Occurrence Characteristics Of Microplastics In The Benthic Subsystem Of The Intertidal Wetlands Of The Yangtze Estuary

An estuary is a transitional zone between a river and the ocean,a highly dynamic and constantly changing natural complex.The estuarine intertidal zone has important ecological,environmental and resource values and is rich in species diversity.As a new type of pollutant,the occurrence of microplastics has become one of the hot environmental issues of global concern.At present,the estuarine intertidal zone has become one of the hot areas of microplastics research.Macrobenthic invertebrates and sediments in the intertidal zone together constitute the benthic subsystem of the intertidal zone.To study the occurrence characteristics of microplastics in the benthic subsystem of the intertidal zone,and analyze the factors affecting the occurrence characteristics of microplastics in the benthic subsystem of the intertidal zone,which will help to understand the occurrence status of microplastics in the intertidal zone and grasp the rules of its occurrence.Combining with the domestic and foreign research present situation,choose the typical areas in the intertidal wetland of Yangtze Estuary,set up a fixed sampling sites,and conducts quarterly sampling surveys of sediments,macrobenthic invertebrates in the intertidal wetlands and related habitat factors.Analyze the occurrence characteristics of microplastics in the sediments and macrobenthic invertebrates in the intertidal wetlands,and explore the corresponding influencing factors of occurrence characteristics of microplastics.The main research results and conclusions were listed as follows:1.The composition of microplastics in the sediments in the intertidal wetlands of the Yangtze Estuary is diverse.There were obvious spatial and temporal differences in the distribution characteristics of microplastics in sediments from different habitats.Physicochemical factors of the sediments and plant density lead to differences in the distribution of microplastics in the sediments in the intertidal wetlands.(1)There were many types of microplastics in the sediments of mud flat and vegetated area in the intertidal wetlands of the Yangtze Estuary.The shape of microplastics includes fibers,fragments,rods and granules.The colors of microplastics can be divided into light colors(white,transparent,green and yellow)and dark colors(blue,red and black).The material qualities of microplastics includes polypropylene(PP),polyethylene terephthalate(PET),ethylene-propylene copolymer(EPM),polyethylene(PE),cellophane(CP),rayon(RA),polyamide(PA),polystyrene(PS),polyvinyl chloride(PVC),etc.(2)The distribution characteristics of microplastics in the sediments in different regions of the intertidal wetlands of the Yangtze Estuary had obvious seasonal changes.The abundance of microplastics in mud flat sediments was higher in autumn and lower in summer.The size of microplastics in mud flat sediments was higher in autumn and lower in summer.The abundance of microplastics in vegetated area sediments was higher in spring and lower in summer.The size of microplastics in vegetated area sediments was higher in autumn and lower in summer.(3)There were significant differences in the distribution characteristics of microplastics in the sediments at different elevations and different depths.The abundance of microplastics in the sediments of different sites changes differently along the elevation,and there are obvious differences in the abundance of microplastics between different elevations in different seasons.There were significant differences in the depth of the maximum abundance and size of microplastics in different sites,and there were significant differences in the abundance and size of microplastics at different depths in each sites(P<0.05).(4)Physicochemical factors of the sediments and plant density were important factors affecting the distribution of microplastics in the sediments in intertidal wetlands.The abundance and size of microplastics were significantly correlated with the median particle size,TOC and water content,bulk density of the sediments respectively(P<0.05).There were differences in the correlation between the distribution characteristics of microplastics in different sites of sediments and the physicochemical factors of sediments.There was a significant negative correlation between the plant density of Spartina alterniflora and the size of microplastics in the sediments(P<0.05).2.The composition of microplastics in the macrobenthic invertebrates in the intertidal wetlands of the Yangtze Estuary had various types.There are significant differences in the distribution characteristics of microplastics in the different species of macrobenthic invertebrates.The composition and distribution of microplastics in the sediments and the morphological characteristics of macrobenthic invertebrates affect the distribution of microplastics in the macrobenthic invertebrates.(1)There were obvious differences in the composition of microplastics in different species of macrobenthic invertebrates.The shape of microplastics in crabs includes fibers,fragments and rods.The material qualities of microplastics includes PET,PP,CP,RA,PA,and PE.The composition characteristics of microplastics in different crabs were different.The shape of microplastics in shellfishes includes fibers,fragments and rods.The material qualities of microplastics includes PET,RA,PA,CP,and PP.There were differences in the composition characteristics of microplastics in the different species of shellfishes.(2)There were significant differences in the distribution characteristics of microplastics in different macrobenthic invertebrates.The detection rate of microplastics in the stomach of Chiromantes dehaani,Chiromantes haematocheir and Helice tientsinensis were higher than that in the gill.There were significant differences in the abundance of microplastics in the three species of crabs(P<0.05),There was no significant difference in the size of microplastics in the three species of crabs(P>0.05).There was no significant difference between the abundance and size of microplastics in the different species of shellfishes(P>0.05).(3)Microplastics in the sediments and morphological characteristics of macrobenthic invertebrates had an important influence on the distribution characteristics of macrobenthic invertebrates microplastics in the intertidal wetlands.There was a significant correlation between the abundance of microplastics in the crabs and the morphological characteristics of the crabs(P<0.05).There was a significant correlation between the abundance of microplastics in the shellfishes and the morphological characteristics of the shellfishes(P<0.05).There were differences in the correlation between the distribution characteristics of microplastics in the different species of macrobenthic invertebrates and the distribution characteristics of microplastics in the sediments.Overall,there were significant spatial and temporal in the occurrence characteristics of microplastics in the sediments and the macrobenthic invertebrates in the intertidal wetlands of the Yangtze Estuary.The occurrence characteristics of microplastics in the sediments were affected by physicochemical factors of the sediments and plant density.The occurrence characteristics of microplastics in the macrobenthic invertebrate were affected by the composition and distribution characteristics of microplastics in the sediments and the morphological characteristics of organisms.In the future,in the research of microplastics in the intertidal wetlands,it is necessary to pay more attention to vegetation factors and discuss the important role of different vegetation growth characteristics on the composition and distribution of microplastics in the intertidal wetlands.Macrobenthic invertebrates were an intermediate link in the food chain of regional ecosystems.The microplastics ingested and stored in the macrobenthic invertebrates may be passed along the food chain,and they need to be paid attention to in future research.