Water quality assessment for Hailing Bay estuary, China

Based on the quarterly investigation data of the Hailing Bay estuary from 2015 to 2016, in addition to the evaluation of the Nemerow pollution index (P), eutrophication index (E) and nutrient quality index (NQI), we analyzed 16 basic water quality indices, including water temperature, salinity, pH, dissolved oxygen (DO), chemical oxygen demand (COD), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chlorophyll a, petroleum hydrocarbon, sulfide and heavy metal content, so as to evaluate the quality of the fishery environment in this region. The results show that the top four contamination factors in Hailing Bay estuary were petroleum hydrocarbon, DIN, COD and DO, and the degree of contamination and the main pollutants in seawater were different among four seasons significantly (P<0.05). In spring, the DIN value was higher than those in the other seasons significantly, ranging from 0.27 mg·L^–1 to 0.69 mg·L^–1. In summer, the seawater was relatively clean, but the DO value was lower significantly, ranging from 4.69 mg·L^–1 to 5.93 mg·L^–1. In autumn and winter, the seawater was both contaminated by petroleum hydrocarbon whose concentration were 0.069 mg·L^–1 and 0.143 mg·L^–1, respectively (mild pollution). Winter witnessed the highest mass concentrations of COD (3.67 mg·L^–1), Chl-a (13.07 mg·m^–3) and NQI (4.35). The NQI values in 11 sampling stations were over 3, which indicates that seawater in the Hailing Bay estuary is experiencing high eutrophication.