| Abstract
| - A single DGT (diffusive gradient in thin films) probe thatcould measure metals and sulfide simultaneously and at thesame location was deployed in the surface sediment ofa productive lake (Esthwaite Water). It contained a layerof AgI that binds sulfide overlying a layer of chelating resinthat binds metals. Analysis for sulfide in two dimensionsshowed local sources of sulfide, 1−5 mm in diameter, at8−11 cm depth within the sediment. A transect of trace metalsmeasured at 100-μm intervals through the largest sulfide“hot spot” demonstrated concomitant release of Fe, Mn, Cu,Ni, and Co. Substantial supersaturation with respect tometal sulfides was observed for Fe and Co at the site ofmetal generation, but at a distance of less than 1 mm, solutionconcentrations were consistent with equilibration withamorphous FeS and CoS phases. Simple mass balancecalculations were consistent with Fe being supplied fromreductive dissolution of its oxides and with sulfidebeing supplied from reduction of sulfate. The observedconcentrations of Cu, Ni, Co, and Mn could be accountedfor by their release from iron oxides without invokingMn reduction. The metals are removed rapidly (∼1 min)at the edge of the hot spot. These first observations of thesimultaneous release of trace metals and sulfide areconsistent with the known removal of metals by formationof their insoluble sulfides if the in situ kinetics of metalsulfide formation is on this time scale. The coproductionof reduced Fe and S suggests that iron- and sulfate-reducingbacteria may exist together in the same localized zoneof actively decomposing organic matter.
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