Assessment And Prediction Of The Temporal And Spatial Evolution Trends Of Water Quality In The North Canal Basin

In recent years,with the improvement of urbanization level,and rapid development of industrialization and population growth in China,the global climate begins to change,which leads to the deterioration of basin water environment,and relevant issues have drawn the attention of relevant departments.The North Canal is the only river that originates from Beijing and has water in trunk stream all the year round in the five major water systems in Beijing,which undertakes 90%of the drainage tasks of the central city of Beijing.The basin is densely populated with high urbanization level and great discharge of domestic pollutants.As a result,the quantity of pollutants discharged in the North Canal Basin far exceeds the environmental capacity,and the river water is seriously polluted and has the worst quality among the five major water systems in Beijing.In such case,the improvement of water environment quality in the basin is closely related to the people’s life and social production,which is also the core issue concerned by relevant management departments.Therefore,it is of great significance to study the temporal and spatial distribution characteristics and water quality prediction for the management and protection of basin water environment.In this paper,based on the improvement of water environment quality and basin characteristics,the temporal and spatial distribution characteristics of basin water quality are analyzed,and the basin water quality prediction model is constructed.For the survey region,14 water quality monitoring sections in the North Canal Basin are selected for the study and analysis of the temporal and spatial distribution characteristics of water quality and the water quality prediction model.The main research contents and results in this paper mainly fall into the following parts:(1)Water quality monitoring data of 14 monitoring sections in the North Canal Basin during 2015-2019 were collected and collated,including Shaziying,Qinghe Gate,Shawo,Gulou Outer Street,Baishi Bridge,Huayuan Road,New Bali Bridge,Guangbei Binhe Bridge,Upper Dahongmen Gate,Wangjiabai,Old Xia’an Highway,Qinying Yangshui Station,Tumenlou and Beiyang Bridge.Meanwhile,general information of the population,social economy and water conservancy projects in the North Canal Basin was also sorted out.(2)The temporal and spatial evolution trend of water quality in the 14 water quality monitoring sections in the North Canal Basin was evaluated by multivariate statistical analysis method.The water quality shows significant annual variation characteristics in terms of time distribution:the water quality in wet season is better than that in dry season and normal water season,which indicates that regional runoff in flood season can reduce the concentration of pollutants in the river and dilute regional river water to a certain extent,and that the comprehensive utilization and scheduling of stormwater runoff resources play an important role in improving regional water quality.Water quality in normal water season is the worst,which indicates that the disturbance of sediment discharges pollutants into the environment again,and that endogenous secondary pollution is an important pollution source.The 14 monitoring sections are divided into two types in spatial distribution,and the main influencing factors and pollutant concentration values of these sections in both types are similar.The first type of sections includes Gulou Outer Street,Baishi Bridge,Beiyang Bridge,Qinghe Gate,Guangbei Binhe Bridge,Upper Dahongmen Gate and Huayuan Road,while the second type includes Wangjiabai,Qinying Yangshui Station,Tumenlou,Shawo,New Bali Bridge,Shaziying and Old Xia’an Highway.According to spatial difference analysis of the concentration of main pollutants,the water quality in monitoring sections of the second type is better than that of the first type.(3)An artificial neural network model and a time series model were built for water quality prediction in the basin.According to the collected data,five water quality indexes,including dissolved oxygen(DO,mg/L),chemical oxygen demand(COD,mg/L),five-day biochemical oxygen demand(BOD5,mg/L),ammonia nitrogen(NH3-N,mg/L)and total phosphorus(TP,mg/L),were determined as the research objects for analysis and prediction.The prediction results reveal that the water quality in various sections is gradually improved as a whole,and individual indexes of some sections fluctuate to some extent,which may be caused by the interference of local project construction,but the overall development trend is good.Therefore,it’s required to strengthen the supervision and management of water quality to create a better water environment.(4)Based on the temporal and spatial distribution characteristics of water quality and water quality prediction results,the control measures for water environment quality management were put forward.Firstly,start from the source to improve the industrial layout,and promote cleaner production in industrial and agricultural enterprises and parks.Secondly,improve the water quality monitoring and early warning system,and establish an effective public informed and participation system to strengthen the supervision.Thirdly,enhance the investment in pollution control and strengthen end-of-pipe treatment.Furthermore,establish a unified management organization to improve trans-boundary/cross-border environmental management.Finally,clarify different responsibilities of upstream/downstream areas.