Sources, pathways, and impacts of phosphorus loss in geologically phosphorus-rich areas: A case study of Dianchi Lake, China

Phosphorus migration and loss in geologically phosphorus-rich (GPR) areas significantly contribute to water eutrophication. This study comprehensively investigated phosphorus distribution across various environmental media (surface water, groundwater, atmospheric deposition, soils, and sediments) in the Gucheng River watershed and Dianchi Lake, Yunnan Province, China. It also analyzed phosphorus speciation in phosphate-containing solids (raw soil, waste soil, phosphate ore, and phosphogypsum), and quantified the phosphorus release characteristics of phosphate ore and phosphogypsum under simulated conditions. Results indicated that total phosphorus (TP) concentrations in surface water and atmospheric deposition flux in the upstream phosphate processing area were significantly higher (>1.5-fold) than in phosphate mining and agricultural areas. Conversely, TP in groundwater and soil were highest in agricultural areas. Sediment TP in the Gucheng River was 3.43 times higher than in Dianchi Lake, with sediment phosphorus in Dianchi Lake predominantly existed in calcium-bound forms, accounting for 46.64 %, similar to that of Gucheng River. Phosphogypsum contained 45.21 % weakly adsorbed phosphorus and showed over 15 times higher potential phosphorus release than other solids. During simulated rainstorms, phosphorus from phosphate ore was predominantly lost via runoff, while phosphorus from phosphogypsum was released primarily via leaching. Runoff and leachate from improperly managed phosphogypsum during rainfall were significant phosphorus sources to Dianchi Lake, and a soil cover reduced TP in runoff and leachate by 65 %. This study highlights a greater and more persistent eutrophication risk of phosphate processing activities compared to mining, providing valuable insights for risk management in GPR areas globally.