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Ratio of Methylmercury to Dissolved Organic Carbon in Water Explains Methylmercury Bioaccumulation Across a Latitudinal Gradient from North-Temperate to Arctic Lakes
journal contribution
posted on 2017-11-25, 00:00 authored by John Chételat, Murray C. Richardson, Gwyneth A. MacMillan, Marc Amyot, Alexandre J. PoulainWe
investigated monomethylmercury (MMHg) bioaccumulation in lakes across
a 30° latitudinal gradient in eastern Canada to test the hypothesis
that climate-related environmental conditions affect the sensitivity
of Arctic lakes to atmospheric mercury contamination. Aquatic invertebrates
(chironomid larvae, zooplankton) provided indicators of MMHg bioaccumulation
near the base of benthic and planktonic food chains. In step with
published data showing latitudinal declines in atmospheric mercury
deposition in Canada, we observed lower total mercury concentrations
in water and sediment of higher latitude lakes. Despite latitudinal
declines of inorganic mercury exposure, MMHg bioaccumulation in aquatic
invertebrates did not concomitantly decline. Arctic lakes with greater
MMHg in aquatic invertebrates either had (1) higher water MMHg concentrations
(reflecting ecosystem MMHg production) or (2) low water concentrations
of MMHg, dissolved organic carbon (DOC), chlorophyll, and total nitrogen (reflecting lake sensitivity).
The MMHg:DOC ratio of surface water was a strong predictor of lake
sensitivity to mercury contamination. Bioaccumulation factors for
biofilms and seston in Arctic lakes showed more efficient uptake of
MMHg in low DOC systems. Environmental conditions associated with
low biological production in Arctic lakes and their watersheds increased
the sensitivity of lakes to MMHg.