Hydrogen, carbon monoxide, and methane dynamics in Lake Constance

The vertical distributions of dissolved H2, CO, and CH4 and bacterial production (thymidine incorporation) were measured throughout 1987 in Lake Constance (Bodensee) and again in 1988 at a station in a small bight in the lake. Lake waters were supersaturated with respect to atmospheric H2, CO, and CH4, especially in the epilimnion; concentrations in the surface water showed a significant (P < 0.05) positive correlation with either autotrophic picoplankton, primary production, Chl a, pheophytin, or bacterial production. Dissolved H2 and CO did not exhibit a distinct seasonal pattern, but dissolved CH4 regularly increased during stratification and decreased in winter. Vertical profiles showed that surface maxima of CH4 were not due to diffusion from methanogenic profundal sediment. Lateral transects and epilimnetic mass balance indicated that CH4 may have originated from methanogenic littoral sediments along the shoreline and may also have been produced in oxic epilimnetic water by unknown processes. The water samples contained microbes able to oxidize H2, CO, and CH4, but threshold concentrations required to sustain oxidation usually were higher than actual in situ concentrations of these gases. We therefore inferred that epilimnetic production of the gases was balanced by evasion to the atmosphere. With the stagnant film model, we determined that the mean residence times of the gases in the epilimniom were on the order of 2–16 d.