Study On Macrobenthos Community In Different Habits Of Reclamation Wetland In Hengsha Island

Coastal wetlands play an important role in the sustainable development of estuarine and coastal areas because of the functions of regulating climate,material production,carbon sequestration,water purification and biological habitat.However,due to the large-scale reclamation activities,the coastal wetlands and the natural coastline have been reduced sharply,causing some damage to the ecosystem.Therefore,the purpose of this study is to explore the changes of macrobenthos community structure in different development stages of reclamation wetland,so as to provide reference for the development and protection of reclamation wetland.In this study,we selected five wetland areas in Hengsha Island,including bare beach,reclamation wetland in the early stage of development,the middle stage of development,the middle and late stage of development,and natural wetland.At the same time,three types of plant communities were set up in different development stages,namely Phragmites australis community,Phragmites australis-Scirpus mariqueter ecotone community,and Scirpus mariqueter community.Field investigation and determining of vegetation and soil characteristics were conducted to explore the community characteristics and habitat characteristics of macrobenthos in different development stages,different plant community types and different seasons in autumn(October 2019),winter(January 2020),spring(may 2020)and summer(August 2020).The main conclusions of this study are as follows:(1)The density,coverage,height,aboveground and belowground biomass of plant community increased with the growth of development stage.The density and coverage of plant community in the middle stage of development of reclamation wetland can reach the level of natural wetland,but the community height,aboveground biomass and underground biomass are lower than natural wetland.Except for the density,the difference of vegetation characteristics among plant communities in reclamation wetland was smaller than that in natural wetland.With the growth of development stage,soil moisture,porosity,organic carbon and total nitrogen increased,soil electrical conductivity and salinity showed a trend of increasedecrease-increase,soil particle size and pH decreased.In addition to organic carbon and total nitrogen,physiochemical properties of soil in the middle and late stage of reclamation wetland can reach the level of natural wetland.The differences of soil moisture,porosity,organic carbon and total nitrogen among plant communities in reclamation wetland were less than those in natural wetland.The highest coverage,height and aboveground biomass of plant community were found in spring and summer,while the lowest community density and underground biomass were found in summer.The lowest soil porosity,electrical conductivity,salinity,particle size,organic carbon and total nitrogen were found in summer,while moisture and pH were the highest in spring and summer.(2)A total of 37 macrobenthic species were found,belonging to 5 phyla,7classes,17 orders and 34 families.Of which,3 species were Polychaeta,1 species was Phascolosomatidea,10 species were Gastropoda,6 species were Bivalvia,10 species were Crustacea,6 species were Insecta and 1 species was Actinopterygii.In the early stage of development,the dominant species was Corbicula largillierti;In the middle and late development stage,the dominant species was Assiminea estuarina;The dominant species of natural wetland are Assiminea estuarina and Ilyoplax deschampsi.The community structure of macrobenthos was significantly related to the growth and decline of dominant species.The species number,density,diversity and richness of macrobenthos increased with the growth of development stage,Biomass and evenness increased first and then decreased.The species number,density and biomass of macrobenthos in the middle stage of development of reclamation wetland can reach the level of natural wetland,but the diversity,evenness and richness of macrobenthos are lower than those of natural wetland.In the early stage of development,the species number,density,biomass,diversity,evenness and richness of macrobenthos were the highest in the ecotone community.In natural wetland,those were the highest in the Scirpus mariqueter community.The species number,density,biomass and richness of macrobenthos were higher in autumn and winter,but lower in spring and summer.(3)The density,coverage,height,aboveground biomass,underground biomass of plant community,soil moisture,porosity,electrical conductivity,organic carbon and total nitrogen were positively correlated with macrobenthos community structure.Soil particle size and pH were nagatively correlated with macrobenthos community structure.Effects of plant community density,coverage,soil particle size,pH,electrical conductivity were the most significant.Gastropoda,Crustacea,Insecta,Polychaeta,Phascolosomatidea have high positive correlation with plant community coverage and high negative correlation with soil particle size and pH.The community structure of macrobenthos in reclamation wetland is affected by different development stages,plant community types and seasons.The development stage of wetland is the dominant factor affecting the community structure of macrobenthos.Therefore,comprehensive consideration of the changes in the whole development process of wetland is helpful to understand the dynamics of reclamation wetland and provide support for wetland development and protection.