Assessing environmental carrying capacity of sea cage culture in the Yellow Sea, China, using a coupled diffusion model

The rapid development of offshore mariculture brings the environmental challenges and requests for carrying capacity-based management strategy. A pollutant diffusion model coupled hydrodynamic model and 3-D Lagrangian particle-tracking model was implemented to evaluate the environmental carrying capacity of the sea cage in off-coast farming in the Yellow Sea, China. The water level data on August 1-31, 2018 and concentration of nutrient in surface sediment in May, August, November 2018, and January 2019 were used to verify the model. The results showed that the model is reliable to capture the main characteristics of the environmental variables in the study area. Total annual sea bass output were around 335 t per year (t a(-1)), the nitrogen and phosphorus emissions of about 30.95 t a(-1), 5.90 t a(-1), respectively. Total nitrogen in the sediment accumulated to 691.4 mg kg(-1) (0.056 kg m(-2)) on average after a year simulation. The selection of culture sites, especially the current velocity, and settling velocity of the particles play significant roles on the fish output and the diffusion of pollutants. According to the acceptable standards of sediment nitrogenous nutrient, the sea bass culture density can be expanded to 1.46 times the present level to reach the environmental carrying capacity. Feed formulations and feeding regimes are important factors in determining the carrying capacity that need to be strategically improved with developing technology. The model provides a useful tool to sustainable environmental management of sea cage culture.