Water table control of CH4 emission enhancement by vascular plants in boreal peatlands

Removal of the vascular vegetation (Eriophorum vaginatum) at two sites in a Swedish boreal peatland decreased the seasonal CH4 flux by 55 to 85%, while the daily CH4 flux at a Canadian boreal peatland with Carex rostrata removed decreased by over 30%. Dissolved CH4 pore water concentrations in the rooting zone were 1.2 to 2.5 times greater than the storage at similar sites where vegetation was removed by clipping, suggesting that the removal of vascular vegetation decreased CH4 production. Moreover, nighttime CH4 flux enhancement was coincident with the diurnal peak in dissolved CH4 pore water concentration. A positive correlation between mean daily net ecosystem production and mean daily CH4 flux (r² = 0.655, n = 8) at lawn sites with sedge vegetation suggests that sites with greater CO2 fixation had a higher CH4 flux, likely through enhanced methanogenesis and transport. The degree of vascular vegetation CH4 flux enhancement, however, changed throughout the growing season and was correlated to the position of the water table. Under low water table conditions the presence of vascular plant cover has a lesser effect in enhancing CH4 emissions, indicating that CH4 and net ecosystem exchange coupling is limited to vascular plants and only to sites that remain wet with the water table near the surface.