POTENCIAL USO DE LOS MACROINVERTEBRADOS COMO INDICADORES DE LA CALIDAD DEL AGUA EN CUENCAS ALTAS DE BAJO IMPACTO: CASO DE LA CUENCA DEL ARROYO SAN FRANCISCO, URUGUAY

Abstract

Stream macroinvertebrate communities are modulated by different processes at different spatial scales, from watershed to reaches and local scale, which can be directly or indirectly affected by human activities and changes in land use. This study evaluated the effect of water quality on macroinvertebrate structure in the San Francisco drainage basin, Lavalleja, Uruguay. We measured in situ physico-chemical water variables and collected a total of 50 macroinvertebrate samples using a surber in 10 reaches in different stream’s order and basin size. Macroinvertebrate community structure were analyzed using density, richness, and two common bioindicator indexes: percentage of number of Ephemeroptera, Plecoptera and Trichoptera (%EPT) and percentage of Oligochaeta (%Oligochaeta). We did not find a significant relationship between physico-chemical water variables and stream order, the low order streams had comparatively higher water nutrient concentration and higher conductivity. Stream order showed a significant positive relationship with %EPT and a negative relationship with %Oligochaeta. No patterns were found for density and taxonomic richness. Some components of macroinvertebrate community structure in the streams belonging to the San Francisco stream basin could largely be explained by water quality, in this case connected to stream order. We found evidence of the great potential for using macroinvertebrates as environmental quality indicators, even in well preserved drainage basins.