• Fertilizer and rainfall are key factors affecting phosphorus levels in the basin. • Phosphorus enrichment in the lower basin is driven by anthropogenic activities. • Watershed slope influences riverine phosphorus level. • Quantitative regression effectively simulated TP across regions and seasons. Total phosphorus (TP) pollution poses a persistent threat to the surface water environment and ecological protection in large-scale basins. However, the recent seasonal and regional differences and driving factors of TP levels in large-scale basins under the influence of high-intensity anthropogenic activities remain unclear. In this study, the seasonal and regional variations of TP concentrations in the Yangtze River Basin from 2021 to 2023 were analyzed. Combined with water quality, meteorology, topography, anthropogenic parameters, main sources and driving factors of TP were identified, and TP regression models were constructed. The results showed that TP levels were generally higher in wet seasons and lower in dry seasons and exhibited an increasing trend from upstream to downstream areas. The average TP concentrations in the entire river basin were 0.078, 0.066, and 0.061 mg/L in wet, flat and dry seasons, respectively, and 0.06, 0.063, and 0.084 mg/L in upstream, midstream and downstream areas, respectively. The partial least squares regression (PLSR) model of TP established for the flat season in the upstream area had the best testing performance ( R 2 = 0.486, MAE = 0.026 mg/L, RMSE = 0.035 mg/L, NRMSE = 10.56 %). Correlation analysis, principal component analysis (PCA), and quantitative regression analysis showed that nitrogen, dissolved oxygen, temperature, slope and anthropogenic activities influenced the regional and seasonal differences in TP. Phosphate fertilizer, phosphorus-related industry and domestic sewage were main sources of phosphorus. This study can provide reliable support for targeted management of phosphorus pollution in large-scale basins and regional water ecology protection.
Dai et al. (Sun,) studied this question.