The changes in total phosphorus (TP) concentration and form in the Three Gorges Reservoir (TGR) from 1998 to 2019 were studied, and P fluxes were calculated. The entire research period was divided into three stages: 1998–2002 (stage I, before the operation of the TGR), 2003–2012 (stage II, as a transitional period), and 2013–2019 (stage III, after the TGR achieved the normal water level of 175 m and Xiangjiaba Reservoir began to operate). Comparative analysis was mainly on Stages I and III. The results show that the concentrations of suspended sediment (SS) in the TGR decreased to a very low level (average 42 mg/L during 2013–2019 period and 96 mg/L in wet season). From 1998 to 2019, the inflow and outflow of sediment amount showed a downward trend. A huge amount of sediment was retained at the bottom of the reservoir during 2003–2012 (average 154.6 million t/a), while in 2013–2019, the amount of sediment deposition significantly decreased and the sedimentation amount was only 37% of that in 2003–2012. Year 2013 marked a turning point in the trend of phosphorus pollution in TGR from increasing to decreasing. Afterwards, concentrations of TP and DP (dissolved phosphorus) showed a significant downward trend. The form of phosphorus in TGR changed from mainly granular to dissolved, and the percentage of DP in TP in the perennial backwater area increased from 39% before TGR formation to 69% during 2017–2019. 2004–2012 was a period with high deposition for TP when the amount of TP entering the reservoir was large and fluctuated vastly between years, and approximately 60% of phosphorus was trapped (82220 t/a). From 2013 to 2019, there occurred significantly decrease in the TP amount entering the reservoir in accompany with diminishing interannual fluctuation, tending to a balance between input and output of P. Fluxes of TP, DP, and PP (particulate phosphorus) all show a pattern of wet season>even season>dry season. The main driving forces for changes in TP concentration, flux, and form are the reduction in SS concentration and phosphorus pollution level.

研究1998—2019年三峡水库磷浓度及形态变化, 并进行通量汇算。研究时段分为3个阶段: 1998—2002年(阶段I, 三峡水库运行之前)、2003—2012年(阶段II, 过渡时期)和2013—2019年(阶段III, 三峡水库实现175 m正常蓄水位, 且金沙江下游段向家坝水库运行后), 以阶段I和III为重点时段进行对比分析。结果表明, 随着三峡成库、水位抬高及金沙江向家坝水库和溪洛渡水库的运行, 三峡水库悬浮泥沙浓度值已降至很低(常年回水区2013—2019年均值为42 mg/L, 丰水期均值为96 mg/L)。22年间, 泥沙入库量和出库量皆呈下降趋势。三峡成库后的2003—2012年, 泥沙淤积量巨大(平均1.546 亿 t/a); 向家坝成库后的2013—2019年, 泥沙淤积大为减少, 淤积量仅为2003—2012年的37%。2013年是三峡库区磷污染程度由加重趋势至减轻趋势的拐点, 之后三峡水库总磷和溶解态磷浓度皆呈显著下降趋势。三峡水库磷的主导形态由颗粒态变为溶解态, 溶解态磷占比由成库前的39%上升为2017—2019年的 69%。2004—2012年是总磷滞留的高峰期, 期间总磷入库量大且年际波动大, 约60%的磷随泥沙发生沉降, 年均滞留量为8.222 万 t/a; 2013—2019年, 总磷入库量大幅度减小且年际波动变小, 入库和出库磷通量趋于平衡。总磷、溶解态磷和颗粒态磷通量均表现为丰水期>平水期>枯水期。河流泥沙总磷浓度与泥沙含量正相关的实质是颗粒态磷浓度与泥沙含量的正相关。总磷浓度、通量和形态发生变化的主要驱动力是泥沙含量下降和磷污染控制。