Characterization of Phosphorus Fractions in the Soil of Water-Level-Fluctuation Zone and Unflooded Bankside in Pengxi River, Three Gorges Reservoir

Abstract

The concentrations of phosphorus fractions in the soils of the water-level-fluctuating zone (WLFZ) of Pengxi River in the Three Gorges Reservoir were analyzed. The total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) were studied using the standard measurement and test (SMT) procedure. The average TP concentration was 575.29 mg·kg-1 and the average OP concentration was 91.23 mg·kg-1 in the soils of WLFZ. The fractions of phosphorus were analyzed by the Hedley method. In the soils of WLFZ, the relative abundance of WA-Pi (weakly adsorbed inorganic phosphorus), PA-Pi(potential active inorganic phosphorus), and Fe/Al-Pi(Fe/Al-bound inorganic phosphorus) accounted for 11.61% of the extractable Pi, lower than that in the unflooded bankside soils. The relative abundance of WA-Po (weakly adsorbed organic phosphorus) and PA-Po (potential active organic phosphorus) accounted for 22.28% of the extractable Po and the Fe/Al-Po (Fe/Al-bound organic phosphorus) accounted for 66.30%. In addition, the Po content of the soils of WLFZ was lower than that of the unflooded bankside soils and the difference in the Fe/Al-Po content in both soil types was the highest. WA-Pt and PA-Pt were significantly correlated with TP in the soils of WLFZ, which indicated that the active phosphorus content was mainly affected by TP. There was no statistical correlation between different fractions of phosphorus, suggesting different sources of phosphorus fractions. The Fe/Al-Pt content was significantly correlated with OM, implying that the OM content may affect the Fe/Al-Pt content. Therefore, under flood conditions, the potential impacts of phosphorus in the soils of WLFZ on overlying water should not be neglected.