STRUCTURAL AND TROPHIC CHANGES IN A RIVERINE MACROBENTHIC COMMUNITY FOLLOWING IMPOUNDMENT FOR HYDROELECTRIC POWER-GENERATION

Structural and trophic changes in a benthic macroinvertebrate communit y downriver from Valparaiso Reservoir (northwestern Spain) were compar ed before (1986) and after (1990-1991) the creation of that hydropower impoundment. The number of taxonomic groups, total biomass and total density significantly declined under the influence of the new flow reg ulation, with scrapers (as relative density) being the functional feed ing group most adversely affected. The environmental impact decreased with time after the construction of the dam. Taxonomic richness and di versity of predators appeared to be the most sensitive biological indi cators of the progressive recovery of the macrobenthic community.