Sulfur, iron, and phosphorus geochemistry in an intertidal mudflat impacted by shellfish aquaculture
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Dissolved sulfide, iron (Fe), and phosphorus (P) in a mudflat (Jiaozhou Bay, China) impacted by shellfish aquaculture were measured in situ by the diffusive gradients in thin films (DGT) technique. A combination of porewater and solid-phase chemistry was used to characterize the interplays of Fe and S, and their control on P mobilization. Below the subsurface layer, two times higher fluxes (FDGT) of dissolved Fe2+ from porewater to the DGT device than those of dissolved sulfide indicate that dissimilatory iron reduction (DIR) dominates over sulfate reduction (SR). Spatial coupling of dissolved Fe2+ and P points to P release driven mainly by reductive dissolution of Fe. Much higher FDGT values of dissolved Fe2+ relative to dissolved P imply that oxidative regeneration of Fe oxides at the sediment–water interfaces (SWIs) of the transitional mudflat serves as an effective “iron curtain” of upward diffusing P. In the mudflat sediments of DIR prevalence, the accumulation of total reduced inorganic sulfur (TRIS) is dampened, which can largely ascribed to enhanced oxidative loss of sulfide and/or limited availability of degradable organic carbon in the dynamic regimes. Low dissolved sulfide concentrations in the sediments leave the majority of reactive Fe unsulfidized and thus abundantly available to buffer newly produced sulfide.
KeywordsDGT technique Buffering capacity Sulfide toxicity Iron reduction Phosphorus mobilization Biogeochemical cycling
The research was jointly supported by the National Key Research and Development Program of China (grant 2016YFA0601301), the National Natural Science Foundation of China (grants 41576078 and 41776085), and the Shandong Province Natural Science Foundation, China (grant ZR2015DM006).
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