Study On The Cascade Flow Efficiency And Mechanism Of Reactive Nitrogen At The Township Scale In Changshu Area

With the changes of national diet and the acceleration of urbanization and industrialization,food production process has become a main source of reactive nitrogen(Nr).To ensure food production,appropriate Nr supply is necessary.Whereas,a sharp increase in nitrogen flow flux is one of the causes of global ecological problems.In order to achieve our goals of the sustainable development of society and economy,improving the quality of environment and assume international obligations to mitigate climate change,it is urgent for us to understand the environmental effect of Nr,improve the use efficiency of Nr in the cascade flow and reduce the emissions of Nr.In this study,Xinzhuang Town,Changshu City in Jiangsu province was selected as the research target.The sources,fluxes and use efficiencies of Nr in each cascade were compared.The environmental Nr loads of "crop production-livestock breeding-household consumption" system were quantitatively analyzed.The regularity and characteristics of nitrogen cascade at rural scale of Changshu City were identified.Therefore some corresponding measures were proposed in this study.The main results are as follows:(1)The flux of Nr flow in the food chain was decreasing step by step.The use efficiency and recycling rate of Nr in the nitrogen cascade were lower than 20%.The resource and environment cost of food consumption was high.From 2000 to 2012,under the influence of crop planting structure,the degree of production intensification,the level of urbanization and dietary structure,the change trend of Nr flow flux of three subsystems in the food chain of Xinzhuang Town was shown in the following aspects.Crop production subsystem showed a downward trend.Livestock breeding and household consumption subsystems showed a slight upward trend.(2)The environmental nitrogen load of nitrogen cascade in the food chain of Xinzhuang Town was higher than 50%.The environmental nitrogen load was mainly from crop production and 54.1%±2.1%of which entered into water.The result of sensitivity analysis of nitrogen load variables in environmental media showed that,crop planting area and the level of nitrogen application were the common influencing factors of nitrogen load in all the environmental media.The nitrogen load of atmosphere,water and soil included ammonia volatilization rate and volatilization rate of animal excreta,runoff and leaching rate,and denitrification rate,respectively.There was an inverse U-shaped curve between per capita GDP and environmental nitrogen load.The per capita of the environmental nitrogen load in Xinzhuang Town was 11.9 kgN/person,which was lower than the average value of our country(31.5 kgN/person).The unit area of the environmental nitrogen load in Xinzhuang Town was 8.7 tN/km2,which was higher than the average value of our country(4.3 tN/km2).(3)The nitrogen use efficiency and recycling rate in Xinzhuang Town were low.The evaluation result of the nitrogen flow efficiency in the food chain indicated that the comprehensive evaluation value showed a declining trend in recent years(from 0.70 to 0.41).The main reasons were that the level of nitrogen fertilizer application was high,the recycling rate of waste nitrogen was low,and the quantity of animal nitrogen in food consumption of the residents was increasing.There was a certain difference in the trend of the evaluation value of the nitrogen flow efficiency of the three subsystems.Crop production subsystem showed a slight upward trend,livestock breeding subsystem showed a significant increase trend,and household consumption subsystem showed a rapid decline since 2008.(4)Based on the studies of characteristics,environmental nitrogen load and efficiency evaluation of nitrogen cascade,four strategies of Nr regulation were proposed:①Adjusting the structure of planting and breeding,improving the cascade utilization rates of Nr.②Advocating the recycling utilization of waste,improving the recycling rate of nitrogen.③Adjusting dietary structure,planning table,advocating"clear your plate" campaign.④Improving management technology,formulating policies and regulations.