| Rivers are the main carriers of water resources,and they play a very important role in the survival and development of human beings.In recent decades,the rapid expansion of human urbanization and the rapid expansion of population have led to increasing health problems in rivers.Understanding the temporal and spatial laws and main influencing factors of river water quality change is the scientific basis for river water quality management.However,due to the continuity of rivers and the significant differences in natural conditions and human activities in the basins where they are located,the spatiotemporal differentiation characteristics of river water quality on a regional scale are still unclear,and effective methods for predicting water quality are still lacking.Jilin Province is an important grain production area and industrial base in China,and the pollutants generated by its production and processing have brought enormous pressure on the water environment in Jilin Province.At the same time,the water pollution of the rivers in central Jilin Province has become an important water environmental issue.In the central region of Jilin Province,there are two major watersheds-the Songhua River Basin and the East Liaohe River Basin.The Songhua River in Jilin Province is collectively referred to as the second Songhua River,which is the birthplace of the Songhua River.It flows through Baishan City,Jilin City,and Changchun City in Jilin Province and flows into Heilongjiang Province after merging with the Nenjiang River in Songyuan City.The East Liaohe River basin is divided into the eastern and western East Liaohe River sections in Jilin Province.The western East Liaohe River section is a seasonal river in Jilin Province.The eastern East Liaohe River section,as the birthplace of the East Liaohe River,flows through Liaoyuan City and Siping City before entering Liaoning Province.Although the water quality of large rivers generally tends to improve with the increase of flow,the water quality change rules of rivers in central Jilin Province are greatly affected by human activities around them,and the change rules of related factors such as water quality status and flow are unclear.Clarifying the temporal and spatial characteristics of water quality in important rivers in Jilin Province,conducting predictive research on their water quality changes,and proposing corresponding water quality management methods can recognize their main influencing factors,promote the development of river water environmental science,and provide support for regional sustainable development.In order to clarify the characteristics and changing rules of river water quality in the central region of Jilin Province,this paper selected The second Songhua River and the Jilin section of the East Liaohe River as the research areas,and arranged 36 and 16 water quality monitoring sections respectively in The second Songhua River and the Jilin section of the East Liaohe River.From 2016 to 2020,continuous monitoring of water quality was conducted for 5 consecutive years,and 24 items including routine surface water testing items were measured.According to the monitoring results,typical pollutants in the water quality of the study area were selected.Based on the selected pollutants,the pollutant distribution maps of East Liaohe River and Songhua River regions were presented using GIS methods,and the temporal and spatial variation laws and characteristics of river pollutants in Jilin Province were analyzed.On this basis,the Wasp7.3 water quality model was selected to simulate and predict the two main indicators of COD(Chemical Oxygen Demand)and ammonia nitrogen in The second Songhua River and the Jilin section of the East Liaohe River in sections.Finally,a joint water quality and quantity control plan was set according to different scenarios.The main research conclusions are as follows:(1)The water quality of The second Songhua River and the Jilin section of the East Liaohe River shows significant spatiotemporal heterogeneity.The comprehensive water quality testing results and screening analysis indicate that the typical pollutants in the rivers of the study area from 2016 to 2020 are COD,BOD(biochemical oxygen demand),permanganate index,and ammonia nitrogen.(2)The analysis results of water quality indicators show that COD has a positive correlation with BOD and permanganate index,so ammonia nitrogen and COD can be used as typical pollutant simulation indicators for The second Songhua River and the Jilin section of the East Liaohe River.The spatial analysis of pollutants in The second Songhua River and the Jilin section of the East Liaohe River in the study area from2016 to 2020 shows that the upstream water quality of The second Songhua River is good.During the period 2016-2020,the pollutant concentrations of COD,BOD,permanganate index,and ammonia nitrogen have a significant downward trend.After flowing through the urban area of Jilin,the pollutant concentrations have significantly increased.However,the flow of The second Songhua River is large,and the pollutant concentrations in the downstream reach have significantly decreased.The concentration of pollutants in The second Songhua River presents a rule of dry season>wet season>normal season.The water quality in the Jilin section of the East Liaohe River is poor,with a slight downward trend in water pollution during 2016-2020.Due to the small number of tributaries that flow into the East Liaohe River and the small flow rate of each tributary,and each tributary accepts the input of urban sewage outlets,the pollution situation is still relatively serious.The variation of pollutant concentration in the Jilin section of the East Liaohe River during the year is different from that in The second Songhua River,and the pollutant concentration presents a rule of dry season>normal season>high season.(3)Through generalizing and segmenting the two rivers in The second Songhua River and the Jilin section of the East Liaohe River,the Wasp7.3 model was used to simulate the COD and ammonia nitrogen in the two river sections.The simulation results were significantly positively correlated with the measured results,indicating that the model could meet the requirements for simulating and predicting the spatiotemporal changes in the pollutant concentrations in The second Songhua River and the Jilin section of the East Liaohe River.The simulation results show that the concentration of COD pollutants in The second Songhua River will decrease by 2023,and the concentration of ammonia nitrogen pollutants in the simulated river section will also decrease.In the Jilin section of the East Liaohe River,the concentrations of COD and ammonia nitrogen pollutants have significantly decreased but are still in a polluted state.The simulation results show that the pollution degree of COD and ammonia nitrogen is proportional to the river water volume.This result is evident in The second Songhua River,due to the large flow rate and strong self purification ability of the river water in The second Songhua River.The pollution in the Jilin section of the East Liaohe River clearly shows that the contribution rate of non-point source pollution is greater than that of point source pollution.(4)Based on the prediction results of The second Songhua River and the Jilin section of the East Liaohe River and the analysis of the contribution rate of pollutants entering the river,the pollutant carrying capacity of The second Songhua River and the Jilin section of the East Liaohe River is calculated,and based on the results,the regulation and control preset based on the water quality objectives of the river section is carried out,and the regulation and control suggestions for segmented governance are given to strengthen the water environment protection in Jilin Province.The research results can provide technical support for improving the quality of water environment in Jilin Province. |
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