Moss and peat as monitors of contemporary and past rates of atmospheric dust deposition in the Athabasca Bituminous Sands Region

  • Author / Creator
    Mullan-Boudreau, Gillian M
  • Research Problem Since the introduction of open pit mining of the Athabasca Bituminous Sands (ABS) in 1967, this industry has generated considerable quantities of mineral dust that when released is injected into the atmosphere and settles in the surrounding environment. Despite this, a full profile of atmospheric dust deposition in the area has not been studied. The purpose of this research was to reconstruct contemporary and past rates of atmospheric dust deposition, using Sphagnum moss and peat cores as biomonitors respectively. To address the purpose of this research, samples were analyzed to identify the variation in natural “background” dust deposition rates in the area, and to determine the size, mineralogy, and morphology of the particulate mineral matter, in the hopes to better understand the impact of industry in the ABS region. Methods of Investigation Sphagnum moss samples were collected from 30 ombrotrophic (rain-fed) peat bogs surrounding ABS region and 5 ombrotrophic peat bogs in central Alberta for comparison (URSA, CMW, BMW, WAG, and EINP). Peat cores were collected from 7 ombrotrophic peat bogs (MIL, JPH4, McK, McM, ANZ, UTK, and SEB). The samples were ashed and reacted in HCl to separate the acid insoluble ash (AIA) (mineral matter) and the acid soluble ash (ASA) (macronutrients) fractions. The morphology and mineralogy of the dust mineral particles were studied using scanning electron microscopy and energy dispersive X-ray analysis, as well as the particle size distributions using a XPT (optical microscopy). Both 210Pb and 14C age-dating were used to create a combined age-depth model for each peat core. A major ion analysis was performed on the ASA fraction of the 2015 moss samples. ii Contemporary Dust Deposition The mean AIA content of the living layer of the moss samples increased from 0.4±0.5% to 4.7±2.0% over a 30 km distance towards industry. For comparison, the moss samples from the URSA control site had a mean value of 0.29 0.07%. Mass accumulation rates (g/m2 yr) were used to calculate the total amount of dust deposited within a 30km radius of industry. The result obtained using this approach (21,000 tonnes/ 4 month growing season) is beyond the current estimate (18,842 tonnes/yr) reported by the federal government (Environment and Climate Change Canada, 2015). Particle size was found to increase in variation closer to the ABS region and larger particles were more abundant. No major changes in mineralogy were found. Major ion analysis on ASA fractions showed the availability of P, Ca, Mg, Fe, Mn, S and K. Phosphorous, a growth limiting nutrient, was found to be 7 times greater at the sites with more AIA than those with background levels. Past Dust Deposition The concentrations of AIA and Th (a surrogate of mineral matter concentration) were determined to establish dust deposition and to calculate changes in mass accumulation rates over time. While it is uncertain if there was an increase in dust deposition since the ABS region operations began in 1967, there was a notable increase in AIA with distance from industry. Large quantities of fly ash were present in the top layers of the peat cores closest to the ABS region, but otherwise no notable changes in mineralogy were found. Near industry there was an increase in size variation of the particles and fly ash increased in abundance with depth. The average accumulation rates of AIA are up to 5x greater in the cores collected near industry. A comparison of AIA inventories with the pH of the porewaters suggest that the ASA fraction of the dusts deposited may impact the chemical composition of the bog waters.

  • Subjects / Keywords
  • Graduation date
    Spring 2017
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.