National Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; School of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China; School of Environment, Tsinghua University, Beijing 100091, China.
National Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Sci Total Environ. 2020 Jun 20;722:136964. doi: 10.1016/j.scitotenv.2020.136964. Epub 2020 Feb 6.
As an important phosphorus (P) source in water, sediment P release can influence water quality in the tributary backwater zone of "river-type" reservoir. Chemical sequential extraction and diffusive gradients in thin films technique (DGT) were applied to study sediment P mobility in the Daning River backwater zone (DNB) in the Three Gorges Reservoir (TGR). Influenced by the TGR backwater intrusion, both of water P forms and sediment P forms in the DNB zone exhibited increased spatial distributions from upper reach to lower reach. Sediment particles in the upper, middle, lower reaches were mainly derived from the settled particles (with high Ca contents) carried by the Daning River outflow, the former and sedimentary dead algal, the settled particles carried by the TGR backwater, respectively. According to P adsorption/desorption experiment results and concentration gradients of DGT-labile P at the sediment-overlying interface (SWI), sediments in the DNB zone acted as P source for overlying water during the sampling period. In the lower reach of the DNB zone and the adjacent TGR mainstream, iron oxides reduction in the anoxic or anaerobic sediments drove the synchronous release of labile P and Fe(II). Whereas, algal decomposition directly produced labile P and S(-II) in the top 0 to -10 mm sediment layer in the middle reach, and then the downward increases of labile P and Fe(II) in the depth of -30 to -80 mm were caused by iron oxides reduction. In the upper reach, the released labile P in sediments might be re-trapped by precipitating with Ca(II) or being adsorbed onto the newly formed iron oxides near the SWI. Sediment P release in DNB zone had a limited influence on water quality, but the influence would be significant in the future time after the external P source is reduced efficiently.
作为水体中重要的磷（P）源，沉积物 P 的释放会影响“河流型”水库支流回水区域的水质。本研究采用化学连续提取法和扩散梯度薄膜技术（DGT）研究了三峡水库丹江口库区（DNB）沉积物 P 的赋存形态和生物可利用性。受三峡水库回水影响，DNB 区域水体和沉积物中各形态 P 的空间分布呈现出自上游至下游逐渐增加的趋势。上游、中游和下游的沉积物颗粒主要来源于丹江流出携带的沉降颗粒（高 Ca 含量）、前积和死亡藻类、三峡水库回水携带的沉降颗粒。根据 P 吸附/解吸实验结果和 DGT-可提取磷在沉积物-水界面（SWI）处的浓度梯度，在采样期间，DNB 区域的沉积物为上覆水提供了 P 源。在 DNB 区域的下游和相邻的三峡水库主流区，缺氧或厌氧沉积物中的铁氧化物还原驱动了可提取磷和 Fe(II)的同步释放。而在中游，藻类分解直接在 0 到-10mm 沉积物层产生可提取磷和 S(-II)，随后在-30 到-80mm 深度范围内可提取磷和 Fe(II)的增加是由铁氧化物还原引起的。在上游，沉积物中释放的可提取磷可能通过与 Ca(II)沉淀或被 SWI 附近新形成的铁氧化物吸附而重新被捕获。DNB 区域沉积物的磷释放对水质的影响有限，但在有效减少外部磷源后，未来时间内这种影响可能会显著增加。
