Modeling the influence of floating net aquaculture and nutrient loads from catchment on the trophic status of a tropical volcanic lake

Abstract

Lake Maninjau in West Sumatra Province of Indonesia is a 10,779 Ha tropical volcanic lake with 12,951 Ha of the catchment area. Having been used as a power plant, tourism, catch fishery, and floating net aquaculture, the lake was said to have become eutrophic since almost two decades ago. Maninjau is one of National Priority Lakes in Indonesia which means that it needs to be revitalized. Many studies mentioned aquaculture and land use change in the catchment as the driver of eutrophication. However, none of these studies could pinpoint which of the two factors give a greater impact on the lake’s eutrophication process. This could lead to an error in determining priorities in revitalization measures. The objective of this study is to assess the influence of aquaculture and catchment load on Lake Maninjau eutrophication by using a combination of catchment and lake model which consists of SWAT model, 2-dimensional multilayers hydrodynamics and water quality model. Results showed that floating net aquaculture generally gives major impact (>97%) on eutrophication not only in the lakeshore area but also in the entire water body. Catchment area gives minor impact and only observed in a relatively shallow area. The results suggest that the important part and higher priority of restoration strategy should be reducing the nutrient load from floating net aquaculture.