Analysis On Trend And Study On Prediction Model Of Water Quality In The Estuaries Of Rivers Entering The Nansi Lake

Nansi Lake is important as it is a water conveyance channel and storage lake in the East Route of the South-to-North Water Diversion Project.The water quality of the rivers entering the lake will affect the water quality of the Nansi Lake directly,and further affect whether the water quality of the diversion can reach the standard.Therefore,according to the monitoring data of water in the estuaries of the lake,water quality assessment,pollution analysis and water quality prediction were carried out.The corresponding preventing and protecting measures for the management of the water environment in the Nansi Basin are provided.The scientific and technological support and guarantee for the water quality of the East Route of the South-to-North Water Diversion Project to reach the standard steadily are provided,too.Based on the water quality monitoring data of 38 main estuaries of the Nansi Lake from 2010 to 2017 and the water quality characteristics in the basin,the water-quality indexes COD_Cr,NH₃-N,TP,TN and COD_Mnn were selected as the research indexes of estuaries water.The water quality assessment was carried out by using the comprehensive water quality identification index method.The main sewage discharged rivers and main pollutants were analyzed.The seasonal Kendall test method was used to analyze the trends of the water quality.The grey GM?1,1?models were established to predict the future water quality.Finally,the main pollution causes and prevention suggestions of the rivers flowing into the Nansi Lake were discussed.The main results are as follows:?1?According to 14 water quality monitoring data of the main estuaries in the Nansi Lake from 2010 to 2017,the water quality assessments in different periods,different lake regions and the overall water were carried out.The results show that the water quality of estuaries in spring is generally worsen than that in autumn.The water quality in the estuaries entering the upper lake is better than that entering the lower lake.And the overall water quality of the estuaries is improved year by year.By 2017,81.6%of the monitoring points have met the water requirements of Class III in the water environment functional zone.?2?The pollution characteristics of the estuaries'water in the Nansi Lake were analyzed.The pollution load entering the lake showed a downward trend as a whole.And the total pollution load entering the lake in 2017 decreased by 86.01%compared with 2010.The main pollutant entering the lake is TN,and the main sewage rivers in the 38 rivers are the Old Canal,the Guangfu River,the Baima River,the Zhuzhaoxin River,the Chengguo River and the Si River.?3?The seasonal Kendall test method was used to analyze the water quality's trend in the estuaries of the lake.According to water quality monitoring time,it was divided into three series:annual,spring and autumn.The results show that the concentrations of COD_Cr,NH₃-N,TP,TN and COD_Mnn decreased in general,while the concentration of TP had no obvious changing trend.In spring,there are much concentrations of single pollution factors in the estuaries of the lake is increasing.Most of the water quality indicators are consistent with the characteristics of non-point source pollution.The water quality in the estuaries of the lake is mainly affected by pollutant emissions,and the influence caused by variation in discharge is relatively small.?4?Based on the monitoring data of water quality in the estuaries of the Nansi Lake,the concentrations of the main water indexes of main sewage rivers are predicted by using the GM?1,1?prediction model.The predicting process is reasonable and the results has certain reference value for application.?5?On the basis of assessment,analysis and prediction of water quality in the estuaries of the Nansi Lake,the causes of water pollution in the rivers entering the lake are discussed,and some suggestions for pollution preventing and controlling are put forward.