Ecological effects of small dams on benthic macroinvertebrate communities of mountain streams (Cordoba, Argentina)

We assessed the effect of small dams on stream habitats and on the structure and function of benthic macroinvertebrate communities in mountain streams of Cordoba, Argentina. Two streams with small dams (impacted streams) and two streams without dams (control streams) from the Carcarana. River upper sub-basin were selected. Dominant hydraulic units were identified and benthic samples were collected in each of these units during high and low water periods. According to this study small dams may have impact on the function and structure of the invertebrate community, though hydraulic habitats would not be affected. Fourteen hydraulic units were found and changes due to dams were not observed as assessed by the detrended correspondence analysis. The canonical correspondence analysis grouped samples mainly in relation to hydraulic habitats whereas TWINSPAN grouped samples according to the presence of dams. Nested ANOVAs showed changes in richness and diversity, in the abundance of filterers and shredders and in the abundance of certain species. Small dams generate quite small reservoirs and their permeability may be greater than those of large dams. The behaviour of macroinvertebrate populations in drift and colonization processes, the continuity of the riparian structure and the discharge of planktonic algae downstream the dams may be some factors determining the ecological changes produced by small impoundments.