Global Biogeochemical Cycles

Belowground carbon turnover in a temperate ombrotrophic bog



[1] To examine belowground carbon (C) turnover in peatlands, we measured fluxes of carbon dioxide (CO2) and methane (CH4) by chamber measurements, estimated respiration by in situ incubations of peat, and in situ production of dissolved carbon (CO2; CH4; and dissolved organic carbon, DOC) by pore water modeling at an ombrotrophic temperate bog. Ecosystem respiration (ER) averaged 205 mmol m−2 d−1 in summer and was related to temperature, but not water table position, and in situ rates of heterotrophic respiration in the unsaturated zone were also temperature-dependent, with Q10 = 5.0 − 6.4. In the saturated zone, concentrations of 0.1 − 2.5 mmol L−1 (CO2), 0 to 0.6 mmol L−1 (CH4), and <10 − 120 mg L−1 (DOC) were recorded. Turnover was dominated by DOC unrelated to respiration, which ranged from <0.5 to 7 mmol m−2 d−1 and amounted on average to < 1% of ER. Peat decomposition constants kd were 0.060 yr−1 to 0.034 yr−1 in the unsaturated and <0.002 yr−1 in the saturated zone. Monthly averages of CH4 fluxes ranged from 0 to 1.6 mmol m−2 d−1 and were higher than modeled diffusive fluxes when threshold concentrations for CH4 ebullition were recorded closer to the peatland surface. Our results suggest that the saturated zone is of little relevance to ER in this dry temperate bog and that mobilization of DOC is a potentially more relevant process. Temperature is a more important control on ER than water table position because most of the ER is generated close to the peatland surface. Concurrent, moderate increases in temperature and soil moisture are thus likely to increase losses of CO2 from ER and of CH4 from this type of peatland.