Influences on bioaccumulation and biota-sediment accumulation factors for methyl-mercury in High Arctic lake food webs.

Mercury (Hg) concentrations in the fillets of Arctic char (Salvelinus alpinus) differ widely among neighboring oligotrophic lakes on Cornwallis Island (Nunavut, Canada), but the reasons for these differences are poorly understood. Climate change is likely affecting Hg cycling in lakes, although studies report conflicting or mixed responses. We quantified Hg bioaccumulation (BAFs), biota-sediment accumulation (BSAFs), and trophic transfer factors (TTFs) for chironomids and Arctic char in Char, Small, Resolute, and Meretta Lakes to explain lake-to-lake differences. Simultaneously, we leveraged the natural differences in water temperatures and productivity to explore how warming may impact Hg cycling. Length-adjusted total Hg (tHg) concentrations in Arctic char from the four populations ranged from 0.11 ± 0.01 to 0.50 ± 0.18 µg/g dry weight. The BAFs for Arctic char and chironomids relative to water were high relative to lower-latitude lakes and Arctic marine food webs. The BAFs and BSAFs for Arctic char and chironomids were generally lower in the shallow lakes (Meretta and Small). The TTFs were highest in the deeper, colder study lakes (Char and Resolute). Bioaccumulation factors for chironomids and Arctic char did not correspond to Hg methylation potentials in sediments. A principal component analysis uncovered significant correlations with dissolved organic carbon in lake water, and tHg in lake water and pore water, with TTFlarvae and lake temperature. The comparisons of BAFs and BSAFs among these lakes, taken together with the results of previous studies, suggest that MeHg bioaccumulation may decrease as the Arctic continues to warm, and yet the reasons for higher bioaccumulation in colder lakes require further study. Our results confirm the highly context-dependent nature of Hg bioaccumulation in freshwater and provide insights into temperature-dependent responses that may occur under continued climate change.