农业流域水-氮循环相互作用机制及其系统均衡模拟

The interaction between water and nitrogen cycles are the most inseparable and complicate, and are critical to understand the laws of nitrogen utilization and loss in agricultural catchment. The agricultural catchment is also the largest contribution area of non-point source pollution. The ecological mechanisms of water and nitrogen cycles in the field ecosystem, and the migration function of water cycle at catchment scale have been further investigated. However, the interaction mechanisms among multi-processes in water and nitrogen cycles should be strengthened, as well as their coupling. This study explored the interaction mechanisms between water and nitrogen cycles at field and basin scales by mechanism experiment, numerical simulation and computer optimization. An integrated water system model of agricultural catchment was developed by treating the water and nitrogen cycles as critical linkages among all the water-related processes, and was applied to well capture the critical hydrological and nitrogen elements in the highly polluted Shaying River Catchment which is the biggest tributary drainage area of Huai River Basin. Finally, the interactions between water and nitrogen cycles were separated and quantified at the field and catchment scales. This study will be expected to promote the multidisciplinary studies on interaction mechanism among the water related processes, to improve the research theory and method of integrated basin water system and to provide reference for the development and application of integrated water system model.

农业流域是水-氮循环相互作用最紧密、最复杂的地区，也是非点源污染最大的贡献区。水-氮循环相互作用机制是认识农业流域氮素利用和流失规律的关键。随着深入认识田间生态系统水-氮循环生态学机理和流域水循环的运移特征等，亟待加强田间和流域尺度水氮循环多过程相互作用机制的探索和耦合。本文结合生态、水文和环境科学等学科研究途径，通过机理实验、数值模拟和计算机优化等多种技术手段，探讨田间和流域不同尺度水-氮循环相互作用机制；以此为基础，以水循环和物质循环为纽带，构建农业流域水-氮循环多过程耦合模拟系统，提出模型多过程均衡率定思路，并应用于淮河支流沙颍河流域水量与不同形态氮素水质均衡模拟中；最终分离和量化水-氮循环相互作用关系。本研究将促进多学科交叉研究，为认识流域与水相关多过程的影响机制提供科学依据；完善流域水系统研究的理论和方法，也为流域水系统模型的研制和应用提供参考和借鉴。

本项目采用室内机理实验、野外长期观测、数值模拟和计算机优化等技术手段，揭示了作物生长影响下水-氮循环相互作用机制，实现了多过程耦合模拟和均衡率定，探明了不同情景下水-氮循环作用非线性规律和贡献量化，并成功用于我国典型农业流域非点源氮素模拟和规律分析。重要成果包括：（1）揭示了田块尺度玉米生长过程中水-氮循环作用机理，以及流域尺度氮素时空变化和土地利用影响，淮河上游流域氨氮和生化需氧量等污染与旱地、城镇用地等关系密切。（2）利用APSIM模型和流域水循环系统模型(HEQM)，构建了室内田块、鄱阳湖实验小流域和沙颍河流域等多尺度作物生长与水-氮循环耦合模型；基于多目标优化算法实现了作物生长与水-氮循环逐过程模拟和均衡率定。APSIM和HEQM均能较好模拟叶面积指数(LAI)和土壤含水量(SW)变化；APSIM对土壤氨氮(NH4+-N)浓度模拟较好，HEQM对土壤硝态氮(NO3--N)浓度模拟较好；微小牺牲LAI和SW模拟效果可明显提高不同形态氮素浓度模拟效果。（3）利用HEQM模型和情景分析，揭示了施肥和灌溉对水-氮循环作用规律及贡献。LAI和SW存在显著负相关关系，SW和不同形态氮素浓度均呈显著非线性关系；灌溉强度增加导致LAI和SW增加，贡献分别为3%和14%；也导致土壤NH4+-N和NO3--N浓度减小，贡献分别为39%和29%；施肥强度是引起土壤氮素浓度变化的直接原因。（4）模型用于探索鄱阳湖实验小流域、淮河、海河和东南沿海流域水-氮流失的区域特征及其对水污染的影响，辨识了区域差异性的主要影响因素。非点源氮素对水污染的贡献已不容忽视，且南方流域明显高于北方流域，地形、环境因子和农业管理方式是影响水-氮流失区域差异的重要因素；退耕还林可减少河道下游的农田和果园面积等，有效降低农业非点源氮流失，改善河流环境。截止目前，已发表学术论文27篇（含SCI 15篇），授权国家发明专利1项和软件著作权5项，超额完成各项考核指标。成果为认识流域水循环多过程的影响机制提供科学依据，也对农业面源污染防治和流域水环境治理等具有重要的现实意义。