prevent the thermal stratification required for cyanobacterial blooms to develop is described in Maier, et al. 2001 and Webster, et al. 2000.

  • Baker, P. D., and A. R. Humpage. 1994. Toxicity associated with commonly occurring cyanobacteria in surface waters of the Murray-Darling basin, Australia. Australian Journal of Marine and Freshwater Research 45:773–786.

    DOI: 10.1071/MF9940773Save Citation »Export Citation »E-mail Citation »

    This paper illustrates the initial work necessary to understand cyanobacterial blooms in a particular river basin, including determining the spatial extent and frequency and duration of the blooms. Identification of bacterial species and associated toxicity is also necessary. Here, 42 percent of samples taken over three summers indicated neurotoxicity and hepatotoxicity.

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  • Baldwin, D. S., G. N. Rees, A. M. Mitchell, G. Watson, and J. Williams. 2006. The short-term effects of salinization on anaerobic nutrient cycling and microbial community structure in sediment from a freshwater wetland. Wetlands 26:455–464.

    DOI: 10.1672/0277-5212(2006)26[455:TSEOSO]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    Paper provides an example of the subtle and complicated effects of salinity on freshwater ecosystems: here, a shift in microbial community structure that alters carbon dynamics in a Murray River floodplain wetland. The paper illustrates an experimental approach to investigating these processes, based on salt additions to wetland sediments.

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  • Humpage, A. R., J. Rositano, A. H. Bretag, et al. 1994. Paralytic shellfish poisons from Australian cyanobacterial blooms. Australian Journal of Marine and Freshwater Research 45:761–771.

    DOI: 10.1071/MF9940761Save Citation »Export Citation »E-mail Citation »

    A type of toxin previously identified from red tide dinoflagellates and contaminated shellfish also occurs in cyanobacterial blooms across the Murray River basin. These toxins have caused fish kills in lakes elsewhere and bioaccumulate in shellfish, creating hazards for humans consuming freshwater shellfish.

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  • Jolly, I. D., D. R. Williamson, M. Gilfedder, et al. 2001. Historical stream salinity trends and catchment salt balances in the Murray-Darling basin, Australia. Marine and Freshwater Research 52:53–64.

    DOI: 10.1071/MF00018Save Citation »Export Citation »E-mail Citation »

    Despite sparse water-quality data, the authors used statistical techniques to analyze the spatial distribution of stream salinization and relate salt concentrations to physical processes associated with precipitation and soil characteristics. Regions of increasing salinity correlate with rising levels of saline groundwater and saline irrigation return flows to the river.

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  • Khan, S., M. N. Asgahr, S. Mushtaq, and A. Ahmad. 2008. On-farm options for managing stream salinity in irrigation areas: An example from the Murray-Darling basin, Australia. Hydrology Research 39:157–170.

    DOI: 10.2166/nh.2008.036Save Citation »Export Citation »E-mail Citation »

    Catchment-scale land use changes to decrease salinity may not be economically viable, but this paper analyzes alternative local-scale strategies, such as evaporation ponds and serial biological concentration of salts. In the latter, water is transferred to successive fields with increasingly salt-tolerant crops.

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  • Maier, H. R., M. D. Burch, and M. Bormans. 2001. Flow management strategies to control blooms of the cyanobacterium, Anabaena circinalis, in the River Murray at Morgan, South Australia. Regulated Rivers: Research and Management 17:637–650.

    DOI: 10.1002/rrr.623Save Citation »Export Citation »E-mail Citation »

    Paper describes an algal management strategy based on maintaining river flows that limit the thermal stratification required for algal blooms. Wind speed strongly influences thermal stratification during low flows, so this paper analyzes the probability of stratification under differing flow regimes incorporating thirty years of wind speed data.

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  • McKay, J., and A. Moeller. 2001. Is risk associated with drinking water in Australia of significant concern to justify mandatory regulation? Environmental Management 28:469–481.

    DOI: 10.1007/s002670010237Save Citation »Export Citation »E-mail Citation »

    Australia has water-quality guidelines, but no mandatory drinking water standards. This paper reviews the range of contaminants present in the Murray-Darling and other Australian rivers, and argues that the risk associated with drinking water in Australia is sufficient to warrant mandatory regulations.

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  • Webster, I. T., B. S. Sherman, M. Bormans, and G. Jones. 2000. Management strategies for cyanobacterial blooms in an impounded lowland river. Regulated Rivers: Research and Management 16:513–525.

    DOI: 10.1002/1099-1646(200009/10)16:5%3C513::AID-RRR601%3E3.0.CO;2-BSave Citation »Export Citation »E-mail Citation »

    This paper demonstrates the development of persistent thermal stratification in river water during low flows as a requirement for the formation of cyanobacterial blooms. It also suggests strategies to minimize blooms by setting a minimum discharge, pulsing the discharge, changing discharge height, and altering the depth of water withdrawal.

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Nile River, Africa

Africa’s huge Nile River contains many sources of pollution, and it exemplifies some of the issues that arise in rivers that have very low rates of discharge because they drain primarily arid regions. Flow regulation can exacerbate naturally low stream flow by storing peak flows and reducing base flows, as also illustrated by the Nile and discussed in the context of microbial water quality in Rabeh 2009, and in the context of nutrient export in Yasin, et al. 2010. Among the other works cited here, Elewa 2010 provides an example of using distinctive chemical signatures of pollutants to trace the contamination back to source areas or activities. El-Kady, et al. 2007 assesses the spatial distribution and potential health risks to humans of PCBs in river sediments and fish tissues at multiple sites in the Nile River basin. Fishar and Williams 2008 develops chemical and biotic pollution indices using multiple parameters. El-Otify, et al. 2011 assesses the effects of fertilizer factory effluent on cyanobacteria communities in the Nile. El-Sheekh 2009 evaluates the interacting effects of diverse pollutant sources and stream flow dilution on health risks to humans, and Malhat 2011 documents the distribution of heavy metals in fish and the implications for fish consumption by humans.

  • El-Kady, A. A., M. A. Abdel-Wahhab, B. Henkelmann, et al. 2007. Polychlorinated biphenyl, polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran residues in sediments and fish of the River Nile in the Cairo region. Chemosphere 68:1660–1668.

    DOI: 10.1016/j.chemosphere.2007.03.066Save Citation »Export Citation »E-mail Citation »

    Levels of PCBs, PCDDs, and PCDFs in sediment and fish samples varied across the Nile River basin, but typically did not exceed permissible limits for consumption of fish and shellfish. Concentrations were greatest near industrial areas. All pollutants were ubiquitous, despite the current ban on the use of PCBs in Egypt.

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  • El-Otify, A. M., M. M. El-Sheekh, and H. Saber. 2011. Detrimental effects of industrial effluents on the growth and metabolic products of the Nile planktonic cyanobacteria. Fresenius Environmental Bulletin 20:2911–2919.

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    This case study of the effects of fertilizer factory effluent on two species of planktonic cyanobacteria provides an example of evaluating the ecotoxicity of a specific pollutant for individual riverine species. Exposure resulted in growth and metabolic disorders of the cyanobacteria, suggesting limited environmental tolerance for the effluent.

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  • El-Sheekh, M. 2009. River Nile pollutants and their effect on life forms and water quality. In The Nile: Origin, environments, limnology, and human use. Edited by H. J. Dumont, 395–405. Dordrecht, The Netherlands: Springer.

    DOI: 10.1007/978-1-4020-9726-3Save Citation »Export Citation »E-mail Citation »

    Industrial wastewater, oil, municipal wastewater, agricultural drainage, and cyanotoxins from algal blooms contribute pollutants that can affect riverine phytoplankton and fish. Dilution limits the direct health risks to humans, however, except in the vicinity of cities or industrial discharges, or where Coliform bacteria limit water use for irrigation or fisheries.

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  • Elewa, H. H. 2010. Potentialities of water resources pollution of the Nile River delta, Egypt. Open Hydrology Journal 4:1–13.

    DOI: 10.2174/1874378101004010001Save Citation »Export Citation »E-mail Citation »

    Paper explains the use of distinctive water chemistry parameters as hydrochemical fingerprints that can be used to distinguish among potential point (industrial and sewage) and nonpoint (agricultural) sources of polluted water. Among the parameters used are ratios of chloride and sulfate solutes, heavy metals, and the nutrients nitrate and ammonia.

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  • Fishar, M. R., and W. P. Williams. 2008. The development of a biotic pollution index for the River Nile in Egypt. Hydrobiologia 598:17–34.

    DOI: 10.1007/s10750-007-9137-7Save Citation »Export Citation »E-mail Citation »

    Chemical variables were used to calculate a chemical pollution index for sites with diverse pollution levels. Characteristics of invertebrate fauna from the same sites were used to develop a biotic pollution index. Broader inclusion of taxa in the biotic index limits the weight given to any one taxon.

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  • Malhat, F. 2011. Distribution of heavy metal residues in fish from the River Nile tributaries in Egypt. Bulletin of Environmental Contamination and Toxicology 87:163–165.

    DOI: 10.1007/s00128-011-0314-zSave Citation »Export Citation »E-mail Citation »

    Distribution patterns of several heavy metals indicate high levels in canals draining farm lands, which serve as nonpoint sources because of heavy metal impurities in fertilizers, pesticides, and sewage sludge. Lead and cadmium in these canals exceed concentrations recommended by the UN Food and Agricultural Organization for fish consumption.

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  • Rabeh, S. A. 2009. Bacteria and viruses in the Nile. In The Nile: Origin, environments, limnology, and human use. Edited by H. J. Dumont, 407–429. Dordrecht, The Netherlands: Springer.

    DOI: 10.1007/978-1-4020-9726-3Save Citation »Export Citation »E-mail Citation »

    Microbial water quality along the Nile varies in relation to discharge, water use, population density, water treatment, domestic and industrial discharges, and agricultural runoff. Low flow exacerbates water quality deterioration in the vicinity of cities and industrial and agricultural drainage. Coliform bacteria greatly exceed Egyptian standards in many places.

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  • Yasin, J. A., C. Kroeze, and E. Mayorga. 2010. Nutrients export by rivers to the coastal waters of Africa: Past and future trends. Global Biogeochemical Cycles 24:GB0A07.

    DOI: 10.1029/2009GB003568Save Citation »Export Citation »E-mail Citation »

    Total nutrient export from the Nile River increased dramatically following the 1965 completion of the Aswan High Dam. This reflects increased intensive agriculture, which now occupies 40 percent of the basin area. The population of the basin also doubled between 1970 and 2000, with changes toward greater meat consumption and additional fertilizer use.

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Ob River, Russia

The Ob River drains north through Siberia into the Arctic Ocean. The 2.93 million square kilometers drained by the river contribute a variety of particularly persistent and toxic contaminants. Contaminants include wastes from nuclear weapons production and testing, as discussed with respect to downstream patterns in Cochran, et al. 2000; with respect to sources in Cooper, et al. 2000; and with respect to mechanisms of transport and concentration in Stepanets, et al. 2009. Kenna and Sayles 2002 describes how nuclear wastes occur in riverine sediments along the entire length of the Ob and into the delta. Other contaminants come from chemical manufacturing and hydrocarbons from fossil-fuel development, as described in Melnikov, et al. 2003. Dispersal of these pollutants is influenced by the presence of a large dam, the Novosibirsk Dam, within the river basin. As concern has increased in recent decades over contamination of the Arctic Ocean water, sediments, and biota, numerous studies have documented the contributions of the Ob and other Siberian rivers. As discussed in Carroll, et al. 2008, the Ob is a major point source of PCBs, PBDEs, and pesticides to the Arctic Ocean. Harms, et al. 2000 illustrates how incorporation of contaminants into sea ice is a major transport pathway within the Arctic Ocean, and Shmel’kov and Stepanets 2010 presents a numerical model of contaminant dispersal in the ocean.

  • Carroll, J., V. Savinov, T. Savinova, S. Dahle, R. McCrea, and D. G. Muir. 2008. PCBs, PBDEs and pesticides released to the Arctic Ocean by the Russian Rivers Ob and Yenisei. Environmental Science & Technology 42:69–74.

    DOI: 10.1021/es071673lSave Citation »Export Citation »E-mail Citation »

    Samples of Ob River water collected in 2005 indicate that the river is one of the major point sources of contaminants, including PCBs, PBDEs, and pesticides, to the Arctic Ocean, although concentrations in Ob discharge are similar to other coastal regions of the Arctic.

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  • Cochran, J. K., S. B. Moran, N. S. Fisher, T. M. Beasley, and J. M. Kelley. 2000. Sources and transport of anthropogenic radionuclides in the Ob River system, Siberia. Earth and Planetary Science Letters 179:125–137.

    DOI: 10.1016/S0012-821X(00)00110-2Save Citation »Export Citation »E-mail Citation »

    This paper documents how downstream increases in concentrations of human-induced radionuclides along the Ob River reflect differing sources. Global stratospheric fallout occurs throughout the drainage, but tropospheric fallout from former test sites and reprocessing of spent fuel contribute to greater radionuclide loads downstream.

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  • Cooper, L. W., J. M. Kelley, L. A. Bond, K. A. Orlandini, and J. M. Grebmeier. 2000. Sources of the transuranic elements plutonium and neptunium in arctic marine sediments. Marine Chemistry 69:253–276.

    DOI: 10.1016/S0304-4203(99)00109-7Save Citation »Export Citation »E-mail Citation »

    Radioactive isotopes in Alaskan Arctic marine sediments reflect stratospheric and tropospheric fallout, whereas isotopes in Ob River sediments reflect the presence of nuclear fuel reprocessing within the river catchment. Sediments of the Eurasian Arctic Ocean also reflect radioactive contamination from the Ob and Yenisei Rivers of Russia.

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  • Harms, I. H., M. J. Karcher, and D. Dethleff. 2000. Modelling Siberian river runoff: Implications for contaminant transport in the Arctic Ocean. Journal of Marine Systems 27:95–115.

    DOI: 10.1016/S0924-7963(00)00062-2Save Citation »Export Citation »E-mail Citation »

    This modeling study focuses on pathways and transit times of Siberian river water in the Arctic Ocean. Sediment and adsorbed contaminants are incorporated into freezing sea ice near the Ob estuary. This ice mostly drifts toward the Barents Sea and melts close to Svalbard, contaminating the Barents and Nordic Seas.

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  • Kenna, T. C., and F. L. Sayles. 2002. The distribution and history of nuclear weapons related contamination in sediments from the Ob River, Siberia as determined by isotopic ratios of plutonium and neptunium. Journal of Environmental Radioactivity 60:105–137.

    DOI: 10.1016/S0265-931X(01)00099-6Save Citation »Export Citation »E-mail Citation »

    This study uses unique isotopic signatures in sediments of tributaries draining sources of non-fallout radioactive contamination to identify sources of contaminants in downstream sediments. Persistent sources of contamination include facilities on the Irtysh and Tobol Rivers, and these contaminants have been transported to the Ob delta.

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  • Melnikov, S., J. Carroll, A. Gorshkov, S. Vlasova, and S. Dahle. 2003. Snow and ice concentrations of selected persistent pollutants in the Ob-Yenisey River watershed. Science of the Total Environment 306:27–37.

    DOI: 10.1016/S0048-9697(02)00482-5Save Citation »Export Citation »E-mail Citation »

    Mean concentrations of oil hydrocarbons, PAHs, DDTs, PCBs, and other contaminants are consistent in snow and ice throughout the Ob drainage basin and are similar to those in Arctic Canada, except for DDT, which is an order of magnitude higher in the Ob.

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  • Shmel’kov, B. S., and O. V. Stepanets. 2010. Numerical estimation of the scale of possible radioactive contamination of the water area of the Kara Sea related to 137Cs discharge from the Ob and Yenisei Rivers. Geochemistry International 48:624–628.

    DOI: 10.1134/S001670291006011XSave Citation »Export Citation »E-mail Citation »

    This short paper illustrates numerical modeling used to understand dispersal of radioactive contaminants discharged into the Arctic Ocean from the Ob River. Model results can be used to predict ecological effects of contaminant spread and to design sampling programs to monitor contaminant dispersal.

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  • Stepanets, O. V., A. N. Ligaev, A. P. Borisov, et al. 2009. Geoecological investigations of the Ob-Irtysh River basin in the Khanty-Mansi Autonomous Region: Yugra in 2006–2007. Geochemistry International 47:657–671.

    DOI: 10.1134/S0016702909070027Save Citation »Export Citation »E-mail Citation »

    This paper focuses on concentrations of anthropogenic radionuclides in three portions of the Ob River system. Sorption processes accumulate 137Cs in streambed sediments at sites near nuclear fuel reprocessing facilities, although a substantial portion of radioactive contaminants remain in solution and travel with river discharge.

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