Spatial distribution and release of phosphorus in purple soils in the water fluctuation zone of the Three Gorges Reservoir

The process of P release and transfer becomes more complex in environments strongly disturbed by human activities. In this paper, purple soils (about 37.8% of total soils) from areas with different sea level elevations and land use were sampled in the Water Fluctuation Zone (WFZ) in the Three Gorges Reservoir (TGR) along the Yangzi River. This research investigated the P distribution characteristics of purple soils in alternately waterlogged and drained environments the WFZ of the TGR. Combining with field samples and inundating experiments in the lab, the effect of alternately waterlogged and drained environments on soils characteristics and P release were studied. The results showed that the maximum P-sorption capacities (Q m ) of purple soils decreased from 263.1 to 71.2 mg/kg during the draining period. The concentration of oxalate-extractable iron (Fe ox ) and oxalateextractable aluminium (Al ox ) of the various soils increased from 668 mg/kg and 613 mg/kg to 2958 mg/kg and 678 mg/kg, respectively, after first inundation. The concentration of different fractions of P obtained by the sequential extraction method, such as Ca 2 -P, Ca 8 -P, Al-P, Fe-P, O-P and Ca 10 P, changed greatly during the alternate waterlogging and draining process. The Ca 10 -P in purple soil increased from 31.3% to 38.7%, after three inundating-draining processes. The concentration of Fe-P was stable during each waterlogging and draining period, but the concentration decreased after every inundating-draining process. The Q m was positively correlated with the concentration of Fe ox , Al ox and organic matter contents (OM) in the purple soils. There was a trend for P release from the purple soils in the WFZ of the TGR. The P total release (including soluble and particulate forms) from soils to water was calculated, and a preliminary assessment was performed on soil P release contributions to the eutrophication of water in the TGR after the first inundating process.