The potential for releasing methane from artificial lakes in Central Germany--a 13C study

Methane is a strong greenhouse gas. Inland waters are thought to be important sources of methane, although detailed studies of emissions (diffusion and ebullition) are limited. This is the reason why we investigated the sediments of three anthropogenic lakes with respect to methane formation. Methane of microbial origin could be proved in any case. In one case, methane was released into the atmosphere by ebullition. The measured fluxes ranged between 134 and 935 mg CH(4) m(-2)d(-1). The fluxes close above the sediments were higher (274-4107 mg CH(4) m(-2)d(-1)). The decrease of methane content in the bubbles from greater to lower sampling depths is connected with an increase in its delta(13)C values. The Rayleigh equation has been used to calculate fractionation factors alpha between 1.0104 and 1.0163, which means that the changes are due to oxidation processes within the predominant oxic water column. However, large amounts of methane still reach the atmosphere.