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<p>Phosphorus (P) loss from agricultural soils is a major contributor to freshwater eutrophication, yet soil-specific thresholds for P leaching remain poorly defined, particularly in reservoir catchments. This study assessed P migration and environmental risk in the Xiangxi River watershed, a representative tributary of the Three Gorges Reservoir, China. Column leaching experiments were performed on four typical soils—purple soil (PS), yellow soil (YS), calcareous soil (CS), and yellow-brown soil (YBS)—under controlled rainfall and fertilization scenarios, complemented by sorption isotherm and flooding incubation tests. Distinct soil-specific responses were observed: PS and YS exhibited substantially higher P leaching losses, while CS and YBS demonstrated greater sorption capacity and retention potential. Sorption behavior followed the Langmuir model, with maximum sorption capacity (<i>Q</i><sub>m</sub>) ranked as CS &gt; YBS &gt; PS &gt; YS. Although the degree of P saturation (DPS &lt; 5%) remained low, the equilibrium P concentration (EPC<sub>0</sub> = 0.7–1.2 mg·L<sup>− 1</sup>) exceeded established eutrophication thresholds for freshwater systems. Critical Olsen-P values, determined via split-line regression, ranged from 10.5 to 23.2&#xa0;mg·kg<sup>− 1</sup>, above which leaching risk increased markedly. Overall, the findings demonstrate that P leaching potential is strongly soil-dependent. Under current fertilization practices, PS and YS likely exceed their safe Olsen-P thresholds, whereas CS and YBS remain less vulnerable. These results emphasize the need for soil-specific P management strategies—such as threshold-based fertilization and hydrological mitigation—to reduce diffuse P pollution and protect water quality in the Three Gorges Reservoir region.</p>

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Soil-specific phosphorus leaching thresholds and environmental risks in the Three Gorges Reservoir region

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月11日

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  • Xiao Ma,
  • Quan Zhang,
  • Xingyu Liu,
  • Qiao Xiong,
  • Hongtao Wu,
  • Yuxuan Li

摘要

Phosphorus (P) loss from agricultural soils is a major contributor to freshwater eutrophication, yet soil-specific thresholds for P leaching remain poorly defined, particularly in reservoir catchments. This study assessed P migration and environmental risk in the Xiangxi River watershed, a representative tributary of the Three Gorges Reservoir, China. Column leaching experiments were performed on four typical soils—purple soil (PS), yellow soil (YS), calcareous soil (CS), and yellow-brown soil (YBS)—under controlled rainfall and fertilization scenarios, complemented by sorption isotherm and flooding incubation tests. Distinct soil-specific responses were observed: PS and YS exhibited substantially higher P leaching losses, while CS and YBS demonstrated greater sorption capacity and retention potential. Sorption behavior followed the Langmuir model, with maximum sorption capacity (Qm) ranked as CS > YBS > PS > YS. Although the degree of P saturation (DPS < 5%) remained low, the equilibrium P concentration (EPC0 = 0.7–1.2 mg·L− 1) exceeded established eutrophication thresholds for freshwater systems. Critical Olsen-P values, determined via split-line regression, ranged from 10.5 to 23.2 mg·kg− 1, above which leaching risk increased markedly. Overall, the findings demonstrate that P leaching potential is strongly soil-dependent. Under current fertilization practices, PS and YS likely exceed their safe Olsen-P thresholds, whereas CS and YBS remain less vulnerable. These results emphasize the need for soil-specific P management strategies—such as threshold-based fertilization and hydrological mitigation—to reduce diffuse P pollution and protect water quality in the Three Gorges Reservoir region.