Water use and quality and stream flow in a Mediterranean stream

We examine how the use and management of water resources and waste-water in puts affect the stream flow and its biological quality in a Mediterranean s tream, the Congest (NE Spain). Agricultural, farming, urban and industrial activities take place from its headwaters to its lower section, and there a re many weirs and wells along the stream. The effects of four sewage plants , built in the basin in the last 5 years, on river flow and water quality a re analysed. Today most of the river flow comes from the sewage plants and few or any dilution from natural stream exist. In the upper part of the bas in two biological plants are located, due to the lack of dilution, the biol ogical recovery of the freshwater community is poor, although coarse fish c ommunities may be found at the end of this section. In the middle and lower parts of the stream, water is treated in two physicochemical plants, and a s a result, the stream in this section has no fish or macrofauna at ail. It is concluded that in Mediterranean streams, end-pipe measures, even using biological plants, may be insufficient for the recovery of stream communiti es due to the lack of natural flow related to the climate and the high dema nd of the water resources. (C) 2000 Elsevier Science Ltd. All rights reserv ed.