Understanding watershed phosphorus source apportionment in mining regions: Insights from five-year data of phosphorus industry

Effective control of phosphorus loss during mining and production activities is key to sustainable management of phosphorus resource, which requires accurate source apportionment in mixed-source watersheds. However, it remains challenging especially in phosphate mining regions, because of a lack of understanding on phosphorus industry wastewater. Based on five-year monitoring data from 30 phosphorus plants (designed capacity>100,000 t/year), we found that phosphorus discharge from phosphorous chemical plants is generally stable as a typical point source. But wastewater discharge from phosphate mining plants exhibits non-point source pollution characteristics, with phosphorus concentration and load significantly increased with discharge volume. Then, we proposed a modified Load Apportionment Model for Phosphorus Industry (LAM-PI) to quantify load contribution of phosphorus industry. By applying it in a typical watershed in the main phosphate mining region, we quantified that wastewater from phosphorus industry (PIW) accounts for 12%-36% of total phosphorus loads in the watershed for different hydrological years. The main contribution (36%-74% of total loads) comes from non-point sources transferred with surface runoff (SR), including agricultural sources as well as phosphorus-rich dust deposition, soil erosion and river resuspension as a result of present and past mining activities. In addition, both PIW and SR loads are higher in high-flow periods, which makes critical periods of <13% total time contributing 82% of the total load. These findings highlight the necessity of emergency management of wastewater during rainstorm events, as well as life-cycle management of phosphorus industry which targets not only wastewater but also dust and solid waste management.