Methane and CO2 production in the wetland Lake Podpeč (Slovenia)

Abstract

Purpose This study deals with the identification of CH4 and CO2 sources in the high-carbonate wetland Lake Podpeč in the Ljubljana Marshes, Slovenia. Materials and methods Lake Podpeč is situated on the periphery of the Ljubljana Marshes in central Slovenia. A combination of chemical analysis and natural abundance analysis of stable carbon and hydrogen isotopes of CH4, along with analysis of dissolved inorganic carbon (DIC), was employed in an incubation experiment. Results and discussion The isotopic composition of dissolved inorganic carbon (δ13CDIC) suggests three main processes occurring during incubation: oxic degradation of organic matter (OM), anoxic OM degradation, and methanogenesis. During oxic degradation of OM, the δ13CDIC values slightly decrease from − 13.2 to − 14.5‰. However, after 50 days, the δ13CDIC values started to increase, reaching − 12.2‰ by the end of the experiment. 13C enrichment coincided with the formation of CH4, which began to increase simultaneously. The CH4 produced had an average δ13CCH4 value of − 67 ± 1‰ and δ2HCH4 value of − 389 ± 3‰, suggesting that CH4 is formed through acetate fermentation. The contribution of calcite dissolution to DIC increased during the degradation of OM by 53%. However, during methanogenesis, there was no significant change in the concentrations of Ca, and the estimated contribution to DIC was only 3%. Conclusions This study enhances our understanding of methane production in wetland Lake Podpeč and its relevance in the context of other high-carbonate lakes. The findings offer insights into the complex interactions between OM degradation, methane production pathways, and carbonate dissolution, which has implications for the global carbon cycle and greenhouse gas emissions.