Ecological Environment Quality Assessment on Petrochemical Sewage Discharge Waters of Daya Bay in Winter

Daya bay, a typical subtropical marine genetic resource pool in the South China Sea, is one of the most important inshore fisheries areas in Guangdong province. However, the marine environments has been threatened and effected by rapid developments of the petrochemical industry in recent years. In current study, the ecological environment quality has been assessed. Based on the ecological and environmental investigation in January 2012, the states of ecological environment quality of the Daya Bay petrochemical sewage discharge waters was assessed with four factors, including sea water quality, nutrient structure and level, sediment quality, primary productivity and food organism level. The comprehensive index method was used for integrated assessment, as well. The results show that most of the water quality factors, including dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, sulfide, phosphorus, dissolved inorganic nitrogen and heavy metals of Cu, Pb and Cd, were all conforming to Grade II of the National Sea Water Quality Standard of China. However, some factors, including petroleum hydrocarbon of 66.7% sites, pH of 91.7% sites, and Zn of several sites, exceed the Grade II of the National Standard with the average value of water quality comprehensive index at 1.215. The status of above factors consequently reached a low-level pollution without any pollution caused by organic pollutants. What makes unoptimistic is the concentration of nutrients in sea water is relatively high. Fortunately, the quality of sediment is very good and conforming to the Grade I of National Marine Sediment Quality Standard, with the com-prehensive pollution index at 0.478. Furthermore, the status of primary productivity reached the level of medium because of the high abundance of phytoplankton, zooplankton and benthic. According to the references and data of this study, the investigated petrochemical sewage discharge waters of Daya Bay was slight polluted by total petroleum hydrocarbons (TPHs), with the ecological environment comprehensive quality index of 1.129.