Ecohydrology

by

Valeriy Ivanov, Simone Fatichi, Edoardo Daly

• LAST REVIEWED: 28 August 2019
• LAST MODIFIED: 28 August 2019
• DOI: 10.1093/obo/9780199363445-0120

Introduction

Ecohydrology is a cross-disciplinary field that emerged in the early 2000s as a result of recognition of the need to better understand complex, multifaceted interactions occurring in terrestrial ecosystems and their connection to the water cycle. In this article, ecohydrology is viewed as the science that studies how water in all its forms links living organisms and their abiotic environment to define their function, interactions, structure, and distribution. As a highly interdisciplinary field, ecohydrology draws from hydrology, ecology, atmospheric sciences, plant ecophysiology, biophysics, hydrodynamics, soil science, geomorphology, biogeochemistry, agronomy, and even landscape architecture. Basic science questions and land and water resource management issues are addressed in the field. A range of temporal scales, from minutes (such as in stomatal response to a changing environment) to millennia (such as that characteristic of landscape evolution period), is relevant to studies in ecohydrology. Likewise, spatial extent of analysis covers a spectrum ranging from ~10^–6 m (e.g., concerned with leaf stomatal cavities or soil pores), to regional scales at ~10⁶ m. As other sciences, ecohydrologic research relies on theoretical analysis, observation-based inference and experimentation, and computational approaches. The latter are becoming powerful, permitting experimentation and tests of mathematical descriptions of relevant processes and mechanisms. As evidenced by the publication record, one the main scopes of ecohydrology has been to understand how water available to ecosystems is used by vegetation and impacts the water cycle through the process of evapotranspiration. This review draws from this literature thus having a prevailing emphasis on vegetation control of water fluxes (i.e., transpiration) and the bilateral interactions between vegetation and abiotic environment. This perspective is justified by the key role of transpiration in the water cycle: it is the largest water flux from vegetated land to the atmosphere. The field of ecohydrology has analyzed different climatic regions and areas. Arid and semiarid ecosystems, where water is the major limiting factor of ecosystem functioning, are viewed as one of the key foci in ecohydrologic studies, largely driving the establishment of the field. The role that transpiration has on rainfall via water recirculation and the potential effects of deforestation are the emphasis of tropical ecohydrology. The large changes in the hydrologic budget associated with urbanization are addressed in urban ecohydrologic studies. One may expect that future focus will be on understanding of the transformation of terrestrial ecosystems, as we know them, due to ongoing and anticipated changes in the hydrologic cycle.

General Overviews

Perhaps because of its strong interdisciplinarity and only recent emergence as a recognized, specific area of research, ecohydrology has received several treatises, influenced by the respective fields of contributing authors. While not explicitly associated with the term ecohydrology, one of the earliest works in the field is Noy-Meir 1973, a review article on water-limited ecosystems that drew much attention of the ecosystem and hydrologic science communities. Conversely, the early use of the term by ecologists predominantly referred to aquatic or wetland ecosystems (e.g., Ingram 1987). Later works have expanded its meaning. Hatton, et al. 1997 treated ecohydrology as a science of plant-water interactions, while Zalewski, et al. 1997 proposed a broader view, as a unifying platform for studying the interactions of freshwater ecosystems and hydrologic processes. A collection of research articles by Baird and Wilby 1999 expanded these earlier views by reviewing plant-water interactions in a range of environments. A diverse set of contributions from ecologists, plant physiologists, and hydrologists in this collection meaningfully reflected the interdisciplinary nature of the field. Arguably, the field of ecohydrology was not fully endorsed by the community until after the opinion paper by a renowned hydrologist and nonlinear dynamicist I. Rodriguez-Iturbe, who provided an inspiring and thought provoking philosophical view of the emerging field (Rodriguez-Iturbe 2000). Further attempts to distill the disciplinary focus of ecohydrology was discussed by Hannah, et al. 2004, which analyzed biases in disciplinary (hydrology vs. ecology) views of the emerging field and further called for an integrated approach. Later publications drew attention to emerging branches and sub-disciplines within the field, such as ecohydrology of semiarid and arid environments. For example, in a special feature of Ecology journal, Wilcox and Newman 2005 provided the context and scope emerging from a conference that brought together ecologists and hydrologists in 2002. Overall, for well-understood reasons of importance and therefore high competition for water as a resource and sensitivity to environmental change, semiarid and arid environments arguably received the largest attention of the community over the last decade (e.g., Newman, et al. 2006). A review of advances and future research needs seeking to link ecophysiology of plant-water relations and hydrologic sciences at various spatial and temporal scales was offered by Asbjornsen, et al. 2011.

• Asbjornsen, H., G. R. Goldsmith, M. S. Alvarado-Barrientos, et al. 2011. Ecohydrological advances and applications in plant-water relations research: A review. Journal of Plant Ecology 4.1–2: 3–22.

  DOI: 10.1093/jpe/rtr005

  A plant-water relations perspective on advances and outstanding challenges in describing vegetation-hydrology interactions, with specific emphasis on the issues of ecohydrologic scaling and variability.

• Baird, A. J., and Robert L. Wilby. 1999. Eco-hydrology: plants and water in terrestrial and aquatic environments. New York: Routledge.

  A collection of articles authored by ecologists and hydrologists searching for a coherent view of ecohydrologic systems.

• Hannah, D. M., P. J. Wood, and J. P. Sadler. 2004. Ecohydrology and hydroecology: A “new paradigm”? Hydrological Processes 18.17: 3439–3445.

  DOI: 10.1002/hyp.5761

  A critical analysis of what constitutes platforms for emerging interdisciplinary fields of hydroecology and ecohydrology.

• Hatton, T. J., G. D. Salvucci, and H. I. Wu. 1997. Eagleson’s optimality theory of an ecohydrological equilibrium: Quo vadis? Functional Ecology 11.6: 665–674.

  DOI: 10.1046/j.1365-2435.1997.00159.x

  Stemming from Eagleson 1982 (see under Darwinian Ecohydrology), a proposal of ecological optimality, this work lays out a theoretical foundation that links ecology and hydrology.

• Ingram, H. A. P. 1987. Ecohydrology of Scottish peatlands. Earth and Environmental Science Transactions of The Royal Society of Edinburgh 78.4: 287–296.

  DOI: 10.1017/S0263593300011226

  One of the earliest uses of the term “ecohydrology” in this work reflects its specific focus on aquatic systems at that time.

• Newman, B. D., B. P. Wilcox, S. R. Archer, et al. 2006. Ecohydrology of water‐limited environments: A scientific vision. Water Resources Research 42:W06302.

  DOI: 10.1029/2005WR004141

  A detailed analysis and a call for adoption of ecohydrological perspectives in studies of water-limited systems, including a proposal of effective strategies.

• Noy-Meir, I. 1973. Desert ecosystems: Environment and producers. Annual Review of Ecology and Systematics 4.1: 25–51.

  DOI: 10.1146/annurev.es.04.110173.000325

  Appearing in literature many years before establishment of ecohydrology as a science, this work presented a holistic synthesis on the form, structure, and function of water-limited ecosystems, serving as one of foundational platforms for the new science.

• Rodriguez-Iturbe, I. 2000. Ecohydrology: A hydrologic perspective of climate‐soil‐vegetation dynamics. Water Resources Research 36.1: 3–9.

  DOI: 10.1029/1999WR900210

  A visionary opinion on opportunities in the emerging field of ecohydrology. Emphasizes soil moisture as the cornerstone element in water-limited ecosystems.

• Wilcox, B. P., and B. D. Newman. 2005. Ecohydrology of semiarid landscapes. Ecology 86.2: 275–276.

  DOI: 10.1890/04-0631

  An introductory paper to a series of five manuscripts published in a special feature of Ecology journal as an outcome of the American Geophysical Union Chapman Conference Ecohydrology of Semiarid Landscapes. The paper provides the context and an overview of the manuscripts in this special feature, focusing on water-related processess in semiarid landscapes.

• Zalewski, M., G. A. Janauer, and G. Jolankai. 1997. Ecohydrology: A new paradigm for the sustainable use of aquatic resources. UNESCO IHP Technical Documents in Hydrology no. 7, IHP-V Projects 2·32·4. Paris: UNESCO.

  This work presents a perspective on ecohydrology as a science warranted for water resource management and conservation practices, in which watershed is viewed as central for understanding relevant functional linkages.