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Accumulating Mercury and Methylmercury Burdens in Watersheds Impacted by Oil Sands Pollution
journal contribution
posted on 2019-10-16, 21:14 authored by Vivian Wasiuta, Jane L. Kirk, Patricia A. Chambers, Alexa C. Alexander, Faye R. Wyatt, Rebecca C. Rooney, Colin A. CookeBitumen mining and
upgrading in northeastern Alberta, Canada, releases
toxic pollutants into the atmosphere, including mercury (Hg) and methylmercury
(MeHg). This Hg and MeHg is then deposited to the surrounding landscape;
however, the fate of these contaminants remains unknown. Here, we
compare snowpack chemistry to high-frequency measurements of river
water quality across six watersheds (five impacted by oil sands development
and one unimpacted). Catchment scale snowpack Hg and MeHg loads normalized
to watershed area were highest near oil sands operations. River water
Hg concentrations and loads tracked discharge and tended to be higher
downstream of mining operations, while MeHg concentrations and loads
increased through the summer, reflecting peak summer MeHg production
rates. Except in the reference watershed, snowpack Hg and MeHg loads
equaled or exceeded the amount of Hg and MeHg exported during freshet
and, in some cases, the entire hydrologic year. This suggests landscapes
across the oil sands region, which are dominated by low-relief wetlands
and other shallow-water systems, are accumulating Hg and MeHg. Importantly,
during years of high discharge, these low-relief systems appear to
become better connected and flush MeHg (and Hg) from the watershed.
Thus, these watersheds may act as temporary, rather than as permanent,
natural repositories of oil sands contaminants.