Abstract. Peatlands are a large source of methane (CH4) to the
atmosphere, yet the uncertainty around the estimates of CH4 flux from
peatlands is large. To better understand the spatial heterogeneity in
temperate peatland CH4 emissions and their response to physical and
biological drivers, we studied CH4 dynamics throughout the growing
seasons of 2017 and 2018 in Flatiron Lake Bog, a kettle-hole peat bog in
Ohio. The site is composed of six different hydro-biological zones: an open
water zone, four concentric vegetation zones surrounding the open water, and
a restored zone connected to the main bog by a narrow channel. At each of
these locations, we monitored water level (WL), CH4 pore-water
concentration at different peat depths, CH4 fluxes from the ground and
from representative plant species using chambers, and microbial community
composition with a focus here on known methanogens and methanotrophs.
Integrated CH4 emissions for the growing season were estimated as 315.4±166 mgCH4m-2d-1 in 2017 and 362.3±687 mgCH4m-2d-1 in 2018. Median CH4 emission was highest in
the open water, then it decreased and became more variable through the
concentric vegetation zones as the WL dropped, with extreme emission
hotspots observed in the tamarack mixed woodlands (Tamarack) and low
emissions in the restored zone (18.8–30.3 mgCH4m-2d-1).
Generally, CH4 flux from above-ground vegetation was negligible
compared to ground flux (<0.4 %), although blueberry plants were
a small CH4 sink. Pore-water CH4 concentrations varied
significantly among zones, with the highest values in the Tamarack zone,
close to saturation, and the lowest values in the restored zone. While the
CH4 fluxes and pore-water concentrations were not correlated with
methanogen relative abundance, the ratio of methanogens to methanotrophs in
the upper portion of the peat was significantly correlated to CH4
transfer velocity (the CH4 flux divided by the difference in CH4 pore-water concentration between the top of the peat profile and the
concentration in equilibrium with the atmosphere). Since ebullition and
plant-mediated transport were not important sources of CH4 and the peat
structure and porosity were similar across the different zones in the bog,
we conclude that the differences in CH4 transfer velocities, and thus
the flux, are driven by the ratio of methanogen to methanotroph relative
abundance close to the surface. This study illustrates the importance of the
interactions between water-level and microbial composition to better
understand CH4 fluxes from bogs and wetlands in general.
The ratio of methanogens to methanotrophs and water-level dynamics drive methane transfer velocity in a temperate kettle-hole peat bog