鄱阳湖典型入湖流域农业非点源氮素流失机制解析与时空分异模拟

Diffuse nitrogen losses is one of the major causes for surface water and groundwater nitrate pollution. In this study, we select Ganjiang catchment as study site, which is an major inflow catchment of Poyang lake. Long-term monitoring of soil water content, nitrogen concentrations in surface runoff and soil solution will be conducted at field scale under representative land use (forest, dry field, rice field and grassland). A physically based nitrogen leaching model LEACHN will be used to simulate water movement, nitrogen transport and transformation at typical fields. Denitrification in soil will be investigated using laboratory incubation experiments to determine the degradation rates. Using up-scaling approach, results from monitoring, experiments and modeling of nitrogen leaching and transformation will be used to set up a spatially distributed hydrological model HYPE, to simulate nitrogen transport and transformation at the study catchment. Based on global parameter sensitivity analysis, a Bayesian inference and Markov Chain Monte Carlo random sampling algorithm will be used for multi-objective parameter calibration and uncertainty analysis. The temporal and spatial variations of nitrogen fluxes will be simulated. Critical area and time of nitrogen losses will be identified. Based on scenario analysis, the impacts of changes in climate and land use on catchment nitrogen losses will be estimated, the effects of agricultural management practices on reduction of nitrogen fluxes will be assessed. The outcomes of this study may give insights into diffuse nitrogen transport and transformation regimes, support decision making on management and control of catchment nitrogen pollution.

非点源氮素流失是导致地表水和地下水硝酸盐污染的主要原因之一。本课题选择鄱阳湖典型入湖流域—赣江流域作为研究区，长期监测地块尺度代表性土地利用（林地、旱地、水田、草地）土壤水分动态、地表径流和渗漏液中各形态氮素浓度，构建氮素迁移转化模型LEACHN，开展土壤反硝化培养实验，综合揭示土壤氮素流失与转化机制；采用空间尺度拓展方法，依据地块氮素流失与转化实验监测及数值模拟，构建流域分布式氮素输移转化模型耦合HYPE，开展参数全局敏感性分析和基于贝叶斯理论与随机采样的多目标参数率定与不确定性分析，实现流域非点源氮素流失时空分异的精准模拟，揭示氮素流失的热点区域、时间及主控环境因子；基于情景分析，预测气候变化和土地利用改变对流域氮素流失的影响，评价农业管理措施对流域氮素污染负荷的削减效果。本研究将为揭示流域非点源氮素流失和转化的影响机制提供理论依据，为制定靶向性的流域氮素污染综合管控措施提供科学支撑。

流域非点源营养盐流失是导致地表水和地下水氮磷污染的主要原因之一。本项目选择鄱阳湖典型入湖流域——赣江流域及其代表性子流域（宜丰河流域）作为研究区，基于长期气象水文和水质观测数据，构建基于过程的流域水文与氮磷输移耦合模型HYPE，通过参数敏感性分析识别影响流域径流和氮磷输出的关键水文、生物地球化学过程及相应敏感参数；基于观测数据和模型模拟结果分析水质和氮磷输出的时空变化及其与流域特征的关系；借助于情景分析评估气候变化和农业化肥使用对流域氮输出的影响。结果表明：（1）HYPE模型能很好地模拟具有不同气象和自然地理特征流域的河流流量动态，径流量与降水量呈显著正相关；（2）模型能够捕捉氮磷负荷的年际、季节变化，氮磷输出主要发生在降雨径流集中的丰水期（3-8月）；（3）无机氮输出主要受化肥使用速率和土壤与河网反硝化过程控制，磷输出主要受地表径流侵蚀、土壤中磷吸附/解吸附过程控制，枯水期点源输入对河流总磷浓度影响很大；（4）过去20年间宜丰河流域城镇用地面积增加，化肥使用量显著上升，且与河流硝态氮浓度呈显著正相关；（5）在中、高排放情景下流域无机氮负荷将增加，降低化肥使用速率有助于减少流域氮输出。研究成果有助于加深对亚热带湿润区流域氮磷输移过程的认识，对制定流域面源污染防治措施具有一定的科学参考价值。