Partitioning CO2 production with stable carbon isotopes in a peatland ecosystem

We developed an isotope mass-balance model to predict the percent of CO2 formed from either organic-matter fermentation or methanogenesis using pore water δ13C-CO2 and δ13C-CH4 in a peatland ecosystem. Our second objective was to determine percent CH4 loss using CO2 and CH4 concentrations and the predicted percent of CO2 from methanogenesis. The assumption that methanogenesis produces equimolar amounts of CH4 and CO2 and multiple field and incubation measurements that show higher concentrations of CO2 indicate that organic-matter fermentation is an important respiration pathway in these systems. Lower concentrations of CH4 could be accounted for by ebullition and vascular-plant transport. A closed system incubation study was done to determine if predicted CO2 and CH4 concentrations calculated using isotopes compared to measured concentration values. The average difference between the two approaches was 3.5%. Using the model to analyze field measurements, we found that a higher percent of CO2 was produced from methanogenesis than organic matter fermentation in both bog and fen environments. At depths, bogs had a slightly higher percent of CO2 from methanogenesis (100%) than did fens (90%). Surface depths shallower than 50cm produced a significantly larger (20%) amount of CO2 from organic-matter fermentation than deeper depths. Bogs and fens showed a similar amount of methane loss between 85-100% depending on depth.