Carbon dynamics in forest fire affected permafrost soils
Aaltonen H. (2020). Carbon dynamics in forest fire affected permafrost soils. https://doi.org/10.14214/df.288
Abstract
Northern Hemisphere permafrost soils store approximately 50% of the global soil carbon (C), a quarter of which could thaw by the end of the century. Thawing exposes previously frozen soil organic matter (SOM) to decomposition, resulting in release of greenhouse gases (GHG) from the soils. Vast areas of permafrost soils are covered by boreal forests currently acting as sinks of C. As global warming is strongest at northern latitudes, the occurrence of boreal forest fires may increase. Forest fires further advance permafrost thaw and forest soils may turn from sinks to sources.
This thesis examines how forest fires affect the quality of SOM and GHG emissions from permafrost soils in boreal forests by conducting chemical fractionation of SOM and soil incubations, as well as manual chamber measurements of GHGs.
Forest fires increased the active layer depth on top of permafrost, altered species composition of vegetation and affected the organic layer depth and the SOM pools. Fires decreased the quality of SOM, observed as reduction in the proportional amount of labile SOM fraction and increased SOM temperature sensitivity, as well as enrichment with heavier isotopes of 13C and 15N. GHG measurements showed that fire initially decreased carbon dioxide flux from the soil and it returned to its pre-fire status approximately 50 years after the fire. The effects of fires on methane and nitrous oxide fluxes were not significant.
Forest fires have significant effects on the release of GHGs from permafrost soils. In the future, the fate of permafrost stored SOM is dependent on its degradability, the frequency of fire events and the ability of forests to regenerate, allowing permafrost recovery, in the changing climate. There is a demand for further studies investigating the specifics of different permafrost ecosystems and building a complete picture to estimate total emissions from permafrost regions.
Keywords
soil organic matter;
soil respiration;
Q10;
13C;
greenhouse gas emissions;
15N
Published 27 February 2020
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Available at https://doi.org/10.14214/df.288 | Download PDF
Original articles
Aaltonen H., Köster K., Köster E., Berninger F., Zhou X., Karhu K., Biasi C., Bruckman V., Palviainen M., Pumpanen J. (2019). Forest fires and soil organic matter in Canadian permafrost region: the combined effects of fire and permafrost dynamics on SOM quality. Biogeochemistry 143(2): 257-274.
https://doi.org/10.1007/s10533-019-00560-x
Aaltonen H., Palviainen M., Zhou X., Köster K., Köster E., Berninger F., Pumpanen J. (2019). Temperature sensitivity of soil organic matter decomposition over a forest fire chronosequence in Canadian permafrost region. Journal of Environmental Management 241: 637-644.
https://doi.org/10.1016/j.jenvman.2019.02.130
Köster E., Köster K., Berninger F., Aaltonen H., Zhou X., Pumpanen J. (2017). Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada. Science of the Total Environment 601-602: 895-905.
https://doi.org/10.1016/j.scitotenv.2017.05.246
Köster E., Köster K., Berninger F., Prokushkin A., Aaltonen H., Zhou X., Pumpanen J. (2018). Changes in fluxes of CO2 and CH4 caused by fire in Siberian boreal forest with continuous permafrost. Journal of Environmental Management 228: 405-415.