Limnetica 39

Despite the fundamental importance of hydroelectric power for socioeconomic development, the presence of hydropower plants cause large-scale alterations to the natural flow regime of rivers and profoundly influences aquatic processes and biodiversity. This study evaluates the seasonal impact of small hydropower stations by analysing and measuring macroinvertebrate community composition. Our objectives were to (1) examine whether the abundance and richness of benthic macroinvertebrates vary according to alterations to the river, (2) identify the families of macroinvertebrates most sensitive to depletion as a consequence of the impact of a hydropower station, and (3) determine whether there is a seasonal component in river regulation that impacts on macroinvertebrate communities. A 167 848 individuals were sampled from 6 different phyla and 10 different orders of Arthropoda representing 116 different macroinvertebrate families, whose distribution and abundance depended on the river, sampling time and sampling site. Ephemeroptera, Diptera, Trichoptera, Coleoptera and Plecoptera were the most representative orders in all seasons of the year, and also had the most abundant families (Baetidae, Caenidae, Chironomidae and Simuliidae). There was no great variation in autumn and winter for the most abundant taxa but it was important variation in spring and summer. Our findings point to differences in macroinvertebrate abundance and richness in aquatic systems impacted by hydropower stations and to a recovery process downstream, where the water level and habitats are not negatively affected by these stations.