Nitrogen And Phosphorus Source And Sink Analysis And BMPs Of Non-point Source Pollution In Typical Orchards In Beijing

With the rapid development of Chinas agricultural economy,water environment problems caused by agricultural nonpoint source pollution have attracted widespread attention.Elemental nitrogen and phosphorus are important factors that degrade the water environment,and the intensification of human activities is the main cause of its outbreak.Orchards are an important part of agriculture,and it is increasingly important to effectively assess the problem of nitrogen and phosphorus pollution in orchards due to human activities.Therefore,it is necessary to quantitatively analyze the input and output of nitrogen and phosphorus elements in orchards and to find effective measures to prevent the problem of nonpoint source pollution in orchards.In this study,the main sources of nitrogen and phosphorus in the study area were quantified based on the NANI model and NAPI model,and the main destinations of nitrogen and phosphorus in the study area were investigated through monitoring,and effective measures to control nonpoint source pollution in orchards were found by combining relevant research data at home and abroad,so as to provide data support for the study of excessive nitrogen and phosphorus in typical orchards in Beijing.This paper provides data support for the study of excessive nitrogen and phosphorus in typical orchards in Beijing.The main findings of this paper are as follows.(1)The NANI value in the study area was 471.70 kg/hm~2,which was derived from four components,fertilizer input of 416.21 kg/hm~2(79.20%),atmospheric deposition of 64.71 kg/hm~2(12.31%),biological nitrogen fixation of 17.70 kg/hm~2(3.37%)and food/feed input of-26.92 kg/hm~2(-5.12%)consisting of three components,fertilizer input 145.96 kg/hm~2(102.64%),crop products-5.97 kg/hm~2(-4.20%)and human feces and urine 2.22 kg/hm~2(1.56%).Fertilizer input is a major component of NANI and NAPI,and its fertilizer application is much higher than the average in China,and this component poses a greater pressure on the regional ecological environment.(2)Nitrogen in the study area goes to four parts:nitrogen volatilization 15.12 kg/hm~2,accounting for 3.20%,plant uptake 73.00 kg/hm~2,accounting for 15.48%,surface runoff loss 1.73 kg/hm~2,accounting for 0.37%,remaining in the soil 381.86 kg/hm~2,accounting for 80.95%,including 276.09 kg/hm~2 above80 cm soil layer and 105.77 kg/hm~2 below 80 cm soil layer.Phosphorus goes to three parts,8.55 kg/hm~2(6.01%)is absorbed by plants,0.15 kg/hm~2(0.11%)is lost by surface runoff,and 133.51 kg/hm~2(93.88%)is retained in the soil,including 132.06 kg/hm~2 above 80 cm soil layer and 1.45 kg/hm~2 below 80 cm soil layer.This part can continue to be absorbed and used by plants and will not cause any major environmental problems.By monitoring the water quality of the ditch,we found that the nitrogen and phosphorus elements lost by surface runoff enter the downstream water bodies directly without treatment,which will pose a great threat to the water environment.(3)A database of best management practices(BMPs)was established by collecting relevant literature on BMPs from home and abroad.The database includes BMP name,classification,abatement rate,vegetation type,soil type,project cost,etc.The measures include terraces,horizontal ditches,horizontal steps,fish scale pits,grass-planted ditches,vegetation filter strips,artificial wetlands,soil and water conservation tillage measures,soil and water conservation grass planting,ecological slope protection,etc.,totaling 213 items.Based on the database,a screening system for BMPs was developed for the severity of nonpoint source pollution using the shortest path idea with C++programming language.The system can screen out the best management measures suitable for the study area through the target abatement rate,and provide a reliable basis for the abatement of pollutants in the area.After screening,it was concluded that the measure deployment in the study area was vegetation filter belt+gravel paving,and the reduction rate of total nitrogen reached 15.12%and total phosphorus reached 8.57%before and after the measure deployment.