【作者】 刘昱；

【导师】 陈吉宁； 王灿；

【作者基本信息】 清华大学 ， 环境科学与工程， 2016， 博士

【摘要】 农业是中国的基础产业。大力发展农业经济以适应粮食需求长期以来一直是中国农业的首要发展目标;与此同时,随着农业集约化发展,农业温室气体排放和面源污染日益增加,农业已成为最重要的污染源之一,中国农业面临着粮食安全与环境污染的双重压力。因此,如何有效地考察重要元素在农业生态系统中的流动,直观地识别污染途径和污染源,定量评估中国农业生态系统污染排放,是亟需解决的科学问题和技术难点。本研究旨在通过构建适合中国农业生态系统特征的碳氮循环平衡模型,为农业污染评估及推行低碳、绿色农业发展策略提供参考与技术支撑。本论文基于物质平衡原理,以中国农业生态系统为研究对象,在中国农业生态系统氮流动模型的基础上构建了农业生态系统碳氮平衡模型。利用该模型,本论文模拟了中国农业生态系统在1980、1990、2000、2010和2013年5个选定年份内各子系统的碳氮输入量与输出量等碳氮循环流通指标,系统地识别了影响碳氮流动的关键途径与机制,考察了主要污染源及污染强度,分析了农业生态系统碳氮循环长期动态变化特征。同时,利用现有农业数据与模拟估算结果,对农田子系统的碳氮耦合关系进行了探索与研究。在此基础上,本论文进一步对现行的中国农业污染控制政策进行了情景分析,探讨了不同情景下农业生态系统碳氮盈亏及污染物排放状况以判断政策执行效果。研究结果表明,在研究时段内中国农业生态系统始终表现为碳亏损和氮盈余;植物光合作用固碳和化肥施用分别是是碳氮输入最主要的来源;最主要的碳输出途径为作物呼吸与土壤呼吸,约有80%以上的碳通过呼吸作用排放进入大气环境;氨挥发损失、硝化反硝化作用损失以及地下水淋失是最主要的氮输出途径。耦合关系拟合结果显示,水田和旱地的大气碳氮排放量之间、土壤碳氮输入量之间均存在显著正相关关系;水田和旱地的耕层土壤碳氮比与作物单位面积光合作用碳吸收量之间、与作物单位面积呼吸作用碳排放量之间均呈负相关关系。对选定政策的定量模拟分析表明,杜绝秸秆露天焚烧及用作燃料燃烧可直接有效地控制碳氮的大气排放;增加秸秆和畜禽粪尿还田比例的同时,优先选择秸秆用作饲料而非生物能源,可有效降低整个农业生态系统的净碳亏损量。更多还原

【Abstract】 As one of the basic industries of China,the primary objective and task of agriculture has long been developing the agriculture economy to meet the ever growing demand for food.Compounding this challenge,agriculture is now a dominant source of many environmental threats,including greenhouse gas emission,water pollution and degradation of land.Under the dual pressures of food security and environmental pollution,modern agriculture is facing great challenges in production engineering and development model.As agro-ecosystem is an open and complex system,efficient techniques of examining chemical element flows,identifying pollution avenues and sources as well as quantifying emissions of pollutants are the major scientific and technical issues to be addressed.Therefore,in order to analyze the properties of China’s agro-ecosystem and reveal the disturbance of agricultural activities on the natural recycling of carbon and nitrogen,this study aimed to establish carbon and nitrogen balance models adapted to the characteristics of China’s agriculture.Besides,the models can also provide reference and technical support for assessing various sources of agricultural pollution and developing low-pollution agriculture.According to the material balance theory,this study established national-scaled carbon and nitrogen balance models for China’s agro-ecosystem based on the material flow method and the main carbon/nitrogen cycling processes.With the models,this study simulated inputs and outputs of carbon and nitrogen in China’s agro-ecosystem in 1980,1990,2000,2010 and 2013,identified the key pathways and mechanisms regulating carbon and nitrogen cycles,investigated primary agricultural pollution sources and intensities,and analyzed characteristics of long-term dynamic variation of agroecosystem carbon and nitrogen cycles.In the meantime,with available agricultural data and model estimates,this study also sought to identify the coupling relationships of carbon and nitrogen in farmland ecosystem.On this basis,this study further analyzed the policies of China’s agricultural pollution control and discussed the surplus/deficit of carbon and nitrogen as well as the pollutant emissions under different designed scenarios so as to evaluate the effectiveness of such policies.Results showed that: China’s agro-ecosystem represented as carbon deficit and nitrogen surplus in all five selected years;the main input source of carbon was by photosynthesis of plants while chemical fertilizer brought most nitrogen into the agroecosystem;the main ways of carbon emission were plant respiration and soil respiration,as more than 80% of agricultural carbon was emitted into the atmospheric environment through respiration;ammonification,nitrification/denitrification and groundwater leaching were the main output ways of nitrogen.The results of coupling research revealed the positive correlations between atmosphere/soil carbon and nitrogen input amounts as well as output amounts of farmland ecosystem,and the negative correlations between carbon fixation by photosynthesis/carbon emission by respiration per unit of crop area and the carbon-nitrogen ratio in soil plough layer respectively.Quantitative simulation and analysis of selected policies shows that avoiding burning straw in the open air and using straw as fuel can directly control carbon and nitrogen emissions;raising the proportion of straw and livestock manure that is returned to the field as well as using straw as feed rather than as biofuel can effectively reduce the net carbon deficit of agro-ecosystem.更多还原