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Thomas Pacoureau


Ph.D. student

Centre Eau-Terre-Environnement, INRS-ETE

Centre Eau Terre Environnement
490, rue de la Couronne
Quebec, Canada
G1K 9A9

418.654.4677 extension 3772




Research project

Priming effect induced by primary production on terrestrially-derived organic carbon mobilized by permafrost thawing in small arctic lakes

Thermokarst systems, where active processing of organic matter by the microorganisms takes place, cover huge areas of the northern hemisphere. Because of climate warming and subsequent « Greening of the Artic », the biogeochemical regime of these environments could be altered. Indeed, the expected stimulation of primary production could bring more labile carbon to aquatic systems and accelerate the consumption of allochtonous carbon coming from peat decomposition associated to permafrost thaw trough priming effect. By triggering millennium-old carbon released in the atmosphere as greenhouse gases (GHG), this priming effect could represent a positive feedback mechanism on climate and should thus be taken into consideration.
The aim of this project is to test the hypothesis that priming effect significantly increases the mineralization of allochtonous organic matter.

Field studies will be carried out in July 2016 at Bylot Island (Nunavut), in the continuous permafrost zone, where a full range of aquatic systems is represented: thermokarstic lakes, kettle lakes, trough and polygonal thaw ponds, with varying levels of colonization by benthic algae and aquatic plants. Organic matter samples will be collected in various layers of permafrost, according to the age of the carbon stored, as well as organic matter recently fixed by algae and plants. Samples will be used to produce leachates (dissolved organic matter) of various age/sources. A series of experiments will be conduct by incubating different proportions of the leachates (« old » and « young » carbon) at ambient conditions, with or without amendment in nutrients and with a controlled light exposure.

During these incubation experiments, the properties of dissolved organic matter will be monitored, as well as GHG production and oxygen consumption, as proxies for respiration. Other biomarkers, such as fatty acids, and stoechiometric ratios, will be used to assess microbial activity. Stable isotopes analyses will be performed to follow carbon fluxes in order to quantify the priming effect. Productivity measures by incorporation of 3H-Leucine and monitoring of enzymatic activity and microbial biomass (microscopy and flux cytometry) will allow us to estimate bacterial growth efficiency. Produced CO2 will be collected at the end of the incubation period for 14C dating. These experiments will be carried out preferably on the field but some may be conducted under controlled conditions at the laboratory. In the second year, more study sites will be selected especially at the southern limit of the permafrost, near Kuujjuarapik's station, where the nature of organic carbon (age, lability) and the activity of aquatic plants differ.

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