Improving river water quality by identifying risk paths and critical source areas of non-point source pollution at watershed scale

Optimizing landscape pattern is an effective way to improve river water quality at the watershed scale. Identifying the risk pathways and key source areas of pollutants entering rivers is essential for mitigating non-point source pollution (NPSP). This study used the minimum cumulative resistance (MCR) model to identify the risk of NPSP in a highly urbanized watershed. The results showed that the very high and high risk levels accounted for 64% of the watershed. The distribution range of the risk paths of different types of critical source areas (CSAs) was farmland > tea garden > residential land, and the pollution intensity was in the order of residential land > farmland > tea garden. The risk paths in farmland had the widest distribution, whereas those in residential land were the most likely to cause river pollution. The core control distance was 0.4–0.6 km in the mountainous areas and 1.2–1.4 km in the plain areas. Reducing human activities within the core control distance can effectively mitigate the pollutants. Best management practices for risk paths to reduce the possibility of pollutants entering the river were proposed. This study provides a comprehensive and practical framework for identifying and managing NPSP risk.