Environmental capacity of chemical oxygen demand in the Bohai Sea： modeling and calculation

A three-dimensional advection-diffusion model coupled with the degradation process is established for describing the transport of chemical oxygen demand （COD）. Comparison of the simulated distribution of COD at the surface in the Bohai Sea in August, 2001 with field observations, shows that the model simulates the dataset reasonably well. The Laizhou Bay, Bohai Bay, and Liaodong Bay were contaminated heavily near shore. Based on the optimal discharge flux method, the Environmental Capacity （EC） and allocated capacities of COD in the Bohai Sea are calculated. For seawater of Grades I to IV of the Chinese National Standard, the ECs of COD in the Bohai Sea were 77× 10 4 t/a, 116× 10 4 t/a, 154× 10 4t/a and 193× 10 4 t/a, respectively. The Huanghe （Yellow） River pollutant discharge accounted for the largest percentage of COD at 14.3%, followed by that of from the Liugu River （11.5%）, and other nine local rivers below 10%. The COD level in 2005 was worse than that of Grade II seawater and was beyond the environmental capacity. In average, 35% COD reduction is called to meet the standard of Grade I seawater.