Preskienis, Vilmantas; Bouchard, Frédéric; Laurion, Isabelle; Fortier, Daniel
(2014).
Greenhouse Gas Emissions From Arctic Lakes And Ponds As Influenced By Carbon Lability.
In: Artic Change 2014, 8-12 décembre 2014, Ottawa, Canada.
Résumé
The rapid climate warming in Arctic regions has induced
extensive permafrost thawing and the consequent mobilization
of a large reservoir of organic carbon that was frozen for
millennia. Although the release of this old carbon into the
atmosphere, either as carbon dioxide (CO2) or methane (CH4),
acts as a positive feedback mechanism to global warming, very
little is known about the extent and rate of the gas release and
the biochemical processes involved as the different carbon
pools are becoming available to ecosystems of Arctic lakes and
ponds. As a part of an interdisciplinary project investigating
the influence of geomorphological and limnological factors
on GHG emissions from lakes and ponds on Bylot Island,
Nunavut, the present study aims to determine the lability and
accessibility of the different carbon pools to microorganisms.
In 2014, lability experiments were performed on four sediment
types found in organic-rich polygonal patterned ground
landscape and possessing specific characteristics (e.g., annual
thermal regime, C/N ratio): upper-half portion of the active
layer, lower-half of the active layer, permafrost, and thermokarst
lake sediment. The different soil samples were incubated
in-situ in shaded conditions, in one of the shallow tundra
ponds. These incubation tests were repeated in controlled and
stable temperature conditions in laboratory. Leachates were
also produced from the same soils and incubated similarly
both in the field and in the laboratory. Dissolved oxygen (O2)
and headspace CH4 and CO2 concentrations were measured
regularly over a period of up to two weeks, and the rates of
consumption or production were calculated. Preliminary
results show that O2 consumption rates were higher in upper
active layer samples, while it depleted more slowly in other
incubations, suggesting the presence of active aerobic consumers
of organic matter in active layer soils naturally exposed to O2.
On the other hand, the production of CO2 was faster in lake
sediments, whereas permafrost soils showed highest rates of
CH4 production and lowest rates of CO2 production, possibly
indicating a variable balance between different CH4 pathways
in soils that are naturally anaerobic. Overall, the rates of CO2
production were not inversely correlated to O2 consumption
rates, suggesting complex microbial communities inhabiting
different niches in such Arctic landscapes, with a wide range of
possible responses to the expected increase in carbon availability
as permafrost thaws. These results also indicate the need to
employ a wider array of indicators to assess C lability of Arctic
soils.
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