Eco-hydrology is the sub-discipline of scientific study shared by the ecology and hydrology. Eco-hydrology research investigates the effects of hydrological processes on the distribution, structure, and function of ecosystems, and on the effects of biotic processes on elements of the water cycle.
Until recently, the term eco-hydrology had been applied to a few distinct areas of interdisciplinary study. No one has yet attempted a comprehensive description of the sub-discipline, which potentially encompasses the entire biosphere. The IHP identifies eco-hydrology with a new paradigm for sustainable management of water resources [Zalewski et al., 1997]. Even so, its seems unlikely that a single unifying paradigm could cover the range of water-mediated interactions between biotic components of all ecosystems and their abiotic environments. It is more likely that eco-hydrology, the science, will embrace the formulation, testing, and application of conceptual models to describe these interactions within specific constraints of scale and geomorphic setting. Some of these are described below.
Peter Eagleson [Eagleson, 1978, 1982] investigated the interaction of hydrology, vegetation and soil properties in water-limited ecosystems. Rodriguez-Iturbe et al.  and others have recently taken up and extended this early work. Eagleson’s approach represents dynamics of the terrestrial water balance at a point in terms of a spatially aggregated reservoir of soil moisture responding to a stochastic climate. Soil properties and the varying moisture content of the soil control the partitioning of rainfall between infiltration and runoff. Vegetation controls the loss of soil moisture by evapo-transpiration, but evaporation and drainage by percolation also occur. Eagleson’s model explicitly excluded the effects of lateral flows and interactions between soil moisture and a shallow water table. In spite of this underlying simplicity, Eagleson’s investigations generated fundamental insights into the relationship among the dynamic and interdependent properties of soil, vegetation, and climate [Hatton et al., 1997].
Research on wetlands has played a central role in the development of eco-hydrology in Europe and the United Kingdom [Baird and Wilby, 1999]. Hydrologic and ecological processes are intimately connected in wetlands, and their interaction has consequences not only for these ecosystems, but also for the functions they serve on larger scales. For example, water, ice, and permafrost constitute an important component of the organic soil formed in the extensive wetland regions found at high latitudes in the Northern Hemisphere. The interaction of hydrology and ecological processes involved in soil diagenesis influences stream flow, water quality, and geomorphology in the local drainage basin and the carbon cycle and climate on a global scale. Under a warming climate, these soils will thaw, dry, and oxidize, releasing stored carbon back into the atmosphere [Gorham, 1991].
Groundwater, surface water, and sediment transport interact to influence the structure and functioning of river and stream ecosystems. These ecosystems comprise distinctive channel and flood plain geomorphic components that are physically shaped by stream flow and sediment transport [Petts and Bradley, 1997]. Cycles of flood and recession modulate ecological interactions between the channel and the adjacent margin, as well as maintain their characteristic morphology. Groundwater exchange with the channel establishes base flow and influences temperature of the surface water. As well, groundwater mediates the exchanges of solutes laterally between channel and flood plain and vertical exchanges between water flowing in the channel and subsurface water in the hyporheic zone. At the scale of the entire basin, the equilibrium structure of river and stream ecosystems varies predictably from headwaters to mouth, as described by the river continuum concept of Vannote et al. . This hypothesis and its corollaries have proven useful in understanding the natural, undisturbed state of river ecosystems and the response of these systems to human activities that affect stream flow and sediment movement.
As a final example, consider the influence that river flow and its variation exert on estuarine and near shore ecosystems. Although the mechanisms involved are not yet fully known, empirical evidence links the rate of fresh water discharge to the productivity of estuarine and coastal fisheries. Certainly, the supply of nutrients carried in the discharge is part of the story [National Research Council, 2000]. But, just as flow and sediment discharge interact to determine the geomorphology of river and stream ecosystems, freshwater discharge and internal mixing processes interact to determine the salinity regime, stratification of the water column, and circulation characteristic of each estuary. Changes in hydrology derived from climate and human activities on the watershed have both long- and short-term effects on coastal ecosystems. Long-term effects include changes to the rate of sediment accretion that is necessary to maintain the stability of the coastline in low-lying areas [Working Group on Sea Level Rise and Wetland Systems, 1997]. Short-term effects include changes in fishery yields [Loneragan and Bunn, 1999] and overall structure and productivity of the food web [Livingston et al., 1997].
Baird, A. J., and R. L. Wilby, Eco-hydrology: Plants and Water in Terrestrial and Aquatic Environments, 402 pp., Routledge, London, 1999.
Eagleson, P. S., Climate, soil, and vegetation. 1. Introduction to water balance dynamics, Water Resour. Res., 14, 705-712, 1978.
Eagleson, P. S., Ecological optimality in water-limited natural soil-vegetation systems. 1. Theory and hypothesis, Water Resour. Res., 18, 325-340, 1982.
Gorham, E., Northern peatlands: Role in the carbon cycle and probable responses to climatic warming, Ecol. Appl., 1, 182-195, 1991.
Hatton, T. J., G. D. Salvucci, and H. I. Wu, Eagleson’s optimality theory of an ecohydrological equilibrium: quo vadis? Functional Ecol., 11, 665-674, 1997.
Livingston, R. J., G. C. Woodsum, N. Xufeng, and F. G.Lewis, Freshwater input to a gulf estuary: Long-term control of trophic organization, Ecol. Appl., 7, 277-299, 1997.
Loneragan N. R., and S. E. Bunn, River flows and estuarine ecosystems: Implications for coastal fisheries from a review and a case study of the Logan River, southeast Queensland, Austral. J. Ecol., 24, 431-440, 1999.
National Research Council, Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution, 405 pp., National Academy Press, Washington, D.C., 2000.
Petts, G. E., and C. Bradley, Hydrological and ecological interactions within river corridors, in Contemporary Hydrology, edited by R. L. Wilby, pp. 241-271, John Wiley and Sons, Chichester, 1997.
Rodriguez-Iturbe, I., A. Porporato, F. Laio, and L. Ridolfi, Plants in water-controlled ecosystems: Active role in hydrologic processes and response to water stress I. Scope and general outline, Adv. Water Resour., 24, 695-705, 2001.
Vannote, R. L., G. W. Minshall, K. W. Cummins, J. R. Sedell, and C. E. Cushing, The river continuum concept, Can. J. Fish. Aquat. Sci., 37, 130-137, 1980.
Working Group on Sea Level Rise and Wetland Systems, Conserving coastal wetlands despite sea level rise, Eos, Trans. AGU, 78, 257-262, 1997.
Zalewski, M., G. A. Janauer, and G. Jolankai, Ecohydrology: A New Paradigm for the Sustainable Use of Aquatic Resources, 58 pp, International Hydrological Programme, UNESCO, Paris, 1997.
Eco-hydrology – integrated science for ecosystem management
www.eco-hydrology.com • Last update: November 9th, 2005