Biomonitoring of Pesticides in Agricultural River Catchments: a Case Study from Two River Catchments in Tropical Sri Lanka

Monitoring of pesticide pollution in aquatic systems is a complex process and often constrained by high costs and methodical complexities associated with pesticide measurements in many regions of the world. A trait-based Species at Risk (SPEAR) biomonitoring approach has been conducted to test the responsiveness of the SPEAR_ pesticides index to pesticide effects in two tropical river catchments in Sri Lanka. The effects of pesticide toxicity (TU (D.magna ) ), water quality parameters, channel quality (CQI), and landuse on SPEAR pesticides index and other biotic indices, i.e., family richness of macroinvertebrates (FR) and %EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxa in streams were tested using stepwise multiple linear regression analysis approaches. The analyses revealed that the SPEAR_ pesticides index and FR respond favorably to the TU ( D.magna ) and CQI ( p < 0.05). % EPT did not significantly respond to any of the measured instream variables. The catchment scale agricultural activities negatively affected the SPEAR_ pesticides and FR, while riparian forest cover acted to improve both indices. The findings of the study suggest the possibility of using SPEAR_ pesticides for pesticide impacts assessment in tropical regions.