Identification of Critical Diffuse Pollution Sources in an Ungauged Catchment by Using the Swat Model- A Case Study of Kolleru Lake, East Coast of India

Freshwater ecosystems are facing severe threats from human activities. As a consequence of this, they can get disturbed. In developing countries, like India, freshwater lakes are endangered primarily by agricultural activities, which often accelerate erosion and the runoff. The massive application of pesticides and chemical fertilizers to agricultural lands is one of the reasons for eutrophication in Kolleru Lake. The different natural and anthropogenic influences increase the highly complex ecosystem of the lake. Therefore, the objectives of this study are to ascertain the priority control areas, aiming at socio-economic development for the protection of the lake water quality by applying the Best Management Practices (BMPs).

For this purpose, the Soil and Water Assessment Tool (SWAT) was used to identify the critical areas of the lake's catchment in terms of pollution from agricultural runoff into the tributaries of the Kolleru Lake and the lake itself. The results demonstrated that the diffuse pollution load in the western and downstream watersheds the highest and that agricultural land was the primary pollutant source besides the accumulation of nutrients in the downstream areas. The differences in the sub-basin loads were observed in the catchment mainly depends on the topographic features, soil properties, land use, vegetation, and drainage patterns. From where the major outlet sub-basin has the highest accumulation of nitrate-nitrogen (NO3_N), and total phosphorus (TP) emissions were quantified. The temporal distribution of runoff and diffuse sources were estimated from 2008 – 2014. The runoff mainly governed diffuse pollution was found to be a significant contributing factor to the lake. Further, suggestions were provided for the implementation of agricultural management practices to minimize pollution levels.