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. [2001] 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.
[1980]. 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