太湖流域典型土地利用坡面水文土壤过程对氮素流失和排放影响机制

太湖流域丘陵区土地利用从林地向茶果园转变剧烈。土壤水文过程（如土壤水分、地表径流和壤中流）也发生着相应的变化，极大影响着土壤氮生物地球化学循环和迁移过程。在前一个基金中，已充分揭示太湖流域2个具有相似地形但不同土地利用类型（林地和茶园）坡面的土壤水文过程。在此基础上，本研究将在各坡面选取代表典型土壤水文和地形特征的样点5-10个，长期监测土壤水分动态，土壤、渗漏液和地表径流不同形态氮的浓度以及土壤氮氧化物（N2O和NO）的排放速率，揭示不同样点土壤氮流失和排放的特征，构建其与土壤水文过程和环境因子的定量关系。同时，通过构建坡面土壤水动力模型和生物地球化学模型，计算不同土地利用坡面土壤氮流失和排放的通量及其时空分异，识别土壤氮流失和排放热点时间和区域，并评价其风险。本研究将为揭示土壤氮流失和排放的影响机制提供理论依据，并有助于制定靶向性更强的坡面土壤氮流失和排放的调控措施。

The hilly area in Taihu Lake Basin has been encountering extensive land use change from forest to tea and fruit plantation. Along with this land use change, hydropedological processes (e.g., soil water and subsurface flow) also change accordingly, which affects the biogeochemical cycling and transportation of soil nitrogen severely. In my previous NSFC project, the hydropeodogical processes have been revealed comprehensively for two hillslopes with distinct land use types (forest and tea garden) but similar topographic features. In this study, we will select 5-10 monitoring sites on each land use hillslope to represent typical hydropedological and topographic features, regularly sample the soil, surface flow and soil solution to analyze the nitrogen concentrations in different forms, and monitor the emission rates of NOx. Based on this, we will investigate the leaching and emission characteristics of soil nitrogen, and quantitatively reveal the relationships among hydropedological processes, soil nitrogen losses through leaching, surface runoff and emission, and other environmental factors. In the meantime, we will construct the soil hydro-dynamic model and biogeochemical model on these two hillslopes, determine the hot spots and hot moments and evaluate the risks of soil nitrogen losses through leaching, surface runoff and emission. This study will provide theoretical foundation for revealing the controlling mechanisms of soil nitrogen leaching and emission, and will be benefit for designing the more target-orientated regulation policy for controlling hillslope soil nitrogen leaching and emission.