Remobilization mechanism and release characteristics of phosphorus in saline sediments from the Pearl River Estuary (PRE), South China, based on high-resolution measurements

Lei Gao; Rui Li; Zuobing Liang; Chang Yan; Aiping Zhu; Shaoheng Li; Zhigang Yang; Haijun He; Huayang Gan; Jianyao Chen

doi:10.1016/j.scitotenv.2019.134411

Remobilization mechanism and release characteristics of phosphorus in saline sediments from the Pearl River Estuary (PRE), South China, based on high-resolution measurements

Sci Total Environ. 2020 Feb 10:703:134411. doi: 10.1016/j.scitotenv.2019.134411. Epub 2019 Sep 12.

Authors

Lei Gao¹, Rui Li¹, Zuobing Liang¹, Chang Yan¹, Aiping Zhu¹, Shaoheng Li¹, Zhigang Yang¹, Haijun He², Huayang Gan², Jianyao Chen³

Affiliations

¹ School of Geography and Planning, Sun Yat-Sen University, Guangzhou 510275, China.
² Guangzhou Marine Geological Survey, Guangzhou 510760, China.
³ School of Geography and Planning, Sun Yat-Sen University, Guangzhou 510275, China. Electronic address: chenjyao@mail.sysu.edu.cn.

PMID: 31734506
DOI: 10.1016/j.scitotenv.2019.134411

Abstract

The internal loading of phosphorus (P) is commonly considered an essential factor contributing to eutrophication in freshwater bodies. However, investigation of the lability and remobilization characteristics of P in estuarine saline sediments has been limited. In this study, a sequential chemical extraction procedure and high-resolution measurement using the diffusive gradients in thin film (DGT) technique were employed to explore the lability, potential remobilization mechanism and release characteristics of sediment P in the Pearl River Estuary (PRE), South China. The P accumulated significantly in sediments along the west coast of the PRE due to the combined effects of terrestrial P inputs and specific hydrological conditions. The geochemical fractions of sediment P followed the order of organic P (Org-P) (mean: 58.6%) > iron-bound P (Fe-P) (23.4%) > calcium-bound P (Ca-P) (17.4%) > loosely bound P (LS-P) (0.63%). Synchronous vertical variations in DGT-labile Fe and P in the upper and middle parts of the sediment profiles confirmed that Fe-coupled P mobilization occurred in saline sediments. In contrast, sulfate reduction in bottom sediments supposed to decouple the Fe-P cycling relationship. Additionally, the formation of an "iron curtain" (Fe oxyhydroxides) in the oxic surface sediments efficiently prevented upward diffusion of P, leading to relatively low effluxes of P (0.098-6.59 ng cm^-2 d^-1) across the sediment-water interface.

Keywords: Decoupling of Fe-P cycling; Diffusion flux; Diffusive gradients in thin-films (DGT); Fe-coupled P mobilization; Pearl River Estuary (PRE).