乌江汇入对三峡水库局部水体中磷质量浓度的影响

乌江水体中总磷与三峡水库相关水域存在差异。通过对相关水体中磷质量浓度变化特征的分析，结果表明：2008年前乌江TP显著低于三峡水库相关水域，其汇入对后者主要表现为“稀释”作用，可使清溪场断面TP年均值最大降低约0.02 mg·L⁻¹；2009年后乌江TP急剧升高，其汇入后清溪场断面2009—2013年TP年均值最大升高约0.057 mg·L⁻¹；2014年后乌江汇入基本不会使清溪场断面TP年均值明显改变；1998—2006年乌江TDP与三峡水库相关水域相近，乌江汇入对清溪场断面TDP年均值基本无影响；之后乌江TDP快速上升，2007—2013年乌江汇入最大可使清溪场断面TDP年均值升高约0.061 mg·L⁻¹；2014年后乌江TDP大幅回落，其对水库影响降低，最大可使清溪场断面TDP年均值升高约0.008 mg·L⁻¹；乌江汇入对三峡水库局部水体磷质量浓度的影响在不同时段其程度、趋势均不一致；乌江干流水电建设导致的水文条件变化和乌江上游区域磷矿开发过程中含磷废水排放使得乌江水体中磷质量浓度发生改变，进而间接、持续对三峡水库局部水体中磷质量浓度产生影响。该研究结果可为三峡水库的水生态环境监管提供参考。

The impact of inflow of Wujiang River on phosphorus concentrations of local reach of the mainstream of Three Gorges Reservoir

The total phosphorus concentration (TP) in the Wujiang River was different from that in the mainstream of the Three Gorges Reservoir (TGR) on the Yangtze River. The analysis on the characteristics of phosphorus concentration changes in related water areas indicates that: In 1998 – 2008, the average concentration of TP in the Wujiang River was significantly lower than that in the reach of TGR mainstream near the Wujiang mouth (here namely QXC reach), and the inflow of the Wujiang River had a dilution function on TP in QXC reach, which reduced the average TP at Qingxichang section (QXC) (~10 km downstream from the mouth) by 0.01 mg·L−1. However, in 2009 – 2013, extremely high TP in Wujiang River resulted in significant rise of TP at QXC with 0.057 mg/L as the highest among the annual average increments. In 2014 – 2019, the difference between two rivers near the mouth was not significant, and the impact of Wujiang on TP in QXC reach was negligible. In 1998 – 2006, The average concentration of TDP (the dissolved part of TP) in the Wujiang River was close to that in QXC reach, and the inflow of Wujiang had little impact on TDP in QXC reach. Subsequently, TDP in Wujiang River rose sharply, and the inflow resulted in marked increase of TDP at QXC section with 0.061 mg·L−1 as the highest. After 2013, the TDP in the Wujiang River dramatically declined, and its impact on TDP in QXC reach weakened, and the increments of the annual average TDP at QXC section resulting from Wujiang inflow were ≤0.008 mg·L−1. The degree and trend of the influence of Wujiang River inflow on the phosphorus concentration in the local water body of the Three Gorges Reservoir are inconsistent in different periods. Construction of a series of hydropower stations and the discharge of P-containing wastewater during the development of phosphate mines in Wujiang River results in fluctuation of P concentrations in Wujiang River, and furthermore influences on P concentrations in QXC reach.