Local factors drive the richness, biomass and composition of benthic invertebrate communities in Neotropical reservoirs

Abstract

Dams affect aquatic biota in running water by altering the environmental dynamics. One of the communities affected are benthic invertebrates, that perform important functions such as nutrient cycling and energy transfer in reservoirs. We investigated the influence of the following factors: spatial, abiotic variables, reservoir characteristics and land use on the richness, biomass and composition of benthic invertebrates in 29 reservoirs in southern Brazil. Sediment samples and abiotic variables were collected in the littoral and profundal zones of reservoirs during the dry (July) and rainy (November) seasons in 2001. We used principal coordinates of neighbour matrices to obtain the spatial factors. We analysed the unique and overall effects of the four factors. We found that the factors analysed significantly influenced the composition and biomass of the invertebrates (22%). The percentage of variation explained by the unique effects of the different factors showed similar values, but the spatial factors showed the highest value (4%). This indicates that closer reservoirs have higher similarities in terms of composition and biomass of benthic invertebrates. On the other hand, the abiotic variables had the highest explained value when evaluating the overall effects (10%). Therefore, for invertebrate richness, only the reservoir characteristics were significant for the overall and unique effects (49%). More specifically, we observed lower taxon richness in older reservoirs, probably because the age of such artificial aquatic ecosystems influences other variables, which structure the benthic communities. In conclusion, the structure of benthic invertebrate communities in reservoirs of southern Brazil are mainly driven by spatial and reservoir characteristics.