Remobilization characteristics and diffusion kinetic processes of sediment zinc (Zn) in a tidal reach of the Pearl River Estuary, South China

Lei Gao; Rui Li; Zuobing Liang; Chenchen Yang; Zaizhi Yang; Lei Hou; Lei Ouyang; Xiuhua Zhao; Jianyao Chen; Ping Zhao

doi:10.1016/j.jhazmat.2023.131692

Remobilization characteristics and diffusion kinetic processes of sediment zinc (Zn) in a tidal reach of the Pearl River Estuary, South China

J Hazard Mater. 2023 Sep 5:457:131692. doi: 10.1016/j.jhazmat.2023.131692. Epub 2023 May 24.

Authors

Lei Gao¹, Rui Li², Zuobing Liang², Chenchen Yang², Zaizhi Yang², Lei Hou³, Lei Ouyang⁴, Xiuhua Zhao⁴, Jianyao Chen², Ping Zhao⁴

Affiliations

¹ Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China. Electronic address: nvtoo@sina.com.
² School of Geography and Planning, Sun Yat-Sen University, Guangzhou 510275, China.
³ College of Ecology and Environment, Southwest Forestry University, Kunming 650224, China.
⁴ Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.

PMID: 37257381
DOI: 10.1016/j.jhazmat.2023.131692

Abstract

Exploration of the remobilization mechanism of trace metals in estuarine sediments remain challenging because of dynamic hydrochemical conditions. This study integrated a chemical sequential extraction procedure (BCR), the diffusive gradient in thin films (DGT) and high-resolution dialysis techniques, and Visual MINTEQ ver.3.1 to identify the seasonal mobilization characteristics of sediment Zn within a tidal reach, South China. The mobility of sediment Zn based on the BCR procedure contradicted the results of DGT analysis. In summer, reductive dissolution of Fe/Mn oxides was the key driver of sediment Zn remobilization; during winter, cation exchange reactions facilitated the mobilization of Zn in the brackish water zone. The time-dependence ratios of DGT-labile Zn and dissolved Zn concentrations (mean: 0.34-0.81) indicated the sediment solid phase had partially sustained capacity to resupply Zn to the porewater in both seasons. Sediments generally functioned as a source of Zn in the freshwater zone with organically complexed Zn being diffusively released into the water column at rates of 0.3-15.5 μg·m^-2·d^-1. In the brackish water zone, the dominant Zn species were transformed into free Zn ions and Zn-inorganic complexes and migrated into sediment, with respective influxes of 18.9-70.7 μg·m^-2·d^-1 and 18.9-68.3 μg·m^-2·d^-1, which shifted to a sink of Zn.

Keywords: Diffusive flux; Resupply capacity; Saltwater-freshwater interzone; Source/sink phases; Zn speciation.