Vegetation influence and environmental controls on greenhouse gas fluxes from a drained thermokarst lake in the western Canadian Arctic
<p>Thermokarst features are widespread in ice-rich regions of the circumpolar Arctic. The rate of thermokarst lake formation and drainage is anticipated to accelerate as the climate warms. However, it is uncertain how these dynamic features impact the terrestrial Arctic carbon cycle. Methane (...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-09-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/17/4421/2020/bg-17-4421-2020.pdf |
| Summary: | <p>Thermokarst features are widespread in ice-rich regions of the
circumpolar Arctic. The rate of thermokarst lake formation and
drainage is anticipated to accelerate as the climate warms. However,
it is uncertain how these dynamic features impact the terrestrial
Arctic carbon cycle. Methane (<span class="inline-formula">CH<sub>4</sub></span>) and carbon dioxide
(<span class="inline-formula">CO<sub>2</sub></span>) fluxes were measured during peak growing season using
eddy covariance and chambers at Illisarvik, a 0.16 <span class="inline-formula">km<sup>2</sup></span>
thermokarst lake basin that was experimentally drained in 1978 on
Richards Island, Northwest Territories, Canada. Vegetation in the
basin differs markedly from the surrounding dwarf-shrub tundra and
included patches of tall shrubs, grasses, and sedges with some bare
ground and a small pond in the centre. During the peak growing season,
temperature and wind conditions were highly variable, and soil water
content decreased steadily. Basin-scaled net ecosystem <span class="inline-formula">CO<sub>2</sub></span>
exchange (NEE) measured by eddy covariance was
<span class="inline-formula">−</span>1.5 [CI<span class="inline-formula"><sub>95 %</sub>±0.2</span>] <span class="inline-formula">g</span> <span class="inline-formula">C−CO<sub>2</sub></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"><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="39pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="f49fea5538a36980ffb2f1013d46d025"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-17-4421-2020-ie00001.svg" width="39pt" height="13pt" src="bg-17-4421-2020-ie00001.png"/></svg:svg></span></span>; NEE followed
a marked diurnal pattern with no day-to-day trend during the study
period. Variations in half-hourly NEE were primarily controlled by
photosynthetic photon flux density and influenced by vapour pressure
deficit, volumetric water content, and the presence of shrubs within
the flux tower footprint, which varied with wind direction. Net
methane exchange (NME) was low (8.7 [CI<span class="inline-formula"><sub>95 %</sub>±0.4</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 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 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="488a4208ed88168a6d2d19a7a7a45932"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-17-4421-2020-ie00002.svg" width="78pt" height="16pt" src="bg-17-4421-2020-ie00002.png"/></svg:svg></span></span>) and had little impact on the
growing season carbon balance of the basin. NME displayed high spatial
variability, and sedge areas in the basin were the strongest source of
<span class="inline-formula">CH<sub>4</sub></span> while upland areas outside the basin were a net
sink. Soil moisture and temperature were the main environmental
factors influencing NME. Presently, Illisarvik is a carbon sink during
the peak growing season. However, these results suggest that rates of
growing season <span class="inline-formula">CO<sub>2</sub></span> and <span class="inline-formula">CH<sub>4</sub></span> exchange rates may
change as the basin's vegetation community continues to evolve.</p> |
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| ISSN: | 1726-4170 1726-4189 |