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TitleAlgal scavenging of mercury in preindustrial Arctic lakes
AuthorOutridge, P M; Stern, G A; Hamilton, P B; Sanei, H
SourceLimnology and Oceanography vol. 64, 2019 p. 1-14,
Alt SeriesNatural Resources Canada, Contribution Series 20180211
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
ProvinceNunavut; Northwest Territories; Yukon
NTS58H/07SE; 107C/03NE; 115A/01NE; 115A/08SE
AreaCanadian Arctic; Devon Island; Nesbitt Lake; Mackenzie Delta; Kusawa Lake
Lat/Long WENS -89.3103 -89.3097 75.5703 75.5697
Lat/Long WENS-134.0297 -134.0297 69.2167 69.1833
Lat/Long WENS-136.1833 -136.1833 60.2667 60.2333
Subjectsenvironmental geology; geochemistry; surficial geology/geomorphology; limnology; surface waters; lakes; mercury geochemistry; biogeochemistry; microorganisms; algae; lake sediment geochemistry; lake sediment cores; organic carbon; sedimentation rates; carbon nitrogen ratios; titanium geochemistry; statistical analyses; environmental baseline studies; lacustrine sediments; ecozones; barren tundra ecozone; grassy tundra ecozone; boreal forest ecozone; organic matter; total organic carbon
Illustrationstables; time series; plots; schematic representations
ProgramManagement, Environmental Geoscience
Released2019 02 27
AbstractThe geochemical speciation of total mercury (THg) was examined in pre-1800 Arctic lake sediments to improve understanding of the factors controlling 'natural baseline' THg. Solid-phase binding forms of THg were determined by sequential extraction of dated cores from three lakes in different ecozones (barren tundra, grassy tundra, and boreal forest). Sediment organic matter (OM) was mostly of algal origin. Mercury was highly concentrated in the sediment OM fraction (OM-Hg), comprising 60-87% of THg, while OM (as total organic carbon) constituted only 0.6-13% of sediment dry weight (DW). OM-Hg concentrations were equivalent to 159 ± 13 to 776 ± 215 ng Hg /g DW in algal OM and were enriched 2-39 times compared to sediment THg, indicating that even small changes in algal OM inputs could significantly alter THg. OM-Hg explained 76-96% of the variation in THg concentrations over many centuries. Concentrations of S2 carbon (an algal productivity proxy) and OM-Hg were significantly correlated in two lakes but not in the boreal forest lake possibly because of OM remineralization in its deep water column. Fluxes of S2 carbon, OM-Hg, and THg were highly correlated in the barren tundra lake but could not be calculated for the other lakes. The results overall indicate that high algal Hg concentrations due to scavenging of available Hg controlled OM-Hg flux to sediments, thus driving changes in THg concentrations and fluxes. These findings improve our understanding of the long-term stability of baseline THg in northern lakes under a changing climate, including in the modern era.
Summary(Plain Language Summary, not published)
When algae in freshwaters and seawater take up mercury (Hg)and eventually die, they fall to the bottom of those lakes and oceans and remove the Hg from the system. Variations in algal primary productivity may affect how rapidly Hg is removed in this way, although this suggestion is controversial. Here, we provide more evidence of this process by looking at how changes in the geochemical associations of Hg in Arctic lake sediments were affected by the scavenging process. This study has significant implications for how lake sediments are used uncritically to reconstruct atmospheric Hg deposition, and for Hg pollution studies.