Numerical simulation on marine environmental capacity in the open sea area of Northern Jiangsu Province using a three-dimensional water quality model based on FVCOM

Abstract Under the influence of high-intensity human activities, the discharge of chemical pollutants in coastal waters increases progressively year by year and exceeds the marine self-purification capacity, which in turn leads to major marine ecological environmental problems such as eutrophication and excessive heavy metals in water bodies. Hence, studies on the marine environmental capacity (MEC) are the basic work for the total discharge control and water quality improvement of land-based pollutants. In the article, a three-dimensional (3D) water quality model was established based on the unstructured-grid, finite-volume, free-surface and primitive equation coastal ocean model (FVCOM). Then, the mathematical model was calibrated with the data monitored in 2013 and 2014, and the MEC of dissolved inorganic nitrogen (DIN), chemical oxygen demand (COD) and petroleum hydrocarbons (PHs) in the main rivers entering the sea was calculated using the self-purification process integration method. The results indicate that the annual MEC of DIN, COD and PHs pollutants are 3.6 × 104 t/a, 45 × 104 t/a and 0.15 × 104 t/a respectively. By comparing and analyzing the current pollution load, the reduction rates of ammonia nitrogen (NH4-N) and total nitrogen (TN) in the study area are equivalent to more than 70% of the current load into the sea while COD does not need to be reduced. Only a few river units still have surplus allocated capacity (AC) while the remaining ones need to be cut down. Consequently, the control of total pollutants emission is an urgent issue to be solved. The evaluation on MEC of coastal waters can not only provide technical support for the offshore aquaculture industries, but also provide scientific basis for the total control of terrigenous pollutants in coastal cities in Northern Jiangsu Province.