Article pubs.acs.org/est
Sphagnum Moss as an Indicator of Contemporary Rates of Atmospheric Dust Deposition in the Athabasca Bituminous Sands Region Gillian Mullan-Boudreau,† Rene Belland,† Kevin Devito,‡ Tommy Noernberg,† Rick Pelletier,† and William Shotyk*,† †
Department of Renewable Resources and ‡Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2H1 Canada S Supporting Information *
ABSTRACT: Sphagnum moss was collected from ombrotrophic (rain-fed) peat bogs to quantify dust emissions from the open-pit mining and upgrading of Athabasca bituminous sands (ABS). A total of 30 bogs were sampled in the ABS region, and 5 were sampled in central Alberta. Ash was separated into the acid-insoluble ash (AIA) and acid-soluble ash (ASA) fractions using HCl. The AIA concentrations increase toward industry from 0.4 ± 0.5% to 4.7 ± 2.0% over a distance of 30 km; the control site at the Utikuma Region Study Area (URSA) yielded 0.29 ± 0.07% (n = 30). Mass accumulations rates showed similar spatial variation. The morphology and mineralogy of the AIA particles were studied using scanning electron microscopy and energy-dispersive Xray analysis and the particle size distributions using optical methods. Particle size was more variable in moss closer to industry. Major ions in the ASA fraction showed elevated accumulation rates of Ca, K, Fe, Mg, P, and S, with P being up to 5 times greater in samples nearest industry compared to those in distal locations. Given that P has been regarded as the growth-limiting nutrient in bogs, fertilization of nutrient-poor ecosystems, such as these from fugitive emissions of dusts from open-pit mining, may have long-term ecological ramifications.
1. INTRODUCTION
well as impact the growth of vegetation in the surrounding environment.9 Dust deposition in the ABS region is currently being monitored by the Wood Buffalo Environmental Association (WBEA, now part of Alberta Environment and Parks), and their focus is the deposition, characterization, and source assessment of PM2.5 and PM10.10−12 Apparently, however, they do not monitor the full range of size categories of particulate matter emitted by industry.9,13 To date, there has been limited published research on total dust deposition in the ABS region. To investigate dust deposition in the vicinity of open-pit mines and upgraders of this increasingly industrialized region, Sphagnum moss was collected from 35 ombrotrophic (rainfed) bogs, 30 of which are in the area surrounding open-pit bitumen mines and upgraders, and 5 from other regions of Alberta that are not directly affected by development. The main objective of this study was to quantify rates of both total dust and mineral dust deposition to terrestrial ecosystems
The Athabasca Bituminous Sands (ABS) region currently produces over 165 000 m3/day of bitumen from open pit mining and steam assisted gravity drainage (SAGD) operations.1,2 During 2015 alone, it was suggested that 41 390 tons of total particulate matter was injected into the surrounding atmosphere within 30 km of industrial activities such as open pit mining, gravel roads, bitumen upgrading, and an assortment of by-products such as soil, overburden, coke, and sulfur.3 Once airborne, these dusts may travel considerable distances depending on such factors as wind speed, particle size and shape, density, and composition.4 Dust in the form of particulate matter is considered a primary pollutant and can be composed of a wide variety of substances both solid and liquid;5 however, the focus of this study was the mineral fraction. Mineral dusts are largely composed of pedogenic particles derived from wind erosion of soils; however, these dusts can also include particles from pyrogenic and industrial sources.6 In the ABS region, it has been found that mineral dusts are the dominant source of heavy metals,7 and dust from coke piles is the dominant source of PAHs.8 Increased exposure to mineral dusts can cause health risks as © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
December 7, 2016 May 23, 2017 May 30, 2017 May 31, 2017 DOI: 10.1021/acs.est.6b06195 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 1. Moss sampling sites for 2015 (30 bogs within the ABS region plus URSA, CMW, BMW, EINP, and WAG). Active upgraders, the midpoint between the two central upgraders (reference point), and the Wabamum Transalta Sundance Coal-Fired Generating Station are also depicted. Image produced using ArcMap.45 All displayed vector data are derived from either Geogratis Canada46 or GeoDiscover Alberta47 or was created by authors.
in the ABS region. Specifically, our purpose was to estimate contemporary deposition from industrial sources, to illustrate their spatial variation, and to compare these with natural “background” values. The content of mineral matter within the living layer of Sphagnum moss was obtained by distinguishing the acid-insoluble (AIA) and acid-soluble (ASA) ash fractions. Concentrations of ash, AIA, and ASA were combined with estimated growth rates of the moss to calculate current rates of dust deposition. A secondary objective was to characterize the dusts in respect to particle size, mineralogical composition, and morphology. Our over-arching concern is the potential ecological significance of these dusts for terrestrial ecosystems,
and this was addressed by estimating the availability of plant nutrients (P, Ca, Mg, K, S, Fe, and Mn) in the ASA fraction.
2. MATERIALS AND METHODS 2.1. Sample Collection. The samples used in this study were collected between 2013 and 2015. 2.1.1. 2013 Moss. A total of three replicate samples per site were collected from 24 bogs surrounding the ABS region in 2013 (Figure S1). A total of 20 of these bogs were sampled for a separate study,14 but part of each sample was provided to this project. In addition to moss from these bogs, samples were collected from other bogs in the vicinity of industry (MIL, JPHB
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slightly, grading from cinnamon brown above to fuscous below.21 To circumvent the challenge of distinguishing living from dead material, a standard length of 2 cm was chosen for consistency.14 Given that the stems of the plants are never perfectly straight, the upper limit on the plant material selected for study is estimated to be 2.5 cm. The cleaned samples were dried at 105 °C overnight in 120 mL polypropylene jars and weighed after drying to determine water content. A total of 1 g of each dried sample was then ashed at 550 °C for 16 h in a muffle furnace (MLS Pyro HighTemperature Microwave Muffle Furnace, Leutkirch, Germany) to determine ash content. The samples were then placed into a desiccator for 24 h to prevent moisture uptake while cooling. A schematic of the complete procedure is featured in Figure S3. 2.3. Acid-Insoluble Ash. To obtain the AIA, each ashed sample was reacted in 1 M HCl for 15 min. After the reaction, the solution was removed using 10 mL polypropylene syringes and then filtered (0.45 μm) using syringe filters (PTFE Teflon in polypropylene casing) to collect the insoluble ash residue.22 The filters were dried using a vacuum pump (Air Admiral diaphragm vacuum and pressure pump, Cole-Parmer, Canada). To access the AIA remaining on the filters, the casings of the syringe filters were removed using a cleaned, precise mechanical lathe (Schaublin 135, Bevilard, Switzerland) covered in plastic film to minimize contamination. Although the pH of the ASA fraction was not measured, future studies should consider adding this step, as it might provide insight into the chemical reactivity of the soluble components in the ash. 2.4. Scanning Electron Microscopy and EnergyDispersive X-ray Analysis. Selected AIA samples were analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) to determine the mineralogy and morphology of the particles. Specifically, a Zeiss EVO LS15 EP-SEM with Bruker EDX (Department of Earth and Atmospheric Sciences, University of Alberta) was used under the following operating conditions: X-ray resolution of 123 eV and a 10 mm2 window area, gun conditions of 25 kV and 200 pA, in variable pressure (VP) mode, using backscattered electron detector (BSD) imaging. 2.5. Particle Size Distribution. A XenParTec (XPT-C) Optical Particle Analysis System (PS Prozesstechnik GmbH, Basel, Switzerland) was used to determine particle size distribution profiles in the range 1 to 300 μm. Portions of selected AIA samples were diluted in 10 mL of surfactant (1% Fisherbrand FL-70 concentrate solution), stirred, and allowed to run through the device for 1 min before taking a measurement to ensure a representative analysis. Each sample was run for 15 min to stabilize the distribution and provide statistically significant particle counts. After each run, the XPTC was cleaned using 18.2 Milli-Q water to remove any remaining particles in the line. 2.6. ICP-OES Analysis of ASA. Major elements were determined in one ASA sample from each of the 2015 sites using inductively coupled plasma optical emission spectrometry (ICP-OES) in the Natural Resources Analytical Laboratory (NRAL) of the Department of Renewable Resources at the University of Alberta. The concentrations of a long list of elements were determined (Table S4), but here, we focus on Ca, Fe, K, Mg, P, and S. For more information on the ICP-OES results and the quality assurance−quality control procedure, see Table S3 and Appendix S1. 2.7. Statistical Analyses. The average ash and AIA contents were determined using three replicate samples from
4, McK, and ANZ), in triplicate, by W.S., as described elsewhere.7 2.1.2. 2014 Moss. A total of three replicate samples per site were collected from three additional bogs by W.S. and G.M.-B.: McM, which is near industry; UTK, which is remote; and from SEB, which is approximately 90 km W of Edmonton (see Figure S1). All of the samples collected by Vile et al.14 and by W.S. were collected by hand while wearing polyethylene (PE) gloves and packed as large handfuls into PE bags. The set of samples from three bogs at Utikuma Region Study Area (URSA, control site) were collected later in the year and the same handling procedure was used as the 2015 moss samples (see below). 2.1.3. 2015 Moss. During 2015, 3 replicate samples per site were collected from 30 bogs surrounding the open pit mines and upgraders. The bogs ranged from 7 to 50 km from the reference point, which is defined as the midpoint between the two central upgraders (Figure 1). The sites were inaccessible by road, so a helicopter was used and the samples collected by a team of 4 over 3 days. The samples were collected in open sections of the bogs to minimize interference from the tree canopies. While Sphagnum f uscum was the preferred moss species, other species were collected as well and a list of all species studied is provided in Table S1, and the GPS coordinates are provided for each site in Table S2. A medical grade stainless steel knife and polypropylene container (463 cm2 surface area) were used to collect the samples while wearing PE gloves. The polypropylene container was inverted into the moss layer, and the knife was used to trace around the container creating a cut-out of the container in the moss mat (Figure S2). The container was then pushed down so the moss cut-out filled the container. To extract the sample, the knife was used to cut the moss level with the container opening (underneath the sample cut-out). The sample, now free of the mat, was sealed in the container with a polypropylene lid. 2.1.4. 2015 Control Sites. Samples were also collected from the Utikuma Region Study Area (URSA), which is the center of long-term studies of peatland hydrology and biogeochemistry in Alberta15−17and located 264 km SW of the midpoint between the two upgraders (Figure 1). For comparison, samples were also collected from the Birch Mountain Wildlands (BMW) and Caribou Mountain Wildlands (CMW); these are 101 and 321 km from the reference point, extremely remote and can only be accessed using helicopter. The Sphagnum samples from URSA (n = 30), BMW (n = 3), and CMW (n = 3) provide background values for ash contents, AIA, ASA, and their accumulation rates. All sites were chosen with distance from the nearest road in mind to reduce possible exposure of the plants to road dust. Dust deposition is known to be enhanced within 100 m of roads;9,18 therefore, all samples were collected at a minimum of 100 m from the nearest road. The distances from the nearest roads for all collection sites are listed in Table S2. 2.2. Cleaning, Drying, and Ashing of Samples. Each moss sample was hand-picked using surgical stainless steel tweezers, while wearing PE gloves and a hairnet, to remove all foreign biological materials (leaves and branches of other plants, other species of moss, insects, root fragments, etc.).19 Determining the length of the moss stem corresponding to the living layer was a challenge because the annual growth rates of Sphagnum are variable.20 A visual distinction between the living and dead layers of S. f uscum are especially difficult, as the color of the living section and the underlying dead remains differ only C
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Figure 2. Average concentrations of ash (weight percent) and the relative abundance of AIA and ASA of moss sampled during 2015 (30 bogs with the ABS region plus URSA, CMW, BMW, EINP, and WAG). Active upgraders and the midpoint between the two central upgraders (reference point) are also depicted. The circle size represents the ash content (%), while the fractions of each circle represent the relative proportions of AIA (orange) and ASA (cream). The Interpolated values for the moss maps were created using ArcMap.45 All displayed vector data are derived from either Geogratis Canada or GeoDiscover Alberta47 or was created by authors.
each bog. To test for first-order spatial autocorrelation, Global Moran’s I and the Mantel test were performed on average values of both ash and AIA data for each site. Moran’s I for both data sets was close to zero (0.005 and −0.002), and the large p values (0.7 and 0.8) indicated that the null hypothesis of zero spatial autocorrelation could not be rejected at α = 0.05. The Mantel test indicates that no significant correlation was present because the observed values were close to zero (0.003 and 0.006) and that the p values were very large (0.5 and 0.5). No significant spatial autocorrelation was detected in the data sets; thus, independent statistical analysis of each site was performed as described below. The average of the three replicate samples was used as the data point for that site. The standard deviation of the three replicate samples was used to find a confidence interval, with α = 0.05 for each site location. Some irregularity and variation in AIA concentrations were expected due to the inherent differences among samples in terms of growth rate, productivity, and site conditions.20 For a complete list of ash, AIA, and MAR results, confidence intervals, and ranges for the 2015 moss samples, see Tables S5 and S6.
2.8. URSA Control Site. The Utikuma Region Study Area is a complex mosaic of wetlands, making it possible to sample three bogs located on distinct glacial landforms but all within a few kilometers of each other. At each of the three bogs, 10 samples of Sphagnum moss were collected using random number assignments in a 10 × 10 grid (Figure S4). A total of 30 samples from URSA allowed background values to be established for ash content (1.95 ± 0.11%) and AIA (0.29 ± 0.07%). URSA is a remote location, and these samples provide contemporary background values for the both ash content and AIA in Sphagnum moss to serve as a reference level against which the moss samples from the ABS region may be compared.
3. RESULTS AND DISCUSSION 3.1. Ash and Acid-Insoluble Ash. 3.1.1. 2013−2014 Moss. A total of three samples from each bog were used to calculate the mean values for ash contents and the relative abundance of AIA and ASA (Figure S5). Clearly, the ash contents decrease with distance from the industrial reference point, with higher concentrations following the predominant D
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Figure 3. Map48 of mass accumulation rates (g/m2/year) of ash and AIA for moss sampled during 2015. Calculated using moss accumulation rates determined from volumetric dry weights.
bogs near the ABS region are clearly impacted by enhanced inputs of dust. 3.2. Color Variation in Plant Ash. During the determination of the ash content of Sphagnum, it was observed that the ash samples displayed a large variation in color from light blue to rust brown. The colors were recorded using microscope imaging and mapped (Figure S7). There appears to be a correlation between the color of the ash sample and the AIA content: brown samples correspond to elevated concentrations of AIA, whereas blue samples correspond to the lower concentrations of AIA. 3.3. Mass Accumulation Rates. Using the plant growth rates, mass accumulation rates (MAR) of ash and AIA were calculated as described elsewhere (Appendix S2) and mapped (Figure 3). The values calculated represent one growing season (approximately 4 months), but for simplicity, the MAR are expressed on an annual basis. The average accumulation rate for Sphagnum, which we obtained for 30 bogs in the ABS region, using the volumetric sampling approach described here, is 215 ± 65 g/m2/year; this is comparable to the average value (259 ± 9 g/m2/year) recently reported for Sphagnum collected at MIL, JPH4, McK, McM, and ANZ that was obtained using the socalled “cranked-wire method”29 as well as the value (234 ± 3 g/ m2/year) reported earlier for these bogs by the same investigators.30 The MAR for ash ranges from 6.0−27.3 g/ m2/year, and the MAR for AIA ranges from 1.0−11.9 g/m2/ year, with the values decreasing with increasing distance from industry. For comparison, the background values calculated from the three bogs studied at URSA yielded 3.65 ± 0.36 g/ m2/year of ash and 0.53 ± 0.12 g/m2/year of AIA. For additional perspective, the moss samples from BMW averaged 6.27 ± 3.18 g/m2/year of ash and 0.58 ± 0.73 g/m2/year of AIA, whereas at CMW the corresponding values are 4.51 ± 3.28 and 1.16 ± 0.37 g/m2/year, respectively. Compared to the bogs at URSA, BMW, and CMW, the MAR of ash and AIA are much greater in the vicinity of the ABS mines and upgraders. For additional perspective, the Oreste bog, located in Southern
wind direction, which trends to the southeast (see Figure S6). The greatest concentrations of AIA (up to 2.8%) were within a zone 20−25 km from the midpoint between the two central upgraders; beyond this distance, the concentrations of AIA decrease to values comparable to the background concentrations of AIA found at URSA (0.29 ± 0.07%). In the 2013− 2014 sample set, ASA exceed those of AIA, especially at the bogs closer to the industrial reference point. 3.1.2. 2015 Moss. For the 2015 samples, three samples per bog were used to calculate the mean concentrations of ash, which are shown, along with the relative proportions of ASA and AIA, in Figure 2. Again, the ash contents of the moss decrease with distance from the reference point. There is a notable decrease in the proportion of the AIA fraction, relative to ASA, as distance increases from industry. The greatest ash contents (up to 10.1%) and AIA (up to 4.7%) are all located close to the most industrialized area (15−20 km), beyond which the values decline to background values. To view these findings in perspective, consider the following background values. First, at URSA (30 samples collected from 3 bogs), the ash contents average 1.95 ± 0.11%, and the concentrations of AIA average 0.29 ± 0.07% (n = 30). Second, at the even more remote sites, BMW averaged 1.69 ± 0.31% ash and 0.16 ± 0.23% AIA (n = 3); at CMW (the most-remote region investigated), the moss averaged 1.19 ± 0.34% ash and 0.33 ± 0.06% AIA. Considering these results, the values for ash contents and AIA concentrations closest to the ABS region are clearly elevated. For additional perspective, in Saskatchewan, S. f uscum had an ash content ranging from 1.6% (remote wilderness area) to 5.5% (predominantly agricultural area).23 The average value for ash content of Sphagnum calculated using results taken from published studies at other locations19,20,23−28 is 3.0% (Table S6), which is greater than the values for the samples from URSA (1.95 ± 0.11%) but much lower than the values found closest to industry within the ABS region. Compared with background sites in Alberta and published studies of ash contents of Sphagnum moss from other areas, the E
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Figure 4. Maps49 of phosphorus and calcium accumulation rates (mg/m2/year) in ASA of moss sampled in 2015. One out of three samples (sample “a”) was analyzed from each site. These values were calculated using the concentrations of elements determined using ICP-OES analyses of the ASA, the dilution factor, the ASA concentrations of the moss, and the moss accumulations rates.
m2/year (Figure 4), with values clearly increasing with proximity to industrial activity. We assume that the ASA fraction of mineral dust is the primary supply of available P for vegetation in the region as organic forms (e.g., in pollen grains) would be less readily available. Phosphorus can occur in several forms in dust: authigenic−biogenic minerals of the apatite family, Al and Fe hydroxides to which P is adsorbed, anthropogenic particles, organic P compounds, and CaCO3associated P,4,33 and these would be expected to either dissolve, desorb, or dissociate in the acidic surface water, which are characteristic of ombrotrophic bogs. In a recent study, the growth rates of S. f uscum were significantly greater in the vicinity of open pit mines and upgraders but were not positively correlated with atmospheric N deposition,29 even though it is commonly assumed that N deposition to bogs is growth limiting. Given these findings, and considering the variations
Isla Navarino, Chile, was found to have an average mineral matter accumulation rate (expressed as AIA) of 0.43 ± 0.12 g/ m2/year,22 which is consistent with the background values obtained from the three bogs at URSA. The accumulation rates of mineral matter in Sphagnum moss collected in the vicinity of industrial activity, expressed as the MAR of AIA, exceed the background values obtained from the bogs at URSA by approximately 2 to 22 times. 3.4. Major Ions Present in ASA Fraction. The ASA fraction of the dust supplied to ombrotrophic bogs represents a suite of elements essential to plant growth,31 including Mg, P, S, K, Ca, Mn, and Fe. Of this list of elements, P has been identified as the single most important nutrient that limits plant growth in ombrotrophic bogs,32 mainly due to the low concentrations of P typically found in wet and dry deposition. In the ASA, P accumulation rates ranged from 40 to 200 mg/ F
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Figure 5. SEM images highlighting the size, morphology, and mineralogy of AIA. (a) Large variation in morphology and size from a site close to industry, dominated by angular mineral fragments, some very large. The aluminosilicates depicted here are typical of all the samples examined (in this case, sample S07-a). (b) Less variation in the morphology and size typical of samples from sites far from industry (in this case, sample S14-a). Notice that the size and roundness of the quartz particle (c) gypsum crystals found in some samples (sample URSA 524-a) are artifacts of the combustion process and insoluble in HCl and (d) spherical fly ash particles present in proximal sites; note their small size. An iron-bearing aluminosilicate is depicted (sample S02-c).
the minimum rates by 4 to 5 times. In contrast, the maximum rates of Fe accumulation exceed the minimum rates by 30 times (Figure S8). The large difference in rates of atmospheric Fe deposition is one obvious explanation for the reddish color of the ash in samples collected near industry (Figure S7) but perhaps also suggests that Fe may play a less obvious role in plant nutrition, which might help to explain the elevated rates of moss growth near industry.29 3.5. Mineralogy, Morphology, and Size of Particles in AIA Fraction. The main sources of mineral dusts in the ABS region include open-pit mines, beaches and dykes of tailings ponds, exposed overburden, and gravel roads.9,11,13 Using physical methods of analysis, mineral matter from these sources is difficult to distinguish from the natural background of atmospheric dusts supplied by wind erosion of soils. In general, the AIA samples contained quartz, feldspar, mica (biotite), amphibole, zircon, and clay minerals (Figure 5), which are the most common mineral phases in the bituminous sands and other coarse-grained sedimentary rocks.36,37 Some samples of AIA contained gypsum (Figure 5c), which did not dissolve in the HCl reaction as it is only partly soluble in HCl.38 Spherical fly ash particles were found in some of samples nearest industry (Figure 5d). The majority of the fly ash was siliceous, commonly consisting of aluminosilicates with some phases containing trace elements such as Fe and Ti. These particles are typical of fly ash in respect to size, morphology, and composition.39,40 In contrast to early studies,41 which predate the installation of electrostatic precipitators, no trace metals were found in the fly ash when analyzed using energy-dispersive X-ray fluorescence spectroscopy, but this may be because of the relatively high limit of detection (∼1000 mg/kg).
reported here in rates of deposition of soluble P (as well as other nutrient elements found in the ASA fraction), the impacts of these dusts on plant growth rates deserves a more detailed examination. An increase in atmospheric deposition of plantavailable P from anthropogenic sources may inadvertently act as a fertilizer, promoting plant growth and potentially increasing competition from plants typically found in minerotrophic peatlands. Increased competition in an environment in which there is naturally very little could have consequences for the species that dominate ombrotrophic bogs, such as S. f uscum. Calcium is also an extremely important plant nutrient in peatland ecosystems. Pioneering studies in the early part of the 20th century showed that the species of Sphagnum moss found in ombrotrophic bogs were far less tolerant of Ca (i.e., are “calcifuge”) than Sphagnum species found in minerotrophic fens and swamps (see the review of early work summarized elsewhere).24 In the ASA fraction of Sphagnum moss, the Ca accumulation rates ranged from 199 to 832 mg/m2/year and, again, is clearly elevated in the vicinity of industry (Figure 4). Elevated deposition of base cations (Ca2+, Mg2+, and Na+) centered on industry in the ABS region have been reported by other workers.34 In a study of atmospheric N and S deposition using moss and peat from several of the same bogs used in this study (MIL, JPH4, McK, ANZ, and McM), Ca deposition rates in the area were found to range from 2.0 to 7.1 kg/ha year,35 which corresponds to 200 to 710 mg/m2/year, and is consistent with our findings. K, Fe, Mg, and S (Figure S8) display spatial trends similar to those of Ca, which shows there is enhanced deposition of a range of elements essential to plant nutrition. We note that the maximum rates of accumulation of P and Ca (Figure 4), as well as those of K, Mg, and S (Figure S8), exceed G
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(2015) of plant collection at only 30 sites, they are consistent with the data obtained from the moss samples collected during 2014 at a smaller number of sites. While the calculated dust inputs to these bogs are not definitive and do not account for variation in deposition over the year, both approaches do suggest that the extent of dust deposition may have been considerably underestimated. Moreover, the findings presented here suggest that the amount of mineral matter in Sphagnum moss might be a useful tool in future monitoring studies of atmospheric dust deposition in this region. 3.7. Consequences of Elevated Dust Deposition. Increased mineral dust deposition in the ABS region could eventually have consequences for surrounding ecosystems. Naturally acidic ecosystems, such as bogs, are home to plants accustomed to (and dependent upon) acidic (pH 4) low ionic strength waters. The bogs with the greatest dust deposition rates could be, or may become at risk due to elevated inputs of soluble minerals: their dissolution increases the availability of plant nutrients. The dissolution of carbonate minerals in the dust generated by open pit mining may gradually increase the pH of bog surface waters thereby creating an environment more welcoming for competition by plants normally unable to grow in bog environments.42 Studies have shown that bogs closer to a significant source of dust deposition will have less Sphagnum and other acidophilus mosses present. Specifically, these effects were seen with road dust deposition rates ranging from 25.6 to 912.5 g/m2/year, with notable declines in Sphagnum becoming apparent once deposition rates reached 365 g/m2/year.6,18,19,43 While the mass accumulation rates of dust in the ABS region today are at least a factor of 10 below this value, further expansion of the industry and the cumulative inputs of dust deposition may eventually have an impact on the surrounding acidophilus mosses and other vegetation. Hopefully the current deposition rates presented here will prove to be helpful, providing a reference level against which potential changes in future may be compared. Understanding the quantitative and ecological significance of dust deposition today can become part of a strategy to reduce emissions, if necessary, e.g., by watering or minimizing surface disturbances.9,44
The SEM imaging revealed a larger diversity in particle sizes in samples from bogs closer to industry (Figure 5a) than in samples farther away (Figure 5b). The variability in particle size with proximity to industry was confirmed with particle size distributions performed on selected samples (Figure S9): AIA samples closer to industry have much more variation in particle sizes than the distal and background samples. 3.6. Estimating Dust Deposition in The ABS Region Using Sphagnum Moss. Given the estimate of total particulate matter emissions within 30 km of the ABS industry (41 390 tons during 2015),3 it is worthwhile to estimate total deposition based on the ash, AIA, and ASA contents of Sphagnum moss for comparison. Spatial autocorrelation among sites can be estimated using Moran’s Index (I), which ranges from −1 (sites are perfectly dispersed) to +1 (for positive spatial autocorrelation). Because the Moran’s I statistical test on our data indicated very little spatial autocorrelation (0.10), it is reasonable to calculate an average mass accumulation rate for the sites within a 30 km radius of the reference point (18 sites), where the average annual accumulation of ash and AIA is 11.0 ± 1.3 and 3.5 ± 0.5 g/m2, respectively. To correct for natural background dust deposition, the accumulation rates obtained from the URSA samples were subtracted from these values to obtain the average anthropogenic dust accumulation rates, which are 7.4 ± 1.2 g/m2 (ash) and 3.0 ± 0.4 g/m2 (AIA). Using these results, we obtain an estimated 21 000 ± 3400 tons of total anthropogenic dust (based on ash contents) consisting of 8500 ± 1100 tons of insoluble material (based on AIA) and 12 500 ± 2300 tons of soluble material (based on ASA). For context, the contemporary, natural background rate of dust deposited at URSA, calculated using the same surface area, was estimated as 10 300 ± 500 tons total dust (based on ash), 1500 ± 170 tons of insoluble material (based on AIA), and 8800 ± 330 tons of soluble matter (based on ASA). The arrangement of the study sites and small number of samples collected (Moran’s I requires 30 points as a minimum) could call into question the result of the spatial-autocorrelation analysis. Given the location of industrial activity (roads and stacks), it is possible that spatial structure exists at a larger scale but remains undetected by the statistic. If this is the case, then a spatial autocorrelation-based interpolation should be used to estimate the total dust deposition in the ABS region. Therefore, ordinary kriging was used to create a simple prediction surface of ash and AIA deposition. The sum of the area-based prediction surface values suggest that anthropogenic activities in the region supply fluxes similar to those presented earlier: 23 000 tons of dust (ash), 9300 tons of insoluble material (AIA), and 13 700 tons of soluble material (ASA). The amount of dust calculated by Environment and Climate Change Canada3 represents one full year of emissions for the Fort McMurray area. However, as previously stated, the data presented in this paper represents mineral matter found in the living layer of Sphagnum moss representing one growing season, i.e., approximately 4 months. Over the course of one year, within 30 km of industry, both sets of our calculations infer annual deposition considerably greater than that presented in the Environment and Climate Change Canada database.3 Using the average mass accumulation rates, we obtained 63 000 tons of total dust, with 25 500 tons of insoluble matter and 37 500 tons of soluble material per year, while by using ordinary kriging, we found 69 000 tons of total dust, with 27 900 tons of insoluble matter and 41 100 tons of soluble material. Although our findings are based upon a single year
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.6b06195. Figures showing sampling locations; moss sample collection procedures, preparation, and analysis; sample grids; maps illustrating concentrations; wind rose diagrams; range of color observed; examples of color variation; maps of accumulation rates; and particle size distribution. Tables showing a list of moss species, a list of GPS coordinates, ICP-OES major ion analysis results, and moss sample ash and AIA analysis values. Appendices showing notes in ICP-OES analysis, calculation of mineral MAR, and calculation of the percent volume of particle size distribution. (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Phone: 780-492-7155; fax: 780-492-4323; e-mail: shotyk@ ualberta.ca. H
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Athabasca Oil Sands Region, 1st ed.; Elsevier Ltd.: New York, 2012; Vol. 11. (12) Landis, M. S.; Patrick Pancras, J.; Graney, J. R.; White, E. M.; Edgerton, E. S.; Legge, A.; Percy, K. E. Source apportionment of ambient fine and coarse particulate matter at the Fort McKay community site, in the Athabasca Oil Sands Region, Alberta, Canada. Sci. Total Environ. 2017, 584−585, 105−117. (13) Wang, X.; Chow, J. C.; Kohl, S. D.; Percy, K. E.; Legge, A. H.; Watson, J. G. Characterization of PM 2.5 and PM 10 fugitive dust source profiles in the Athabasca Oil Sands Region. J. Air Waste Manage. Assoc. 2015, 65 (12), 1421−1433. (14) Vile, M. A.; Wieder, R. K.; Berryman, S.; Vitt, D. H. WBEA 2010 Annual Report: Development of Monitoring Protocols for N & S Sensitive Bog Ecosystems; Wood Buffalo Environmental Association: Alberta, CA, 2010. (15) Devito, K.; Mendoza, C.; Qualizza, C. Conceptualizing water movement in the Boreal Plains: Implications for watershed reconstruction; Canadian Oil Sands Network for Research and Development, Environmental and Reclamation Research Group: Edmonton, AB, 2012; p 164. (16) Petrone, R.; Devito, K. J.; Mendoza, C. Utikuma Region Study Area (URSA) - Part 2: Aspen Harvest and Recovery Study. For. Chron. 2016, 92 (1), 62−65. (17) Devito, K. J.; Mendoza, C.; Petrone, R. M.; Kettridge, N.; Waddington, J. M. Utikuma Region Study Area (URSA) - Part 1: Hydrogeological and ecohydrological studies (HEAD). For. Chron. 2016, 92 (1), 57−61. (18) Walker, D. A.; Everett, K. R. Road dust and its environmental impact on Alaskan taiga and tundra. Arct. Alp. Res. 1987, 19 (4), 479− 489. (19) Santelmann, M. V.; Gorham, E. The influence of airborne road dust on the chemistry of Sphagnum mosses. J. Ecol. 1988, 76 (4), 1219−1231. (20) Malmer, N. Patterns in the growth and the accumulation of inorganic constituents in the Sphagnum cover on ombrotrophic bogs in Scandinavia. Oikos 1988, 53 (1), 105−120. (21) Braithwaite, R. The Sphagnaceae or Peat Mosses of Europe and North America; David Bogue: London, U.K., 1880. (22) Sapkota, A. Mineralogical, Chemical, and Isotopic (Sr, Pb) Composition of Atmospheric Mineral Dusts in an Ombrotrophic Peat Bog, Southern South America; University of Heidelberg: Heidelberg, Germany, 2006. (23) Gorham, E.; Tilton, D. L. The mineral content of Sphagnum f uscum as affected by human settlement. Can. J. Bot. 1978, 56 (180), 2755−2759. (24) Shotyk, W. Review of the inorganic geochemistry of peats and peatland waters. Earth-Sci. Rev. 1988, 25 (2), 95−176. (25) Shotyk, W. Natural and anthropogenic enrichments of As, Cu, Pb, Sb, and Zn in ombrotrophic versus minerotrophic peat bog profiles, Jura Mountains, Switzerland. Water, Air, Soil Pollut. 1996, 90, 375−405. (26) Damman, A. W. H.; Tolonen, K.; Sallantaus, T. Element retention and removal in ombrotrophic peat of Haadetkeidas, a boreal Finnish peat bog. Suo 1992, 43 (4−5), 137−145. (27) Vuorela, I. Field erosion by wind as indicated by fluctuations in the ash content of Sphagnum peat. Bull. Geol. Soc. Finl. 1983, 55 (1978), 25−33. (28) Gorham, E. Water, ash, nitrogen and acidity of some bog peats and other organic soils. J. Ecol. 1961, 49, 103−106. (29) Wieder, R. K.; Vile, M. A.; Albright, C. M.; Scott, K. D.; Vitt, D. H.; Quinn, J. C.; Burke-Scoll, M. Effects of altered atmospheric nutrient deposition from Alberta oil sands development on Sphagnum f uscum growth and C, N and S accumulation in peat. Biogeochemistry 2016, 129 (1−2), 1−19. (30) Wieder, R. K.; Vitt, D. H.; Burke-Scoll, M.; Scott, K. D.; House, M.; Vile, M. A. Nitrogen and sulphur deposition and the growth of Sphagnum fuscum in bogs of the Athabasca Oil Sands Region, Alberta. J. Limnol. 2010, 69 (1s), 161−170.
William Shotyk: 0000-0002-2584-8388 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Thanks go to Alberta Innovates for funding all of the fieldwork and analytical costs (AI-EES 2040) and to the University of Alberta, the Faculty of Agricultural, Life and Environmental Sciences, the Department of Renewable Resources for supporting the SWAMP laboratory. Thanks go to the Land Reclamation International Graduate School (LRIGS) and NSERC CREATE for providing financial support to G.M.-B., with special thanks going from W.S. to Anne Naeth for her leadership at LRIGS. Thanks go to Natural Resources Analytical Laboratory (NRAL) for performing the major ion analysis on the 2015 ASA samples. Tracy Gartner and Karen Lund provided administrative support, and Chad Cuss and Muhammad (Babar) Javed provided laboratory support and instruction. Anita Nowinka aided in the preparation of ash and AIA samples of the moss samples. Thanks go to Melissa Dergousoff and April Cormack for their hard work on sample cleaning and preparation. Also, big thanks go to Melanie Vile and Kelman Wieder for acquainting our team with the bogs used in this study. Finally, thanks go to Lee Foote and Claudio Zaccone for project guidance and to Emer Mullan for reviewing this manuscript.
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REFERENCES
(1) Alberta Energy Regulator. Alberta’s Energy Reserves 2014 and Supply/Demand Outlook 2015−2024; Alberta Energy Regulator: Calgary, Canada, 2015; pp 3−12. (2) Stringham, G. Energy Developments in Canada’s Oil Sands, 1st ed.; Elsevier Ltd.: New York, NY, 2012; Vol. 11. (3) Environment and Climate Change Canada. NPRI Bulk Data Release: sourced from NPRI source 2016. https://www.ec.gc.ca/inrpnpri/default.asp?lang=en=0EC58C98. (accessed October 2016). (4) Muhs, D. R.; Prospero, J. M.; Buddock, M. C.; Gill, T. E. Identifying sources of aeolian mineral dust: Present and past. In Mineral Dust: A Key Player in the Earth System; Springer Science & Business Media: Dordrecht, Germany, 2014; pp 385−409. (5) Cooper, C. D.; Alley, F. C. Air pollution control: a design approach., 4th ed.; Waveland Press: Long Grove, IL, 2011. (6) Mattson, S.; Koutler-Andersson, E. Geochemistry of a raised bog; Annals of the Royal Agricultural College: Sweden: Uppsala, 1955; pp 321−356. (7) Shotyk, W.; Bicalho, B.; Cuss, C. W.; Duke, M. J. M.; Noernberg, T.; Pelletier, R.; Steinnes, E.; Zaccone, C. Dust is the dominant source of “heavy metals” to peat moss (Sphagnum f uscum) in the bogs of the Athabasca Bituminous Sands region of northern Alberta. Environ. Int. 2016, 92−93, 494−506. (8) Zhang, Y.; Shotyk, W.; Zaccone, C.; Noernberg, T.; Pelletier, R.; Bicalho, B.; Froese, D. G.; Davies, L.; Martin, J. W. Airborne petcoke dust is a major source of polycyclic aromatic hydrocarbons in the Athabasca Oil Sands Region. Environ. Sci. Technol. 2016, 50 (4), 1711−1720. (9) Watson, J. G.; Chow, J. C.; Wang, X.; Kohl, S. D.; Yatavelli, L. N. R. Windblown Fugitive Dust Characterization in the Athabasca Oil Sands Region; Desert Research Institute: Reno, NV, 2014; pp 1−19. (10) Graney, J. R.; Landis, M. S.; Kru Coupling Lead Isotopes and Element Concentrations in Epiphytic Lichens to Track Sources of Air Emissions in the Athabasca Oil Sands Region. Dev. Environ. Sci. 2012, 11, 372−401. (11) Landis, M. S.; Pancras, J. P.; Graney, J. R.; Stevens, R. K.; Percy, K. E.; Krupa, S. Receptor Modeling of Epiphytic Lichens to Elucidate the Sources and Spatial Distribution of Inorganic Air Pollution in the I
DOI: 10.1021/acs.est.6b06195 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology (31) Steinmann, P.; Shotyk, W. The geochemistry of major elements in peats from two contrasting Sphagnum bogs, Jura Mountains, Switzerland. Chem. Geol. 1997, 138, 25−53. (32) Small, E. Ecological significance of four critical elements in plants of raised spagnum peat bogs. Ecology 1972, 53 (3), 498−503. (33) Hudson-Edwards, K. A.; Bristow, C. S.; Cibin, G.; Mason, G.; Peacock, C. L. Solid-phase phosphorus speciation in Saharan Bodélé Depression dusts and source sediments. Chem. Geol. 2014, 384, 16− 26. (34) Watmough, S. A.; Whitfield, C. J.; Fenn, M. E. The importance of atmospheric base cation deposition for preventing soil acidification in the Athabasca Oil Sands Region of Canada. Sci. Total Environ. 2014, 493, 1−11. (35) Vile, M. A.; Wieder, R. K.; Vitt, D. H.; Berryman, S. Final Report: Development of monitoring protocols for nitrogen-sensitive bog ecosystems, including further development of lichen monitoring tools; WBEA Final Report; Wood Buffalo Environmental Association: Alberta, Canada, 2013; pp 1−91. (36) Bichard, J. A. AOSTRA Technical Publication Series #4: Oil Sands Composition and Behaviour Research; Alberta Oil Sands Technology & Research Authority (AOSTRA): Edmonton, Alberta, 1987; pp 3−2 & 3−14. (37) Welton, J. E. SEM Petrology Atlas; The American Association of Petroleum Geologists: Tulsa, OK, 2003. (38) Azimi, G.; Papangelakis, V. G.; Dutrizac, J. E. Development of an MSE-based chemical model for the solubility of calcium sulphate in mixed chloride-sulphate solutions. Fluid Phase Equilib. 2008, 266 (1− 2), 172−186. (39) Yoo, J. G.; Jo, Y. M. Utilization of coal fly ash as a slow-release granular medium for soil improvement. J. Air Waste Manage. Assoc. 2003, 53 (1), 77−83. (40) Jang, H.; Etsell, T. H. Morphological and mineralogical characterization of oil sands fly ash morphological and mineralogical characterization of oil. Energy Fuels 2005, 19 (5), 2121−2128. (41) Shelfentook, W. An Inventory System for Atmospheric Emissions in the AOSERP Study Area; Alberta Oil Sands Environmental Research Program by SNC Tottrup LTD; Edmonton, Alberta, 1978. (42) Pearsall, W. The pH of natural soils and its ecological significance. J. Soil Sci. 1952, 3 (1), 41−51. (43) Farmer, A. M. The effects of dust on vegetation - a review. Environ. Pollut. 1993, 79, 63−75. (44) Wang, X.; Chow, J. C.; Kohl, S. D.; Yatavelli, L. N. R.; Percy, K. E.; Legge, A. H.; Watson, J. G. Wind erosion potential for fugitive dust sources in the Athabasca Oil Sands Region. Aeolian Res. 2015, 18, 121−134. (45) ESRI. ArcGis, version 10.3; Environmental Systems Research Institute, Inc.: Redlands, CA, 2016. (46) Geogratis Canada. https://www.nrcan.gc.ca/earth-sciences/ geography/topographic-information/free-data-geogratis/11042 (accessed October 2016). (47) GeoDiscover Alberta. GeoDiscover Alberta Home Page. https://geodiscover.alberta.ca/geoportal/ (accessed October 2016). (48) TerraMetrics. Map data ©2016 Google Imagery ©2016 http:// www.gosur.com/google-earth/. (49) TerraMetrics. Map data ©2017 Google Imagery ©2017 http:// www.gosur.com/google-earth/.
J
DOI: 10.1021/acs.est.6b06195 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
