Reconstructing Past Rates of Atmospheric Dust Deposition in the Athabasca Bituminous Sands Region Using Peat Cores from Bogs

Abstract

Open‐pit mining of the Athabasca Bituminous Sands generates considerable quantities of mineral dusts, but there is no published record of the amount of material deposited in the surrounding environment via the atmosphere since the industry began in 1967. Contemporary and past rates of atmospheric dust deposition were reconstructed using age‐dated peat cores (210Pb and 14C) collected from five bogs in the vicinity of mines and upgraders and from two bogs far removed from industrial activities. The main objective of this study was to quantify the impact of industry on dust emissions, and to do this, the variation in natural “background” rates of mineral matter accumulation also had to be determined. A second objective was to characterize the size, mineralogical composition, and morphology of the particulate matter emitted to better understand potential environmental consequences of dust emissions. The concentrations of acid insoluble ash and Th (a surrogate for insoluble mineral matter) were determined to calculate dust accumulation rates. Scanning electron microscopy with energy‐dispersive X‐ray analysis failed to reveal much variation in mineralogical composition, but near industry, the size of the particles was more variable. The abundance of fly ash particles increased with depth, which suggests that emissions from upgrader stacks may have declined over time. A comparison of acid‐insoluble ash inventories with the pH of the porewaters suggests that the acid‐soluble ash fraction of the dusts deposited may have impacted the chemical composition of the bog waters. Copyright © 2017 John Wiley & Sons, Ltd.

Testate amoeba records indicate regional 20th‐century lowering of water tables in ombrotrophic peatlands in central‐northern Alberta, Canada

“…After 1860 CE, a rapid succession of Phryganella acropodia , D. pristis type, Nebela militaris , T. arcula , Trigonopyxis minuta and A. muscorum was reconstructed and water tables fluctuated until the second half of the 20th century followed by a marked apparent drop relative to the surface, in the early 1990s. A strong increase in AIA flux, from <2 g m −2 year −1 in 1976 CE up to 10–12 g m −2 year −1 in the 21st century (Mullan‐Boudreau et al., ), characterized the top of the sequence. The increase in AIA flux did not have the hypothesized effect on testate amoeba assemblages as mineral matter CWMs decreased around 1960 CE and mixotrophic taxa were virtually absent since the start of the 20th century.…”

“…In addition, all cores showed low AIA fluxes in the first half of the 20th century (<8 g m −2 year −1 ) but strongly increasing values in the peat cores from the ABS sites (McK, JPH4 and MIL) after 1960 CE (Figure ). Given the location and the timing of the increase, there is little doubt that this trend in AIA flux is linked with the industrial activity of the ABS (Mullan‐Boudreau et al., ,b). This attribution of dust sources is supported as well by elevated thorium (Th) concentrations, reflecting the abundance of insoluble mineral particles, attaining 0.40 mg/kg in JPH4, 0.38 mg/kg in McK and 0.34 mg/kg in MIL.…”

“…Ash content (%) was measured after the dried peat samples were combusted at 550°C for 16 hr in a muffle furnace (Andrejko, Fiene, & Cohen, ). Acid‐insoluble ash (AIA) was used as a proxy for dust deposition and was determined quantitatively after reaction of ash samples in 1 m HCl for 15 min, followed by filtering under vacuum to recover the insoluble fraction (Mullan‐Boudreau et al., ). The AIA flux (g m −2 year −1 ) was quantified using the peat accumulation rates as obtained from the age–depth modelling.…”

“…These mines, and their associated tailings, beaches and ponds as well as extensive network of gravel roads, generate large volumes of mineral dusts which is clearly seen in Sphagnum moss collected from these same sites (Mullan-Boudreau et al, 2017a). Studies of mineral matter in peat cores from these bogs reveal an increase in dust deposition over time since mining and upgrading began in 1967 CE, with impacts increasing with distance towards industry (Mullan-Boudreau et al, 2017b).…”

“…These mines, and their associated tailings, beaches and ponds as well as extensive network of gravel roads, generate large volumes of mineral dusts which is clearly seen in Sphagnum moss collected from these same sites (Mullan‐Boudreau et al., ). Studies of mineral matter in peat cores from these bogs reveal an increase in dust deposition over time since mining and upgrading began in 1967 CE, with impacts increasing with distance towards industry (Mullan‐Boudreau et al., ). Atmospheric deposition of mineral dusts, whether they are supplied by natural or anthropogenic sources, may affect testate amoeba communities and these effects may be identified using selected functional traits of the tests.…”