The dominant role of sunlight in degrading winter dissolved organic matter from a thermokarst lake in a subarctic peatland
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Published:2022-08-31
Issue:17
Volume:19
Page:3959-3977
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Mazoyer Flora,Laurion Isabelle,Rautio Milla
Abstract
Abstract. Dissolved organic matter (DOM) leaching from thawing permafrost
may promote a positive feedback on the climate if it is efficiently
mineralized into greenhouse gases. However, many uncertainties remain on the
extent of this mineralization, which depends on DOM lability that is
seemingly quite variable across landscapes. Thermokarst peatlands are
organic-rich systems where some of the largest greenhouse gas (GHG) emission
rates have been measured. At spring turnover, anoxic waters release
the GHG accumulated in winter, and the DOM pool is exposed to
sunlight. Here, we present an experiment where DOM photoreactivity and bioreactivity
were investigated in water collected from a thermokarst lake in a subarctic
peatland during late winter (after 6 months of darkness). We applied
treatment with or without light exposure, and manipulated the bacterial
abundance with the aim to quantify the unique and combined effects of light
and bacteria on DOM reactivity at ice-off in spring. We demonstrate that
sunlight was clearly driving the transformation of the DOM pool, part of
which went through a complete mineralization into CO2. Up to 18 % of the initial dissolved organic carbon (DOC, a loss of 3.9 mgC L−1) was lost
over 18 d of sunlight exposure in a treatment where bacterial abundance
was initially reduced by 95 %. However, sunlight considerably stimulated
bacterial growth when grazers were eliminated, leading to the recovery of
the original bacterial abundance in about 8 d, which may have contributed
to the DOC loss. Indeed, the highest DOC loss was observed for the treatment
with the full bacterial community exposed to sunlight (5.0 mgC L−1),
indicating an indirect effect of light through the bacterial consumption of
photoproducts. Dark incubations led to very limited changes in DOC,
regardless of the bacterial abundance and activity. The results also show
that only half of the light-associated DOC losses were converted into
CO2, and we suggest that the rest potentially turned into particles
through photoflocculation. Sunlight should therefore play a major role in
DOM processing, CO2 production and carbon burial in peatland lakes
during spring, likely lasting for the rest of the open season in mixing
surface layers.
Funder
Natural Sciences and Engineering Research Council of Canada Fonds de recherche du Québec – Nature et technologies
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
Reference89 articles.
1. Adams, H. E., Crump, B. C., and Kling, G. W.: Temperature controls on aquatic
bacterial production and community dynamics in arctic lakes and streams,
Environ. Microbiol., 12, 1319–1333,
https://doi.org/10.1111/j.1462-2920.2010.02176.x, 2010. 2. Arlen-Pouliot, Y. and Bhiry, N.: Palaeoecology of a palsa and a filled
thermokarst pond in a permafrost peatland, subarctic Québec, Canada, The
Holocene, 15, 408–419, https://doi.org/10.1191/0959683605hl818rp, 2005. 3. Bégin, P. N. and Vincent, W. F.: Permafrost thaw lakes and ponds as
habitats for abundant rotifer populations, Arct. Sci., 3, 354–377,
https://doi.org/10.1139/as-2016-0017, 2017. 4. Berggren, M., Laudon, H., and Jansson, M.: Landscape regulation of bacterial
growth efficiency in boreal freshwaters, Global Biogeochem. Cy., 21, GB4002,
https://doi.org/10.1029/2006GB002844, 2007. 5. Berggren, M., Gudasz, C., Guillemette, F., Hensgens, G., Ye, L., and
Karlsson, J.: Systematic microbial production of optically active dissolved
organic matter in subarctic lake water, Limnol. Oceanogr., 65, 951–961,
https://doi.org/10.1002/lno.11362, 2020.
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