Manganese,iron and sulfur diagenesis and diffusive fluxes of porewater iron and manganese in sediments of Laizhou Bay,Bohai Sea
Based on analyses of solid-phase and porewater chemistry of sediment cores at four sites collected from Laizhou Bay of the Bohai Sea,we revealed diagenetic cycles of iron,manganese and sulfur and their responses to terrestrial inputs and anthropogenic perturbations.Results suggest that water eutrophication of the bay has not giv-en rise to organic carbon(OC)enrichment in the sediments.Actually,contents and lability of sediment OC are gen-erally low,largely due to the inputs of terrestrial refractory OC and intense sediment resuspension induced by natur-al processes and anthropogenic perturbations in the river-dominated area.This feature greatly dampens sulfate re-duction,resulting in low accumulation of total reduced inorganic sulfide(0.28-88 μmol/g).Porewater Mn2+is mainly from reductive dissolution of amorphous and poorly crystalline Mn oxides,while precipitation of MnCO3 is mainly responsible for Mn2+consumption in sediment below 10 cm depth.Intense sediment resuspension and re-fractory nature of sediment OC encourage dissimilatory iron reduction,with relative contribution of this pathway to total anaerobic OC mineralization of about 51%,on average.At the site(S6)heavily influenced by the Huanghe River input,dynamic depositional regime facilitates reductive dissolution of manganese oxides,but dampens reduc-tion of iron oxides and sulfate to some extent.Upward diffusive fluxes of porewater Mn2+and Fe2+in the sediments are at the lower end for sediments of other areas dominated by major river inputs,which is attributable to overall low lability of sediment OC.
Diagenesisporewatersulfidediffusive fluxmarine sedimentironmanganeseLaizhou Bay
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