In situ, high-resolution evidence of phosphorus release from sediments controlled by the reductive dissolution of iron-bound phosphorus in a deep reservoir, southwestern China

摘要

Reservoirs in southwestern China are encountering the challenge of eutrophication, in which internal phosphorus (P) release from sediments plays an important role. Studies on the high-resolution profile variations and release mechanisms of P at the sediment-water interface (SWI) are rare in these reservoirs until now. In this study, monthly monitoring (Nov 2017 to Oct 2018) using a composite diffusive gradient in thin films (DGT) technique was taken to determine the temporal and vertical profile variations of the DGT-labile P (Fe) at the SWI in Hongfeng Reservoir. The results showed that the average concentrations of the DGT-labile P (Fe) in surface sediments were 0.63 +/- 024 mg.L-1 and 4.61 +/- 1.12 mg.L-1, respectively, with significantly higher concentrations during the summer anoxic period than that during the winter aerobic period. The DGT-labile P (Fe) concentrations in sediments presented a significant positive correlation (r(2) 0.70, p 0.001), supporting the simultaneous release of reactive P and reactive Fe from the sediments and indicating that the reductive dissolution of ironbound P dominates the P release from sediments. The release rates of P ranged from 0.01 mg.m(-2)d(-1) to 0.83 mg.m(-2)d(-1) (mean: 0.22 mg.m(-2)d(-1)) in Hongfeng Reservoir, which are higher than that in heavily eutrophic shallow lakes in eastern China, such as Lake Taihu. There is a higher P loading, stronger P reactivity, faster P release rates, and higher pollution potential in deep reservoirs of southwestern China than that in natural shallow lakes of eastern China, highlighting the importance and urgency of treating internal P pollution in deep reservoirs. Further studies on the mechanisms and controlling factors of the coupled Fe-P-S cycle in deep reservoirs are desirable in the future, so as to provide a scientific foundation for exploring effective internal P treatment techniques adaptive to deep reservoirs in southwestern China. (C) 2019 Elsevier B.V. All rights reserved.