太湖流域氮流特征及其影响机制

Human activities have increased nitrogen input to the terrestrial ecosystem resulted in a series of environmental negative effects. In this study, Taihu area is selected as the research target region. The nitrogen migration characteristics in the agriculture-village of Xinzhuang Town and aquaculture-village of Shajiabang Town are to be compared. The nitrogen input, transfer and output processes in Crop Plant System, Livestock Breeding or aquaculture System and Household Consumption System are considered, respectively. The village-scale nitrogen flow model will be constructed. Therefore, the nitrogen flow flux, efficiency and key control factors in the system of Crop Plant-Livestock Breeding or aquaculture-Household Consumption are identified. Meanwhile, the way of nitrogen loss to the environment including atmosphere and water is discussed. The contribution of nitrogen loss to the environment, characteristics of changes of nitrogen contents with time and space and influence factors are revealed. The statistical method and system dynamics method are used to determine the regulation and control mechanism of nitrogen in Taihu area. The detailed measures are then put forward. This study provides a scientific basis for understanding environmental effects of village-scale nitrogen, improving nitrogen utilization efficiency in each process and reducing nitrogen emissions.

人类活动持续增加陆地生态系统的氮投入，由此引发一系列的环境负效应。本项目以太湖流域为研究靶区，对比研究以农业种植为主的辛庄镇和以水产养殖为主的沙家浜镇氮素迁移特征的差异，充分考虑氮素在农田生产、畜禽/水产养殖和家庭消费过程中的输入、迁移和输出过程，构建乡镇尺度氮流模型，定量分析“农田生产—禽畜/水产养殖—家庭消费”系统氮素梯级流动通量、效率与各过程的关键控制因素，探讨系统环境氮损失途径，揭示各损失途径对环境（大气、水）氮负荷的贡献，氮素在环境介质中的时空变化规律及其影响因素。运用数理统计和系统动力学方法，明确太湖流域活性氮调控机制，并提出针对性的调控对策。本研究为认识乡镇尺度活性氮的环境效应，提高活性氮在梯级流动中各环节的利用效率，降低活性氮排放量提供科学依据。

本项目以太湖流域为研究靶区，构建了乡镇尺度食物系统氮流动模型，分为3个子系统，即作物生产子系统、畜禽养殖子系统和人类食物消费子系统。研究遵循质量平衡原则，计算各子系统氮素输入和输出项的通量和系统氮库变化量。并运用该模型对比研究了辛庄镇等3个乡镇食物系统氮流动通量、效率和时空变化规律。该模型补充了食物系统氮流尺度研究的空缺。采用DPSIR模型评价食物系统及其各子系统从2000年至2018年氮素流动环境负荷及其关键驱动因素。探讨了提高农田生产子系统和畜禽养殖子系统氮素利用率、减少食物浪费、提高循环利用率、优化膳食结构和加强食物系统废弃物处理等情景下降低食物系统氮环境负荷的效应。利用氮代价分析生产单位含氮食品需要投入的氮量。氮素投入强度、动物性食物的需求和食物的对外依存是导致氮素利用效率时间变异的主要因素。分析系统环境氮损失途径，明晰了研究区氮流过程的调控机制。结合太湖水环境氮容量和流域土地利用方式20年来的变化，发现虽然耕地面积逐年减少，畜禽和水产养殖面积也减少，农业面源污染强度居高不下，对水环境氮素来源的贡献率依然超过50%。提高作物生产子系统的氮效率必须降低氮投入强度。在畜禽养殖子系统中，氮利用率与养殖的畜禽种类有关，猪等氮效率低的畜牧在动物食品中所占比例越大，畜禽养殖子系统的氮效率越低，对太湖水环境氮容量的贡献越大。