北运河上游非点源污染风险空间分布特征研究

非点源污染是流域水环境污染的重要原因之一，非点源污染风险分区是有效治理水污染的重要前提.本文采用指数函数法改进潜在非点源污染指数（Potential Non-Point Pollution Index，PNPI）模型基于专家评价法主观赋权的不足，并采用改进后的PNPI模型解析北运河上游流域非点源污染风险空间分布特征.结果表明：①指数函数法通过构建土地利用指标、径流指标和距离指标的指数函数描述污染源因子与运输因子之间的关系，能够直观反映研究区内非点源污染风险的空间分布特征；②研究区2017年非点源污染风险呈现出东南高西北低的空间分布特征，极低、低、中等、高和极高风险区面积占比分别为52.4%、0.5%、12.4%、25.1%和9.6%；③研究区非点源污染极高风险区主要集中在人口密集的东南平原区河道两侧，主要土地利用方式为城镇用地；极低风险区则主要分布在人口稀疏且距离河道较远的西北山区，主要土地利用方式为有林地.PNPI模型模拟结果可为北运河上游流域非点源污染防治和生态清洁小流域分区治理提供科学参考.

Spatial distribution of non-point source pollution risk in the upper Beiyun River Watershed

Non-point source pollution is the one of the major causes of water pollution, and its risk zoning is the essential prerequisite for effective control of water pollution. In this study, the Exponential Function Method (EFM) was employed to avoid the problem associated with the subjective evaluation in the Potential Non-Point Pollution Index (PNPI) model, and the revised PNPI was applied to simulate the spatial distribution of non-point source pollution risk in the upper Beiyun River Watershed. The results show that the EFM, which uses the exponential function among land use, runoff, and distance indicators to quantitatively describes the relationship between non-point pollution source and transportation factors, can effectively simulate the spatial distribution of non-point source pollution risk in the upper Beiyun River Watershed. The non-point source pollution risk is high in the southeast and low in the northwest of the watershed. The proportions of areas with extremely low, low, medium, high, and extremely high risk are 52.4%, 0.5%, 12.4%, 25.1%, and 9.6%, respectively. The areas with extremely high risk are mainly distributed in the densely populated regions along both sides of the rivers in the southeast plain where the main land use type is urbanized land, while the areas with extremely low risk are located in the northwest mountainous regions covered with forests and far away from the rivers. Those results could provide scientific reference for the integrated watershed management as well as the ecological clean small watershed construction projects in the upper Beiyun River Watershed.