Nitrogen Flow In Food Production And Consumption System In Shanghai Based On N-Calculator And Material Flow Model

Nitrogen pollution caused by nutrient flow in food chain is an important and urgent environmental problem in the world.At present,the study of food nitrogen pollution has become a frontier and hot scientific issue in the research of nitrogen cycle.The study of nitrogen flow in food production and consumption systems plays an important role in controlling nitrogen emission intensity and promoting sustainable nitrogen management in the food chain.This paper took Shanghai as the research area and estimated the per capita food nitrogen footprint(including food production and consumption nitrogen footprint)of Shanghai from 2000 to 2018 based on the N-Calculator model,and calculated and analyzed the changes of the input and output of reactive nitrogen and the environmental load caused by farmland production system,livestock and poultry breeding system and food consumption system of Shanghai from2000 to 2018 based on the material flow model.The main research achievements obtained in this study include:(1)Based on the N-calculator model,the study shows that the per capita food nitrogen footprint in Shanghai from 2000 to 2018 ranged from 18.10 to 21.60 kg N/a.Among them,per capita consumption nitrogen footprint is the main part of per capita food nitrogen footprint,and per capita food nitrogen footprint is positively correlated with per capita food consumption.In recent years,with the increase of per capita consumption of animal food including meat and aquatic products,the per capita food nitrogen footprint showed an increasing trend.According to the ARIMA model,the per capita food nitrogen footprint of Shanghai increased slowly from 21.95 kg N/a to 23.71kg N/a from 2019 to 2024,which was close to the high nitrogen level of developed countries.The current food consumption pattern in Shanghai is not conducive to the low nitrogen development of food production and consumption system.(2)The total food nitrogen footprint in Shanghai is positively correlated with per capita disposable income and population density,negatively correlated with engel’s coefficient,and weakly correlated with food price index.In addition,according to the Chinese dietary guidelines and the per capita food nitrogen footprint in Shanghai,the residents should increase the intake of vegetarian food including vegetable and fruit,non-staple food including egg and milk,and reduce the intake of high-nitrogen food including grain,meat,and aquatic products to promote balanced nutrition of residents and reduce environmental nitrogen pollution caused by high nitrogen food consumption structure.(3)Based on the material flow model,the research shows that,in terms of farmland production system,the agricultural planting area decreased by about 49.34%from 2000to 2018,and the amount of reactive nitrogen input decreased by about 59.07%.The average amount of reactive nitrogen input per planting area is 457.20 kg N/hm~2,which has an increasing trend in recent years.Atmospheric nitrogen load,which is dominated by ammonia volatilization,is the main form of environmental nitrogen load.This warns that the city still needs to strengthen the management of nitrogen in the farmland production system.In terms of livestock and poultry breeding system,because the government controlled the number of livestock breeding,the amount of reactive nitrogen input decreased by about 73.79%from 2000 to 2018.Water nitrogen load caused by the loss of livestock feces and urine is the main form of environmental nitrogen load in livestock and poultry breeding systems.The nitrogen load per animal increased from 0.19 kg N/p to 0.45 kg N/p.It warns that the city still needs to strengthen the management of nitrogen in livestock excrement and urine.In terms of food consumption system,recently,the food consumption structure of Shanghai residents tends to be highly nitriding and diversified and the total amount of reactive nitrogen input increased by 65.56%.Water nitrogen load in is the main sink of nitrogen discharge in food consumption system and direct discharge of human excrement and urine and tail water are the main link of environmental nitrogen load,so the resource utilization of sewage is the primary task to reduce the environmental nitrogen load of food consumption system in Shanghai.By comparison,the amount of reactive nitrogen input and environmental nitrogen load of the farmland production system are the main sources of the total amount of reactive nitrogen input and environmental nitrogen load of the food production and consumption system in Shanghai.(4)Based on scenario simulation to quantify the contributions of agricultural planting area,population growth,dietary structure,and livestock and poultry breeding quantity on the reactive nitrogen input of food production and consumption system,the contribution rates were found to be-67.43%–-100.14%,1.10–23.52%,-11.34%–12.58%,and-4.70–-23.80%,respectively.In addition,currently,the utilization efficiency of reactive nitrogen and the level of resource utilization in the food production and consumption system in Shanghai are generally higher than the average level in China,but there is still a large development space for the utilization rate of reactive nitrogen in the farmland production system(18.43–27.6%).In addition,by calculating the amount and rate of surplus deficiency food reactive nitrogen of Shanghai,it is found that food consumption mainly depended on foreign input,especially animal food.Therefore,it is urgent for food production and consumption system in Shanghai to improve the utilization rate of reactive nitrogen and ensure food security.(5)By comparing the results of N-calculator and the material flow model,it is found that,the material flow model is more applicable to study the income and expenditure of reactive nitrogen in each link of the food chain system of Shanghai and the N-calculator model is more applicable to study the environmental nitrogen loss caused by food consumption behavior of Shanghai.