A sand tank experimental study of distribution, migration and transformation mechanism of iron and phosphorus species under redox fluctuation in a simulated riparian zone

The coupling transformation of iron and phosphorus in the riparian zone is of great significance on the biogeochemical cycle of iron and pollutants in surface water-groundwater interaction system. However, the spatial and temporal distribution, biochemical transformation and its pollution interception in the interaction zone is poorly understood. In this study, we used the sand tank experiment to investigate the migration and the transformation of iron and phosphorus under the redox fluctuation forced by the river stage in the riparian zone. Results show that there is a good correlation between the changes of Fe/Al coupled P and amorphous total Fe. Additionally, more attention should be paid to the effect of organic carbon rather than dissolved oxygen on the redox condition in the underground environment. It was also found that aqueous phosphorus usually accumulates in the transition area of the riparian zone regardless of the recharge or discharge relationship between river and groundwater. This study thus revealed the distribution, migration and transformation mechanism of iron and phosphorus in the typical fine sandy riparian zone, providing theoretical support for tracing and controlling the source of phosphorus pollution in riparian aquifer.