Human Manipulation of the Global Nitrogen Cycle

by

Eve-Lyn S. Hinckley

• LAST REVIEWED: 03 June 2019
• LAST MODIFIED: 10 March 2015
• DOI: 10.1093/obo/9780199363445-0023

Introduction

Ecosystems and all living beings are bathed in atmospheric N₂, a nearly inert gas, which must be “fixed” by bacteria associated with plant roots or free-living in soil. These bacteria possess the enzyme nitrogenase, which allows them to convert N₂ to reactive and bioavailable forms of N, including ammonium (NH₄⁺) and nitrate (NO₃^-). N is a limiting nutrient in most ecosystems, so excess inputs of reactive N can have negative consequences, including changes to forest structure and function, and eutrophication of aquatic systems. Since the 1900s, humans have tripled the amount of reactive N cycling globally through air, land, and water systems. Both fossil fuel combustion and the advent of the Haber-Bosch process have contributed to accelerated N cycling. These hallmarks of modern society arose as a result of industrialization in the developed world and the pressure to produce synthetic N fertilizers that could support a growing human population. While they were considered great economic boons, these developments have had a cascade of unintended negative consequences for the biosphere. Combustion of fossil fuels releases N oxides into the atmosphere that can be transported large distances from their sources and cause acid rain and fertilization of downgradient terrestrial and aquatic systems. Widespread application (and over-application) of synthetic N fertilizers has caused increases in production of greenhouse gases (e.g., nitrous oxide) locally in croplands, and pollution of downgradient aquatic ecosystems from N-rich runoff. This article addresses the topic of human manipulation of the N cycle in a variety of ecosystems, as well as a number of specific locations around the globe. It does not serve as a general introduction to the N cycle. Those readers looking to start with the basics of N cycling, and biogeochemistry more generally, should see W. H. Schlesinger’s article on Biogeochemistry in Ecology.

General Overviews

The works in this section provide important pieces of the big picture, with respect to humans’ dramatic manipulation of the global nitrogen (N) cycle. Vitousek, et al. 1997 describes the major human activities—fossil fuel combustion, fertilizer N use, land use change, and invasive species introductions—that have changed the way N cycles in air, land, and water systems, while Canfield, et al. 2010 gives an evolutionary and microbial perspective. Also included are primary examples of human impacts on the N cycle; Driscoll, et al. 2001 discusses the generation of acid rain from fossil fuel combustion and the consequences for receiving forest and aquatic ecosystems. The overviews Galloway, et al. 2004 and Galloway, et al. 2008 focus on global estimates of N fluxes and provide recommendations for the management of reactive N (e.g., ammonium and nitrate), acknowledging that it is a problem of “too much” in industrialized regions of the world and “too little” in others, such as parts of the African continent. This section also includes papers on the manipulation of N in rapidly developing countries, including an analysis of China (Cui, et al. 2013), and the potential links between human manipulation of the N cycle and public health (Townsend, et al. 2003). Finally, Fowler, et al. 2013 provides information on current understanding of the global N cycle. Together, these works are meant to give readers an introduction to the vast influence that humans are having over a biogeochemical cycle fundamental to sustaining life on Earth, and to provide context for exploring particular parts of this story in greater detail.

• Canfield, D. E., A. N. Glazer, and P. G. Falkowski. 2010. The evolution and future of Earth’s nitrogen cycle. Science 330.6001: 192–196.

  DOI: 10.1126/science.1186120

  A discussion of human manipulation of the global N cycle from the perspective of microbial ecology and Earth’s evolution.

• Cui, S., Y. Shi, P. M. Groffman, W. H. Schlesinger, and Y.-G. Zhu. 2013. Centennial-scale analysis of the creation and fate of reactive nitrogen in China (1910–2010). Proceedings of the National Academy of Sciences 110.52: 20882–20887.

  DOI: 10.1073/pnas.1012878108

  Manipulation of the N cycle and negative consequences of these activities is currently a major concern in rapidly developing China. This article provides an overview of the major issues for the future.

• Driscoll, C. T., G. B. Lawrence, A. J. Bulger, et al. 2001. Acidic deposition in the Northeastern United States: Sources and inputs, ecosystem effects, and management strategies. BioScience 51.3: 180–198.

  DOI: 10.1641/0006-3568

  An overview of how anthropogenic emissions of N (and sulfur, S) form acid rain, which has negative consequences for receiving terrestrial and aquatic ecosystems. Acid rain and its ecosystem effects have been widely studied and publicized in the northeastern United States and Europe since the mid-20th century.

• Fowler, D., J. A. Pyle, J. A. Raven, and M. A. Sutton. 2013. The global nitrogen cycle in the twenty-first century: Introduction. Philosophical Transactions of the Royal Society 368.1621.

  DOI: 10.1098/rstb.2013.0165

  An introduction to a suite of papers updating current understanding of the global N cycle, following a meeting at the Royal Society on 4–6 December 2011.

• Galloway, J. N., F. J. Dentener, D. G. Capone, et al. 2004. Nitrogen cycles: Past, present, and future. Biogeochemistry 70:153–226.

  DOI: 10.1007/s10533-004-0370-0

  This paper synthesizes several datasets to predict the global N budget in 2050, and highlights human activities that are most impacting the N cycle.

• Galloway, J. N., A. R. Townsend, J. W. Erisman, et al. 2008. Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions. Science 320.5878: 889–892.

  DOI: 10.1126/science.1136674

  Updates current understanding of reactive N creation and impacts, including the points: reducing reactive N creation is difficult, but not impossible, and attention to areas with large populations but insufficient N is important, so that they might develop ways to increase food production while minimizing negative impacts on ecosystems.

• Townsend, A. R., R. W. Howarth, F. A. Bazzaz, et al. 2003. Human health effects of a changing global nitrogen cycle. Frontiers in Ecology and the Environment 1:240–246.

  DOI: 10.1890/1540-9295(2003)001

  This paper outlines the potential human health risk of an altered global N cycle. Discusses how air- and water-borne N are linked to respiratory conditions, heart disease, cancers, and potentially the spread of vector-borne diseases.

• Vitousek, P. M., J. D. Aber, R. W. Howarth, et al. 1997. Human alteration of the global nitrogen cycle: Sources and consequences. Ecological Applications 7:737–750.

  DOI: 10.1890/1051-0761(1997)007

  This is now considered a classic work documenting the primary evidence for human manipulation of the global N cycle.