Distribution and transport of phosphorus species along with large-scale water diversion project in the Taihu Lake basin of China: Transformation between sediment and water

To date, there remains a lack of comprehensive understanding regarding the impacts of water diversion project on large-scale receiving watersheds. Large-scale water diversions not only introduce external phosphorus but also alter hydrological conditions, leading to the redistribution of phosphorus within the watershed. In this study, the distribution of phosphorus species in sediments and waters was examined in detail through a case study of a water diversion project in the Taihu Lake Basin, China. The concentration of total phosphorus (TP) increased in both surface waters and sediments following the commencement of the project, particularly in surface waters, where it was 1.27 times higher. In terms of spatial distribution, the concentrations of TP in both waters and sediments exhibited a pattern of initial decrease followed by an increase along with the direction of water flow. The highest average TP levels were observed in area A (311.56 μg/L in water and 670.98 mg/kg in sediment, respectively), where water was diverted, due to the introduction of a significant amount of particulate phosphorus (PTP). As the deposition of PTP occurred, the TP concentrations in area B dropping to 222.64 μg/L in water and 523.42 mg/kg in sediment. However, there was an slight increase in colloidal phosphorus (CTP) and dissolved phosphorus (DTP) in area B. Turbidity and conductivity measurements suggested that water transfer may have facilitated the conversion of PTP or slightly disturbed the sediment, leading to the production of CTP and DTP. In area C, where rivers converged, the TP concentrations in water and sediment increased to 313.83 μg/L and 551 mg/kg, respectively. The increased turbidity indicated that the convergence of rivers had a significant impact on the release and redeposition of PTP between sediments and overlying water. This study provided new sights for the dynamic changes of phosphorus species with large-scale water diversion projects.