Pollution loads and its impact on Lake Toba

Human activities in Lake Toba area have contributed to the supply of pollutant on these aquatic ecosystems. Organic material and nutrient especially phosphorus component is estimated to be quite dominant of pollutant load. This study aims to recognize the level of organic load (in the form of Chemical Oxygen Demand; COD) and nutrient components (Total Phosphorus; TP) and its influence on the aquatic environment condition. This research was conducted in Lake Toba in November 2017, by observing selected locations in several inlet rivers of the lake and the lake waters area. The pollutant load from the land area, which is organic material (in the form of COD) reaches 90,712 tons/year, while the nutrient load (in the form of TP) reaches 138 tons/year. From aquaculture activities, organic loads released into the waters (in the form of feces and uneaten feed) are estimated at 14,265.4 tons/year, while the phosphorus load (in the form of TP) is 570.33 tons/year. The phosphorus load that enters the waters of Lake Toba as a whole has exceeded the permissible loading levels and changed the trophic status of the Lake Toba waters. Meanwhile, the organic pollutant load will increase the anoxic column on the hypolimnion area of the lake.