Variable Effects of Iron (Fe (III)) Additions on Potential Methane Production in Boreal Lake Littoral Sediments

We studied potential methane (CH4) production and Fe (III) oxide reduction activity in sediments sampled from 12 vegetated littoral sites at eight lakes in Finland. The effects of added amorphous Fe (III) oxyhydroxide and organic substrate (acetate) on methanogenic and Fe (III) reduction activities were studied in anaerobic laboratory incubations (in vitro). The concentration of total iron in the sediments varied between 0.3 and 7.7 % (DW) and their organic matter content (loss of ignition) varied between 1 and 64 % (DW). The potential methane production at vegetated littoral sites varied greatly and was between 0.4 and 312 μmol CH4 kg−1d−1. Fe (III) addition suppressed methane production by over 50 % if the total iron content in the studied littoral sediment was ≥3 % (DW). Our results show that Fe (III) reduction is an important factor for organic matter decomposition in boreal freshwater littoral sediments. In addition to affecting methanogenesis, iron may also play a role in suppressing other microbial activities in anaerobic soils and sediments.