Potential accumulation of selected pollutants in dry zone reservoirs utilised for inland fisheries

Abstract

Sri Lanka’s dry zone reservoirs are one of the oldest historically recorded systems in the world. They are critical sources for water storage, irrigation and inland fisheries, and there is potential to be influenced by anthropogenic pollutants. This study examines the dynamics of the criteria water pollutants, selected pesticides and heavy metals and microplastics in 7 reservoirs utilised for inland fisheries practices. Results indicate significant variations in pH levels, TSS, biochemical oxygen demand (BOD), nutrient concentrations and microbial contamination, driven by anthropogenic activities and natural hydrodynamic conditions. The presence of oil and grease, lead and pesticide residues highlights pollutant retention mechanisms, with Urusita wewa and Wanela exhibiting notable contamination trends. Microplastic accumulation, particularly in Vijayakatupotha reservoir, suggests site-specific pollution sources and sediment deposition dynamics. Despite localised pollution concerns, most reservoirs maintain water quality parameters within permissible limits, ensuring fisheries sustainability. However, the absence of regulatory thresholds for fecal coliform contamination underscores the need for enhanced water quality monitoring. Understanding pollutant interactions, bioaccumulation risks and environmental retention patterns is vital for sustainable reservoir management and fisheries conservation. This study emphasises the importance of adaptive pollution control strategies, community engagement and policy interventions to mitigate contamination risks and maintain long-term aquatic ecosystem health.