Study On Ecological Vulnerability Assessment Method In Estuarine Waters

Ecological environment vulnerability,also called ecological vulnerability,refered to the nature of the ecosystem itself,which is easy to respond to its own changes and external interference in a certain space and time,the responses can be expressed by the biological and environmental factors in the ecological,when the outside world interferes with the ecosystem,most of the ecosystem develops in a direction that is not conducive to itself and human beings,and if the interferes beyond a certain limit,it cannot return to its original state.The ultimate goal of ecological vulnerability research was to understand the status of the ecosystem,prevented the continuous deterioration of the ecosystem under the damage of human activities,and repaired the degraded ecosystem at the same time,so as to realize the rational utilization of ecological resources and the sustainable development of human economy and society.Located between the freshwater ecosystem of the River and the Marine ecosystem,the ecosystem of the river estuary is a transitional zone of two ecosystems,it has a strong marginal effect and very complex ecological environment,whoes is a very fragile ecological environment.At the same time,the geographical location of the river estuary was very special,and its surrounding cities are densely populated and highly developed in social economy.The interference of human activities to the environment aggravated the ecological vulnerability of the estuary.Estuarine are very important to the development of regional economy and even national economy,however,there are few researches on the ecological vulnerability of the estuary.It was of great theoretical and practical significance to correctly understand and evaluate the ecological vulnerability of the river estuary to formulate policies for protecting the ecological environment,to put forward suggestions for the restoration of the fragile region,and to promote the sustainable development of the region and the country.In this paper,the interannual variation of the structural vulnerability of theYangtze River Estuary was discussed by using the changes in the integrity of the ichthyoplankton community in the Yangtze River Estuary,and the interannual variation trend of the stress-type vulnerability in the Yangtze River Estuary was discussed by using the changes in the environmental factors such as nutritions,organic pollutants and heavy metals.This paper constructed an index system to evaluate the ecological vulnerability of estuarine based on the conceptual models of structural vulnerability and stress vulnerability,and water quality eutrophication status index,water oil,dissolved oxygen,sediment oil,zooplankton density,phytoplankton density,phytoplankton species number,chlorophyll a and jellyfish/zooplankton density ratio were selected from the aspects of water layer environmental factors,sediment environmental factors and biological factors.In this paper,the weight of each index was determined by principal component analysis,and the data collected in August2014 were used to evaluate the ecological vulnerability of the Yangtze estuary in a short time scale,and the following conclusions were obtained:(1)The research found that 1986,1999,2007 and 2016,four different periods of ichthyoplankton communities completeness score is 52,40,36,34,respectively corresponding to the integrity of the grades are "good","fair","fair-poor" and "poor",show that 1986 Yangtze River Estuary waters ecosystem by human interference,less ithphyoplankton community species diversity is rich,high degree of biological integrity,ecological system has high stability,strong resilience,structured fragile ecological environment is relatively low,Since the beginning of the 21 st century,natural factors and human activities have aggravated the disturbance of the ecosystem in the Yangtze River Estuary,resulting in a decrease in the number of species and the number of low-pollution resistant species,and an increase in the structural vulnerability of the ecological environment.(2)The research found that in the physical and chemical environmental factors monitored in recent years,the nutrient content of PO4-P and DIN changed the most,among which the content of PO4-P increased from less than 0.01 mg/L in the 1980 s to more than 0.05 mg/L in the first 10 years of the 21 st century after two jumps from1987 to 1988 and 2003 to 2005.DIN was lower than 0.10 mg/L in the 1980 s,and higher than 1mg/L in 1987-1989 and 2003-2005,respectively,after two transitions.Thecontents of organic pollutants such as COD and petroleum,heavy metals such as Hg,Cu,Pb and Cd,as well as other types such as DO and p H,varied little.The study shows that the increase of nutritions is one of the main reason for the increasing trend of stress vulnerability in the Yangtze River Estuary.(3)The degree of ecological vulnerability in the Yangtze estuary was generally high,which was basically above the level of moderate vulnerability,most of which were in the state of severe vulnerability,and some areas even reached extreme vulnerability.On the one hand,this result was due to the rapid change of the ecological environment and low structural stability of the Yangtze estuary,on the other hand,it was due to the large amount of environmental pollutants imported from the outside world.The spatial distribution of the ecological vulnerability of the Yangtze estuary showed that the vulnerability of the north branch of the Yangtze estuary was lower than that of the south branch,the ecological vulnerability of the waters near the mouth of the Yangtze estuary was higher than that near the offshore sea,and the vulnerability of the waters near the islands with strong human activities was higher than that of the uninhabited sea.In a short time scale,the external stress brought by human activities has a great impact on the ecological vulnerability of the Yangtze estuary.In order to reduce the ecological vulnerability of the Yangtze estuary,measures must be taken to reduce the external stress.