Study On The Relationship Between River Pollutant Flux,Lake Water Quality And Aquatic Plant Community And In Lake Datong Basin

The input of exogenous pollutants is the main source of eutrophication in many lakes in China,especially the input of exogenous pollutants via rivers is the main cause of water quality deterioration and ecosystem damage in lakes.Therefore,the study of the spatial and temporal patterns of pollutants in major rivers is essential to combat lake pollution.The flux of pollutants into the lake is the main reason for the difference in the spatial distribution of lake water quality,and the change of pollutant flux will also affect the aquatic plant community.At present,there are few researches on the relationship between pollutant flux and lake water quality and aquatic plant community.In this thesis,pollutant fluxes in and out of the lake rivers and channels were estimated using high frequency discharge and water quality monitoring at4h/time from January 2021 to October 2022 in the context of the Lake Datong basin.Based on the temporal and spatial characteristics of pollutant flux and water quality in Lake Datong Basin,combined with the investigation of aquatic plant communities in lake estuary wetlands in different seasons,the responses of water quality and aquatic plant community characteristics to pollutant fluxes in Lake Datong were analyzed,which could provide theoretical reference for the comprehensive management of the Lake Datong basin and the improvement of water quality of the Lake Datong.The main findings are follows:（1）Overall pollutant fluxes showed the characteristics of high fluxes in summer and autumn seasons and low fluxes in spring and winter seasons.The maximum inlet and outlet lake fluxes of nitrogen,phosphorus and COD among pollutants all occurred in the summer during the abundant water period,among which,the fluxes of COD,TP,TDP,TN and NH₄⁺-N and NO₃^--N in Su River were the highest among all inlet and outlet rivers/channels,reaching 8105.05t,44.37t,13.11t,437.33t,257.08t and184.87t respectively.Among the outlet rivers/channels,the Mingshan channel was the main outlet channel.The fluxes of each pollutant were dominated by a net entry into the lake,with significant inlet retention.Total inlet dissolved inorganic nitrogen（mainly NH₄⁺-N and NO₃^--N）accounted for 80.1%of the total inlet flux of total nitrogen into the lake.In 2022,the flux of pollutants in and out of the lake decreased by 41.69%～78.04%compared with that in 2021.In terms of spatial pattern,the flux proportion of pollutants in and out of the lake in Nanxian area was higher than that in Lake Datong area.（2）The SAL and p H of the lake in 2022 were significantly higher than that in2021,and the COD of the river in 2022 was significantly higher than that in 2021.The concentrations of TP,TN and NO₃^--N in Lake Datong were consistent with the response of riverine TP,TN and NO₃^--N influent fluxes.The amount of water entering the lake was a key factor influencing the fluxes into the lake,and the total fluxes of TP,TN,NH₄⁺-N and COD into the lake were significantly and positively correlated with the amount of water entering the lake.Rainfall significantly influenced the fluxes of pollutants into the lake,with the total fluxes of TP,NO₃^--N and COD into the lake showing a significant positive correlation with monthly rainfall.（3）During the survey period,16 species were found in three major rivers（Jinpen Canal,Wuqi Canal and Su River）,including 10 species of hygrophytes,5 species of emergent plants and 1 species of floating plants.Among them,Alternanthera philoxeroides（Mart.）Griseb.was the most abundant invasive plant,followed by Eichhornia crassipes（Mart.）Solme.Myriophyllum aquaticum,an exotic plant,was the smallest.Aquatic plant community biomass showed clear seasonal dynamics,with the highest community biomass in autumn and the largest in the Su River,followed by the Wuqi Canal.During the summer high water period,floating invasive aquatic plants such as E.crassipes,native emergent aquatic plants such as Zizania latifolia（Griseb.）Stapf,Nelumbo nucifera Gaertn.,and emergent invasive plants A.philoxeroides were the dominant species in the plant communities of the three rivers.The species richness and Margalef index of plant communities were the highest in spring,but there was no significant difference between other seasons.The Margalef index,Shannon-wiener and Pielou evenness indices for spring riverine plant communities were all maximum,at 0.69,1.30 and 1.03 respectively.Total aquatic plant community biomass increased with increasing TP and TN pollutant fluxes,and both emergent and floating plant biomass showed significant positive correlations with COD flux.COD flux was the most significant environmental variable affecting plant community abundance.In summary,this study analyzed the spatial and temporal characteristics of pollutant fluxes in and out of the Lake Datong basin and their relationship with the water quality of Lake Datong and the characteristics of the aquatic plant community in the estuary,providing a theoretical reference and basis for the comprehensive management of the water environment in the Lake Datong basin and the management of the water quality objectives of Lake Datong.