Spatial Distribution Modeling of Nutrient Waste from Aquaculture Activities in Response to Increased Wastewater Discharge in Bojo Bay, Indonesia

Bojo Bay, located in Barru Regency, South Sulawesi, Indonesia, is a coastal area experiencing increasing ecological pressures due to aquaculture expansion. The intensification of aquaculture has led to the accumulation of organic waste, with the potential to degrade water quality, trigger eutrophication, and disrupt ecosystem balance. This study aimed to model the spatial distribution of nutrient waste from aquaculture under varying production intensities in Bojo Bay. Simulations were conducted using MIKE 21 software by integrating the Hydrodynamics (HD) and ECOLAB modules to model current dynamics and key water quality parameters, including dissolved oxygen (DO), biochemical oxygen demand (BOD), ammonia, nitrate, and phosphate. Two scenarios were applied: existing conditions and a 100% increase in waste load. The results showed that intensified aquaculture significantly reduced water quality by elevating nutrient concentrations and expanding the spatial extent of waste distribution. Waste accumulation was concentrated in the inner bay during high tide, while concentrations decreased during low tide, reflecting local hydrodynamic circulation. These findings demonstrate that increased waste discharge without treatment negatively affects water quality and provide a scientific basis for developing sustainable aquaculture waste management strategies in Bojo Bay.