PARTITIONING PEAT RESPIRATION IN THE CATOTELM

Methane production dominates respiration in peatland environments. In these systems, pore water CO₂ concentrations are consistently higher than CH₄ concentrations although methanogenesis should produce equimolar amounts of each gas. These findings suggest alternative modes of CO₂ production as well as the possibility of methane loss due to ebullition and vascular-plant transport. We developed an isotope mass-balance approach that uses δ¹³C_CO2 and δ¹³C_CH4 to determine the relative proportions of CO₂ formed from organic-matter fermentation and methanogenesis. Subsequently the model uses the measured concentrations of CO₂ and CH₄ with the calculated proportion of CO₂ from methanogenesis to determine the percent loss of CH₄. To test our model and to show that we can predict CO₂ and CH₄ concentrations using isotopic values, we conducted an anaerobic closed-system incubation experiment. The average difference between measured concentration and those predicted from isotopic values was 3.5%. Our results showed that CO₂ partitioning in peatlands can be determined using our isotope mass-balance model. Applying our isotope mass-balance model to field data showed a higher percent of CO₂ production from methanogenesis in bogs (100%) than fens (90%) overall. CO₂ formed from organic-matter fermentation at depths above 50cm was found to be on average 20% greater than deeper depths suggesting a greater role for fermentation in surface peats. The percent methane loss between bogs and fens was shown to be either slightly higher in fens than bogs or similar between the two (85–100%).