Distribution characteristics and influencing factors of heavy metals at the sediment-water interface in the southern waters of the Miaodao Archipelago

The Miaodao Archipelago, located at the confluence of the Yellow Sea and Bohai Sea, exhibits complex mechanisms related to the transport and transformation of heavy metals due to dynamic interactions between runoff and tidal currents. In this study, we investigated the deposition, migration, and accumulation mechanisms of seven heavy metals (Cu, Pb, Zn, Cd, Cr, Hg, and As) in the southern archipelago waters by analyzing survey data from 2020, which encompassed coastal waters and sediments surrounding the five southern islands. The key findings revealed that the adsorbed heavy metals in sediments exhibited significantly higher contamination levels and greater environmental stability compared to the dissolved fractions in the water column. Pearson correlation analysis and principal component analysis identified distinct distribution patterns: the dissolved heavy metals were primarily influenced by dilution-mixing processes, while the adsorbed heavy metals exhibited significant correlations with the organic carbon content and phytoplankton biomass. The sediment-water partition coefficients indicate the occurrence of phase-specific distribution patterns, with chromium exhibiting preferential accumulation in particulate phases and mercury exhibiting an affinity for the aqueous phase, reflecting the element-specific responses to the coupled hydrodynamic forces. Significant inter-element correlations were identified for all of the element pairs, except for AsHg, AsZn, and CrAs. Through multivariate analysis, three primary pollution sources were identified: industrial wastewater discharge and port activities, agricultural runoff, and atmospheric deposition. The phase-dependent distribution patterns and source apportionment results provide critical insights for developing integrated land-sea management strategies aimed at controlling heavy metal pollution in ecologically sensitive coastal zones.