平原河网地区缓冲带植物-土壤系统水动力过程及氮素运移试验研究

With the densely covered farmlands and rivers in plain river network region, the emission of agricultural runoff pollution causes serious damage to water environment quality. Buffer strip, as the most economical and efficient approach to controlling agricultural runoff pollution, has caused great concern both at home and abroad. However, the study on the hydrodynamic process and the nitrogen transfer of its plant-soil system is very weak. In this paper, stable isotope tracer and δ18O, δ2H and δ15N fractionation effect variance analysis were used to explore lateral and vertical hydrologic connectivity and dynamic process of plant-soil system under buffer strip. Buffer surface runoff, soil retention, infiltration and transpiration water allocation was quantified, and runoff nitrogen in plants-soil system of dynamic migration transformation rule was revealed as well. Combining with plant roots growth, leaf transpiration and other physiological and ecological indexes and spatial and temporal dynamic synchronous observation of soil physical and chemical properties, the mechanism and key parameters impacting on hydrodynamic change and nitrogen transformation and transportation were managed. According to this, nitrogen migration model of plants-soil system in buffer strip was built to simulate the changing process of nitrogen transfer dynamically under different spatial and temporal scales and provide theoretical foundation for the nitrogen pollution control of the agricultural runoff in plain river network and the design and construction of the water-green corridor.

平原河网地区农田、河流交错密布，农田径流污染排放严重危害水环境质量。缓冲带作为控制农田径流污染最为经济、有效的手段已引起国内外的高度关注，然而其植物-土壤系统的水动力过程和氮素运移研究十分薄弱。本研究通过室内外试验、稳定同位素示踪和δ18O、δ2H、δ15N分馏效应差异分析相结合的方法，探究缓冲带作用下植物-土壤系统的横向、垂向水力联系及动态运移过程，定量描述缓冲带地表产流、土壤滞留、入渗补给和植物蒸腾等水分分配，揭示径流氮素在植物-土壤系统中的动态迁移转化规律。结合植物根系生长发育、叶片蒸腾等生理生态指标和土壤理化性质的时空动态同步观测，掌握影响缓冲带水动力变化和氮素迁移转化的机制和关键参数，并依此建立缓冲带植物-土壤系统氮素迁移归趋模型，动态模拟氮素迁移的时空变化过程，为平原河网地区农田径流氮污染控制及河流水绿廊道的设计、建设提供理论依据。

平原河网地区农田、河流交错密布，农田径流污染排放严重危害水环境质量。缓冲带作为控制农田径流污染最为经济、有效的手段已引起国内外的高度关注，然而其植物-土壤系统的水动力过程和氮素运移研究较为薄弱。本项目通过室内外试验、稳定同位素检测分析、模型模拟等技术手段，开展了平原河网地区缓冲带植物-土壤系统水动力及氮素运移的试验研究。具体为：（1）通过实验室同位素检测及试验基地跟踪试验观测，获取了不同植物缓冲带植物生理生态、土壤和空气微环境以及土壤-植物-径流渗流δ18O和δ2D同位素丰度等数据，分析回答了缓冲带土壤-植物系统水量分配、水分运移及其影响机制。（2）利用实验室受控环境及试验基地现场试验，研究了缓冲带植物土壤系统植物-土壤-渗流的δ18O和δ15N同位素丰度及氮素示踪来源，探明了不同植物缓冲带氮素污染负荷削减能力，并揭示了影响氮素削减及运移的机制及驱动因素。（3）基于不同降雨强度、植物类型、土壤性状等参数观测数据，构建了平原河网地区缓冲带植物-土壤系统水动力及氮素迁移归趋模型，结合典型平原河网地区青浦区河流缓冲带的空间格局和解译分析结果，模拟预测了不同降雨条件下缓冲带产流、氮素迁移的时空变化过程，提出了河流水-绿廊道建设优化调控建议，分析了缓冲带建设生态效益。以上研究成果可为平原河网地区农田径流氮污染控制及河流水绿廊道的设计、建设提供理论依据。