Water use and quality and stream flow in a Mediterranean stream

We examine how the use and management of water resources and waste-water inputs affect the stream flow and its biological quality in a Mediterranean stream, the Congost (NE Spain). Agricultural, farming, urban and industrial activities take place from its headwaters to its lower section, and there are 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 are 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 basin two biological plants are located, due to the lack of dilution, the biological recovery of the freshwater community is poor, although coarse fish communities 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 as a result, the stream in this section has no fish or macrofauna at all. It is concluded that in Mediterranean streams, end-pipe measures, even using biological plants, may be insufficient for the recovery of stream communities due to the lack of natural flow related to the climate and the high demand of the water resources.