The Influence Of Agricultural Production On Water Resources And Non-point Source Pollution In Sanjiang Plain Irrigation Area

Sanjiang Plain,located in the northeast of Heilongjiang Province,is the national important commodity grain production base,the shortage of groundwater resources and non-point source pollution have become prominent environmental problems faced by agricultural production in this area.In order to protect the water environment effectively,based on the concept of environmental friendliness,this paper chooses 290 irrigation area,a typical irrigation area in Sanjiang Plain,as the research object,through field investigation and systematic research,the research results can help solve the problems of environmental water resources and non-point source pollution caused by irrigated agriculture in Sanjiang plain area,and expand the wetland with ecological function value for this area,to improve the ecological environment quality of this area,It will provide strong technical support for promoting the transformation of irrigation area agriculture in Sanjiang Plain to environment-friendly agriculture and realizing sustainable development.By means of field investigation,the basic situation of the irrigation area is carefully understood,the problems of environmental water resources and non-point source pollution caused by agriculture in irrigation area were analyzed and identified.The results of analysis and identification of environmental problems show that the average groundwater level in the irrigation area decreased from 5.25 meters to 6.3 meters in 2010-2017,with a decrease of about 1.1 meters,the water level declined obviously,and water resources was in serious shortage.The excessive application of chemical fertilizers and pesticides in irrigation areas has resulted in surface water pollution in different degrees in Sanjiang Plain.The range of excessive COD,BOD5 and total nitrogen is 21.4-37.7 mg/L,4.4-8.4 mg/L and 1.2-1.4 mg/L,respectively.By using mathematical model method,qualitative and quantitative analysis method,Research on joint operation of groundwater and surface water and water saving irrigation technology in irrigation area is carried out.The results show that,after the joint dispatch of groundwater and surface water has been implemented,compared with 14960 hectares of the current irrigation area,the groundwater exploitation of 21953.33 hectares in the planned irrigation area decreased by 77.4795 million m3/a,which is helpful to restore the groundwater level.After the implementation of water-saving irrigation technology,compared with the water consumption under conventional flooding irrigation conditions,the planned irrigation area can save 3.7711 million m3/a of water,and the water-saving effect is remarkable.Compared with the current irrigation area,the amount of groundwater supplied by irrigation water infiltration increased by 12.821 million m3/a,which has a significant effect on restoring groundwater resources.By using the methods of literature study,pollutant discharge coefficient and qualitative and quantitative analysis,the scientific fertilization and pesticide application technology and the feasibility of surface flow constructed wetland purification technology were studied in the irrigation area.The environmental effects show that,after the implementation of scientific fertilization and pesticide application technology,compared with the current fertilizer application level,the amount of fertilizer application in the planned irrigation area decreased by 3841.83t/a,with a reduction of 38.89%,and the loss of nitrogen and phosphorus decreased by 310.42t/a.Compared with the current application level of pesticide,the application amount of pesticide in the planned irrigation area decreased by 7.9 t/a,with a reduction of 15.72%,the input of chemical fertilizers and pesticides and the output load of nitrogen and phosphorus nutrients to the environment have been effectively reduced from the source of agricultural production in irrigation areas.After the implementation of surface flow constructed wetland purification technology,the emission reduction of COD,ammonia nitrogen,total nitrogen and total phosphorus after surface flow constructed wetland purification in planned irrigation area are 635.92 t/a,51.17 t/a,31.85 t/a and 7.02 t/a,respectively,and the emission reduction ranges are as high as 59.72%,83.91%,63.52% and 60.62%,respectively.The emission concentration of ammonia nitrogen,COD,total nitrogen and total phosphorus all meet the requirements of Class III quality standard of Surface Water Environmental Quality Standard(GB3838-2002).After the drainage of irrigation area is purified by constructed wetland,the discharge load of agricultural non-point source pollutants is effectively reduced,which has a very significant effect on improving and protecting water environment.