CH20s SOaq 2HCOiaq HSq Hq

This process is widespread in marine sediments but is most important in continental margin sediments, where organic matter accumulation is largest. Sulphate reduction in sediments occurs at depths (varying from a few millimetres to metres below the sediment/water interface) where seawater SO4- can readily diffuse, or be pumped by the actions of sediment-dwelling organisms. The reaction yields highly reactive hydrogen sulphide (HS-), most of which diffuses upward and is reoxidized to SO4- by oxygenated seawater in the surface sediment. However, about 10% of the HS- rapidly precipitates soluble Fe(II) in the reducing sediments to yield iron monosulphide (FeS).

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