Hydrogen metabolism in a mildly acidic lake sediment (Knaack Lake)

Hydrogen metabolism was studied in anoxic Knaack Lake sediments by measuring the in situ concentrations of dissolved H2, as well as the Vmax, turnover rate constant, and Km for H2. The results show that the relatively low rate of H2/CO2-dependent methanogenesis is paralleled by a low turnover of the dissolved H2 pool. H2-dependent acetate formation did not appear to be of importance based on the discrepancy of the Km for H2 consumption between the sediment and the prevalent homoacetogenic microbial population. In this mildly acidic lake sediment, H2 turnover apparently was limited by H2 production from organic matter. During incubation of sediment under a gaseous headspace, H2 escaped from the aqueous phase, and steady state concentrations of dissolved H2 were significantly lower than under in situ conditions. H2 concentrations increased upon addition of various organic substrates. H2 turnover within the sediment appeared unrelated to the concentration of H2 detected in the water column, especially in the epilimnetic water layers.