ICMGP - Conference Presentation

Abstract Information :

Lake Hazen, the largest lake by volume north of the Arctic Circle, has been impacted by climate warming bringing about an approximately 10x increase in glacial meltwater since the mid-2000s, increased frequency of summer ice-free conditions, and greater turbidity of inflowing and nearshore lake waters. Arctic char (Salvelinus alpinus), the only fish species in the lake, are landlocked, and thus excellent sentinels of Hg/methyl Hg in this system. Adult char (>200 g) were collected in June-July by gillnetting or angling with 20 collection years since 1990. Two morphotypes of char were evident, with the larger form being higher on the trophic scale than the smaller form (average ?15N 13.4 ñ 0.6 and 9.3 ñ 0.7?, respectively) and having higher Hg concentrations than the smaller form (average 0.39 ñ 0.24 and 0.09 ñ 0.06 ng/g dry weight, respectively). Average Hg concentrations in the large form char declined from the mid-1990s to 2005, increased during the period 2006-2012, and then began declining again from 2013 to 2021. For the small char, Hg concentrations declined significantly from 1992 to 2019 (P=0.036). During the study period, atmospheric gaseous elemental Hg concentrations declined at Alert, a nearby monitoring station. Preliminary models linked Hg trends in the small form char Hg with winter temperature (-) and snow depth (-), as well as glacier mass balance (+), summer rainfall (+), and lake ice area in summer (+). For the large form char, glacial runoff (-), lake ice phenology (+), and spring rain (+) were important predictors of Hg concentration. Long-term monitoring of these char has revealed divergent Hg trends among the subpopulations. This analysis indicates their differing life histories link them to unique climatic trends amid mixed Hg trends (declines in atmospheric Hg, increases in glacially sourced Hg to Lake Hazen) in their environment.