Objective To analyze and compare the temporal and spatial differences in soil heavy metal content in the water-fluctuation zone of the Three Gorges reservoir area, study the current situation of metal pollution in this area, and put forward prevention and control measures.

MethodsThe soils in the flooded area (elevation 145-175 m) and unflooded area (elevation 175-185 m) from the water-fluctuation zone of the Three Gorges reservoir area in the Zigui section in 2008, 2014, and 2018 were used for the study. We examined the physicochemical properties and copper (Cu), iron (Fe), manganese (Mn), and zinc (Mn) contents of these samples through the digestion method.

ResultsThe results showed that: (1) The contents of soil total nitrogen (TN), total phosphorus (TP) and organic matter (SOM) in the flooded area continued to decrease from 2008 to 2018. The soil pH increased compared with 2008 and it was close to 7 in 2018. (2) As of 2018, the contents of Cu, Fe, Mn and Zn in the soil of water level fluctuating zone have been increasing. The geological accumulation index pollution degree of Zn in the middle and lower part of water level fluctuating zone (elevation 145～165 m) and the soil in the non-flooded area was “strong”; Cu in the lower part of the water level fluctuating zone (elevation 145～165 m) and Zn in the soil in the middle and lower part of water level fluctuating zone and non-flooded area had caused slight ecological risks. (3) The correlation analysis between soil physical and chemical properties and the contents of four heavy metals in water level fluctuating zone showed that the rise of soil pH might bring the risk of increasing the accumulation of four heavy metals. The increase of soil TP might reduce the accumulation of four heavy metals in the soil, while the increase of soil TN content might cause the increase of soil Fe and Mn in the non-flooded area and the decrease of Cu and Zn in the flooded area.

Conclusion In summary, the operation of the Three Gorges Dam has caused a decline in the quality of soil nutrients such as reducing nitrogen and phosphorus contents. The status of soil heavy metal pollution in water level fluctuating zone cannot be ignored, especially the ecological risks of Cu and Zn. Therefore, long-term monitoring should be continued, and artificial intervention means such as changing vegetation composition can be considered if necessary.