Integrated Ecosystem Health Assessment Of Jiangsu Coastal Area

Ecosystem health assessment is a vital part of ecosystem protection and monitoring.Integrative assessment of coastal ecosystem health,which should be proceeded with comprehensive and accurate assessment system,has become a focus of ecology research in recent years and the stabilization and maintenance of costal ecosystem is becoming the ultimate goal for more and more environmental protection and management departments.Jiangsu coastal ecosystem,which starts from Xiuzhen estuary in the north and ends at the northern shore of Yangtze estuary in the south,is composed of three areas-Haizhou Bay,radiative sand ridges,aquiculture area and the northern shore of Yangtze estuary-from north to south.It is a typical complex ecosystem with significant effect of human activity.Very few systematic and integrative research of Jiangsu coastal ecosystem health was accomplished so far.The temporal and spatial variation of Jiangsu coastal ecosystem health was quantitatively assessed by utilizing ecology indexes,including species abundance and biomass,diversity index,multi variable analysis method;thermal dynamics indexes,such as eco-exergy and structural eco-exergy with temporal and spatial distribution characteristics of Jiangsu coastal water and sedimentaryenvironment as background values based on its status.Jiangsu coastal ecosystem is divided into three sub-systems-plankton ecosystem(including phytoplankton and zooplankton),benthos ecosystem and nekton ecosystem.CAA analysis and spatial ordering are utilized to find out the major environmental factors.Such factors affect spatial and temporal variation of all and dominant species community structure in each subsystem.Furthermore,the relevance of ecosystem's internal(community structure)and external(environmental factors)status is further explored based on CCA ordination diagram.The integrative assessment system of Jiangsu coastal ecosystem is set up on this basis from the perspective of community structure and eco-exergy.The main contents and conclusions are as follows:(1)Definition and assessment method of ecosystem healthThe definition and assessment method of coastal ecosystem health are summarized and presented at the beginning.Integrative assessment index system of Jiangsu coastal ecosystem health,set up based on its ecological characteristics and status,has enriched the assessment theory of ecosystem health.(2)Background analysis of environmental factorsAnalysis result of seawater physical and chemical indexes:The content of suspended sediments(SS)is generally higher near-shore while the infralittoral content is inclined to be uniform,which presents us with a trend decreasing little by little from north to south.And the content is decreasing with season variation in a sequence of winter,spring,autumn,summer.Nutrient indexes mainly include inorganic nitrogen(DIN),active phosphate and active silicate.Its concentration decreases progressively toward infralittoral water and is generally higher in the southern area.High nutrient salt concentration area may form in spring and summer;therefore,most stations have N and P limitation.The content of surface dissolved oxygen(DO)is slightly higher in near-shore and relatively higher in spring and winter while the lowest in summer.The peak content of chlorophyll a(Chl-a)emerges in summer and Jiangsu southern coastal area(including the northern shore of the Yangtze estuary and nearby aquiculture area)is the high value area.Analysis result of sediment physical and chemical indexes:In the C-N-P sediment cycle,TOC is positively related to TN while there is no significant relation between TP and TN,TOC and TP,which indicate the homology of organic carbon and nitrogen.Risk assessment of heavy metal content determined the degree of pollution:Hg>As>Cu>Zn>Pb>Cr>Cd,among which,Hg is the major contributor for ecological risk and possesses potential risk.(3)The spatial and temporal variation and grading of community structure indexThe seasonal and inter-annual variation characteristics of phytoplankton,zooplankton,large benthic fauna,and nekton communities are analyzed based on indexes of species composition,density,biomass,diversity,evenness,species abundance,etc.Phytoplankton community,which concentrates in Jiangsu southern(the northern shore of Yangtze estuary and nearby aquiculture area)and northern(Haizhou Bay)coastal area,is mainly composed of diatom;zooplankton community,which concentrates in fishery and estuary,is mainly composed of jellyfish,copepods and planktonic larva;benthos community,which concentrates in Haizhou Bay,is mainly composed of polychaete,crustacea and molluscs;nekton community,which concentrates at the northern shore area of Yangtze estuary,is mainly composed of fish.The common seasonal characteristic of all communities is their higher density and diversity in summer;they all decreased during 2009-2012 except phytoplankton community.All samples are divided into 4 quadrants with the two virtual dimensions of Euclidean distance model,and the community structure grade is determined based on spatial distance and quadrant of each sample.(4)The spatial-temporal variation and grading of eco-exergy indexEcosystem overall exergy is reflected by eco-exergy(Ex)and structure eco-exergy(Exst).One ecosystem's exergy grade can be determined by Ex and Exst deviation from its average exergy-ecosystem with high Ex and Exst is classified as Grade I,one with high Ex and low Exst is Grade ?,one with low Ex and high Exst is Grade ? and one with low Ex and Exst is Grade ?.Despite the seasonal and annual variation,eco-exergy of Jiangsu coastal ecosystem is mainly composed of Grade ? and ?.Zooplankton ecosystem has the biggest proportion of Grade ?and phytoplankton,large benthic fauna,and nekton ecosystems have the biggest proportion of Grade ?.(5)Correlation analysis of Jiangsu coastal biological communities with environmental factorsCCA tells us that though the environmental factors having a bearing on the spatial-temporal distribution of species abundance in the ecosystem are changing with the seasons in terms of sorting,such factors as water temperature,nutritive salt and salinity in the ecosystems discussed have also played an important part.Different factors have different effects on different creatures,for example,water temperature,nutritive salt,DO,SS and other environmental factors are vital to quantity and distribution of plankton;water depth,nutritive salt,DO in the bottom water,and particle sizes of sediments as well as organic carbon,all have a great effluence on the macro-benthos.As far as nekton is concerned,it is closely related to the nutritive salt,temperature,salinity,concentration of suspended matters,DO and organic carbon.At the same time,the distribution of nekton in part is bound up with the abundance of plankton and benthos,and such relevancy is heavily relying on the feeding behavior of nekton.(6)Integrative assessment of ecosystem healthEcosystem health grade is changing with seasons,years and space,which are respectively demonstrated by decreasing grade in a sequence of autumn,spring and winter,summer;higher level throughout Jiangsu coastal area in 2006,and the lowest in 2009,that is gradually decreasing in 2006,2012,2009,reflecting the overall downward trend of inter-annual variability;higher in the south sea area,high in the north area and the lowest in the middle area.Except serving as a gap for the spatial-temporal distribution features of ecosystem health in Jiangsu coastal area,the findings provide a systematic,efficient and operable method to conduct a integrative assessment of ecosystem in Jiangsu coastal area,and lay a theoretical basis for setting up an index system to evaluate the ecosystem health,and act as a guide to manage,monitor and measure the costal ecosystem.