Controlling factors on methanogenesis in the deep sediment of Lake Kinneret

This study investigates the controlling parameters on methanogenesis in deep Lake Kinneret (Israel) sediments and their link to methanotrophy process. Our findings suggest that in the sediments methanogenesis is restricted to a zone between 3 and 25 cm depth and ends abruptly. Below this zone there is a sink of methane, and sets of geochemical data show that this methane sink is related to anaerobic oxidation of methane (AOM) that it is likely driven by iron reduction rather than sulfate reduction. In order to explore this ending of methanogenesis and its link to the deep AOM in-situ profiles in the sediments as well as slurry incubation experiments in modified conditions were conducted. Profiles of dissolved organic carbon and acetate show increase in concentrations with depth, suggesting that the ending of methanogenesis is not trivial. Incubation experiments show accumulation of acetate with depth in natural conditions, and that indeed methanogenesis limitation occur at certain depths, even with addition of acetate. Considering that the common substrates concentrations increase at this depth, the abrupt absence of methanogenesis is surprising. Different additions to the slurries suggest a link between methane, sulfur and iron at that depth that affects both methanogenesis and the deep AOM process.