Abstract
Urban surface water runoff contains high levels of salt and nitrate, particularly in northern climates of the USA. We hypothesized that increased salt and nitrate concentrations would reduce total biomass and cause complete taxonomic shifts of benthic algae. To investigate and quantify the multi-tiered responses of benthic algal assemblages to the impacts of road salt and nitrate, we created artificial flow-through streams with terracotta vessels with nutrient diffusing substrates (NDS) containing varying concentrations of both salt (0–7500 mg/L) and nitrate (0–5.9 mg/L) and incubated for 56 days during the summer. Diatom concentrations were significantly impacted by salt, and the combination of salt and nitrate on sampling days 4 and 28. Over the range of tested nitrate conditions, some cyanobacteria increased over time. Within the eukaryotic community, several algal family abundances changed significantly over time. The response of diatoms was complex, with treatment only significantly impacting specific genera. Overall, this study shows salt and nitrate, as well as the combined effects of the two, significantly impact benthic algae assemblages and community development.