Comprehensive Assessment Of Health Level Of Mangrove Swamp Ecosystem In Zhangjiang Estuary

The Zhangjiang Estuary Mangrove Swamp in Fujian Province is an important wetland zone with the largest northern distribution of mangrove area in China.It is a critical station for the waterbird migration in East Asia,which is important for maintaining local ecological safety,protecting rare animals and plants,promoting regional economic development.At present,there are few domestic and international researches on the health status of the Zhangjiang Estuary mangrove swamp ecosystem.There are few studies using multiple years of remote sensing data to explore the health status and development trends of different sub-regions.In the research,the mangrove swamp in Zhangjiang Estuary was selected as the study area,and Google Earth(GE)images in 2005,2011,2015,2017 and 2019 were used as the basic data source.Combining with the pressure-state-response(PSR)model and the land cover classification data,the mangrove swamp health assessment index system of Zhangjiang Estuary was established.Combing a subjective weighting method(analytic hierarchy process)and an objective weighting method(entropy weighting method),the weight of each index was calculated.An ecosystem health index was established to quantify the comprehensive health level of the mangrove swamp in the study area.On this basis,spatio-temporal differentiation characteristics of ecosystem health and their driving force factors of health level for mangrove swamp were analyzed.The main results were as follows:(1)The area of mangrove in Zhangjiang Estuary increased from 50.88hm~2 to 73.49 hm~2 from 2005 and 2019,with a growth rate of 1.62 hm~2/a.The area of Spartina alterniflora increased by 140.89 hm~2,indicating a growth rate was 10.06 hm~2/a.The area of aquaculture ponds increased from566.47 hm~2 in 2005 to 639.97 hm~2 in 2019,presenting a growth rate was5.25 hm~2/a.The area of other land cover types increased less.In comparison,the area of mudflat decreased most drastically.(2)From 2005 to 2019,the health status of mangrove swamp in Zhangjiang Estuary deteriorated gradually,and the health level changed from sub-health to general health.From 2005 to 2019,the pressure of health level increased significantly and changed from sub-health to fragile.The state of health level was in sub-health during the study periods.The health response level changed from health to general with the response health index decreased significantly.(3)There were significant differences of health status among different regions in the study area.In 2019,the wetland health level of southern region was fragile,the western and northern region were average,and the central and eastern region were sub-healthy.In 2005 and 2011,the wetland health index in order was western region>central region>eastern region>northern region>southern region.In 2015,2017 and 2019,the health index in order was eastern region>central region>western region>northern region>southern region.The health condition in the western region deteriorated significantly,while in the eastern region presented good.(4)From 2005 to 2019,the decline of the health level for mangrove swamp in Zhangjiang Estuary was caused by many factors.The rapid growth of Spartina alterniflora and the continuous increase of the aquaculture industry had adversely affected the original niche of mangroves.Meanwhile,large areas of mudflat and intertidal zones were occupied,making mangroves lose their suitable habitats for reproduction and proliferation.In addition,sea-level rise,seawall construction and garbage pollution pose certain adverse effects to the survival and expansion of mangroves on the offshore side and in front of the seawall.However,the construction of the reserve and the positive protection measures play a positive role in the health maintenance of mangrove swamp.