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<p>The Water Level Fluctuation Zone (WLFZ) is a land-water ecotone serving the sink of exogenous phosphorus (P) but also the source of P release into reservoir water. However, the characteristics and mechanisms of soil P mobilization in the WLFZ in respond to long-term wet-dry alternations still remain poorly understanding. Through fieldwork and simulating experiments, this study aimed to investigate the periodic variation and mobilization mechanism of soil P forms in the WLFZ of the Pengxi River, a tributary of the Three Gorges Reservoir (TGR), during two scheduling periods. From the low water level period (August 2022) to the drainage period (March 2023), the WLFZ soils showed reductions in iron oxides, calcium content and fine particle proportions, together with decreases in iron-bound P (FeP), calcium-bound P (CaP) and oxalate-extractable P. Wet-dry alternating conditions promoted the transformation of FeP and CaP into loosely-bound P in the WLFZ soils, facilitating the transfer of dissolved and fine particulate P into overlying water. Simulating experiments estimated that the amount of P released by the WLFZ soils reached 0.0012–0.0047&#xa0;mg/g under two wet-dry cycles. Despite the WLFZ soils exhibited FeP reduction, CaP dissolution and microbial recovery in the shift from drying state to flooding state, particle deposition from the TGR backwater led to total P accumulation in the WLFZ soils, particularly in the downstream tributary near the stream junction. Overall, wet-dry alternating conditions can enhance the risk of soil P release, and more attention needs to be given to soil P loss management in reservoir WLFZs.</p>

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Wet-dry alternating conditions regulated soil phosphorus mobilization in the water level fluctuation zone of the Three Gorges Reservoir tributary, China

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • Chaonan Han,
  • Yimei Wang,
  • Tianhao Dai,
  • Hao Wu,
  • Yu Tang,
  • Yingqun Ma

摘要

The Water Level Fluctuation Zone (WLFZ) is a land-water ecotone serving the sink of exogenous phosphorus (P) but also the source of P release into reservoir water. However, the characteristics and mechanisms of soil P mobilization in the WLFZ in respond to long-term wet-dry alternations still remain poorly understanding. Through fieldwork and simulating experiments, this study aimed to investigate the periodic variation and mobilization mechanism of soil P forms in the WLFZ of the Pengxi River, a tributary of the Three Gorges Reservoir (TGR), during two scheduling periods. From the low water level period (August 2022) to the drainage period (March 2023), the WLFZ soils showed reductions in iron oxides, calcium content and fine particle proportions, together with decreases in iron-bound P (FeP), calcium-bound P (CaP) and oxalate-extractable P. Wet-dry alternating conditions promoted the transformation of FeP and CaP into loosely-bound P in the WLFZ soils, facilitating the transfer of dissolved and fine particulate P into overlying water. Simulating experiments estimated that the amount of P released by the WLFZ soils reached 0.0012–0.0047 mg/g under two wet-dry cycles. Despite the WLFZ soils exhibited FeP reduction, CaP dissolution and microbial recovery in the shift from drying state to flooding state, particle deposition from the TGR backwater led to total P accumulation in the WLFZ soils, particularly in the downstream tributary near the stream junction. Overall, wet-dry alternating conditions can enhance the risk of soil P release, and more attention needs to be given to soil P loss management in reservoir WLFZs.