Variation in CO2 and CH4 Fluxes Among Land Cover Types in Heterogeneous Arctic Tundra in Northeastern Siberia

• Main Authors: Juutinen, Sari, Aurela, Mika, Tuovinen, Juha-Pekka, Ivakhov, Viktor, Linkosalmi, Maiju, Räsänen, Aleksi, Virtanen, Tarmo, Mikola, Juha, Nyman, Johanna, Vähä, Emmi, Loskutova, Marina, Makshtas, Alexander, Laurila, Tuomas
• Format: Other/Unknown Material
• Language: English
• Published: 2022
• Subjects: Arctic; Tiksi; Tundra; Siberia
• Online Access: https://doi.org/10.5194/bg-2022-5; https://bg.copernicus.org/preprints/bg-2022-5/

Arctic tundra is facing unprecedented warming, resulting in shifts in the vegetation, thaw regimes, and potentially in the ecosystem-atmosphere exchange of carbon (C). The estimates of regional carbon dioxide (CO 2 ) and methane (CH 4 ) budgets, however, are highly uncertain. We measured CO 2 and CH 4 fluxes, vegetation composition and leaf area index (LAI), thaw depth, and soil wetness in Tiksi (71° N, 128° E), a heterogeneous site located within the prostrate dwarf-shrub tundra zone in northeastern Siberia. Using the closed chamber method, we determined net ecosystem exchange (NEE) of CO 2 , dark ecosystem respiration (ER), ecosystem gross photosynthesis (Pg), and CH 4 fluxes during the growing season. We applied a previously developed high-spatial-resolution land-cover map over an m area of 35.8 km 2 . Among the land-cover types varying from barrens to dwarf-shrub tundra and tundra wetlands, the light-saturated NEE and Pg scaled with the LAI of vascular plants. Thus, the graminoid-dominated tundra wetlands, with high LAI and the deepest thaw depth, had the highest light-saturated NEE and Pg (up to −21 (uptake) and 28 mmol m −2 h −1 , respectively) and were disproportionately important for the summertime CO 2 sequestration on a landscape scale. Dry tundra, including the dwarf-shrub-dominated vegetation and only sparsely vegetated lichen tundra, had only small CO 2 exchange rates. While tundra wetlands were sources of CH 4 , lichen tundra, including bare ground habitats, consumed atmospheric CH 4 at a substantial rate. On a landscape scale, the consumption by lichen tundra and barrens could offset ca . 10 % of the CH 4 emissions. We acknowledge the uncertainty involved in spatial extrapolations due to a small number of replicates per land-cover type. This study, however, highlights the need for distinguishing different land-cover types including the dry tundra habitats to account for their consumption of the atmospheric CH 4 when estimating tundra C-exchange on a larger spatial scale.