Phosphorus fractions and soil release in alternately waterlogged and drained environments at the water-fluctuation-zone of the Three Gorges Reservoir

The Water-Fluctuation-Zone (WFZ) of the Three Gorges Reservoir (TGR) has a special combination of aquatic and terrestrial ecological systems that are exposed to human activity. In this work, three kinds of soil were sampled along the Yangzi River in the TGR-WFZ. Our study focused on phosphorus (P) sorption characteristics and the change in inorganic P fractions for soils in alternately waterlogged and drained environments in the TGR-WFZ. Experiments were carried out to assess P sorption capacities and their relation to chemical properties in different soils. Concentration changes for different P fractions (e.g. Ca 2 -P, Ca 8 -P, Al-P, Fe-P, O-P and Ca 10 -P) in soils were investigated to study P sorption and desorption characteristics in the soil and to assess effective factors in alternately waterlogged and drained environments. Results showed that, for different soil types, the maximum P-sorption capacities (Q m ) had the following order: yellow earth > purple soil > fluvo-aquic soil. Under cyclic waterlogged and drained conditions, the Q m of waterlogged soil was higher than for drained soil. There was a decreasing trend for Olsen-P concentrations in soils after each draining process. The concentration of Ca 10 -P in purple, yellow and fluvo-aquic soil increased from 31.3%, 40.0% and 42.6% (before inundating) to 38.7%, 48.9% and 51.5%, respectively, after three inundating-draining processes. The percent of stable fractions in soils increased after the inundating-draining process. Total P levels for all types of fractions decreased after every inundating-draining process. This suggests the existence of a P release trend from WFZ soils into the TGR water body, making P in soils a potential threat toward water eutrophication in the TGR.