Dam Effect on Soil Nutrients and Potentially Toxic Metals in a Reservoir Riparian Zone

The unique hydrological regime of Three Gorges Dam (TGD) has brought enormous challenges to the riparian zone (RRZ), which plays an important role in regulating sediment and nutrient transport into the Yangtze River. The soil in a RRZ is one of the key factors that affect the water quality. After 4 years of winter‐flooding, the concentration of soil nutrients and potentially toxic metals between the flooded reservoir RRZ and adjacent non‐flooded upland (Upland) are examined. There are two main results: First, soil organic carbon and soil available potassium concentration were significantly lower in RRZ than in Upland. Soil total nitrogen (TN) concentration showed the same trend, but with no significance. Soil available phosphorus concentration is significantly higher in RRZ. Second, the concentrations of all the tested potentially toxic metals (Cd, Cr, Cu, Pb, Zn), their geoaccumulation index (Igeo) values and potential ecological risk index (Ei) values are significantly higher in RRZ than in Upland. Cd had the highest Igeo and Ei values in RRZ. The present results indicated that the flood–dry–flood cycle caused by TGD has changed the soil nutrient concentrations and increased the potentially toxic metal concentrations. There is a cross‐contamination risk of the soil in RRZ, perhaps related to fertilization. As the last protective barrier for the Yangtze River, soil potentially toxic metals pollution control should deserve a considerable attention in the RRZ formed by TGD. Compared to adjacent non‐flooded upland (Upland), the flood‐dry‐flood cycle caused by Three Gorges Dam has changed soil nutrient concentrations and increased potentially toxic metal concentrations in the riparian zone (RRZ), indicating that there is a cross‐contamination risk of the soil in RRZ. Cd is worthy of special attention since it had a considerable ecological risk in RRZ.