This paper studies the influence of the impounding process during flood recession in the TGR on the distribution and rerelease of sediment phosphorus forms in the Xiangxi Bay in 2016. Influenced by the main stream of the Three Gorges Reservoir (TGR) flowing backward during impoundment, the water environmental conditions, sediment grain size and sediment-forming environment of the tributary bays change correspondingly. In this study, it is found that the water temperature (WT), turbidity and oxidation–reduction potential (ORP) of the overlying water in the Xiangxi Bay decrease, while the pH increases after impoundment in the TGR. The backward flow of the main stream containing a large amount of sediments increases the sediment content of the tributary bay, and the difference in sediment particle size between the main stream and tributaries narrows after resedimentation. The phosphorus adsorbed on the sediments increases the total phosphorus (TP) in the sediments of the Xiangxi River to 1.3 times its value before water impoundment. NaOH-P and HCl-P in the Xiangxi River sediments account for 42% and 38% of the TP, respectively, and the contents of the various phosphorus forms are ranked in the following order: NaOH-P > HCl-P > organic phosphorus (OP). After impoundment, HCl-P accounts for 67% of the TP, and the relative contents of the phosphorus forms are ranked as: HCl-P > OP > NaOH-P. Orthophosphate (PO 4 3− -P) in the Xiangxi sediments before and after impoundment acts as a source, and the PO 4 3− -P diffusion flux increases from approximately − 0.0029 to 0.0059 mg (m 2 d) −1 before impoundment to 0.0067–0.1071 mg (m 2 d) −1 after impoundment, which is mainly due to the increased difference in concentration of PO 4 3− -P [ ρ (PO 4 3− -P)] between the sediment interstitial water and overlying water after impoundment. After nutrient recharge of the main stream of the Yangtze River, ρ (PO 4 3− -P) of the overlying water is 3.7 times its value before impoundment, and after the release of NaOH-P in the sediments, ρ (PO 4 3− -P) of the interstitial water is 8.3 times its value before water impoundment. Hence, the risk of nutrient release from the sediments in the Xiangxi Bay increases.

中文翻译：

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三峡水库末端蓄洪对支流库湾沉积物中磷形态影响机制研究

本文研究了三峡水库洪水退水过程对2016年湘西湾沉积物磷形态分布和再释放的影响。支流海湾的水环境条件、沉积物粒度和成沙环境也相应发生变化。本研究发现，在三峡湾蓄水后，湘西湾上覆水的水温（WT）、浊度和氧化还原电位（ORP）降低，而 pH 值升高。含有大量泥沙的干流逆流增加了支流湾的泥沙含量，再沉淀后干支流沉积物粒径差异缩小。吸附在沉积物上的磷使湘西河沉积物中的总磷（TP）增加到蓄水前的 1.3 倍。湘西河沉积物中NaOH-P和HCl-P分别占总磷的42%和38%，各形态磷含量按以下顺序排列：NaOH-P>HCl-P>有机磷(OP)。蓄水后，HCl-P 占总磷的 67%，磷形态的相对含量排列为：HCl-P > OP > NaOH-P。蓄水前后湘西沉积物中的正磷酸盐（PO 4 3- -P）作为源，PO 4 3- -P扩散通量从约-0.0029增加到0。蓄水前的 0059 mg (m 2 d) -1 到蓄水后的 0.0067–0.1071 mg (m 2 d) -1，这主要是由于 PO 4 3− -P [ ρ (PO 4 3− -P)] 在蓄水后沉积物间隙水和上覆水之间。长江干流养分补给后，上覆水的ρ(PO 4 3− P) 是蓄水前的3.7倍，沉积物中NaOH-P释放后，ρ (PO 4 3 − -P) 的间隙水为蓄水前值的 8.3 倍。因此，湘西湾沉积物释放养分的风险增加。这主要是由于蓄水后沉积物间隙水与上覆水之间PO 4 3- -P [ ρ (PO 4 3- -P)] 浓度的差异增加所致。长江干流养分补给后，上覆水的ρ(PO 4 3− P) 是蓄水前的3.7倍，沉积物中NaOH-P释放后，ρ (PO 4 3 − -P) 的间隙水为蓄水前值的 8.3 倍。因此，湘西湾沉积物释放养分的风险增加。这主要是由于蓄水后沉积物间隙水与上覆水之间PO 4 3- -P [ ρ (PO 4 3- -P)] 浓度的差异增加所致。长江干流补给养分后，上覆水的ρ(PO 4 3− P)为蓄水前的3.7倍，沉积物中NaOH-P释放后，ρ (PO 4 3 − -P) 的间隙水为蓄水前值的 8.3 倍。因此，湘西湾沉积物释放养分的风险增加。