农业活动和水热变化是影响非点源磷污染的主要因素。水热条件的变化和农业开发对流域非点源磷流失的影响日益受到人们的关注。一方面水热条件直接影响流域的水文过程，影响非点源磷流失的迁移转化的过程，另一方面，水热条件会影响农作物的种植范围和耕作管理措施，直接或间接的作用于非点源磷流失过程。国内外有关于流域非点源污染的研究大多从单一的影响因素或者单一的时空尺度出发，大多关注农业开发、气候变化对流域磷污染的影响，而有关于非点源磷流失多影响要素和多时空尺度的系统性分析较少。因此，本研究选取了不同水热条件下以水稻种植为主的四个小流域为研究区，以我国农业发展变化情况为背景，基于SWAT模型模拟，构建了流域尺度非点源磷流失风险评价方法，对不同水热条件下流域非点源磷流失关键源区和流失风险期进行了识别，分析了不同水热条件下流域非点源磷流失特征，最后基于河流出口沉积物中的污染物的垂向分布特征，探究了土地利用变化下沉积物中磷和砷对非点源污染的响应。具体的研究内容如下： （1）基于国家统计局1999-2016年的统计数据，分析了我国不同水热条件下农业活动变化特征及其对非点源磷流失的影响。受水热条件的影响，水稻种植主要集中在我国南方，水稻面积变化与温度和降雨的空间分布显著相关，受温度升高和人类活动东北地区的种植面积呈现显著的增长趋势。我国多年平均农田磷肥投入量约为123.4kg/ha，农田磷肥输入的主要来源是化肥和有机肥，在黑龙江省、江西省和广东省化肥施用量的变化与水稻种植面积的变化显著相关。 （2）基于SWAT模型，构建了流域非点源磷流失风险评价方法体系，阿布胶河流域流域和溪河流域大部分区域为轻度污染风险区和中度污染风险区，小府河流域和白陆港流域大部分区域为轻度污染风险区和潜在污染风险区。不同土地利用下旱田非点源磷流失风险>水田>居民用地、草地和林地。受降雨和冻融的影响，阿布胶河流域非点源磷流失风险期主要集中在3月到8月；南方水热条件充足，非点源流失风险与降雨的分布一致，主要集中在春季和夏季。不同气象代表年下各流域和污染风险特征整体表现为润寒年>平年>旱热年，表明降雨量越大非点源磷污染风险越高。阿布胶河流域不同气象代表年下磷污染风险的差异小于其他三个流域，表明水热条件充足的地区，降雨和温度波动变化对流域非点源污染风险的影响越大。 （3）基于SWAT模型探究了不同水热条件下流域非点源磷流失特征。受降雨和冻融的影响阿布胶河流域地表径流深、侵蚀模数和非点源磷流失呈双峰的变化特征，其他流域受降雨和农业施肥的影响，非点源磷流失呈单峰变化特征；不同水热条件下，磷的流失形态主要以颗粒态无机磷为主，降雨量较高的地区其可溶性有机磷流失的量占比较大，且主要发生在夏季；不同土地利用类型下总磷的流失特征与土壤侵蚀的特征相似，旱田非点源磷流失负荷>水田>林地和湿地。相关分析表明流域总磷流失负荷均与地表径流、土壤侵蚀具有较高相关性，水热条件比较充沛流域降雨和总磷负荷的相关性较高。冗余分析表明降雨量和旱田面积的变化与非点源总磷流失相关性较强，旱田面积的变化与非点源磷流失呈现显著的线性相关性，水田和林地面积变化与非点源总磷流失呈负相关关系。 （4）利用沉积物210Pb同位素定年技术开展了不同水热条件下沉积物中污染物浓度变化的驱动力分析。受农业扩张的影响，阿布胶河流域沉积物中总磷的浓度随着深度的减少总体呈现显著的增长趋势。沉积物中磷和砷浓度的变化具有显著的线性相关性。RDA分析表明水热变化对沉积物中砷浓度的影响大于对磷浓度的影响，沉积物中磷浓度的变化主要与土地利用变化以及水土流失有关。旱田的扩张与沉积物中总磷的变化呈正相关关系，水田和林地面积变化和沉积物中磷的浓度为负相关关系主要是由于旱田的非点源磷流失风险相对较高。

Agricultural activities and hydro-thermal changes are the main factors affecting diffuse phosphorus pollution. The impact of changes in hydro-thermal conditions, agricultural development and agricultural management practices on the diffuse phosphorus loss at watershed scale have received increasing attention. On the one hand, diffuse conditions directly affect the watershed hydrological process, and the migration and transformation of diffuse phosphorus loss. On the other hand, hydro-thermal conditions also affect the crop planting range and agricultural management practices, and then directly or indirectly affect the process of diffuse phosphorus loss. In this study, four small watersheds under different hydro-thermal conditions, which were all mainly dominant by rice cultivation, were selected as research areas. Based on the changes of agricultural development in China and Soil and Water Assessment Tool (SWAT) model, a new risk assessment method for diffuse phosphorus loss at watershed scale was constructed. The critical source areas and risk periods of diffuse phosphorus loss in different hydro-thermal conditions were identified. Finally, the vertical distribution characteristics of the pollutants in the sediments of river outlets were analyzed to investigate the response of sediments to diffuse phosphorus pollution under the influence of land-use changes and agricultural management measures. The specific research contents are as follows: (1) Based on the statistical data of the National Bureau of Statistics from 1999 to 2016, the effects of agricultural activities on the diffuse phosphorus loss under different hydro-thermal conditions were analyzed. Under the influence of hydro-thermal conditions, rice cultivation was mainly concentrated in southern China. The change of rice planting area is significantly correlated with the spatial distribution of temperature and rainfall. The planting area of rice in Northeast China is significantly increased due to temperature increase and human activities. The annual average phosphate fertilizer input to farmland was about 123.4kg/ha, which mainly concentrated in the North China and Northwest China. The main sources of phosphorus fertilizer input were chemical fertilizer and organic fertilizer. (2) Based on the SWAT model, a new risk assessment method for diffuse phosphorus loss was constructed. Most areas of the ABJ and XH watershed were light and moderate pollution risk, most areas of the XFH and BLG watershed were light and potential pollution risk. Risk of diffuse phosphorus loss under different land use was upland > paddy > residential land, grassland and forest. Affected by rainfall and freezing and thawing, the risk of diffuse phosphorus loss in the ABJ is mainly concentrated from March to August; influenced by the hydrothermal conditions in the south, and the risk of diffuse phosphorus loss is consistent in spring and summer. In different meteorological year, the risk of diffuse phosphorus loss in wet cold year is the highest, followed by normal year and dry year, indicating that the greater the rainfall, the higher the risk. The difference in phosphorus risk among different meteorological year in ABJ is smaller than that in the other three watersheds, indicating that the temperature and rainfall has greater impact on the risk of non-point source pollution in the areas with sufficient hydrothermal conditions. (3) Based on the SWAT model, the characteristics of diffuse phosphorus loss in different hydro-thermal conditions were investigated. The surface runoff, erosion modulus and diffuse phosphorus loss in the ABJ watershed were characterized by double peaks under the influence of rainfall and the freezing-thawing process. The phosphorus losses of other watersheds were characterized by a single peak under the influence of rainfall and fertilization. The phosphorus loss was mainly composed of particulate inorganic phosphorus. The percentage of soluble organic phosphorus was relatively larger in south China. Under different land use types, the diffuse phosphorus loadings in upland > paddy > forest and wetland. Correlation analysis showed that the TP loading was highly correlated with surface runoff and soil erosion, especially in higher hydro-thermal areas. Redundant analysis showed that the changes of rainfall and upland were strongly correlated with diffuse phosphorus loss. The change of paddy and forest area and diffuse total phosphorus loss were negatively correlated. (4) Using the 210Pb isotope dating technique of sediments, the driving force analysis of pollutant in sediments under different hydro-thermal conditions was analyzed. The concentration of total phosphorus in the river sediments of the ABJ watershed showed a significant increased trend with decreasing depth. Phosphorus and arsenic in sediments showed a significant linear correlation. RDA analysis showed that the effect of hydro-thermal changes on the concentration of arsenic in sediments was greater than that on phosphorus concentration. The change of phosphorus concentration in sediments was mainly related to land-use changes and soil erosion. The expansion of upland was positively correlated with the change of total phosphorus in sediments. The negative correlation between the change of paddy and forest and the concentration of phosphorus in sediments was mainly due to the relatively high risk of diffuse phosphorus loss in upland.