WATER-TABLE CONTROL OF CH4 EMISSION ENHANCEMENT BY VASCULAR PLANTS INBOREAL 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 Care r rostrata removed decreased by over 30%. Dissolved CH4 pore water con centrations in the rooting zone were 1.2 to 2.5 times greater than the storage at similar sites where vegetation was removed by clipping, su ggesting that the removal of vascular vegetation decreased CH4 product ion. Moreover, nighttime CH4 flux enhancement was coincident with the diurnal peak in dissolved CH4 pore water concentration. A positive cor relation between mean daily net ecosystem production and mean daily CH 4 flux (r(2) = 0.655, n = 8) at lawn sites with sedge vegetation sugge sts 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 grow ing season and was correlated to the position of the water table. Unde r low water table conditions the presence of vascular plant cover has a lesser effect in enhancing CH4 emissions, indicating that CH4 and ne t ecosystem exchange coupling is limited to vascular plants and only t o sites that remain wet with the water table near the surface.