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The distribution of anaerobic microbial redox processes was investigated along a 305 m long transect of a shallow landfill-leachate polluted aquifer. By unamended bioassays containing sediment and groundwater, 37 samples were investigated with respect to methane production, sulfate, iron, and manganese reduction, and denitrification. Methane production was restricted to the most reduced part of the plume with rates of 0.003–0.055 nmol CH₄/g dry weight/day. Sulfate reduction was observed at rates of maximum 1.8 nmol SO₄²⁻/g dry weight/day along with methane production in the plume, but sulfate reduction was also observed further downgradient of the landfill. Iron reduction at rates of 5–19 nmol Fe(II)/g dry weight/day was observed in only a few samples, but this may be related to a high detection limit for the iron reducing bioassay. Manganese reduction at rates of maximum 2.4 nmol Mn(II)/g dry weight …