Impacts of land use and hydrological alterations on water quality and fish assemblage structure in headwater Pampean streams (Argentina)

Headwater streams play an essential role in catchment ecosystem processes and are particularly vulnerable to land use degradation and anthropic hydrological alterations. Considering that fish assemblages are reliable indicators of the ecological integrity of streams, we evaluated the ichthyofauna structure in four headwater Pampean streams located at catchment areas with contrasting land uses and hydrological man-made alterations. During autumn and spring of 2017 and 2018, fish assemblages were sampled and physicochemical and water table depth were measured. Specific richness, abundance, and diversity of fish assemblages were estimated. The degree of anthropic intervention of drainage networks and wetland coverage was estimated for each catchment. Statistical analyses assessed the differences between rural and periurban sampling sites in terms of environmental variables and fish assemblage structure, as well as the relationships between the biotic and abiotic variables. Results showed differences among headwater streams according to their land uses, hydrological alterations, and fish assemblage structure, evidencing a combined effect of land use and hydrologic alterations on fish assemblage. Changes in these communities can reflect not only alterations in water quality caused by local land use but also the influence of the catchment environmental integrity related to hydrological modifications and other phenomena that can occur simultaneously and at different geographical scales.