Dynamics of metal immobilization in coastal mariculture sediments: Insights from DGT and DIFS modeling

Coastal sediments play a crucial role in regulating the mobility and bioavailability of metals in marine ecosystems, especially in aquaculture-dominated environments. This study conducted a dynamic assessment of metal release in the sediments of Zhelin Bay, the largest seawater aquaculture region in eastern Guangdong, China, using Diffusive Gradients in Thin Films (DGT) technology and the DGT Induced Fluxes in Sediments (DIFS) model. The distribution patterns of time-dependent R values for ten metals (Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) were analyzed alongside the adsorption (K_f) and desorption (K_b) parameters to elucidate the mechanisms by which metals are immobilized in sediments, limiting their release into the water column. Both the time-dependent R value patterns and K_f/K_b ratios demonstrated that all ten metals exhibited varying degrees of stabilization within the sediment, confirming their immobilization mechanisms in place. The maximum total concentration of Zn reached 347.82 mg/kg, corresponding to a moderate pollution level based on the geoaccumulation index. DGT-labile metals posed a joint ecological risk probability of 27.30 %, mainly due to Mn (11.19 %) and Al (11.15 %). These findings suggest that aquaculture activities and terrestrial nutrient inputs contribute to organic matter accumulation and biogeochemical shifts in sediments, influencing metal stabilization. This study is among the first to quantitatively characterize the dynamics of metal immobilization in coastal mariculture sediments using a combined DGT-DIFS approach.