Methane and Carbon Dioxide in the Sediment of a Eutrophic Reservoir: Production Pathways and Diffusion Fluxes at the Sediment–Water Interface

The estimated diffusion fluxes of methane (CH(4)) and carbon dioxide (CO(2)) at the sediment–water interface in the Rzeszów Reservoir in southeastern Poland are presented. The relevant studies were conducted during 2009, 2010, and 2011. Calculated fluxes ranged from 0.01 to 2.19 mmol m(−2) day(−1) and from 0.36 to 45.33 mmol m(−2) day(−1) for methane and carbon dioxide, respectively. While the values for calculated diffusion fluxes of methane are comparable with those reported for other eutrophic reservoirs, much higher values were obtained here for carbon dioxide. The resulting values of δ(13)C-CH(4) and the fractionation coefficients between methane and carbon dioxide (αCH(4)-CO(2)) suggest that methane in the sediment of the Rzeszów Reservoir is produced by acetate fermentation, while the hydrogenotrophic methanogenic process is of successively greater importance with increasing depth. In the top layer of the sediment, 24–72 % of CO(2) came from methanogenesis, while the contribution made by the degradation of organic matter by methanogenesis to CO(2) was greater in the deeper layer.