Abstract
Abstract. Ecosystems exchange climate-relevant trace gases with the atmosphere, including volatile organic compounds (VOCs) that are a small but highly reactive part of the carbon cycle. VOCs have important ecological functions and implications for atmospheric chemistry and climate. We measured the ecosystem-level surface–atmosphere VOC fluxes using the eddy covariance technique at a shallow subarctic lake and an adjacent graminoid-dominated fen in northern Sweden during two contrasting periods: the peak growing season (mid-July) and the senescent period post-growing season (September–October). In July, the fen was a net source of methanol, acetaldehyde, acetone, dimethyl sulfide, isoprene, and monoterpenes. All of these VOCs showed a diel cycle of emission with maxima around noon and isoprene dominated the fluxes (93±22 µmol m−2 d−1, mean ± SE). Isoprene emission was strongly stimulated by temperature and presented a steeper response to temperature (Q10=14.5) than that typically assumed in biogenic emission models, supporting the high temperature sensitivity of arctic vegetation. In September, net emissions of methanol and isoprene were drastically reduced, while acetaldehyde and acetone were deposited to the fen, with rates of up to -6.7±2.8 µmol m−2 d−1 for acetaldehyde. Remarkably, the lake was a sink for acetaldehyde and acetone during both periods, with average fluxes up to -19±1.3 µmol m−2 d−1 of acetone in July and up to -8.5±2.3 µmol m−2 d−1 of acetaldehyde in September. The deposition of both carbonyl compounds correlated with their atmospheric mixing ratios, with deposition velocities of -0.23±0.01 and -0.68±0.03 cm s−1 for acetone and acetaldehyde, respectively. Even though these VOC fluxes represented less than 0.5 % and less than 5 % of the CO2 and CH4 net carbon ecosystem exchange, respectively, VOCs alter the oxidation capacity of the atmosphere. Thus, understanding the response of their emissions to climate change is important for accurate prediction of the future climatic conditions in this rapidly warming area of the planet.
Highlights
Arctic climate is warming twice as fast as the global average (Post et al, 2019)
We focus on several volatile organic compounds (VOCs) that were assigned to known protonated ions (Yáñez-Serrano et al, 2021) detected with the PTRTOF-MS: methanol (m/z 33.03), acetaldehyde (m/z 45.03), acetone (m/z 59.05), dimethyl sulfide (DMS, m/z 63.03) isoprene (m/z 69.07), and monoterpenes (m/z 81.07 and 137.13)
Isoprene dominated by far the VOC fluxes from the fen at the peak of the season, while after the growing season the fen was characterized by deposition of acetaldehyde and acetone (Fig. 3, Table 1)
Summary
Arctic climate is warming twice as fast as the global average (Post et al, 2019) This is due to a number of climate system feedbacks, including (i) albedo change due to retreating snow cover and sea ice and (ii) the forest cover expansion to the open tundra (Overland et al, 2014; Post et al, 2009). R. Seco et al.: Volatile organic compound fluxes in a subarctic peatland and lake the warming-induced expansion of woody shrubs into tundra ecosystems (Myers-Smith and Hik, 2018) could enhance the photosynthetic uptake of CO2 and offset concurrent increases in heterotrophic respiration (Mekonnen et al, 2018). Far less research has been devoted to VOC emissions in these areas
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