Sustainable management of natural water resources should include environmentally sound dam construction and operation with respect to both upstream and downstream management. Because of slowly evolving alterations in riverine ecosystems following the construction of a dam - due to the sometimes large distances between dams and affected areas, and the interference with other anthropogenic activities - some of the effects of damming may be overlooked. Constructing reservoirs modifies the biogeochemical cycles, such as interrupting the flow of organic carbon, changing the nutrient balance, and altering oxygen and thermal conditions. The consequences of altered processes may not be immediately apparent and may become obvious only after a long period of time or only in combination with other anthropogenic alterations. It is difficult to give precise predictions of the impacts of a particular dam due to the complexity and individuality of aquatic ecosystems. However, this remains the challenge while planning and constructing new dams. Protecting and restoring river basins has been called for by the World Commission of Dams (WCD).
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