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CH3041
REDOX CYCLING
• Anoxic waters are often characterised by the presence of hydrogen sulphide - airport!
• When oxygen is exhausted organisms often use sulphate as the electron acceptor as there is usually sufficient SO42- present.
              2{CH2O} + SO42- ® H2S(g) + 2HCO3-
Around the oxic-anoxic boundary nutrients undergo bacteria catalysed redox cycling.
Oxic      (O2)
Anoxic (H2S)
SO42-
S(s)
H2S
Depth
S(VI)
S(0)
S(-II)