Quantification of Spatial and Temporal Trends in Atmospheric Mercury Deposition across Canada over the Past 30 Years

Mercury (Hg) is a pollutant of concern
across Canada and transboundary
anthropogenic Hg sources presently account for over 95% of national
anthropogenic Hg deposition. This study applies novel statistical
analyses of 82 high-resolution dated lake sediment cores collected
from 19 regions across Canada, including nearby point sources and
in remote regions and spanning a full west–east geographical
range of ∼4900 km (south of 60°N and between 132 and 64°W)
to quantify the recent (1990–2018) spatial and temporal trends
in anthropogenic atmospheric Hg deposition. Temporal trend analysis
shows significant synchronous decreasing trends in post-1990 anthropogenic
Hg fluxes in western Canada in contrast to increasing trends in the
east, with spatial patterns largely driven by longitude and proximity
to known point source(s). Recent sediment-derived Hg fluxes agreed
well with the available wet deposition monitoring. Sediment-derived
atmospheric Hg deposition rates also compared well to the modeled
values derived from the Hg model, when lake sites located nearby (<100
km) point sources were omitted due to difficulties in comparison between
the sediment-derived and modeled values at deposition “hot
spots”. This highlights the applicability of multi-core approaches
to quantify spatio-temporal changes in Hg deposition over broad geographic
ranges and assess the effectiveness of regional and global Hg emission
reductions to address global Hg pollution concerns.