National view of temporal atmospheric mercury deposition across Canada using lake sediment cores

Sarah Roberts1, Jane Kirk2, Derek Muir3, Johan Wiklund4, Marlene Evans5, Amber Gleason6, Paul Drevnick7, Ashu Dastoor8, Andrei Rvjkov9, Benjamin Barst10 and Colin Cooke11

Mercury (Hg) is a pollutant of concern globally which is emitted into the atmosphere largely from coal combustion, gold mining and metal smelting, and can be transported over large distances due to its long atmospheric residence time. Due to a paucity in atmospheric Hg deposition measurements, the relationship between implementation of emission controls and deposition fluxes to the landscape are not well constrained. In this study, we apply statistical methods to Hg flux data obtained from 82 dated lake sediment cores spanning latitudinal and longitudinal gradients across Canada to examine recent trends (post-1990) in atmospheric Hg deposition. Cores were collected from 2007 to 2018 from lakes located nearby known point sources, such as Flin Flon and Thompson (MB) smelters and urban centres (Toronto and Montreal), as well as within remote locations such as Kejimkujik National Park (NS) and Experimental Lakes Area, Northwestern Ontario. Redundancy analyses show that variation in recent anthropogenic Hg flux is driven largely by proximity to point sources. Not surprisingly, lakes located nearby (< 100 km) point sources were hotspots for Hg deposition, such as the Flin Flon smelter. A longitudinal gradient was also observed, with greater recent (post-2005) change in anthropogenic Hg fluxes recorded in eastern lakes. Eastern and remote sites across Canada also exhibited significantly increasing trends in recent (post-2005) anthropogenic Hg deposition while western sites showed either a plateau or decreasing trend. Comparison of sediment-derived anthropogenic Hg fluxes with modelled Hg fluxes across Canada, obtained from the Global Regional Atmospheric Heavy Metals Model (GRAHM) demonstrate that Hg fluxes obtained from these different methods compare well, with the exception of Hg hotspot regions. At sites where Hg in precipitation is being monitored, we are comparing sediment-derived Hg fluxes to Hg wet deposition data and results will be presented. Overall, our results show that dated lake sediment cores, particularly when multiple cores are collected from one region, can reliably track changes in anthropogenic Hg atmospheric deposition over broad geographical areas where monitoring data is lacking.

 

1Environment and Climate Change Canada, sarahlilyroberts@gmail.com
2Environment Climate Change Canada, jane.kirk@canada.ca
3Environment Climate Change Canada, derek.muir@canada.ca
4University of Waterloo, jarvik@rogers.com
5Environment Climate Change Canada, marlene.evans@canada.ca
6Environment Climate Change Canada, amber.gleason@canada.ca
7Alberta Environment and Parks, Paul.Drevnick@gov.ab.ca
8Environment Climate Change Canada, ashu.dastoor@canada.ca
9Environment Climate Change Canada, andrei.ryjkov@canada.ca
10University of Fairbanks Alaska, bdbarst@alaska.edu
11University of Alberta, cookeca@gmail.com