Phosphorus Forms and Distribution Characteristics in the Sediment and Soil of the Water-Level-fluctuating Zone in the Main Stream of the Three Gorges Reservoir

Abstract

Hydrological regimes changed after the Three Gorges Reservoir (TGR) became fully operational, with the water level fluctuating between 145 m and 175 m. This has altered phosphorus (P) distribution within sediments and soils of the water-level-fluctuating zone (WLFZ). Eleven field investigations within the main stream were carried out in June 2016. The aim of the study was to determine lateral (sediment and WLFZ soil) and longitudinal variations (from the end of the backwater area to the Three Gorges Dam) of phosphorus species. P fractions were analyzed using a Standards, Measurements, and Testing (SMT) protocol. Results showed that both TP and NaOH-P content in sediment exhibited a clear increasing trend from the end of the backwater area to the Three Gorges Dam, while HCl-P declined. Average of totals P, OP (organic P), HCl-extracted P (HCl-P, calcium-bond P), and NaOH-extracted P (NaOH-P, metal oxide-bound P) in sediment were (859.6±106.8), (224.6±113.9), (435.3±77.7), and (101.5±31.6) mg·kg-1, respectively. The concentration average of P species in sediment was higher than in WLFZ soil. In both sediment and soil, HCl-P was the main form of P, accounting for 51.3% and 58.2% of TP, while the ratio of NaOH-P to TP was 11.7% and 8.1%, respectively. P fractions with a higher coefficient of variation had greater spatial heterogeneity.