Size-Resolved Fluorescence Underscores Negligible Interaction of Dissolved Organic Matter During Conservative Mixing in a Large Boreal River

Although river mixing occurs widely in nature, the corresponding evolution of dissolved organic matter (DOM) composition remains poorly understood. Here, surface water samples were collected at multiple transects in the lower Athabasca River (LAR) under base-flow conditions. Asymmetric flow field-flow fractionation (AF4) coupled to online excitation-emission measurements (EEMs) and parallel factor analysis (PARAFAC) were utilized to investigate the size distribution of fluorescent DOM components during river mixing and the corresponding variation in size-resolved fluorescence. The majority of fluorescent components occurred at 0.810 and 1.170 kDa, reflecting the small size of the DOM molecules with maximum fluorescence. The loadings of fluorescence normalized to absorbance at 254 nm (A254) were highest for most terrestrial humic-like components, followed by the microbial humic-like component, and the protein-like components. Differences in size-resolved fluorescence were observed between DOM in humic-rich tributaries and in the mainstem of the LAR upstream of tributary inputs. The trend of variations in the A254-normalized PARAFAC loadings of terrestrial humic-like components also illustrates conservative mixing of aromatic-rich terrestrial DOM across size fractions in the LAR. From a molecular point of view, the mixing of fluorescent DOM occurred linearly and simultaneously across sizes without any evidence of aggregation, sedimentation, or changes in the fluorescence or concentration of any size fraction over the >60 km required for complete mixing of the river and its tributaries. Overall, this study provides insights into the size characteristics of fluorescent components of DOM and their conservative mixing behavior in large boreal rivers

High-resolution age modelling of peat bogs from northern Alberta, Canada, using pre- and post-bomb 14 C, 210 Pb and historical cryptotephra

High-resolution studies of peat profiles are frequently undertaken to investigate natural and anthropogenic disturbances over time. However, overlapping profiles of the most commonly applied age-dating techniques, including 14C and 210Pb, often show significant offsets (>decadal) and biases that can be difficult to resolve. Here we investigate variations in the chronometers and individual site histories from six ombrotrophic peat bogs in central and northern Alberta. Dates produced using pre- and post-bomb 14C, 210Pb (corroborated with 137Cs and 241Am), and cryptotephra peaks, are compared and then integrated using OxCal's P_Sequence function to produce a single Bayesian age model. Environmental histories for each site obtained using physical and chemical characteristics of the peat cores, e.g. plant macrofossils, humification, ash content and dry density, provide important constraints for the models by highlighting periods with significant changes in accumulation rate, e.g. fire events, permafrost development, and prolonged surficial drying. Despite variable environmental histories, it is possible to produce high-resolution age-depth models for each core sequence. Consistent offsets between 14C and 210Pb dates pre-1960s are seen at five of the six sites, but tephra-corrected 210Pb data can be used to produce more coherent models at three of these sites. Processes such as permafrost development and thaw, surficial drying and local fires can disrupt the normal processes by which chronological markers and environmental records are incorporated in the peat record. In consequence, applying standard dating methodologies to these records will result in even greater uncertainties and discrepancies between the different dating tools. These results show that using any single method to accurately date peat profiles where accumulation has not been uniform over time may be unreliable, but a comprehensive multi-method investigation paired with the application of Bayesian statistics can produce more robust chronologies. New cryptotephra data for the Alberta region are also reported here, including the historical Novarupta-Katmai 1912 eruption, White River Ash (East), and glass from Mt. St. Helens, Mt. Churchill, and probable Aleutian sources

Peat Bogs Document Decades of Declining Atmospheric Contamination by Trace Metals in the Athabasca Bituminous Sands Region

Peat cores were collected from five bogs in the vicinity of open pit mines and upgraders of the Athabasca Bituminous Sands, the largest reservoir of bitumen in the world. Frozen cores were sectioned into 1 cm slices, and trace metals determined in the ultraclean SWAMP lab using ICP-QMS. The uppermost sections of the cores were age-dated with ²¹⁰Pb using ultralow background gamma spectrometry, and selected plant macrofossils dated using ¹⁴C. At each site, trace metal concentrations as well as enrichment factors (calculated relative to the corresponding element/Th ratio of the Upper Continental Crust) reveal maximum values 10 to 40 cm below the surface which shows that the zenith of atmospheric contamination occurred in the past. The age-depth relationships show that atmospheric contamination by trace metals (Ag, Cd, Sb, Tl, but also V, Ni, and Mo which are enriched in bitumen) has been declining in northern Alberta for decades. In fact, the greatest contemporary enrichments of Ag, Cd, Sb, and Tl (in the top layers of the peat cores) are found at the control site (Utikuma) which is 264 km SW, suggesting that long-range atmospheric transport from other sources must be duly considered in any source assessment

Peat bogs in northern Alberta, Canada reveal decades of declining atmospheric Pb contamination

Peat cores were collected from six bogs in northern Alberta to reconstruct changes in the atmospheric deposition of Pb, a valuable tracer of human activities. In each profile, the maximum Pb enrichment is found well below the surface. Radiometric age dating using three independent approaches (14C measurements of plant macrofossils combined with the atmospheric bomb pulse curve, plus 210Pb confirmed using the fallout radionuclides 137Cs and 241Am) showed that Pb contamination has been in decline for decades. Today, the surface layers of these bogs are comparable in composition to the "cleanest" peat samples ever found in the Northern Hemisphere, from a Swiss bog ~ 6000 to 9000years old. The lack of contemporary Pb contamination in the Alberta bogs is testimony to successful international efforts of the past decades to reduce anthropogenic emissions of this potentially toxic metal to the atmosphere

Metal-free sampling methods for dust, rainwater, surface water, plants, and sediments: A selection of unique tools from the SWAMP laboratory

Contamination control remains one of the greatest challenges for the reliable determination of many trace elements in environmental samples. Here we describe a series of metal-free sampling devices and tools designed and constructed specifically to minimize the risk of contamination by trace elements during sampling of dust, rainwater, surface water, plants, and sediments. Plastic components fabricated using 3-D printing include polylactic acid (PLA), polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG), polypropylene (PP), polycarbonate (PC) and PC with carbon fibre. When additional strength is needed (e.g. supporting structural components), carbon fibre, aluminum (Al), or 316 stainless steel (SS) is used. Other plastics employed include acrylic and vinyl. Epoxy glue or SS may be used for joining components, but do not come into contact with the samples. Ceramic (zirconium dioxide) cutting blades are used where needed. Each plastic material was evaluated for contaminant trace elements by leaching with high purity nitric acid in the metal-free, ultraclean SWAMP laboratory. The devices were tested in the field to evaluate their performance and durability. When combined with appropriate cleaning procedures, the equipment enables ultraclean collection for trace element analysis of environmental media. • Plastic sampling devices were designed and constructed using 3D printing of PLA, PET, PETG or PP. • Leaching characteristics of plastic components were evaluated using high purity nitric acid in a metal-free, ultraclean laboratory. • Each sampling device was successfully field-tested in industrial settings (near open pit bitumen mines and upgraders), and in remote locations of northern Alberta, Canada

Size fractionation of dissolved (<0.45 µm) trace elements from extracted soil with water and CaCl2 using AF4-UV-ICPMS to predict their bioavailability

Dissolved (<0.45 µm) trace elements (TEs) represent the sum of free ions, simple complexes and colloid-associated forms which have different mobility and bioavailability in soils. The distribution of TEs amongst these chemical forms was directly quantified in soil extracts using asymmetric flow field-flow fractionation (AF4) coupled to ultraviolet–visible absorbance spectrophotometry (UV) and inductively coupled plasma mass spectrometry (ICP-MS). The soil extracts were obtained using single extraction method with water and 0.01 M CaCl2, respectively. The yields of dissolved TEs extracted from the soils were profoundly impacted by extractants. Using AF4-UV-ICPMS, we show that dissolved species of Ba, Cr, Li, Mn and Mo were primarily present as “truly dissolved”/mainly ionic species (<1 kDa), e.g., hydrated cations, simple complexes or oxyanions, and therefore, likely represented the most bioavailable fraction. The distribution of these TEs amongst dissolved forms was unaffected by the different extractants. However, their dissolved concentrations were profoundly affected. Distributions of Al, As, Co, Cu, Fe, Ni, Pb, Th, Tl, U, V and Zn among the various chemical forms significantly differed with water and CaCl2 extractants. In water extracts, a greater proportion of these elements was associated with colloidal forms having sizes from 1 kDa to 0.45 µm, i.e., dissolved organic matter (DOM) or/and inorganic colloids. Water not only released greater colloid-complexed concentrations of TEs, like Al, As, Fe, Pb, Th, Tl, U and V, but also liberated greater amounts associated with ionic and small forms. Extractants like water and CaCl2 are useful for recovering bioavailable TEs from soils. However, the dissolved TEs extracted using water or CaCl2 represented TE concentrations and forms with different bioavailability. The AF4-UV-ICPMS technique is useful for directly quantifying TEs existing as mainly ionic species and those bound with DOM and inorganic colloids, and thus offers clear insight into their bioavailability in soils. This method also facilitates a better understanding of the effects of extractants on estimating TE bioavailability

Sources, Spatial-Distributions and Fluxes of PAH-Contaminated Dusts in the Athabasca Oil Sands Region

Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) has increased in northern Alberta, Canada, due to industrial development in the Athabasca oil sands region (AOSR). However, the sources, summertime deposition fluxes and associated spatial patterns are poorly characterized, and the magnitude of contamination has not been directly contrasted with comparable measurements around large Canadian cities. PAHs were measured in Sphagnum moss collected from 30 bogs in the AOSR and compared with reference moss collected from various remote, rural and near-urban sites in Alberta and Ontario. At all 39 locations, strong correlations between depositional fluxes of PAHs and accumulation rates of ash (n = 117, r = 0.877, p &lt; 0.001) implied that the main source of PAHs to moss was atmospheric deposition of particles. Average PAH concentrations at near-field AOSR sites (mean [SD], 62.4 [24.3] ng g-1) were significantly higher than at far-field AOSR sites (44.9 [20.8] ng g-1; p = 0.038) or the 7 reference sites in Alberta (20.6 [3.5] ng g-1; p &lt; 0.001). In fact, average PAH concentrations across the entire AOSR (7,850 km2) were approximately twice as high as in London, ONT, or near petroleum upgrading and major traffic corridors in Edmonton, AB. A chemical mass balance model estimated that both delayed petcoke (33% of PAHs) and fine tailings (38% of PAHs) were the major sources of PAHs in the AOSR. Over the 2015 summer growing season, we estimate that 101 - 110 kg of PAHs (on 14,300 - 17,300 tonnes of PAH-containing dusts) were deposited to the AOSR within a 50 km radius of surface mining. Given that the highest PAH deposition was to the northern quadrant of the AOSR, which includes the First Nations community of Fort MacKay, further dust control measures should be considered to protect human and environmental health in the region

Sphagnum Moss in the Athabasca Bituminous Sands Region Reveals No Significant Atmospheric Contamination by "Heavy Metals"

Sphagnum moss were collected from three sites at each of twenty-one ombrotrophic (rain-fed) peat bogs in the vicinity of and surrounding open pit mines and upgrading facilities of Athabasca Bituminous Sands in Alberta. Compared with contemporary Sphagnum moss from multiple sites at each of four bogs in rural locations of southern Germany, the AB mosses yielded lower concentrations of Ag, Cd, Ni, Pb, Sb and Tl, similar concentrations of Mo, but greater concentrations of Ba, Th and V. Compared to the “cleanest”, ancient peat samples ever tested from the northern hemisphere and dating from the mid-Holocene (ca. 6,000 to 9,000 years old), with the exception of V, the concentrations of each of these metals in the AB mosses are within a factor of three of “natural, background” values. The concentrations of “heavy metals” in the mosses are proportional to the concentration of Th (a conservative, lithogenic element) and therefore are contributed to the plants primarily in the form of mineral dust particles. Although it has been claimed that bitumen mining is a significant source of atmospheric Pb contamination, compared with the surface layer (1 cm slice) of peat cores collected in recent years from across Canada (13 cores in five Provinces from British Columbia to New Brunswick), the Pb concentrations in the mosses from AB are far lower. Vanadium, the single most abundant trace metal in bitumen, is the only exception: on average V in the AB mosses exceeds that of ancient peat by a factor of six; it is therefore enriched in the mosses, relative to Th, by a factor of two.JRC.E.5-Nuclear chemistr

Response to Comment on "Sphagnum Mosses from 21 Ombrotrophic Bogs in the Athabasca Bituminous Sands Region Show no Significant Atmospheric Contamination of “Heavy Metals”"

Blais and Donahue (2015) draw attention to many contemporary environmental issues and concerns regarding the industrial development of the Athabasca Bituminous Sands (ABS), most of which are outside of the scope of our original study (Shotyk et al., 2014). Here we restrict our response to the remarks they made which actually apply to our paper. The focus of our paper was the abundance and spatial variation in concentrations of “heavy metals” (selected chalcophile elements namely Ag, Cd, Pb, Sb, and Tl) as well as V, Ni and Mo (the three elements which are well known to be enriched in bitumen). We compared the concentrations of these elements in Sphagnum moss with those of Th, a conservative, lithophile element which was taken to reflect the abundance of mineral dust particles in the mosses. Concern was expressed by Blais and Donahue for our analysis and interpretation, in particular the use of average concentrations for each sampling location, the variation in metal concentrations with distance from industry, and the contribution of mineral dust particles to the heavy metal concentrations.JRC.E.5-Nuclear chemistr

<i>Sphagnum</i> Moss as an Indicator of Contemporary Rates of Atmospheric Dust Deposition in the Athabasca Bituminous Sands Region

<i>Sphagnum</i> 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% (<i>n</i> = 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 X-ray 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