Seasonal dynamics of СО2 emission from the surface of a raised bog in Central Siberia

The bog ecosystems of the northern regions, with low productivity, can accumulate large amounts of carbon due to the low rate of decomposition and respiration. However, it is expected that climate change will lead to an intensification of assimilation and respiratory activity. In this work we considered the emission activity of a raised bog during the growing season. We also analyzed the main environmental factors that could have a significant impact on the CO2 emission rates from the bog surface. In our study, we examined the seasonal dynamics of CO2 emission from the surface of a raised bog (ryam). The study of soil emission was carried out for three seasons (2018-2020) on sections of the bog area of different heights - ridges and hollows. Soil emission measurements were performed using an LI-8100A infrared gas analyzer (Li-cor Inc., Lincoln, USA). Temperature measurements measured at three depths - 5, 10, and 15 cm from the surface using a Soil Temperature Probe Type E (Omega, USA). A Theta Probe Model ML moisture meter (Delta T Devices Ltd., UK) was used to measure the volumetric moisture (5 cm from the surface). The bog water level was measured during the entire frost-free period using the HOBO Water level logger U20L-04 (Onset, USA). In terms of the temperature regime of soils, the studied areas also differ significantly from each other, demonstrating the big discrepancies in the more humid seasons of 2019 and 2020. The difference in temperature in these seasons was about 1.0 °С, while in the 2018 season with insufficient moisture, the difference was two times less 0.5 °С. The maximum emission fluxes of СО2 in the studied bog massif were recorded in the first half of August, and the lowest - from the middle of September. The highest emission rates were recorded in the 2019 season: CO2 fluxes from the bog surface averaged 4.17 ± 4.55 μmol CO2/ m2/s per season. For all observation seasons, CO2 fluxes on ridges exceeded hollows by more than 60 % (p ≤ 0.05). The strongest dependence was observed between the CO2 emission rate and soil temperature, moreover, in the season with the amount of precipitation below the mean annual norm (http://www.meteo.ru) - 2018, the correlation is higher and the rcoefficient was 0.6 and 0.8 for the ridge and hollow sites, respectively (p ≤ 0.05). The dependence of CO2 emission on moisture conditions, on the contrary, is rather weak for two sites, and is often negative. Thus, based on the results obtained, it can be concluded that the emission flux from the surface of a raised bog during the snow-free period depends not only on the moisture conditions of a particular season, but also on the section of the bog area: the emission of СО2 from local elevations of the microrelief - ridges is much higher than from more watered areas - hollows. A significant response to moisture conditions was found only for the season with insufficient moisture and in an elevated section of the bog area - ridge site. The CO2 emission rate during the growing season is mainly determined by the temperature regime.

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