Analysis On Variation Trend Of Seawater Quality And Assessment Of Eutrophication Status At Yangshan Port

Yangshan Port is located in the north part of Hangzhou Bay, which is the first portbeing built on two islands （Dayangshan Island and Xiaoyangshan Island） in China. Withthe cargo handling capacity of13,000,000TEUs per year, Yangshan Port is becomingthe hinge port for Port of Shanghai. With the construction of Yangshan Port, moreattention should be paid to its changes of ecological environment. According to themonitoring data during2010to2011, we analysed the trend of the water quality andevaluated the water eutrophication of the Yangshan Port water. To provide scientificdata basis for the ecological environment protection, fishery resources evaluation,aquatic products safetyassessment and sustainable development of Yangshan Port, wesystematically studied the annual variation of the area aquatic environment andilluminated the status and changes of the ecological environment in Yangshan Port. Themain conclusions are as follows:（1） According to the monitoring data of the Yangshan Port water in2010and2011,we analysed the annual variation trend of sea water environmental factor systematically.The results showed that there were obviously seasonal changes in DO, salinity,temperature, CODMN, nitrate, nitrite, ammonia nitrogen, DIN, DIP, and reactive silicate,but not in pH. Influenced by terrestrial runoff and kuroshio, the salinity in YangshanPort showed an obvious seasonal variation. The runoff flowing from Yangtze River andQiantang River into sea in summer caused the dramatic decline of salinity in YangshanPort. The average value of mineral nitrogen content in2011was higher than that in2010, which reached its peak in summer and then declined. Nitrate is the main form ofmineral nitrogen, which comprised95.31%and94.77%of the mineral nitrogen in2010and2011, respectively. The average value of inorganic phosphorus in2010was higherthan that in2011. It reached a maximum in October,2010and showed irregularvariation trend afterwards. The average value of inorganic phosphorus in2011showedan up-trend since January and reached a peak in June. The average value of silicatecontent in2010was a little higher than that in2011. The average value of labile phosphate in2010reached a peak in May and showed no dramatic change during theyear, however, it showed dramatic change trend in2011. In2011, the average value ofsilicate concentration was quite high in July, and reached a maximum in August andthen showed the downward trend.（2） The the water quality in Yangshan Port was evaluated by the single factor indexmethod. The results showed that the water was in a degree of pollution. The content ofDO, CODMN, DIN, PO₄^3--P was over the sea water quality standard IV; PO₄^3--P and DINare the main source of pollution. The evaluation results using nutrient quality indexmethod showed that NQI of Yangshan Port waters was2.67, the nutrient level belongsto the grade II overall. The evaluation results using eutrophication index methodshowed that the annual average of EI value in Yangshan Deepwater Port was34.01（much more than1）, which means that the eutrophication level of Yangshan Port wasquite high. Potential eutrophication assessment results showed that the annual averageconcentration of DIN, PO₄^3--P, SiO₃^2--Si was40.71umol/L,1.94umol/L,37.86umol/L,respectively; the ratio of Si:N, Si:P and N:P was0.94,21.76and23.30, respectively.The relatively low concentration of PO₄^3--P was a potential limiting factor for theeutrophication in Yangshan Port. Fuzzy comprehensive evaluation results showed thatYangshan Port was in eutrophication throughout the year. The eutrophication level inspring and summer is higher than that in autumn, which was probably caused by the thehigh level for nitrogen and phosphorus in the great runoff from Yangtze River andQiantang River.（3） The major pollutants of eutrophication in Yangshan Port area were DIN andDIP. DIN was redundant, however the value of DIP was relatively insufficient, whichmight cause the limited growth of phytoplankton. Though there are some differences inthe results of the eutrophication evaluation of Yangshan Port Area using differentevaluation methods, the degree of eutrophication and organic pollution in Yangshan PortArea was conclusively high and the water quality was poor. Comparing two differentevaluation methods between NQI and EI, we considered that fuzzy comprehensiveevaluation method can reflect the pollution situation more objectively with acomprehensive and reasonable result.