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(46-13) Nutrient enrichment downstream from small reservoirs in mountain rivers of Central Spain. Camargo, J.*,1, 1 Universidad de Alcala, Alcala de Henares (madrid), Spain ABSTRACT- One of the most important environmental problems responsible for freshwater pollution on a world-wide scale is the nutrient enrichment of rivers and streams. Major anthropogenic sources causing nutrient enrichment are animal farming, agricultural runoff, industrial wastes and sewage effluents. On the other hand, thousands of deep-release dams have been built in rivers and streams during the last century. Usual downstream effects caused by dams (esp large reservoirs) are short-term flow fluctuations, changes in water temperature regimes and decreases in dissolved oxygen concentrations. Nevertheless, very little attention has been paid to the fact that impounded rivers and streams can experience nutrient enrichment as a consequence of deep releases from dams. In this study I present data on the biotic and abiotic changes downstream from small reservoirs (max depth < 20 metres) located in the headwaters of four mountain rivers (Eresma, Miraflores, Riaza and Tormes rivers) of Central Spain. In all cases, significant (t-test; P < 0.05) increases in total ammonia, nitrate and phosphate concentrations downstream from dams were measured? Increases in concentration of chlorophyl a (from the periphyton community) and in abundance of periphyton-eating scrapers (from the benthic macroinvertebrate community) were also quantified. It is concluded that these small reservoirs act as nutrient accumulators at those headwater areas. Nutrients would ultimately come from forest runoff and extensive livestock. In addition, the fact that the vegetal cover was not probably removed before filling reservoirs would contribute to the nutrient enrichment downstream. Key words: nutrient enrichment, Spanish rivers, reservoirs |
