淇澳岛红树林沉积物镉的空间分布特征和固定-再移动机制OA

With the acceleration of industrialization and urbanization,cadmium(Cd)poses a serious threat to estuarine ecosystems and human health due to its high toxicity.As a typical estuarine wetland,the intertidal mangrove zone provides a pivotal place for the geochemical cycle of heavy metals,yet,the mechanisms regulating Cd migration and transformation in its sediments remain poorly understood.Focusing on the intertidal zone of Qi'ao Island in the Pearl River Estuary,this study systematically analyzed the spatial distribution of total Cd and its geochemical fractions in sediments.We applied the diffusive gradients in thin films(DGT)technique to investigate the seasonal variations of labile Cd across the overlying water-sediment interface,aiming to clarify the spatial pattern and the underlying geochemical mechanisms of Cd fixation and remobilization,thereby providing scientific guidance for regional pollution control.The results show that the total Cd concentrations in mangrove sediments are significantly higher than those in tidal flats(P<0.05).Cd is predominantly present in the acid-soluble fraction(37%-50%),which exhibits high remobilization potential and bioavailability.In winter,the reductive dissolution of Mn oxides is identified as the primary driver for the significantly elevated DGT labile Cd concentration in surface sediments(1.07±0.16)μg/L.In contrast,under high-temperature conditions in summer,the mineralization of organic matter promotes sulfate reduction,leading to the formation of CdS precipitates as the primary control on the decrease in labile Cd concentration(0.07±0.02)μg/L.Moreover,mangrove roots retain suspended particles,and the associated organic-rich,weakly acidic environment facilitates Cd accumulation while suppressing its remobilization.This study provides a scientific basis and theoretical support for controlling sediment Cd pollution and formulating mangrove restoration rstrategies in the Pearl River Estuary.