Tundra is a consistent source of CO₂ at a site with progressive permafrost thaw during 6 years of chamber and eddy covariance measurements

Abstract

Current and future warming of high‐latitude ecosystems will play an important role in climate change through feedbacks to the global carbon cycle. This study compares 6 years of CO2 flux measurements in moist acidic tundra using autochambers and eddy covariance (Tower) approaches. We found that the tundra was an annual source of CO2 to the atmosphere as indicated by net ecosystem exchange using both methods with a combined mean of 105 ± 17 g CO2 C m−2 y−1 across methods and years (Tower 87 ± 17 and Autochamber 123 ± 14). The difference between methods was largest early in the observation period, with Autochambers indicated a greater CO2 source to the atmosphere. This discrepancy diminished through time, and in the final year the Autochambers measured a greater sink strength than tower. Active layer thickness was a significant driver of net ecosystem carbon exchange, gross ecosystem primary productivity, and Reco and could account for differences between Autochamber and Tower. The stronger source initially attributed lower summer season gross primary production (GPP) during the first 3 years, coupled with lower ecosystem respiration (Reco) during the first year. The combined suppression of GPP and Reco in the first year of Autochamber measurements could be the result of the experimental setup. Root damage associated with Autochamber soil collar installation may have lowered the plant community's capacity to fix C, but recovered within 3 years. While this ecosystem was a consistent CO2 sink during the summer, CO2 emissions during the nonsummer months offset summer CO2 uptake each year.

Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic

“…Generally, these also show that interannual variability may not be as significant as variability among land cover types. In a 6-year eddy covariance study in upland tundra in interior Alaska, interannual variability in NEE was~5 0% (Celis et al, 2017), larger than the interannual variability in this study but still smaller than variability among land cover types. However, further north in Alaskan tundra, interannual variability in growing season NEE over 8 years measured with eddy covariance was 13% (Euskirchen et al, 2017), slightly smaller than in this study or in the other interior Alaska site.…”

Nonlinear CO2 flux response to 7 years of experimentally induced permafrost thaw

“…Flux rates were determined using linear regression and converted from volumetric (ppm CO 2 m 2 s −1 ) to mass (μmol CO 2 m −2 s −1 ) using plot‐specific chamber volumes and air temperatures. A recent analysis showed CO 2 fluxes and light response curves from Control plots were comparable to ambient tundra fluxes monitored at an adjacent eddy covariance tower (Celis et al., in review) indicating that there was no adverse effect of chambers on CO 2 fluxes (but see statistical analysis for a note on 2009). Details on filtering can be found in the supplement.…”

“…In 2009, NEE was surprisingly low compared to chamber and eddy covariance estimates in an adjacent watershed (Belshe, Schuur, Bolker, & Bracho, ; Trucco et al., ). We suspect root disturbance from installing the experiment suppressed CO 2 fluxes, but were recovered a year later (2010) (Celis et al., in review). The ability of the system to respond to treatments was not impaired (Natali et al., ), but to avoid overestimating the changes in CO 2 flux over time, temporal trends in Control are reported relative to 2010 (Table ).…”

Methane Efflux Measured by Eddy Covariance in Alaskan Upland Tundra Undergoing Permafrost Degradation

“…Measured versus modeled data are shown in Figure . The gap filling of CO 2 fluxes is as described in Celis et al, .…”

“…Permafrost degradation has resulted in heterogeneous ground subsidence that has affected surface hydrology and soil temperatures, as well as shifting plant species composition from tussock forming sedges to shrub species in areas of increased thaw (Belshe et al, ; Schuur et al, ). Carbon dioxide fluxes from the site have been characterized using chamber‐based and eddy covariance data collection since 2004 (Belshe et al, ; Celis et al, ; Lee et al, ; Trucco et al, ; Vogel et al, ). Thawing of permafrost at Eight Mile Lake (EML) has amplified the CO 2 ‐C cycle during the growing season, stimulating photosynthesis and ecosystem respiration and shifting EML from a historically net sink to CO 2 neutrality like other sites within the tundra biome (Belshe et al, ; Hicks Pries et al, ; Belshe et al, ), and a net source of CO 2 on an annual basis due to nonsummer season emissions (Celis et al, ).…”