九龙江流域河流磷输出对土地利用模式及水文状况的响应

本研究应用现场监测、地理信息技术（GIS）、模型模拟和数理统计等方法，基于2015年3月至2017年2月九龙江流域不同主导土地利用类型源头小流域和两条干流河流表层水总磷（TP）、总溶解态磷（TDP）和颗粒态磷（PP）的浓度监测，探究河流磷浓度与输出负荷的时空变化特征，揭示九龙江流域磷输出对土地利用模式及水文状况的响应.结果发现，九龙江流域河流磷浓度和磷输出负荷具有明显的时空变异性.在空间上，农业流域 > 城市流域 > 自然流域，西溪>北溪.在季节上，不同类型流域不同形态磷浓度总体表现为春、冬季节较高，而夏、秋季节较低.TP、TDP、和PP输出负荷春、夏季高于秋、冬季，与径流深度的变化趋势基本一致.磷浓度、输出负荷与林地和裸地面积百分比呈负相关关系，与耕地、果园面积百分比呈正相关关系.但不同季节，磷浓度和输出负荷对土地利用和水文状况的响应存在差异，在夏季的相关性最强.结果表明农业非点源污染是九龙江流域河流磷的关键源，提升林地比例有助于保持水土，改善河流水质，尤其在雨季.

Responses of Riverine Phosphorus Exports to Land Use and Hydrological Regime in the Jiulong River Watershed

In-situ monitoring, geographic information technology (GIS), watershed model, and statistical techniques were coupled in this study to explore the responses of riverine phosphorus exports to land use pattern and hydrological regime in the Jiulong River Watershed (JRW). We analyzed riverine phosphorus concentrations and exports from March 2015 to February 2017 across a land use gradient spanning 14 monitored sampling sites. Results showed that significantly spatial and seasonal variations of phosphorus concentrations and exports were observed in JRW. Mean phosphorus concentrations and exports were the highest in the agricultural watershed, followed by the urban watershed, whereas the West River reach had higher mean phosphorus concentration and export than the North River reach. Mean concentrations of phosphorus were higher in spring and winter, whereas lower concentrations were observed in autumn and summer. Phosphorus exports were higher in spring and summer, consistent with the seasonal trend of runoff. Phosphorus concentrations and exports had negative correlations with percentages of forest and bare land, and were positively correlated with cropland and orchard. The responses of riverine phosphorus to land use types and hydrological regime varied across seasons, whereas the relationships between phosphorus concentrations/exports and land use or runoff were the strongest in summer, suggesting that non-point source pollution associated with agricultural activities would be the critical source of riverine phosphorus and an increase in forest percentage could be useful for improving water quality. Overall, the spatiotemporal patterns of phosphorus exports were affected by land use pattern, as well as the characteristics of the hydrological regime.