Estimation of the maximum allowable loading amount of COD in Luoyuan Bay by a 3-D COD transport and transformation model

The rapid economic and social developments in the Luoyuan and Lianjiang counties of Fujian Province, China, raise certain environment and ecosystem issues. The unusual phytoplankton bloom and eutrophication, for example, have increased in severity in Luoyuan Bay (LB). The constant increase of nutrient loads has largely caused the environmental degradation in LB. Several countermeasures have been implemented to solve these environmental problems. The most effective of these strategies is the reduction of pollutant loadings into the sea in accordance with total pollutant load control (TPLC) plans. A combined three-dimensional hydrodynamic transport-transformation model was constructed to estimate the marine environmental capacity of chemical oxygen demand (COD). The allowed maximum loadings for each discharge unit in LB were calculated with applicable simulation results. The simulation results indicated that the environmental capacity of COD is approximately 11×10⁴ t year^?1 when the water quality complies with the marine functional zoning standards for LB. A pollutant reduction scheme to diminish the present levels of mariculture- and domestic-based COD loadings is based on the estimated marine COD environmental capacity. The obtained values imply that the LB waters could comply with the targeted water quality criteria. To meet the revised marine functional zoning standards, discharge loadings from discharge units 1 and 11 should be reduced to 996 and 3236 t year^?1, respectively.