Study On Sediment Protist Monitoring And Ecological Health Assessment In Taihu Lake Basin Based On EDNA Metabarcoding

Water pollution causes a decline in biodiversity in aquatic ecosystems.The Taihu Lake basin has been polluted by agricultural and industrial sewage for a long time,and the aquatic ecosystem is seriously degraded.The sediment protist community is an important part of the aquatic ecological environment.The traditional ecological monitoring method of protist is PFU method,which is greatly affected by water quality.Due to this influence,sediment protist monitoring has not been widely carried out.The aim of this study is to establish a set of based on eDNA macrobarcoding monitoring methods for the analysis of sediment protist diversity in the Taihu Lake Basin.The objectives are :(1)To establish a complete set of environmental sample collection and experimental analysis process;(2)Monitoring and identification of the sediment protist in the Taihu Lake Basin;(3)To distinguish the difference in the composition of sediment protist community and the diversity on the time scale in the river,reservoir,lake and Taihu Lake;(4)An ecological health grade evaluation method based on the biological integrity index was constructed.The main conclusions of this study are as follows:(1)A set of environmental DNA(eDNA)metabarcoding monitoring method suitable for the sediment protist community in the Taihu Lake Basin was constructed.The method identified 13 phyla and 44 classes of the sediment protist community in the Taihu Lake Basin.Among them,the dominant phyla are Ciliophora,Cercozoa,Dinophyta and Conosa.(2)Based on environmental DNA(eDNA)macrobarcoding repeatability study,the results showed that the OTU crossover rate of the three samples was low,and the weighted OTU crossover rate was 63.50%on average.The high sensitivity of environmental DNA(eDNA)macrobarcoding,the uneven distribution of organisms in sediments and the low abundance of biological DNA fragments in environmental samples are important reasons for the low average crossover rate.(3)According to the OTU-locus-species matrix method,the diversity of the sediment protist in the Taihu Lake Basin was classified,and the alpha-diversity index T value of the dominant species was tested.The diversity index of Ciliophora,Dinophyta and Cercozoa in spring(March)and autumn(August)was significantly different,while the diversity index of other species was not different.The Bray-Curtis distance of protist communities in rivers,reservoirs,lakes and Taihu Lake was more obvious on the time scale than on the space scale in the non-metric multi-dimensional analysis.(4)By selecting reference points and damage points,we screened the biodiversity index with significant difference between them.Based on these biodiversity indices,the integrity index of sediment protists in the Taihu Lake Basin was constructed,and these indices were unified into a single dimension to evaluate the ecological health of water bodies in the Taihu Lake Basin in spring and autumn.The results showed that the biological integrity index based on eDNA macrobarcoding technology was used to evaluate the ecological health of the Taihu Lake Basin in the two seasons,and the ecological health status of the water body in the two seasons had a good consistency.