Low flow - the river's ecosystem limiting factor

The main objectives of this study were to: (1) find out the minimum water discharge needed to maintain good biological and chemical quality for surface water; (2) achieve categories of biological indicators for water quality; and (3) compare these biological categories with physical-chemical parameters. The study has been carried out on the River Strouma using two approaches: - in time: by determination of the relationship between the biotic indices and the water discharge as a result of the processes that have been realised at the moment of their registration - in space (along the river): by discrete study of specific river stretches dominated by one or more specific anthropogenic impacts on the natural flow regime and/or on the water quality. In a 3-year period, parallel field measurements and hydrobiological samplings have been carried out, supplementing the heretofore existing scarce information. (C) 2000 Elsevier Science B.V. All rights reserved.