Occurrence Characteristics And Influencing Factors Of Microplastics In Surface Sediments Of Dianchi Lake

Microplastics,as a new type of pollutant,has attracted more and more attention.However,most of the previous studies on microplastics still focused on the contaminated and host occurrence of microplastics in the study area environment,there are few reports on the spatial distribution characteristics of microplastics.In the water environment,research reports on microplastics in the marine environment dominate the majority,with relatively few studies on lake sediments.However,lake as one of the important water environment closely related to human production and life,may suffered from more serious microplastics pollution.In order to explore microplastics pollution of plateau lakes in southwest China and provide scientific basis and research foundation for microplastics control and environmental governance,this paper takes Dianchi Lake,a large shallow urban lake on the Yunnan-Guizhou Plateau,as the research object to explore the occurrence characteristics of microplastics in its surface sediments,such as abundance,color,shape,particle size and composition,and analyze the impact of environmental factors on its occurrence characteristics.The main research results are as follows:（1）The abundance distribution range of microplastics in surface sediments of Dianchi Lake ranges from 171.67 pieces/kg to 630.00 pieces/kg,with the average abundance of 338.48 pieces/kg.The spatial distribution is characterized by less in the South and more in the north.By analyzing the physical characteristics of microplastics in surface sediments of Dianchi Lake,it is found that transparent color and blue dominated;In the shape of microplastics,the stripe occupies the absolute dominant position and the foam content is the lowest.Particle size of microplastics,<1000 μm is in the majority.After detect the composition of microplastics,the detection rate of microplastics is 74.04%.Among the 13 kinds of microplastics,polyethylene terephthalate（including polyester,PET）and dyed microplastics accounted for relatively large,32.03% and 31.60%,respectively;polyurethane（PU）,styrene acrylonitrile copolymer（SAN or AS）,polyvinyl chloride（PVC）and low density polyethylene（LDPE）account for more than 5%,and other micro plastics account for less.（2）Land use and surface cover types also have a certain impact on the occurrence characteristics of microplastics in surface sediments of Dianchi Lake.The main urban area in the north of Dianchi Lake has a large population density and more tourist attractions and docks,resulting in more microplastics emissions.Farmland,villages,wetlands and other land cover types will also export microplastics to Dianchi Lake.Forest and grassland have little effect on the content of microplastics in surface sediments of Dianchi Lake.（3）The correlation between the underwater topography of Dianchi Lake and the abundance of microplastics in the surface sediments of Dianchi Lake is analyzed.The results showed that only the curvature has a significant negative correlation with the abundance of microplastics（P < 0.05）,in the whole Dianchi Lake and its inner southern and central regions.That is,the abundance of microplastics will decrease with the increase of curvature,indicating that the abundance of microplastics is higher in the surface sediment of the concave terrain;However,the correlation between roughness,fluctuation,slope,slope direction and water depth with microplastic abundance was not significant（P> 0.05）.In the north of Dianchi Lake,all the topographic factors including curvature with microplastic abundance correlation were not significant（P> 0.05）.（4）Hydrodynamic conditions will affect the spatial distribution characteristics of microplastics in the surface sediments of Dianchi Lake.In the circulation area such like the southern and central parts of Dianchi Lake,with weak hydrodynamic force and stable Lake current,the abundance of microplastics in the surface sediments is high.In the north of Dianchi Lake,due to the influence of rivers entering the lake,the hydrodynamic conditions are complex,which affects the dominance of curvature on the spatial distribution characteristics of microplastics in surface sediments.