Objective To clarity the impact of phosphorus content in water on the migration and transformation of heavy metals in the soil of the alternating dry-wet fluctuation zone is of great significance for the prevention and control of heavy metals in the soil of the Three Gorges Reservoir area.

Method In this paper, 6 sampling points in Xiangxi River reservoir bay, including fluctuation zone and upper edge soil were selected to collect samples. Soil and water samples were monitored for 4 quarters (June 2020 to March 2021) with water phosphorus and soil heavy metals Pb and Cd. In the indoor dry-wet alternation simulation test, 6 phosphorus additions were set up according to the range of phosphorus concentration in Xiangxi River and with the soil of its fluctuation zone. And soil water volume ratio was 1:2.

Result The results showed that total phosphorus in Xiangxi River water was significantly positively correlated with Pb (P<0.05). Effective Pb was significantly positively correlated with effective Cd (P<0.01). The total phosphorus content in the water increased significantly (P<0.05) with increasing dry-wet alternation times. The total phosphorus content of soil in the flooding period was higher than that in the drying period when added concentration of phosphorus was lower than 0.2 mg·L⁻¹ during the second flooding and drying period. Pb and Cd in the soil showed a transition trend from a highly mobile exchangeable state to a weakly mobile residual state; adding low concentrations of phosphorus (0.05 mg·L⁻¹), the soil Pb content decreased significantly (P<0.05), and the soil Cd content increased with the increase of water phosphorus concentration (P<0.05), especially the form change of Cd was more significant and related to the water phosphorus content.

Conclusion There is a migration and transformation of phosphorus between water and soil in the process of dry wet alternation. Phosphorus in the water promote the migration of Pb from soil to water, while inhibiting the migration of Cd from soil to water.