Atmospheric Hg accumulation rates determined using Sphagnum moss from ombrotrophic (rain-fed) bogs in the Athabasca Bituminous Sands region of northern Alberta, Canada

Abstract

Abstract Sphagnum moss was collected from 22 ombrotrophic (rain-fed) bogs near open pit mines and upgraders within the Athabasca Bituminous Sands (ABS) region of Alberta (AB). Mercury was quantified using two approaches: sector-field ICP-MS of acid digests, and a Direct Mercury Analyser (DMA) for solid samples. Using ICP-MS, the mean Hg concentration in moss from the ABS region (34.7 ± 1.5 µg/kg, n = 75) was significantly greater than the control site, Utikuma (26.7 ± 4.0 µg/kg, n = 3). Using DMA, the mean Hg concentration in moss from the ABS region (26.2 ± 0.9 µg/kg, n = 71) was significantly lower than the control site (28.5 ± 1.3 µg/kg, n = 6). These contradictory findings illustrate the challenges associated with comparing the results of two analytical methods, especially given the similarity in Hg concentrations between industrial and background sites, Similar Hg concentrations were also found in Sphagnum moss from two other bogs in AB which are far removed from the ABS region. The Hg concentrations in Sphagnum from the ABS bogs are well below the range found in bog vegetation collected earlier in eastern Canada, and comparable to the lowest values (5th percentile) reported for forest moss collected in 2015 from Norway and Sphagnum moss sampled in 2008 from northern Sweden. Given the rates of Sphagnum accumulation in the ABS region (ca. 215 g/m2/yr), Hg accumulation rates there were 5.8–7.5 µg/m2/yr versus 5.7–6.1 µg/m2/yr at the control site (UTK); these are at the upper limit of the range in pre-anthropogenic rates of Hg accumulation for peat from European bogs. Sphagnum moss is abundant in Canada and found in bogs from coast to coast, offering an opportunity to obtain quantitative information on atmospheric Hg deposition to terrestrial ecosystems from natural as well as anthropogenic sources.