Study On The Characteristics And Contorol Of Non-Point Source Pollution In Tapical Plain River Network Area

In recent years,with the country’s continuous emphasis on water environment governance,point source pollution has been greatly improved,and non-point source pollution has become the main cause of water environment pollution.In the plain river network area of southern China,on the one hand,due to the large population and developed agriculture,the pollution of non-point sources of life and agricultural non-point sources is serious.On the other hand,due to the dense river network and the developed water system,the rainy season lasts long and the rainfall is large.Therefore,surface runoff carries a lot of pollutants into the river,and non-point source pollution in plain river network areas is more significant and sensitive.Therefore,quantitative analysis of the characteristics of non-point source pollution in the plain river network area,and exploration of the source and influencing factors are of great significance for controlling the water environment pollution in the basin.This study is based on the construction of a clean small watershed in Anhui Province.The Zhaohe River Basin is used as a research area.By constructing a non-point source pollution model of the river basin,the amount of nitrogen and phosphorus pollution in the river basin and the non-point source pollution load are simulated and studied.Temporal and spatial distribution characteristics;And predict the pollution characteristics of the river basin planning year,identify the key areas of non-point source pollution,and combine the farming management measures and engineering interception measures to propose the best management measures for non-point source watersheds.The main findings are as follows:(1)Sampling and analysis of the main river water bodies in the Zhaohe River Basin in the study area revealed that 5 of the 12 detected rivers were inferior Type V water,with serious pollution exceeding the standard,and the main indicators exceeding the standard were TN and TP;According to the main stream sequence water quality evaluation and M-K mutation test in the study area,the main stream water quality TN exceeded the standard seriously,and the individual monitoring section was Class V water quality.The trend of water pollution generally showed an insignificant downward trend.(2)A watershed non-point source pollution prediction model based on the SWAT model is established.The model is verified and verified,which shows that the model has good applicability in the Zhaohe River Basin.The simulation results show that the average annual inflow of TN into the study area is 1619 tons/year,and the average annual inflow of TP is 94.82 tons/year.In different hydrological years,the total amount of pollutants entering the river is different,which is expressed as a flood year(2016)>High water year(2014)>Plain water year(2013)>Low water year(2011).Among the sub-basins,the Xian River Basin has the highest proportion of pollution emissions in the high water year and the normal water year,and the highest non-point source pollution emissions in the Huanxu River Basin in the low water year.(3)According to the land use planning and point source growth forecast data of the study area,the annual pollution of the study area is predicted.The results show that the planned annual flow of TN pollution into the river basin is 1855.27-2550.46 tons,an increase of 37.47%-44.89%from the current year,and the amount of TP pollution into the river is 74.79-120.55 tons,an increase of 7.96%-16.97%from the current year;Water quality prediction and evaluation shows that there are 8 sub-basins in the planned watershed with TN content exceeding Class V water standards;and 2 sub-basins with TP content reaching inferior Class V water quality.At the same time,it is shown that the TN contributed by non-point source pollution to the river pollutants reached 58.23%and the TP was 38.57%-61.89%.(4)According to the unit load index method,the non-point source pollution intensity of each sub-basin in the planning year is graded.The Xian,Shicao,Pei and Shengqiao rivers with "heavy"loss intensity and the Huanweihe sub-basin with "heavier" loss intensity were used as non-point source pollution load key areas to apply non-point source control measures.The results show that different control measures have different effects on the control of non-point source pollution.The specific performance is as follows:planting river channel>vegetation filter belt>increasing the depth of chemical fertilizer>reducing the amount of fertilizer application.By optimizing the combination,the best watershed management measures are finally determined as:Increase the buried depth of chemical fertilizer application,reduce the amount of fertilizer application by 50%,1 meter long grass channel,field area and vegetation filter belt area ratio 45.After the implementation of the above measures in the key area watersheds,only the Shicao River subbasin is the TN with a "severe" loss intensity in each sub-basin,and TP has no sub-basins with a"moderate" loss intensity.