Response of sub-Antarctic streams to urbanization: Relevance of assemblage structure and independent reference areas

Abstract

Andean Patagonia is experiencing sudden changes due to unorganized urban expansion. Despite being known for its wilderness areas, southern Patagonian urban streams have been increasingly studied during the last decade, using reference-impact gradients within urbanizing watersheds. Here, we assess urbanization effects on stream integrity by comparing environmental characteristics on independent reference streams vs. urban streams, and the benthic macroinvertebrate community structure along three stream reaches in an urbanization gradient. In comparison to reference sites, urban streams had higher nutrient concentrations, temperature, turbidity, stream flow, and total primary producer biomass, accompanied by lower dissolved oxygen concentrations, substrate particle size, mainly along mid and downstream areas. These variables were the main factors structuring macroinvertebrate assemblage ordination analysis. Macroinvertebrate assemblages from areas upstream from the urbanization differed from their counterparts in reference streams, but not from downstream reference areas. Environmental characteristics and biotic assemblage structure were altered in urban streams, even in reaches located upstream from urbanization, compared to independent upstream reference reaches. This study highlights the importance of a community and comparative vision towards independent areas with low impact to serve as reference values and establish appropriate goals or baselines when assessing ecological conditions and potential restoration.