Study On The Change Trend Of Marine Environment In North Hangzhou Bay

North Hangzhou Bay sea area is an important resource for the development of marine economy in Shanghai,and its marine ecological environment has been paid more attention.This paper based on the monitoring data of Fengxian nearshore and wider sea area in the north shore of Hangzhou Bay from 2011 to 2016,the quality of the seawater and marine sediments in the northern of Hangzhou Bay were assessed year by year and the change trend of elements in seawater and sediments were analyzed and evaluated.This paper focuses on the analysis of seawater eutrophication and the environmental risk of heavy metals in sediments.This paper analyzes the changing trend of the marine environment in the north shore of Hangzhou Bay,and thinks of risk countermeasures,then puts forward some suggestions for the preservation of the marine environment and the sustainable development of the marine economy as scientific basis.The main results of this paper are as follows:1,Assessing by single factor index method,the results of the monitoring results from 2011 to 2016 shows that the environmental factors of seawater in the north shore of Hangzhou Bay are in general good condition except TIN and PO4 above the Lv IV water quality standards.p H is no obvious change,Which long-term in standards Lv I;DO,COD shows certain difference between the high,common and low sea water level in different seasons,but almost below standards Lv II,and the total content of oil in seawater is just fine except for some sites that are particularly high.Heavy metals(Cu,Pb,Zn,Cd,Cr,Hg,As)in seawater meet the requirements of corresponding marine functional zoning.the heavy metal contents have a decreasing trend during the study period,except As.Alsothe TIN and PO4 shows certain difference between the high,common and low sea water level in different seasons,and mainly changing in the high concentration range.2,The results show that the eutrophication of seawater in the north shore of Hangzhou Bay is in a serious state,which is the same as that of other researchers.The eutrophication index E of the annual seawater water during the study period averaged between 20 and 35.However,by analysis the 6 years results,because of mainly declining in the content of TIN,the eutrophication index has a tendency to good change year by year.Due to long-term and large-volume sea entry from the Yangtze River and Hangzhou Bay waters around the land and upstream runoff,it caused the Yangtze River estuary and Hangzhou Bay waters seawater above the water quality standards Lv IV,It must be very long-term and need for the whole basin to carry out environmental protection and governance of the common task to return to normal level of eutrophication of the Hangzhou Bay water quality under this background.3,The annual monitoring of sediments in the Hangzhou Bay shows that the evaluation results of sediment quality meet the standard Lv I and Lv II according to the single factor index method,the ecological risks of heavy metal in sediments are also at a low level.there are rising trend of oil,Cu,Pb,Zn,Cd,Cr and As in sediments except Hg.Due to the cumulative effect of heavy metals in the sediments,the Yangtze River sediment-carrying effect,atmospheric settlement and a variety of land-based sewage superposition,and if the trend is allowed to develop without being controlled,then the heavy metals in the sediments may develop irreversible environmental hazards.