Objective To investigate the soil pH value and metal element content in different altitudes (145～155 m, 155～165 m, and 165～175 m) of the Three Gorges Reservoir area and to master the dynamics over the past decade (2008-2018), so as to provide data for the subsection monitoring and control, as well as the prediction of soil environmental quality evolution in Three Gorges Reservoir area.

Method According to the operation Scheduling of the Three Gorges Reservoir area, three secondary shrub sample lands with similar habitat types were selected in the typical fluctuation zone, and the pH value and metal element content in the soil (0-20 cm) at different altitudes were measured to analyze the differences and variations at different elevations and years in 2008, 2009, 2012, 2014, 2015, 2016 and 2018.

Result (1) With the periodic fluctuation of water level, the annual changes of soil pH value, potassium, calcium and magnesium contents in the fluctuation zone showed a trend of fluctuating increase, and the contents of iron, manganese and zinc showed a trend of fluctuating decrease, while the contents of sodium showed a trend of decreasing year by year from 2008 to 2018. (2) At different altitudes in each year, the soil pH value and K content showed a pattern of 145～155 m > 155～165 m > 165～175 m, the Fe and Mn contents followed the pattern of 145～155 m < 155～165 m < 165～175 m, the Ca content was relatively abundant in the area of 145～155 m, while the Na, Mg and Zn contents showed no significant difference among different altitudes. By 2018, the soils in the 145～155 m and 155～165 m elevations had developed from acidic to alkaline, and the 165～175 m elevations from acidic to neutral. (3) Correlation analysis and regression analysis showed that the soil pH value was closely related to the content of metal elements. There was a significant positive correlation between soil pH value and the contents of potassium, calcium and magnesium (p < 0.01), and a significant negative correlation between the contents of manganese, zinc, sodium (p < 0.01) and iron (p < 0.05).

Conclusion During the period of water level fluctuation for 10 times, the soil pH value and metal element content in different elevation sections of the fluctuation zone changed in varying degrees. It shows that periodic flooding is the main factor affecting the soil properties in the fluctuation zone, and elevation and soil pH value are the important factors affecting the content of metal elements. These conclusion could provide references for the prediction of the evolution trend of soil quality in different elevations of the fluctuation zone in the Three Gorges Reservoir area.