Eutrophication in Lake Batur: current status and management strategies

Lake Batur, designated as one of the National Priority Lakes in Indonesia, has experienced significant eutrophication in recent years. Waste generated from various anthropogenic activities, including agriculture, domestic, tourism, and floating net fishery (FNF), have collectively contributed to the decline in water quality and the eutrophication status of the lake. Our study aimed to evaluate the current eutrophication status of Lake Batur by analyzing the spatial and temporal variations in nutrient parameters, water transparency and phytoplankton biomass. Then we assessed strategies in controlling eutrophication in the lake using the Driving forces-Pressure-State-Impact-Response (DPSIR) framework. Currently, Lake Batur has reached mesotrophic to hypereutrophic levels. We identified that the main driving forces behind these concerning conditions were the significant increase of agricultural and FNF activities, particularly since the outbreak of the COVID-19 pandemic. The main environmental pressures showed that agriculture waste was the most dominant nutrient source to the lake (93.05 % of N and 89.96 % of P loads). The state analysis indicated that high nutrient concentrations and subsequent algal growth led to oxygen depletion, resulting in mass mortality of fish, loss of amenity and tourism value, and reduced availability of clean water. Short-term and long-term strategies for effectively managing eutrophication in Lake Batur has been proposed in this study. However, the best scenario will be chosen by considering both eutrophication issue and social implications.