The ratio of methanogens to methanotrophs and water-level dynamics drive methane transfer velocity in a temperate kettle-hole peat bog
<p>Peatlands are a large source of methane (<span class="inline-formula">CH<sub>4</sub></span>) to the atmosphere, yet the uncertainty around the estimates of <span class="inline-formula">CH<sub>4</sub></span> flux from peatla...
Main Authors: | , , , , , , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2019-08-01
|
Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/16/3207/2019/bg-16-3207-2019.pdf |
Summary: | <p>Peatlands are a large source of methane (<span class="inline-formula">CH<sub>4</sub></span>) to the
atmosphere, yet the uncertainty around the estimates of <span class="inline-formula">CH<sub>4</sub></span> flux from
peatlands is large. To better understand the spatial heterogeneity in
temperate peatland <span class="inline-formula">CH<sub>4</sub></span> emissions and their response to physical and
biological drivers, we studied <span class="inline-formula">CH<sub>4</sub></span> 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), <span class="inline-formula">CH<sub>4</sub></span> pore-water
concentration at different peat depths, <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span> emissions for the growing season were estimated as <span class="inline-formula">315.4±166</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mg</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">CH</mi><mn mathvariant="normal">4</mn></msub><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="78pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="ef20001b32af2721b2dc95616d9bbffd"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3207-2019-ie00001.svg" width="78pt" height="16pt" src="bg-16-3207-2019-ie00001.png"/></svg:svg></span></span> in 2017 and <span class="inline-formula">362.3±687</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mg</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">CH</mi><mn mathvariant="normal">4</mn></msub><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="78pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="76b89e953aa6d4e973a65484dea0a34b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3207-2019-ie00002.svg" width="78pt" height="16pt" src="bg-16-3207-2019-ie00002.png"/></svg:svg></span></span> in 2018. Median <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mg</mi><mspace linebreak="nobreak" width="0.125em"/><msub><mi mathvariant="normal">CH</mi><mn mathvariant="normal">4</mn></msub><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="78pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="22bd542194aabf3918bdd58dbd499748"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3207-2019-ie00003.svg" width="78pt" height="16pt" src="bg-16-3207-2019-ie00003.png"/></svg:svg></span></span>).
Generally, <span class="inline-formula">CH<sub>4</sub></span> flux from above-ground vegetation was negligible
compared to ground flux (<span class="inline-formula"><0.4</span> %), although blueberry plants were
a small <span class="inline-formula">CH<sub>4</sub></span> sink. Pore-water <span class="inline-formula">CH<sub>4</sub></span> 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
<span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span>
transfer velocity (the <span class="inline-formula">CH<sub>4</sub></span> flux divided by the difference in <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span> and the peat
structure and porosity were similar across the different zones in the bog,
we conclude that the differences in <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span> fluxes from bogs and wetlands in general.</p> |
---|---|
ISSN: | 1726-4170 1726-4189 |