Fate of nutrients in human dominated ecosystems - A case study of Jakkur Lake in Bengaluru.

Jakkur Lake in the city of Bengaluru covers an approximate area of 55 hectares and primarily receives inflows from the Jakkur sewage treatment plant (STP) and an open storm drain. Jakkur STP discharges an average of 10 million litres of treated water daily (MLD) into the lake. The open drain discharges about 0.5 MLD of raw sewage into the lake. In the absence of environmental flows it becomes critical to assess the impact of nutrient flux on the quality of water, and design cost effective treatment solutions to address the issues of lake water quality. As part of this study, we have assessed the impact of these two primary inflows on the overall water quality of Jakkur Lake. The results have shown that nutrient inflows have led to the increase of chlorophyll-a levels, eventually causing hypereutrophication of Jakkur lake. We have also used simple mass balance approach to assess the contributions of in-lake activities (sedimentation and reaction) on removal of nutrients from the lake. We have concluded that the phosphorus load has to be reduced by approximately 96% from the current levels to prevent algal blooms within Jakkur Lake.