Effect of dam on phosphorus distribution and transformation in riparian zones along the bypass seepage pathway

Authors:
  • HZHaojie Zhong
    Haojie Zhong
  • GJGuolong Jiang
    Guolong Jiang
  • XGXulei Guo
    Xulei Guo
  • YLYiming Li
    Yiming Li
  • MLMinjing Li
    Minjing Li
  • ZWZhang Wen
    Zhang Wen
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Abstract
Damming plays a significant role in regulating global riverine phosphorus (P) cycling, with the general assumption that it led to the trapping of dissolved and particulate P in upstream sediments. However, in addition to riverine sediments, adjacent riparian zones may also serve as significant sinks for P species. This study investigated the distribution and transformation of groundwater P species in riparian zones along the bypass seepage pathway at two dam sites: the Three Gorges Dam (TGD) site on the Yangtze River and the Xinglong Dam (XD) site on the Han River. At the XD site, total P concentrations in groundwater were 1.5–13.2 times higher than in surface water, indicating significant P enrichment. In contrast, minimal P trapping was observed at the TGD site, where groundwater and surface water had similar total P concentrations and speciation. These differences were attributed to the variations in aquifer type, dam operation and aquifer geochemical conditions. In the fractured-karst aquifer at the TGD site, P species were readily transported, whereas transport was hindered in the Quaternary porous aquifer at the XD site. The water-bearing media in Quaternary porous aquifer had a high adsorption capacity for dissolved P species, resulting in the substantial trapping of P in riparian zones. Redox conditions were also crucial in regulating the distribution and transformation of groundwater P species in both aquifers. This study highlights the overlooked role of damming in regulating groundwater P distribution and transformation in riparian zones.

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