Methane oxidation, production, and emission at contrasting sites in a boreal bog

Boreal peatlands, a major source of atmospheric CH4, are characterized by a rapidly fluctuating water table position and meter-scale variations in rel ief. Regional and ecosystem-based studies show that water table position ge nerally controls CH4 emission from boreal peatlands by influencing the rela tive extent of the zones of CH4 oxidation and production within the peat pr ofile. We used a combined field and laboratory study to assess the influenc e of local hydrology on the short-term dynamics of CH4 production, oxidatio n, and emission from sites in an Alaskan boreal peatland that were characte rized by temporarily (site LB1A) and permanently (LB2) water-saturated subs urface peat during the thaw season. The two sites contrasted sharply with r espect to the dynamics of CH4 cycling. Site LB1A, which showed low CH4 conc entrations in pore water (<2 mu M) and unsaturated peat (<2.6 nM), consumed both atmospheric CH4 and CH4 diffusing upward from the saturated zone for a net flux of 0.9 mg CH4 m(2) d(1). In contrast, LB2 had pore water CH4 con centrations, 300 mu M and emitted CH4 at 69 mg m(2) d(1). Roughly 55% of th e CH4 diffusing upward from the saturated zone at LB2 was oxidized in trans it to the peat surface. Methane oxidation potentials (V-ox) were maximum in the 10-cm zone immediately above the local water table at both sites but w ere greater on a dry mass (dw) basis at LB2 (498-650 ng CH4 g(dw)(1) h(1)) than at LB1A (220-233 ng CH4 g(dw)(1) h(1)). Methane production potentials (V-p) were low (<2 ng CH4 g(dw)(1) h(1)) at LB1A, but the maximum at LB2 (1 39 ng CH4 g(dw)(1) h(1)) was spatially coupled with the maximum V-ox. Metha nogens exposed to O-2 produced no CH4 in a subsequent 48 h anoxic incubatio n, whereas methanotrophs incubated anoxically oxidized CH4 vigorously withi n 20 h of return to an oxic environment, indicating that the former are mor e sensitive than the latter to adverse O-2 conditions. Experiments with (CH 4)-C-14 showed that similar to 71% of assimilated (CH4)-C-14 was respired a s (CO2)-C-14. Respiration by methanotrophs contributes at most similar to 1 .1-1.7% (molar basis) of gross ecosystem respiration (15.6-17.9 mg CO2 m(2) d(1)) at these sites.