Climate change can promote the expansion of the global area occupied by ponds in ice-wedge polygon landscapes. Concurrently, organic material previously sequestered in permafrost becomes accessible to microbial degradation. We aim to identify the drivers of dissolved organic matter (DOM) transformation in these small aquatic systems in order to better understand carbon cycling in Arctic lowlands. During summers 2017 to 2019, ponds displaying different levels of permafrost erosion and colonization by primary producers were sampled in a glacier valley on Bylot Island (Nunavut, Canada). We assessed spatial variations in DOM concentration, absorbance and fluorescence (PARAFAC modelling), and in the speciation of nutrients. Filtered water from 15 ponds was incubated over 180 days in the dark and we quantified the loss of dissolved organic carbon (DOC) over time, with a subset of samples enriched with nutrients. Different aspects of bacterial metabolism were also measured along with environmental conditions. The results show that despite differences in DOM and nutrient availability, DOC decline was similar among ponds; about 30% of DOC was consumed. However, nutrient addition doubled the rate of DOC decomposition in ponds characterized by high permafrost erosion. Hypoxic bottom water layers were also identified as hot spots for the microbial transformation of DOM. A better understanding of DOM processing in these abundant water bodies is key to assess future trends in lateral carbon export along the terrestrial-aquatic continuum in the Arctic, and its impact on futur climate.

Primary Presenter: Thomas Pacoureau, Institut national de la recherche scientifique (thomas.pacoureau@gmail.com)

Authors:

Thomas Pacoureau, Groupe de recherche interuniversitaire en limnologie (GRIL), Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, 490 rue de la Couronne Québec (Québec) G1K 9A9 Canada  (thomas.pacoureau@gmail.com)

Isabelle Laurion, Groupe de recherche interuniversitaire en limnologie (GRIL), Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, 490 rue de la Couronne Québec (Québec) G1K 9A9 Canada  (isabelle.laurion@inrs.ca)

Milla Rautio, Groupe de recherche interuniversitaire en limnologie (GRIL), Département des sciences fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université Chicoutimi (Québec) G7H 2B1 Canada  (milla.rautio@uqac.ca)