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Increasing abundance of the planktonic diatom Asterionella formosa and diatom-inferred pH in lake WF3 (core ALB11).
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Exploitation of the Athabasca Oil Sands has expanded hugely over the last 40 years. Regional emissions of oxidised sulphur and nitrogen compounds increased rapidly over this period and similar emissions have been linked to lake acidification in other parts of North America and Europe. To determine whether lakes in the region have undergone acidific...
Context in source publication
Context 1
... cores show a wide range in organic matter content as illustrated by LOI values ranging from <20% in S3 to >80% in WF2. The presence of dramatic short- term fluctuations in dry weight or LOI can indicate that stratigraphic integrity has been compromised e.g., through discontinuities in the record. While there are few such indications in the present core records, there are small shifts in LOI in the bottom of core ALB04 (lake SM6) and at 5 cm depth in both ALB02 (lake BM3) and ALB05 (lake SM3) (data not shown, see Curtis et al . 2009). Dating of sediment cores using Pb and Cs reveals a large range of sediment accumulation rates, but all 12 cores encompass at least 100 years of accu- mulated sediment. Most cores showed straightforward dating profiles, although three showed possible evidence of missing surface sediments (lakes SM8, WF3 and S3) introducing uncertainty into the interpretation of very recent changes. Age-depth profiles and sedimentation rates for individual cores are presented in Curtis et al . (2009). The sedimentary diatom assemblages examined in the 12 cores displayed a wide diversity of species, both planktonic and benthic, that are closely linked to regional water quality variations as well as to specific local site factors. Many of the species are cosmopolitan but North American species (e.g., Stephanodiscus ni- agarae Ehr., Cyclotella michiganiana Skv.) often con- tribute significantly to the diatom phytoplankton component. Endemic benthic taxa are less significant but occurrences of rare taxa such as Carpartogramma cru- cicula (Grun. ex Cl.) Ross, Pinnularia cuneicephala Smith, P. latevittata v. domingensis Cleve and Stauro- nies stodderi Lewis are noteworthy. Some small navi- culoids in several cores, present in relatively low abundances, were taxonomically problematic. Diatom analysis of the 12 cores indicates that the lakes can be placed broadly into three categories that indicate lake acidification, nutrient enrichment or an absence of significant change. The diatom stratigraphies of three cores are presented to indicate these categories. Only one of the sites (lake NE7, core ALB21) indicates marked recent acidification (Fig. 2). Diatom assemblages in this core were moderately diverse (123 taxa being identified) and showed marked species changes. Although circum-neutral species such as tychoplanktonic Staurosira construens v. pumila dominated the diatom assemblages, acid water indicator diatoms and especially Actinella punctata appear towards the core top (Fig. 2). Actinella punctata indicates strongly acid water and has pH optima of 5.1 in North American (Dixit et al. 1993) and 5.2 in European (Birks et al . 1990) data sets. It appears in the core at between 6 and 7 cm depth ( ca 1970) and increases in abundance particularly in the upper 3 cm or from ca 1990. Other acid indicating species such as the planktonic Asterionella ralfsii and tychoplanktonic Fragilariforma polygonata also showed sharp increases in the upper 3 cm of sediment. Frustulia rhomboides v. saxonica and several circum-neutral Cymbella and Navicula taxa showed small abundance peaks around 5.5–7.5 cm depth ( ca 1950–70). Other circum-neutral and tychoplanktonic taxa such as Staurosira elliptica and several Aulacoseira spp. showed abundance declines towards the core top. No species typical of nutrient enrichment were observed. Overall, this core provides strong evidence that the lake has been recently acidified with a marked DI-pH decline from about pH 6.3 to pH 5.6 since 1970 (Fig. 2). Although two other cores (ALB04 from lake SM6 and ALB09 from lake NE2, Tab. 4) indicated slight acidification, only NE7 displayed a convincing declining pH trend. Several sites showed increases in diatom-inferred pH (alkalinisation) and many of the sites appear to have experienced nutrient enrichment in the recent past (Tab. 4). This is typically demonstrated by the increasing abundance of planktonic diatoms commonly associated with more nutrient rich conditions, for example the major increase of Asterionella formosa in lake WF3 (core ALB11; Fig. 3). This taxon was unrecorded below 12 cm depth and showed a major abundance increase from above 7 cm depth ( ca 1936) to reach almost 50% of the total diatom assemblage in surface sediment. Another planktonic diatom, Aulacoseira ambigua , also indicative of nutrient enrichment, also showed increasing frequency abundances, from the core base to the most recent sediment. Less common but also indicating increased nutrients, Nitzschia gracilis increased in the recent sediment. Commensurate with the increasing abundances of these taxa indicating higher nutrient status, several fragilarioids declined in the core. These taxa are primarily benthic but are easily resuspended into the water column and Staurosira elliptica and St. construens v. venter both show strong declines and only Fragilariforma constricta shows a small increase. Similarly, some of the more uncommon but larger benthic Pinnularia species have also declined in abundance. Possibly, these changes could reflect diminished under- water light availability as a result of the development of the planktonic diatoms and doubtless other phytoplankton; alternatively, nutrient or light optima of the benthic species may have changed. Overall, the diatom stratigraphy of this core shows a large increase in planktonic diatom species that indicates strong nutrient enrichment of the lake. There is a corresponding increase in diatom- inferred pH from pre-1900 to the present day, although higher pH values were also indicated at the core base. Diatom analysis in two cores cores (ALB09 from lake NE2 and ALB04 from lake SM6) showed no marked trend changes in diatom abundances indicating an absence of significant eutrophication or acidification. The diatom frequency diagram for lake NE2 (Fig. 4) showed relatively small changes in species composition. The semi-benthic fragilarioid species Staurosira construens v. venter was common throughout the sediment core with abundances fluctuating around 20% without any clear trend change. Several diatoms showed a small trend towards higher abundances from the core base to around 7–5 cm sediment depth ( ca 1960–1976) before declining. One of these species Aulacoseira ambigua is an indicator of higher nutrient conditions. Only two low abundance species increased above 6 cm depth (1969), Asterionella ralfsii and Staurosira elliptica . The former species is planktonic in habit and could indicate a small acidity change, but the minor increase in A. ambigua could indicate slight nutrient enrichment around 5 cm depth in the core ( ca 1976) with a subsequent decline suggesting that this change was not sustained. Overall, the diatom stratigraphy of this core indicates fairly stable conditions with hints of acidity and nutrient changes which are not detectable in the diatom-inferred pH, which shows no convincing trend. Spheroidal carbonaceous particles (SCPs) provide an unambiguous indicator of contamination from high- temperature fossil fuel combustion (coal and fuel oil, but not gas) because they are not produced from wood, biomass or charcoal combustion (e.g., forest fires) and hence have no natural sources (Rose 2001). SCPs were found at low but detectable concentrations in all cores. The highest recorded concentration exceeded 1000 gDM –1 only in lake NE2 (core ALB09; see Fig. 5). No SCPs were detected below 5 cm in any core suggesting any contamination is recent. This is confirmed by the radiometric dating which shows that the earliest presence of SCP contamination was found in lake SM6 (core ALB04) in the late 1950s and in lake CM2 (core ALB15) in the 1960s (Fig. 5). Temporal profiles are highly irregular and, given the low concentrations, the SCP temporal records are likely to be linked to detection limits of the analytical technique. As a consequence, the first presence of SCPs in the cores is not synchronous across the region and the profiles show no consistent temporal trends. Full SCP inventories were calculated for each core. These provide a measure of the full record of contamination at each lake. These have also been normalised to the 210 Pb inventories for each core in order to allow for both sediment focussing effects in each lake and enhanced catchment inputs from, for example, bare rock areas. Both SCP inventories and SCP/ 210 Pb inventory ratios confirm the low contamination status of all the lakes. Analysis of the full dataset shows no relationship of any SCP parameter (surface and peak concentrations; surface fluxes; inventories and inventory ratios) with distance from the centre of the Oil Sands processing activities. This indicates that these activities are not a major source of these particulate contaminants. The SCP data also show no agreement with the Hg surface sediment concentrations (see below). The δ C and C/N ratio profiles demonstrate the clearest signs of alterations in lake biogeochemistry, including sources of organic matter and changes in productivity. Figure 6 shows the measured δ 13 C profiles ...
Citations
... If oil sands N emissions have distinct stable isotopic signatures, it may be possible to quantify the extent to which these emissions have affected N cycling in surrounding ecosystems. Despite scant data on the δ 15 N signatures from various oil sands sources (notably upgrader stack emissions, diesel-fueled heavy hauler exhaust), several studies have incorporated δ 15 N measurements into research directed toward identifying and quantifying oil sands N deposition effects on forest (Laxton et al., 2010;Jung et al., 2013;Proemse et al., 2016;Hemsley et al., 2019) and aquatic (Farwell et al., 2009;Curtis et al., 2010) ecosystems. Others have assessed the extent to which lichen (Evernia mesomorpha) δ 15 N signatures might be used as a proxy for oil sands N emissions Proemse et al., 2013). ...
Study region
The 140,329 km² Athabasca Oil Sands Administrative Area (OSAA), which contains 8982 km² of bogs. Since the late 1970s, N emissions from oil sands development in the OSAA have steadily increased, reaching over 80,000 metric tonnes yr⁻¹ in 2017.
Study focus
If oil sands N emissions have distinct stable isotopic signatures, it may be possible to quantify the extent to which these emissions have affected N cycling in surrounding aquatic, wetland, and terrestrial ecosystems. To assess the potential for ¹⁵N as a tracer of oil sands N emissions, we measured natural abundance ¹⁵N ratios and tissue N concentrations in 10 plant or lichen species at 6 peatland sites at different distances from the oil sands region, collected on 17 sampling dates over three years (2009–2011).
New hydrological insights
To understand how the pressures of changing N and S deposition regimes and hydrologic disturbance interactively affect the region’s wetlands, it is critical to understand how these pressures act individually. The epiphytic lichen, Evernia mesomorpha, was the only species that exhibited patterns that could be interpreted as being influenced by oil sands N emissions. The paucity of data on δ¹⁵N signatures of oil sands related N sources precludes definitive interpretations of δ¹⁵N in plant or lichen tissues with respect to oil sands N emissions.
... Sediment core studies in the region were conducted by Hazewinkel et al. (2008), Curtis et al. (2010), Kurek et al. (2013) and Laird et al. (2013) to evaluate acidifications effects mainly through diatom-inferred pH changes in boreal lakes to NE of Alberta and one study to the NE of Saskatchewan. These investigations showed no evidence of widespread lake acidification trends associated with oil sands development (Hazewinkel et al., 2008;Curtis et al., 2010;Mushet et al., 2017;Cook et al., 2017). ...
... Sediment core studies in the region were conducted by Hazewinkel et al. (2008), Curtis et al. (2010), Kurek et al. (2013) and Laird et al. (2013) to evaluate acidifications effects mainly through diatom-inferred pH changes in boreal lakes to NE of Alberta and one study to the NE of Saskatchewan. These investigations showed no evidence of widespread lake acidification trends associated with oil sands development (Hazewinkel et al., 2008;Curtis et al., 2010;Mushet et al., 2017;Cook et al., 2017). ...
Study region
This study focuses on boreal lakes in the Athabasca Oil Sands Region (AOSR), Alberta, Canada between latitude 55.68°N and 59.72°N and longitude 110.02°W and 115.46°W. Study focus
This study focuses on interpretation of hydrochemistry from 50 lakes thought to be acid sensitive, and so monitored by the Regional Aquatic Monitoring Program (RAMP) over the last two decades. This study uses basic statistics, principal component analysis, lithological evidence, CO2 saturation estimates, mineral equilibria and δ¹³CDIC measurements to describe and assess controls on pH and to investigate causal factors of observed pH increase in the lakes.
New hydrological insights for the region
Our assessment provides evidence of two main geochemical processes that control pH increase, namely carbonate dissolution and organic matter uptake, the latter a particularly important component of alkalinity in low pH lakes. Lakes in all subregions show strong evidence of dissolution of marine carbonates of undetermined source, and lake water appears to be trending from CO2 super-saturation towards atmospheric CO2 equilibrium. This supports the hypothesis of carbonate input due to permafrost thaw via surface or groundwater pathways, but also reveals likely influence from CO2 dissolution mechanisms related to climatic influence on ice cover duration.
... These studies agree well with spatial analysis of snowpack samples throughout the AOSR (Kelly et al., 2009(Kelly et al., , 2010Cho et al., 2014;Kirk et al., 2014;Manzano et al., 2016). Other paleolimnological studies have focused on environmental and ecological conditions in lakes, regional hydroclimatology, and changes due to climatic trends (e.g., Curtis et al., 2010;Summers et al., 2016Summers et al., , 2019. These studies have been instrumental in quantifying and expanding our understanding of the magnitude and extent of industrial effects within the AOSR, as well as elucidating aspects of the pre-development history of the region. ...
Study region
McClelland Lake, Athabasca Oil Sands Region
Study focus
Effective environmental monitoring requires knowledge of inherent natural variation. In the absence of pre-development monitoring of aquatic ecosystems, paleolimnological approaches have been championed as a scientifically rigorous method to define pre-development conditions. Motivated by regulatory processes and absence of pre-development data, we conducted a comprehensive paleolimnological study at McClelland Lake to determine an appropriate timeframe for defining natural ranges of variation (NRVs) in hydroecological variables before potential onset of mining within its catchment.
New hydrological insights for the region
During the past ∼325 years, five distinctive intervals of hydroecological conditions were identified. The first phase (ca. 1695–1750) coincided with the Little Ice Age (LIA), when arid conditions supported lake levels 2.6–3.5 m below present. Phase II (ca. 1750–1840) encompassed subsequent warming, lake-level rise to 1.2–2.6 m below present and increased aquatic productivity. Phase III included frequent natural disturbance by wildfires (ca. 1840–1900). During Phase IV (ca. 1900–1970), the lake deepened and algal communities diversified. Phase V (post–1970) captured influence of regional industrial development, climate warming and lake-level decline, and wildfires. We propose quantitative definitions of NRVs for McClelland Lake be derived from paleolimnological indicators since 1750, which provide a conservative and relevant range of hydroecological conditions, and explore merits and drawbacks of shorter-duration NRV definition for monitoring change.
... Similarly, studies that have used lake sediment cores to infer pH changes over time around and downwind of the AOSR have not detected region-wide lake acidification or changes in phytoplankton communities (Curtis et al. 2010;Hazewinkel et al. 2008;Laird et al. 2013). ...
This review is part of a series synthesizing peer-reviewed literature from the last decade on environmental monitoring in the oil sands region (OSR) of northeastern Alberta. This paper focuses on atmospheric emissions, air quality, and deposition in and downwind of the OSR. The vast majority of published monitoring and research activities were concentrated in the surface-mineable region in the Athabasca OSR. Substantial progress has been made on understanding oil sands (OS)-related emission sources using multiple approaches: airborne measurements, satellite measurements, source emission testing, deterministic modeling, and source apportionment modeling. These approaches generally yield consistent results, indicating OS-related sources are regional contributors to nearly all air pollutants. Most pollutants exhibit enhanced air concentrations within ~20 km of surface-mining activities, with some enhanced >100 km downwind. Some pollutants (e.g., sulphur dioxide, nitrogen oxides) undergo transformations as they are transported through the atmosphere. Deposition rates of OS-related substances primarily emitted as fugitive dust are enhanced within ~30 km of surface-mining activities, whereas gaseous and fine particulate emissions have a more diffuse deposition enhancement pattern extending hundreds of km downwind. In general, air quality guidelines are not exceeded, although these single-pollutant thresholds are not comprehensive indicators of air quality. Odour events have occurred in communities near OS industrial activities, although it can be difficult to attribute events to specific pollutants or sources. Nitrogen, sulphur, polycyclic aromatic compounds (PACs) and base cations from OS sources occur in the environment, but explicit and deleterious responses of organisms to these pollutants is not as apparent across all study environments; details of biological monitoring are further discussed in other papers from this special issue. However, modelling of critical load exceedances suggests that at continued emissions levels, ecological change may potentially occur in the future. Knowledge gaps, and recommendations for future work to address these gaps, are also presented.
... While an effect is hypothesized (Anas et al., 2014;Cathcart et al., 2016;Makar et al., 2018;Scott et al., 2010), most studies show no discernible responses consistent with the alteration of the pH of lakes over time (i.e., Anas et al., 2014;Hazewinkel et al., 2008;Laird et al., 2013Laird et al., , 2017. Some evidence has been found in two lakes east of the minable region (~54 and~80 km west of Suncor's coker, respectively [Curtis et al., 2010;Laird et al., 2013]), but these changes have not been specifically linked with OSIA. In contrast, alkalization of lakes has been more commonly observed (Curtis et al., 2010), and researchers have suggested that lake characteristics (similar to conclusions regarding Hg [e.g., Emmerton et al., 2018]) may be the driving factors in changes in pH (Curtis et al., 2010). ...
... Some evidence has been found in two lakes east of the minable region (~54 and~80 km west of Suncor's coker, respectively [Curtis et al., 2010;Laird et al., 2013]), but these changes have not been specifically linked with OSIA. In contrast, alkalization of lakes has been more commonly observed (Curtis et al., 2010), and researchers have suggested that lake characteristics (similar to conclusions regarding Hg [e.g., Emmerton et al., 2018]) may be the driving factors in changes in pH (Curtis et al., 2010). Other work suggests a role of fugitive dust rich in cations (Fenn et al., 2015), but analyses of lake sediments have shown no discernible change in Ca over time (Cooke et al., 2017). ...
... Some evidence has been found in two lakes east of the minable region (~54 and~80 km west of Suncor's coker, respectively [Curtis et al., 2010;Laird et al., 2013]), but these changes have not been specifically linked with OSIA. In contrast, alkalization of lakes has been more commonly observed (Curtis et al., 2010), and researchers have suggested that lake characteristics (similar to conclusions regarding Hg [e.g., Emmerton et al., 2018]) may be the driving factors in changes in pH (Curtis et al., 2010). Other work suggests a role of fugitive dust rich in cations (Fenn et al., 2015), but analyses of lake sediments have shown no discernible change in Ca over time (Cooke et al., 2017). ...
We synthesize the information available from the peer‐reviewed literature on the ecological status of lakes and rivers in the Oil Sands Region (OSR) of Canada. The majority of the research from the OSR has been done in or near the minable region and has examined the concentrations, flux, or enrichment of contaminants of concern (CoCs). Proximity to oil sands facilities and the beginning of commercial activities tends to be associated with greater estimates of CoCs across studies. Research suggests greater measurements of CoCs are typically associated with wind‐blown dust, but other sources also contribute. Exploratory analyses further suggest relationships with facility production and fuel use data. Exceedances of environmental quality guidelines for CoCs are also reported in lake sediments, but there are no indications of toxicity including those within the areas of the greatest atmospheric deposition. Instead, primary production has increased in most lakes over time. Spatial differences are observed in streams, but causal relationships with industrial activity are often confounded by substantial natural influences. Despite this, there may be signals associated with site preparation for new mines, potential persistent differences, and a potential role of petroleum coke used as fuel on some indices of health in fish captured in the Steepbank River. There is also evidence of improvements in the ecological condition of some rivers. Despite the volume of material available, much of the work remains temporally, spatially, or technically isolated. Overcoming the isolation of studies would enhance the utility of information available for the region, but additional recommendations for improving monitoring can be made, such as a shift to site‐specific analyses in streams and further use of industry‐reported data. This article is protected by copyright. All rights reserved.
... During industrial processing, bitumen is extracted using hot caustic solutions and then upgraded at elevated temperatures to recover hydrocarbons (Gosselin et al., 2010). Given the scale of industrial development, there is understandable concern about a broad spectrum of environmental impacts (Giesy et al., 2010;Hodson, 2013;Jordaan, 2012;Schindler, 2010Schindler, , 2014Tenenbaum, 2009;Timoney and Lee, 2009), including direct impacts on air and water from changing land use (Rooney et al., 2012;Schwalb et al., 2015), water use (Sauchyn et al., 2015) and water quality (Alexander et al., 2017;Alexander and Chambers, 2016;Guéguen et al., 2011;Evans and Talbot, 2012;Hebben, 2009;Tondu, 2017), greenhouse gas (GHG) emissions as well as releases of N and S compounds (Curtis et al., 2010;Davidson and Spink, 2018;Hazewinkel et al., 2008;McLinden et al., 2012;Percy, 2013;Proemse and Mayer, 2012;Whitfield et al., 2010;Wieder et al., 2016b;Wieder et al., 2016a), generation and release of dusts Phillips-Smith et al., 2017;Wang et al., 2015;Watson et al., 2014;Xing and Du, 2017), and emissions of organic contaminants such as volatile organic compounds (VOCs) (Li et al., 2017;Liggio et al., 2016), polycyclic aromatic hydrocarbons (PAHs) (Ahad et al., 2014;Ahad et al., 2015;Birks et al., 2017;Evans et al., 2016;Graney et al., 2017;Hall et al., 2012;Hrudey, 2013;Jautzy et al., 2015;Kelly et al., 2009;Kelly et al., 2010;Korosi et al., 2016;Kurek et al., 2013aKurek et al., , 2013bMunkittrick and Arciszewski, 2017;Wania, 2014a, 2014b;Thienpont et al., 2017;Timoney and Lee, 2011;Xu, 2018;Zhang et al., 2016) and naphthenic acids (Headley and McMartin, 2004;Ross et al., 2012). Many of the recent environmental changes described in these publications are taking place at a time when the global climate is also changing which can make it more difficult to distinguish between the different types of driving forces (e.g. ...
The Athabasca Bituminous Sands (ABS) in northern Alberta, Canada, represent one of the largest reserves of hydrocarbons on the planet, yet there is remarkably little published data on the abundance of potentially toxic trace elements (TEs) in this resource. Here, we present the concentrations and review the relevance of 30 TEs in bulk samples of ABS as well as the organic and mineral fraction of representative samples. The distribution of TEs is dichotomous: they occur primarily in the organic fraction (Mo, Ni, Re, V and Se) or almost exclusively in the mineral fraction (virtually all of the other TEs). Except for Mo and Re, TEs in the ABS are depleted relative to the composition of the Upper Continental Crust (UCC), a reference level commonly used in quantifying the extent of contamination by TEs in the environment. Based on the published data available for comparison, TE concentrations in ABS are similar to those of sandstones, well below the average value for shale, and far below the values reported for organic-rich, black shales. The data presented here explains why recent studies of contamination of air, water, soil, plants in this region of northern Alberta, when viewed critically, reveal limited enrichments of chalcophile TEs, relative to crustal abundance. The abundance and distribution of TEs in the ABS also explains why atmospheric transport of TEs is largely restricted to the immediate region (< 50 km) surrounding the open pit bitumen mines, and dispersion patterns resemble those of dust deposition. Based on these findings, most of the chalcophile TEs mobilized by mining are expected to have limited bioaccessibility and bioavailability, simply because they are mainly hosted by silicate minerals with limited solubility at ambient pH.
... The observed trends among H lakes contrast the findings of previous studies in the AOSR, which found little evidence to indicate OS emissions contributed to lake acidification. 34,65,66 Considering these previous studies did not independently evaluate the two subpopulations identified in the current investigation, the mixture of H and L lakes throughout the AOSR may have confounded the apparent associations between pH and OS emission transport. Future studies should consider these unique subsets of lakes (high and low), as there are likely unknown lake-specific factors (permafrost and wetland inputs, and DOC composition) that may further explain the observed spatial trends throughout the region. ...
The Athabasca oil sands region (AOSR) in north-eastern Alberta, Canada, contains the world’s third largest known bitumen deposit. Oil sands (OS) operations produce emissions known to contribute to acidic and alkaline deposition, which can alter the chemistry of the receiving surface waters, including dissolved organic carbon (DOC). Little is known regarding the natural variability of aquatic DOC among lakes within the AOSR. Surface-water data from 50 lakes were analyzed; variables known to be associated with the light-absorptive properties of DOC (true color [TC]) were evaluated to investigate the potential variability of chromophoric DOC (CDOC). Comparison of TC and DOC revealed two distinct “high” (H) and “low” (L) lake subpopulations, the former being characterized by high relative TC and low DOC, and the latter by the inverse. The H lakes were defined by variables known to be associated with CDOC, while L lakes appeared well-buffered potentially owing to groundwater inputs. The divergent optical properties between subpopulations appeared partially attributable to pH-limited Fe complexation. Trajectory analysis indicated that H lakes most likely to receive atmospheric deposition from OS sources experienced significantly lower pH. These results are contrary to previous studies that found OS emissions to have minimal acidifying effect over lakes throughout the AOSR.
... Molar C/N values from 8 to 10 signal a dominant phytoplankton source, while values ≥20 represent organic matter from terrestrial plants (Curtis et al., 2010;Meyers, 1994;Overpeck et al., 2013;Thevenon et al., 2012). Intermediate C/N values that range 10-20 generally indicated combined autochthonous (i.e., aquatic) and allochthonous (i.e., terrestrial) sources of organic deposition. ...
A multiproxy record from Baldwin Lake, San Bernardino Mountains, allowed us to examine variation and relationships between erosion, wildfire, vegetation, and climate in subalpine Southern California from 120 to 15 ka. Bulk organics, biogenic silica, and molar C:N data were generally antiphased with magnetic and trace element data and displayed long‐term (10⁵ year) shifts between autochthonous and allocthonous deposition. This was most pronounced during Marine Isotope Stage (MIS) 5, and we hypothesize that local summer insolation was the primary driver for Baldwin Lake's productive and unproductive lake state alternations. Wildfire history was inferred from charcoal concentrations and vegetation change from pollen. Relationships between these ecological processes, basin deposition, and summer insolation were often nonlinear. Sagebrush expansion, wildfire, and weak basin weathering characterized MIS 4, while during MIS 2, the basin was highly erosive, rarely burned, and the forest was impacted by shifts in Southern Californian hydroclimate. Despite coniferous forest cover throughout MIS 3, submillennial oscillations in charcoal, pollen, and bulk organic content occurred, consistent with pollen records from Eurasia's Mediterranean biome that span multiple glacial‐interglacial cycles. Highly resolved global CO2 records and sea surface temperatures in key regions of the Pacific show no apparent relationship to these landscape conditions, and we suggest submillennial hydroclimatic variability as a potential driver. Highly resolved long pollen records from Southern California are an urgent research need to better understand the finer‐scale (≤10³ year) interactions between past vegetation, wildfire, and erosion, given the current natural disaster risks that 21st century climate change poses to both human and ecological communities.
... Decreasing metal concentrations have also been reported in peat cores collected from rain-fed bogs at varying distances from AR6 . Although potential lake acidification risk is highlighted by the CR models, other studies report little evidence of lake acidification based on sediment cores collected in northern Alberta and Saskatchewan (Curtis et al. 2010;Hazewinkel et al. 2008;Laird et al. 2013Laird et al. , 2017. Local chemical and physical influence of industry is apparent in lake sediments (<50 km from AR6), but reduced loadings over time have been observed for some metals (Cooke et al. 2017). ...
... Early work by Environment Canada failed to detect an increase in Hg concentrations in 50 years of sediment accumulation from Lake Athabasca . In contrast, Curtis et al. (2010), reported increasing Hg accumulation rates in a single sediment core collected downwind of the ABS region, but no direct connection was made to the chronology of bitumen mining and upgrading activities. Thus, the trend in increasing Hg concentrations seen in this core (Curtis et al., 2010) may be nothing other the corresponding trend seen in sediments dating from the 20th century in lakes from across North America (Drevnick et al., 2016). ...
... In contrast, Curtis et al. (2010), reported increasing Hg accumulation rates in a single sediment core collected downwind of the ABS region, but no direct connection was made to the chronology of bitumen mining and upgrading activities. Thus, the trend in increasing Hg concentrations seen in this core (Curtis et al., 2010) may be nothing other the corresponding trend seen in sediments dating from the 20th century in lakes from across North America (Drevnick et al., 2016). Sediments collected from 10 lakes in Saskatchewan, downwind from the ABS region yielded "no consistent trends in the concentration or flux of total or individual priority pollutants including lead, mercury, copper, zinc and vanadium" (Laird et al., 2013). ...
Sphagnum moss was collected from 22 ombrotrophic (rain-fed) bogs near open pit mines and upgraders within the Athabasca Bituminous Sands (ABS) region of Alberta (AB). Mercury was quantified using two approaches: sector-field ICP-MS of acid digests, and a Direct Mercury Analyser (DMA) for solid samples. Using ICP-MS, the mean Hg concentration in moss from the ABS region (34.7 ± 1.5 µg/kg, n=75) was significantly greater than the control site, Utikuma (26.7 ± 4.0 µg/kg, n=3). Using DMA, the mean Hg concentration in moss from the ABS region (26.2 ± 0.9 µg/kg, n=71) was significantly lower than the control site (28.5 ± 1.3 µg/kg, n=6). These contradictory findings illustrate the challenges associated with comparing the results of two analytical methods, especially given the similarity in Hg concentrations between industrial and background sites, Similar Hg concentrations were also found in Sphagnum moss from two other bogs in AB which are far removed from the ABS region. The Hg concentrations in Sphagnum from the ABS bogs are well below the range found in bog vegetation collected earlier in eastern Canada, and comparable to the lowest values (5th percentile) reported for forest moss collected in 2015 from Norway and Sphagnum moss sampled in 2008 from northern Sweden. Given the rates of Sphagnum accumulation in the ABS region (ca. 215 g/m2/yr), Hg accumulation rates there were 5.8-7.5 µg/m2/yr versus 5.7-6.1 µg/m2/yr at the control site (UTK); these are at the upper limit of the range in pre-anthropogenic rates of Hg accumulation for peat from European bogs. Sphagnum moss is abundant in Canada and found in bogs from coast to coast, offering an opportunity to obtain quantitative information on atmospheric Hg deposition to terrestrial ecosystems from natural as well as anthropogenic sources.
