A Method of Identifying the Critical Source Areas for Phosphorus Loss in Geological Phosphorus-rich Watersheds

Abstract

The principal cause of eutrophication in some freshwater systems is diffuse phosphorus (P) loss. The identification of critical source areas (CSAs) is identified to be the most effective way to minimize the difficulty of nonpoint source (NPS) P pollution management in watersheds. How to efficaciously identify CSAs for phosphorus loss in geological phosphorus-rich (GPR) watersheds is still a challenging hassle. An assessment approach primarily based on QGIS was applied to assess the risk of P loss and identified CSAs for a case study in the Huangbai River watershed of south China, which is a typical geological P-rich (GPR) watershed. In the modified P ranking scheme, total soil P (TP) content in various land use types was used as a source factor; the topographic index (TI) and distance-to-streams were considered as transport factors. P index calculation results showed that 92.2% of the watershed was low risk area, while 7.8% for medium and high risk of P loss. Meanwhile, higher risk areas were associated with the shorter distances from the stream, higher TI, and higher soil P content. Also, CSAs are normally located in phosphate mining sites and concentrated arable land in the karst mountainous areas. The introduction of a simplified P index scheme provides a convenient and practical tool to target CSAs for P loss from GPR areas in data-poor watersheds, thus assisting decision makers to implement remediation actions as to reduce P loss to sensitive waterbodies.