Characteristics And Sources Of Nitrogen And Phosphorus Pollution In Futou Lake

As an important part of water ecosystem,lakes have functions of regulating regional climate and maintaining regional ecological balance.With the process of urbanization in China,the lake environment has been greatly threatened,especially in the Yangtze River Basin.Grasping the current situation of lake water environment plays an important role in the planning and management of ecological environment.Based on the monitoring and testing data from 2009 to2020,the Nemerow index method and other evaluation methods were used to comprehensively evaluate the water environment of Futou Lake.Correlation analysis,principal component analysis,cluster analysis and seasonal Kendall test were used to conduct multivariate statistical analysis on the spatiotemporal variation characteristics of nitrogen（N）and phosphorus（P）related indexes in the lake.The characteristics and environmental factors of adsorption and release of sediment N and P were studied by static simulation experiment to evaluate the risk of endogenous release of N and P.The source analysis of N and P pollution was carried out using the comprehensive source list analysis method.The main conclusions were as follows:（1）The comprehensive evaluation results of the Futou lake water environment demonstrated that the water environment quality of the whole lake was relatively stable from 2009 to 2016 with water quality grades II and III.After 2016,N and P concentrations exhibited a significant upward trend.The overall water environment of the lake was seriously polluted by eutrophication and organic pollution.The water quality in southern waters was most polluted by N and P,while other areas were relatively light and the N and P substances in water had higher homology.（2）The results of sediment adsorption and release experiment illustrated that the adsorption kinetics of N and P conformed to Elovich equation,parabolic equation and pseudo-second order rate equation,and the adsorption process followed the Freundlich isotherm model.Under the same conditions,the release of N and P in the southern and western waters was greater than that in the eastern and northern.The risk of releasing P from sediment in different waters was different from that of releasing N.For the whole lake area,the risk of releasing P from sediment was higher than that of releasing N.In a certain range,the release amount of N and P increased with the increase of temperature and disturbance intensity,and disturbance intensity had a great influence on the release of N and P.When beyond a certain range,the release capacity of N and P would be limited to a certain extent.The concentration difference between water and sediment interface was one of the key factors affecting the adsorption/release amount and rate.（3）The N and P pollution in the basin was mainly affected by exogenous inputs and endogenous inputs.The exogenous inputs were mainly non-point source pollution caused by agriculture and animal husbandry.The non-point source contribution rates of ammonia nitrogen（NH₄⁺-N）,total nitrogen（TN）and total phosphorus（TP）were 83.00%,71.08%and 89.93%,respectively.Textile industry,wood processing and wood products industry,papermaking and printing and dyeing industry were the key points of exogenous point source input in the basin,and the contribution rates of NH₄⁺-N,TN and TP point source were 9.94%,15.35%and 5.02%,respectively.In recent years,the proportion of N and P input increased gradually,and the endogenous contribution rates of NH₄⁺-N,TN and TP were 7.06%,13.57%and 5.04%,respectively,which gradually became one of the main sources of N and P pollution in the Futou lake.