Impacts of Agricultural Practices on Water Quality in Uma Oya Catchment Area in Sri Lanka

Abstract

Sustainability of global food production is highly depending on the quality of the environment. In many parts of the world increase of agricultural production heavily depend on intensive agricultural practices which are having negative impact on the environment. The impacts of agricultural practices on surface water quality is given special attention currently since the safe and ample supply of freshwater is fundamental to humans and for the sustainability of ecosystem function. Intensive agricultural practices in river catchments often pose threat to the ecological integrity of river ecosystems. Uma Oya watershed in the upper Mahaweli watershed in Sri Lanka is an intensively cultivated landscape. In most parts of the catchment previously forested lands have been cleared and converted to agricultural lands. However, the empirical evidence on quantitative assessment of such land use conversion impacts on stream ecological health is lacking in the context of river catchments in Sri Lanka. Therefore the present study was aimed at evaluating the agricultural land use impacts on stream physical habitat quality, water quality and macroinvertebrate indices in the Uma Oya catchment at different spatial scales. The relationship between catchment and site scale % agricultural lands, water quality and macroinvertebrate indices were evaluated using univariate and multivariate approaches. The results indicated that stream physical habitat quality, water quality parameters and macroinvertebrate indices are significantly (p<0.05) affected by catchment scale % agricultural land cover. Among the water quality variables that were tested NO₂-N, NH₃-N, PO₄-P and BOD₅ level in sites with higher percentage of agricultural land cover exceeded the drinking water quality standards during dry season. PO₄-P and BOD₅ level in those sites exceeded the proposed ambient water quality standards for inland waters in Sri Lanka for aquatic life and for irrigation purposes. Findings of the present study suggest that catchment scale interventions are crucial for the management of Uma Oya watershed and for the improvement of water quality and sustainable agricultural production.