Temporal dynamics of soil nutrients in the riparian zone: Effects of water fluctuations after construction of the Three Gorges Dam

The Three Gorges Dam (TGD) plays a vital role in the hydropower supply of China, which has a substantial impact on the riparian zones along the Yangtze River. Knowledge about how riparian soil properties respond to such changes remains limited. To explore how water regulation disturbs the status of soil nutrients in the riparian zone, a long-term monitoring program was implemented at sites with secondary shrubland (SB) and abandoned farmland (AFD). A total of 288 composite soil samples collected from the two riparian areas were investigated. Compared with 2009, long-term flooding changed the distribution of soil organic matter (SOM) and available phosphorus (AP) contents in various soil layers. The fluctuation of the water level reduced the SOM content, which the range of SOM variation was greater in the early stage of submergence. In 2018, the SOM content in the 10-20 cm at 155-165 m above sea level (a.s.l.) of the AFD was 9.46 g/kg, which reduced by 74.30% compared with 2019. In all the 0-10 cm soil layer, except for 145-155 (a.s.l.) in the AFD plot, soil total nitrogen contents in 2018 were significantly higher than those in 2009. Compared with 2009, the soil AP content in the 10-20 cm layer at 145-155 m (a.s.l.) of SB decreased by 90.90% in 2018. The total potassium (TK) content of AFD increased from 2009 to 2015 but decreased in 2018. However, the soil TK content in 2018 was significantly higher than that in 2009. In AFD, soil pH increased from 2009 to 2015 and reached a maximum value (8.21). In 2018, the pH value of some soil samples showed a downward trend but was always significantly higher than during 2009. Moreover, according to the redundancy analysis, the elevation, soil layer, and flood cycle could explain 56.64% of the changes in soil properties. Our study demonstrates that dam operation was an indirect driver for the changes in the temporal dynamics of soil nutrients, providing a reference for the management of the TGD.

Automated summary

This study investigates how the Three Gorges Dam operation affects the soil nutrient dynamics in riparian zones along the Yangtze River. Long-term flooding and water level fluctuations influenced the distribution of soil organic matter, available phosphorus, total nitrogen, total potassium, and pH. The elevation, soil layer, and flood cycle were found to be key factors in explaining the changes in soil properties.