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B. Ecohydrology as a tool for enhanced absorption capacity of ecosystems

During the 20^th century, environmental scientists focused their attention on single species, single factors, and single process, and, consequently, had great difficulty in providing solutions to problems of environmental resource degradation. These problems occur as a result of an highly complex interplay between the abiotic environment and biotic processes –both of which, to various extents, have been modified by humankind.

Ecohydrology (Zalewski et al. 1997; Zalewski 2000) is a new concept in environmental problem-solving which is based upon the suggestion that sustainable development of water resources is dependent on the ability to maintain evolutionarily established processes of water and nutrient circulation and energy flows at the basin scale. This depends on a profound understanding of the whole range processes involved that have a two-dimensional character. The first dimension is temporal: spanning a time frame from the past, paleohydrological condition to the present, with due consideration of future, global change scenarios. The second dimension is spatial: understanding the dynamic role of aquatic and terrestrial biota over a range of scales from the molecular- to the basin-scale. Both dimensions should serve as a reference system for enhancing the buffering capacity of ecosystems against human impacts by using ecosystem properties as a management tool. This, in turn, depends on the development, dissemination, and implementation of interdisciplinary principles and knowledge, based on recent advance in environmental science.

Ecohydrological principles as a conceptual tool for sustainable water resources management

The concept of ecohydrology is based on three principles (Zalewski 2000):

1)	Framework - Integration of the catchment and its biota into a single Platonian superorganism. This covers such aspects as:
		SCALE - the meso-scale cycle of water circulation within a basin (the terrestrial/aquatic ecosystem coupling) provides a template for the quantification of ecological processes;
		DYNAMICS - water and temperature have been the driving forces for both terrestrial and freshwater ecosystems;
		HIERARCHY OF FACTORS - while abiotic processes are dominant (e.g., hydrological processes), biotic interactions may manifest themselves when they are stable and predictable (Zalewski and Naiman 1985).
2)	Target - Understanding the evolutionarily established resistance and resilience of the superorganism to stress. This aspect of ecohydrology expresses the rationale for a proactive approach to the sustainable management of freshwater resources. It assumes that it is not enough to simply protect ecosystems, but, in the face increasing global changes that manifest as increases in population, energy consumption, and material and human aspirations, it is necessary to increase the capacity of ecosystems (or their resistance and resilience) to absorb human-induced impacts.
3)	Methodology - The use ecosystem properties as a management tool by using biota to control hydrological processes and vice versa by using hydrology to regulate biota. The large potential of knowledge which has been generated by dynamically developing of the ecological engineering (Mitsh 1993; Jorgensen 1996) should to serious extent accelerate implementation of above concept.

The all three principles are illustrated by Figure 1.2, where the control of eutrophication in a temperate reservoir through application of different ecologically-based measures in the river basin has been focused on a reduction in phosphorus inputs and the limitation of phosphorus dynamics within the nutrient pool. Starting from the top of the catchment, the first step is to enhance nutrient retention within the catchment by reforestation, creation of ecotone buffers, and optimisation of agricultural practices. The buffer zones at the land-water interface also reduce the rate of groundwater flux due to evapotranspiration along the river valley gradient. Nutrient transformation into plant biomass within the ecotone may further reduce the nutrient supply to the river. The wetlands within the river valley and along the river course form the buffer zone: they reduce inputs of mineral sediments, organic matter, and nutrient loads that would otherwise be transported by the river during floods through sedimentation and biological activity. In some artificial wetlands, nitrogen loads can be reduced significantly by regulating the water levels to stimulate denitrification through anaerobic processes. In shaded rivers with high nutrients loads, it is possible to amplify the self-purification capacity of the stream by creating more complex, intermediate ecotones. If despite all the above measures, combined with sewage treatment, the nutrients concentrations in reservoir remain high and the potential for toxic algal blooms exists, other methods can be applied to reduce the recirculation of nutrients within the reservoir. These measures include locking the nutrients within the biomass of macrophytes, or translocating the nutrients to other trophic levels (e.g., by manipulation of the lake’s biological communities, or "biomanipulation". Since the properties of large-scale systems cannot be accurately predicted from the properties of its component elements, such a complex strategy for restoring and controlling nutrients within the catchment landscape and freshwater ecosystem should be assessed continuously at each stage of implementation and adjusted to maximise potential synergistic effects.

Most of the ecohydrological methods mentioned above will be presented in more detail in the following chapters.

Other, parallel attempts to integrate ecology and hydrology (sensu Zalewski et al. 1997) recently have appeared; e.g., ecohydrology which integrates plants, water, and the landscape (Baird and Wilby 1999), water dynamics driven by climate-vegetation-soil relationship (Rodriguez-Iturbe 2000) and hydroecology, linking hydrology and hydraulics with water transfer between the atmosphere, terrestrial vegetation, and soils (Acreman 2001).

In the face of accelerating global changes, in the sense of environment, populations, and climate, the problem of achieving sustainable water resources is becoming so urgent that every intellectual effort to achieve sustainability should be appreciated. These guidelines are intended to provide new insights into the application of the recent developments in ecology, using selected case studies, to the sustainable use of water resources at the catchment scale. These guidelines integrate ecological concepts with the predictive, problem-solving approach of the geomorphological and biological sciences, to predict the response of freshwater biota and ecosystems to variation in abiotic factors over a range of spatial and temporal scales. This approach is based upon an understanding of ecosystem properties and their dependence on, and interplay with, dynamic abiotic factors at the basin scale (principally, temperature and water).

Within this context, ecohydrology emerges as a framework within which to integrate hydrology and ecology across a range of temporal and spatial scales, using, as a template for analysis, water dynamics and nutrient budgets at the basin scale, and ecosystem processes as a management tool. This framework should serve as a background for the development of an holistic approach as well as provide "low-cost, high technology" approaches to water management, which approaches are especially important for developing countries and countries in economic transition.

The concept, from the point of view of scientific methodology, is the result of integrating Popperian experimental falsification of hypotheses with a problem-solving approach. There are two key assumptions: first, that water in the landscape is situated in depressions, so, if not specially protected and managed in an integrated manner based upon an understanding of the links between hydrological and ecological processes, it is vulnerable and, in consequence, limited; and, second, that, when human populations and aspirations are increasing, it is not enough to protect the water resources by reducing energy use and pollutant emissions - rather, it is necessary to enhance the buffering capacity of the catchment using an understanding of both hydrological and ecological processes (Figure 1.3). In short, elimination of threats, without consideration of increased opportunities, cannot lead to the success (Figure 1.4). Thus, ecohydrology incorporates the use of ecosystem properties as a management tool in implementing a program of water resource management.

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