Soil carbon content and CO2 flux along a hydrologic gradient in a High-Arctic tundra lake basin, Northwest Greenland

Abstract:

High Arctic landscapes are composed of watershed basins that vary in size and ecohydrology, but typically have a plant community complex that ranges from dry tundra to moist tundra to wet sedge systems along water body shorelines. The spatial extent of these plant communities reflects mean annual soil moisture and temperature, and is vulnerable to changes in climate conditions. Soil moisture and temperature significantly influence organic matter microbial activity and decomposition, and can affect the fate of soil carbon in tundra soils. Consequently, due to the unique soil carbon differences between tundra plant communities, shifts in their spatial extent may drive future High Arctic biosphere-atmosphere interactions. Understanding this terrestrial-atmosphere trace gas feedback, however, requires quantification of the rates and patterns of CO₂ exchange along soil moisture gradients and the associated soil properties. In summer of 2015, soil CO₂ flux rate, soil moisture and temperature were measured along a soil moisture gradient spanning three vegetation zones (dry tundra, wet tundra, and wet grassland) in a snow melt-fed lake basin near Thule Greenland. Mean soil temperature during the 2015 growing season was greater in dry tundra than in wet tundra and wet grassland (13.0 ± 1.2, 7.8 ± 0.8, and 5.5 ± 0.9°C, respectively). Mean volumetric soil moisture differed among all three vegetation zones where the soil moisture gradient ranged from 9 % (dry tundra) to 34 % (wet tundra) to 51 % (wet grassland). Mean soil CO₂ flux was significantly greater in the wet grassland (1.7 ± 0.1 µmol m^-2 s^-1) compared to wet tundra (0.9 ± 0.2 µmol m^-2 s^-1) and dry tundra (1.2 ± 0.2 µmol m^-2 s^-1). Soil CO₂ flux increased and decreased with seasonal warming and cooling of soil temperature. Although soil temperature was an important seasonal driver of soil CO₂ flux rates, differences in mean seasonal soil CO₂ flux rates among vegetation zones appeared to be a function of the combined effects of soil temperature and soil moisture conditions. These results suggest that the response of vegetation distribution to shifts in precipitation and warmer climate conditions may have significant implications for release of soil carbon as CO₂ in High Arctic tundra ecosystems in Northwest Greenland.