TRACE ELEMENT DYNAMICS AND MICROBIAL SULFATE REDUCTION IN RESPONSE TO HISTORICAL CARBON PULSES IN AN ICE-COVERED HIGH ARCTIC LAKE

Arctic lakes, which remain ice-covered for most of the year, are highly sensitive to accelerating climate change and vulnerable to human impacts. Lake Meretta (NU, Canada, 74°42’N) offers a rare opportunity to study the impacts of human-induced nutrient loads in a High Arctic, ice-covered lake. Its upstream basin (A) received decades of elevated organic carbon inputs from sewage discharges, while the downstream basin (B) remained unaffected. In this study, we collected 40 cm sediment cores beneath a 1.8 m-thick ice cover and sampled both sediments and porewater from the two basins. We analyzed vertical profiles of nutrients (NH₄⁺, PO₄^3-), essential micronutrients (Fe, Mn, S, V, Mo, Co, Cu), sulfides (HS^-), and potential contaminants (Cd, As, Pb) to assess trace element mobility and geochemical processes. Our findings show distinct geochemical dynamics between the two basins: (1) Porewater concentration gradients of NH₄⁺ and PO₄^3- indicate that sediments in both basins act as a source of NH₄⁺, but only basin A continues to release PO₄^3-; (2) Basin A exhibits elevated HS⁻ levels (up to 19.6 µM) and low Fe, pointing to sulfur-driven geochemistry, whereas basin B has high dissolved Fe (up to 274 µM) and comparatively lower HS^-; (3) Dissolved trace element concentrations are generally much higher in basin A, with the exception of Mn and Co, which are more concentrated in basin B. Overall, our results suggest that historical carbon inputs have led to sustained sulfur-reducing conditions, which remain key drivers of nutrient and trace element mobility in the eutrophic basin A.

Presentation Preference: Oral

Primary Presenter: Florence Mercier, Université Laval (florence.mercier.3@ulaval.ca)

Authors:

Florence Mercier, Department of Chemistry, Centre for Northern Studies (CEN), Interuniversity Research Group in Limnology (GRIL), Université Laval, Canada  (florence.mercier.3@ulaval.ca)

Catherine Girard, Department of Fundamental Sciences, Centre for Northern Studies (CEN), Interuniversity Research Group in Limnology (GRIL), Université du Québec à Chicoutimi, Canada  (catherine5_girard@uqac.ca)

Pénélope Blackburn-Desbiens, Department of Fundamental Sciences, Centre for Northern Studies (CEN), Interuniversity Research Group in Limnology (GRIL), Université du Québec à Chicoutimi, Canada  (pbdesbiens@etu.uqac.ca)

Raoul-Marie Couture, Department of Chemistry, Centre for Northern Studies (CEN), Interuniversity Research Group in Limnology (GRIL), Université Laval, Canada  (raoul.couture@chm.ulaval.ca)