Research On Comprehensive Analysis And Prediction Of Water Quality In Nansihu Lake District

Nansi Lake is the necessary place and storage lake for the east route of the South-to-North Water Diversion Project,and its water quality safety is very important.In order to ensure the safety of water quality,it is necessary to conduct comprehensive analysis and water quality prediction research on the water quality changes of Nansi Lake.Based on this,reasonable and effective prevention and control measures are formulated to provide a reference for the water quality control and pollution control of Nansi Lake.Based on the comparative study of three water quality analysis and evaluation methods,the comprehensive water quality identification index method is selected to analyze and evaluate the pollution characteristics of Nansi Lake area from 2010 to2019.On this basis,the gray Markov model was established to predict the water quality change trend of Nansi Lake in the next three years.The main research conclusions are as follows:（1）Based on the water quality spatial monitoring data of 18 times from 2010 to2019,the water quality assessment of Nansi Lake was carried out by regions,seasons and overall.The results showed that the water quality of Nansi Lake has been greatly improved.The water quality gradually geted better from north to south,and the spring was better than autumn,and the subordinate lake was superior to the higher-up lake.The concentration of various water quality indicators showed a downward trend,with occasional fluctuations.Compared with November 2010,the average decrease rates of COD_Cr,NH₃-N,COD_Mn,TP and TN were 16.2%,3.6%,12.3%,51.1%and 5.2%in November 2019.（2）The results of water quality identification evaluation showed that the water quality index of the higher-up and subordinate lakes were decreasing gradually in the past 10 years,among which the comprehensive water quality index of the higher-up lakes was higher than that of subordinate lakes.According to the single water quality identification index of the past 10 years,the proportions of COD_Cr,COD_Mn,TP,TN,and NH₃-N in the higher-up（subordinate）lakes reached Class III water quality standards were 50%（70%）,70%（100%）,10%（70%）,100%（60%）,100%（100%）,respectively.The main pollution indicators are total nitrogen and total phosphorus.Since the water diversion in 2013,the water quality of the higher-up and subordinate lakes has basically been in a stable and up-to-standard state.（3）Combined with the characteristics of water quality data and prediction model of Nansi Lake Basin,the gray Markov model was constructed,and the water quality status and water quality evolution trend of Nansi Lake from 2020 to 2022 were predicted by using the model.The results show that the water quality of Nansi Lake will gradually improve from north to south in the next three years,in which the concentrations of COD_Cr,NH₃-N and COD_Mnwill decrease,while the concentrations of TP and TN will increase slightly,and there is a risk of exceeding the standard.（4）Based on the summary and analysis of water quality evaluation and prediction results,combined with the current situation of water pollution in the Nansi Lake basin,the causes of water pollution in the lake area were analyzed.According to the characteristics of pollution in the lake area,the pollution prevention and control countermeasures were discussed from the aspects of adjusting industrial structure,promoting cleaner production,controlling the pollution of rivers into the lake,ecological protection and restoration,improving the environmental management system and enhancing citizens’awareness of environmental protection.