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

• Main Authors: Skeeter, June, Christen, Andreas, Laforce, Andrée-Anne, Humphreys, Elyn, Henry, Greg
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Canada; Northwest Territories; Richards Island; Thermokarst; Tundra
• Online Access: https://doi.org/10.5194/bg-2019-477; https://www.biogeosciences-discuss.net/bg-2019-477/

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 (CH 4 ) and carbon dioxide (CO 2 ) fluxes were measured during peak growing season using eddy covariance and chambers at Illisarvik, a 0.16 km 2 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 [CI 95 % ± 0.2] g C-CO 2 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 [CI 95 % ± 0.4] mg CH 4 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 CH 4 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.