Vegetation Influence and Environmental Controls on Greenhouse Gas Fluxes from a Drained Thermokarst Lake in the Western Canadian Arctic

Abstract

Abstract. 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 (CH4) and carbon dioxide (CO2) fluxes were measured during peak growing season using eddy covariance and chambers at Illisarvik, a 0.16 km2 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 study period, temperature and wind conditions were highly variable and soil water content decreased steadily. Basin scaled net ecosystem exchange (NEE) measured by eddy covariance was −1.5 [CI95 % ± 0.2] g C-CO2 m−2 d−1; NEE followed a marked diurnal pattern with no trend during the study period. NEE was primary controlled by photosynthetic photon flux density and influenced by vapor pressure deficit, volumetric water content and the presence of shrubs. By contrast, net methane exchange (NME) was low (8.7 [CI95 % ± 0.4] mg CH4 m−2 d−1 and had little impact on the carbon balance of the basin during the study period. NME displayed high spatial variability, sedge areas in the basin were the strongest source of CH4 while upland areas outside the basin were a net sink. Soil moisture and temperature were the main environmental factors influencing NME, having a positive and negative effect respectively.

Ratio of In Situ CO2 to CH4 Production and Its Environmental Controls in Polygonal Tundra Soils of Samoylov Island, Northeastern Siberia

“…As expected, the CH 4 fluxes at the drained polygon rim in our study were very low and less variable than at the wet polygon center sub-site, however, it did not act as a CH 4 sink, as reported in other studies (Jørgensen et al, 2015;Kwon et al, 2017;Skeeter et al, 2020;St Pierre et al, 2019). The lack of water saturation and consequently oxic conditions demonstrated by the VWC, which varied from 28.1% to 31.8% within the study period, is probably the main reason for the lower CH 4 fluxes detected at the rim compared to the center.…”

“…(Andresen et al, 2017;Ström et al, 2012). The CH 4 fluxes found in this study are high if only compared to mineral soil wetlands (Skeeter et al, 2020;Vasiliev et al, 2019;I. Wagner et al, 2019).…”

“…Wagner et al, 2003). These differences can be related to the high spatial and temporal variability of CH 4 fluxes in the Siberian tundra (Skeeter et al, 2020), but also to differences in CH 4 flux calculation. The highest CH 4 flux from water-saturated polygon centers on Samoylov (77.9-100.0 mg m −2 d −1 [Sachs et al, 2010]) was calculated from an initial non-linear CH 4 concentration increase with an exponential model, resulting in higher fluxes than linear models.…”

“…Methane fluxes from the water-saturated polygon center of our study site are also at the lower end compared to other Arctic tundra soils. Studies in the Arctic report CH 4 fluxes in wet tundra environments ranging between 1.53 and 419 mg CH 4 m −2 d −1 (Andresen et al, 2017;Kwon et al, 2017;Skeeter et al, 2020;Ström et al, 2012;Vasiliev et al, 2019;I. Wagner et al, 2019).…”

Impacts of ecological succession and climate warming on permafrost aggradation in drained lake basins of the Tuktoyaktuk Coastlands, Northwest Territories, Canada

“…Our observation that most lakes in the Tuktoyaktuk Coastlands that drained in the last 60 years are dominated by upright shrubs indicates that this localized permafrost degradation will be regionally widespread (Figure 1). Although these areas make up a small proportion of the entire study area, the loss of warm and thin permafrost at these sites will have a significant impact on ecological processes including carbon flux, 107 subsidence caused by lateral thaw, 84 and population dynamics of beavers and moose in tundra ecosystems. 108,109 Our field observations and modeling indicate that drained lakes will be among the first permafrost-free environments to develop under a warming climate in the continuous permafrost zone.…”