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10. SUMMARY AND CONCLUSIONS

A. Principles of Ecohydrology as a framework for integrated basin management

A major cause of the decline of water resources on the global scale has been the emission of pollutants and a reduction of absorption capacity of ecosystems against human impacts.

Ecohydrology is the scientific concept that promotes the integration of hydrology and ecology, and the control of these processes to enhance the absorption capacity of ecosystems. Ecohydrology should be integrated with programs to reduce pollutant emissions, since pollution emissions reduce the absorption capacity of the ecosystem.

The practice of ecohydrology is predicated upon three, basic principles. These are summarised below.

1. The meso-scale water cycle (the mesocycle) forms an appropriate basis for the quantification of energy, nutrient, and pollutants flow within the landscape and freshwater systems. The mesocycle effectively translates into a basin approach to water resources management. Water is the dynamic medium within the landscape, driven by gravity, that forms a definitive link between various types of pollutants:
   
   • Air pollution interacts with the hydrological cycle through evaporation, evapotranspiration, and precipitation. Pollutants can be dissolved in water, transported by the atmosphere, and returned to the land surface which forms the catchment. Pollutants can be transported between continents and river basins in the atmosphere.
   • Pollutants can be dissolved in water, flushed together with minerals and organic sediments during the erosion process, and transported through land and water ecotones to aquatic systems. Some of these pollutants can be retained within the ecotones and decomposed due to microbial and biological activity. If pollutants are transferred to aquatic systems, they can be toxic or become toxic for crucial components of aquatic biota (e.g., cladocerans that form a food resource for higher organisms such as fishes). They may affect the structure and functioning of the ecosystem. In the case of reservoirs, which concentrate pollutants as a result of sedimentation and alteration of flow velocities, they may cause the loss of top down controls on toxic algae blooms. Thus toxins may accumulate in fish tissues already containing the genotoxic pesticides or heavy metals, or be released into drinking water supplies, with negative consequences for human populations.

   The quantitative integration of various types of pollutants at the basin scale–including point source pollution, air pollution, nonpoint source pollution, and pollution returned to the terrestrial and/or aquatic systems (including groundwater) by precipitation–creates possibilities for mathematically modelling of these processes. Modelling, in turn, is a useful tool for testing various scenarios, and providing the necessary background for minimising the costs and maximising the efficiency of remedial measures.

2. An increased understanding of the natural properties of ecosystems enables the development of strategies to preserve and enhance the inherent potential of ecosystems to adapt to permanently changing conditions (mostly climatic) and/or recover from disturbances (natural and anthropogenic). In general, the absorption capacity of the ecosystem against human impacts is larger within river basins where plants are highly involved in the circulation of water, nutrients, and other pollutants. The absorption capacity is dependent upon plant biomass and temperature. Additionally, in temperate climates, the timing of the hydrological-biotic interactions, and the presence of alternative pathways affecting the interplay between hydrological and biotic processes, is of primary importance.
3. The use of ecosystem properties as a management tool requires an increased understanding of the causal relationships among ecological processes within the different types of ecosystems that form the background for the control and regulation of ecological processes for water quality improvement. The consequence of effectively utilising natural ecological processes may be an increase in the rate of "self-purification" within a stream of up to three times (see Chapter I, Figure 1.2). Various ecological processes, and their relative efficiencies in reducing nutrient concentrations in water along the landscape gradients, are described in greater detail in other parts of these Guidelines.

The ecohydrological approach to sustainable river basin management and the control of biological and hydrological processes should be integrated with technical approaches. An example of the necessity of integrating ecohydrological methods with technical ones, to achieve cost-effective pollution reduction, can be seen in the analysis done by IIASA using the case of the Nitra River. According to Somlody, the cost of using the "best available technology" to increase the amount of dissolved oxygen in the river, from 2.1 mg/l to 5.7 mg/l, would be almost U.S. $ 100 million. Using ecohydrological principles, and combining ecological and technical approaches, the cost to improve oxygen conditions in the river, from 3.6 mg/l to 6.2 mg/l, would be less than U.S. $ 20 million. Thus, this lower cost alternative is not only better from the point of view of water quality standards and biodiversity, but also increases the ecosystem’s self-purification potential. These benefits could be achieved by wetland construction, and regulation of light access to the stream system.

B. Final Conclusion

Phytotechnologies and ecohydrology provide an effective and efficient mechanism for the restoration of degraded environments and sustainable development of society. Traditional sewage treatment plants, providing BOD and nutrient load reduction benefits to river systems and freshwater reservoirs, nonetheless continue to reduce the quality of water resources and their recreational value within the context of the river catchment (Figure 10.1). Extending the technical, sewage treatment system by constructing wetlands results in a more efficient reduction in pollutant loads and generates additional societal benefits. The improved water quality increases the appeal of the water resource for tourism, which can contribution to the inflow of capital to a region. Moreover, willow plantations within wetland fringe can provide alternative sources of energy (bioenergy) that can help to reduce CO₂ emissions from burning fossil fuels. The resultant ash can be used to fertilise the forested plantations. Producing bioenergy and timber also generates new employment opportunities and revenue flows while reducing capital outflows for fossil fuel use. The use of ecological concepts, therefore, results not only in a good quality environment, but also can help to elevate the economic status and level of sustainable development in local communities.

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