Effects of Flooding and Drying on the Transformation of Soil Inorganic Phosphorus in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir, China

Abstract

The implementation of the Three Gorges Project formed a water-level-fluctuating zone, and flooding and drying affects the soil properties and water quality of the Water-Level-Fluctuating Zone. The laboratory simulation or field sampling were conducted; however, the results cannot reflect the real conditions in practice. The effects of flooding and drying on the physical and chemical properties of soil and the transformation characteristics of inorganic phosphorus were studied in order to provide a theoretical reference for soil phosphorus loss and water eutrophication in water-level-fluctuating zone of the Three Gorges Reservoir. To investigate the conversion of soil phosphorus, plastic pots with soil were suspended at different depths (0, 2, 5, and 15 m) and submerged for 30, 60, and 180 d, and exposed for 180 d. The effects of submerged depth and time on the soil physical and chemical properties and inorganic phosphorus forms were studied. The results showed that soil pH, organic matter, total phosphorus, and available phosphorus decreased and then increased subsequently during the flooding period. After exposure for 180 d, soil pH, organic matter, and total phosphorus content decreased, while available phosphorus content increased. After flooding, the ratio of various forms of inorganic phosphorus to total phosphorus was Fe-P > Al-P > Ca8-P > Ca2-P. The content of Ca2-P and Ca8-P decreased at 0 m and 2 m and decreased at 5 m and 15 m and then increased with increased flooding time. After exposure for 180 days, the content of inorganic phosphorus increased significantly, and the content of inorganic phosphorus decreased as flooding depth increased. Al-P content increased with the flooding time, but there was no obvious change with flooding depth. The content of Fe-P did not change with the time and the depth of flooding.