Freshwaters such as lakes, rivers and deltas were the loci of the evolutionary development and the origins of man. Subsequently they became centres of settlements from which the earliest civilisations developed and spread. The major rivers of China, the Indus, the Mesopotamic rivers and the Nile have had their hydrological regimes modified mainly for the agricultural benefits of these ancient cultures and more recently Romano-Western developments have had their impacts on streams and rivers which have sought by impoundments to control these systems for power production, transport and water for increasing populations in developing urban settlements. The pace of these developments has been such that there are now few if any river catchments which are untouched. It is at the catchment level that study and management approaches must be considered as there is a summation of impacts which downgrade the ecosystem, reducing its diversity and ability to regenerate itself. Thus to hydraulic engineering by impoundment activities must be added contamination from agricultural, domestic and industrial chemicals. Also must be added bad or non-existent basin management and extractive forestry and farming activities on slopes which increase erosional and depositional problems particularly for the lowland reaches of the river system. Water is used by man and returned more or less dirtied and, therefore, not only is the integrity of the ecosystem threatened by the abiotic environmental modification but water quality and quantity are modified on short, seasonal or longer-term cycles.
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