Multiple stressors in tropical streams: nitrate, sediment, and flow interactions mediate benthic biomass and diatom community responses in experimental streams

Human-induced impacts, such as deforestation and agricultural intensification, pose significant threats to tropical streams by promoting nutrient enrichment, fine sediment input, and altered flow regimes. This study employed outdoor stream mesocosms to assess how nitrate enrichment, fine sediment addition, and flow reduction influence benthic algal biomass (using chlorophyll-a as a proxy) and diatom community structure. Results showed that sediment addition decreased chlorophyll-a under ambient nitrate conditions but increased it at higher nitrate concentrations. Elevated nitrate levels reduced diatom species richness and evenness, increasing dominance, while changes in species composition were primarily driven by reduced flow and increased nitrate or sediment levels. These findings highlight the mechanisms by which agricultural stressors shape diatom community dynamics, providing critical insights for managing freshwater ecosystems under increasing agricultural pressure.