Ecological effects and causal synthesis of oil sands activity impacts on river ecosystems: water synthesis review
Abstract
Oil sands development in the lower Athabasca River watershed has raised considerable public and scientific concerns regarding perceived effects on environmental health. To address this issue for tributaries and the mainstem of the Athabasca River in the Athabasca Oil Sands Region, the Water Component of the Joint Oil Sands Monitoring (JOSM) plan produced monitoring assessments for seven integrated themes: atmospheric deposition, tributary water quality, river mainstem water quality, groundwater quality and quantity, water quality and quantity modelling, benthic invertebrate condition, and fish health. Our review integrates and synthesizes the large and diverse datasets assembled in the seven JOSM theme assessments to (i) evaluate possible environmental effects based on known sources and candidate proximal causes and (ii) determine the importance of cause-and-effect pathways related to contaminant, sediment, and nutrient inputs. Although JOSM research identified ecological effects that appear to be associated with contaminant exposure, the source of this exposure is confounded by co-location of, and inability to differentiate between, oil sands operations (principally released by atmospheric emission) and inputs from the natural bitumen outcrops (e.g., erosional material transported by surface and groundwater flows). Nutrient enrichment from treated municipal sewage effluent was the dominant ecological effect observed for the mainstem Athabasca River, associated with increased fish size and changes in invertebrate assemblages, likely because this pollution source is discharged directly into the river. If the direct release of treated oil sands process water occurs in the future, then the potential ecological impact of these direct industry releases will need to be evaluated carefully. The ecological causal assessment method proved to be a useful tool for better understanding how stressor sources relate to ecological effects through candidate proximate causes. Factors that confound our ability to assess the ecological effects of oil sands development focus on our inability to adequately differentiate between contaminants supplied from natural and anthropogenic contaminant sources. Our causal synthesis identifies options for changes in future monitoring to better anticipate and detect degradation in the ecosystem health of the lower Athabasca River and its tributaries.
Graphical Abstract
Résumé
L’exploitation des sables bitumineux dans le cours inférieur du bassin versant de la rivière Athabasca a suscité une grande inquiétude chez le public et les scientifiques quant aux effets perçus sur la santé environnementale. Afin d’aborder cette question pour les affluents et le cours principal de la rivière Athabasca dans la région des sables bitumineux de l’Athabasca, la composante eau du programme de surveillance conjointe des sables bitumineux (SCSB) a produit des évaluations des surveillances pour sept thèmes intégrés : le dépôt atmosphérique, la qualité de l’eau des affluents, la qualité de l’eau du cours principal de la rivière, la qualité et la quantité des eaux souterraines, la modélisation de la qualité et de la quantité de l’eau, la condition des invertébrés benthiques et la santé des poissons. La synthèse réalisée par les auteurs intègre et résume les vastes et divers ensembles de données rassemblés dans les sept évaluations thématiques du programme de SCSB pour (i) évaluer les effets environnementaux possibles sur la base des sources connues et des causes proximales candidates et (ii) déterminer l’importance des voies de causalité liées aux apports de contaminants, de sédiments et de nutriments. Bien que les recherches du programme de SCSB aient identifié des effets écologiques qui semblent être associés à l’exposition aux contaminants, la source de cette exposition est confondue par la co-localisation et l’incapacité à différencier entre les opérations d’exploitation des sables bitumineux (principalement rejetés par émission atmosphérique) et les apports provenant des affleurements naturels de bitume (par exemple, les matériaux formés par l’érosion transportés par le flux des eaux de surface et souterraines). L’enrichissement en nutriments des effluents d’eaux usées municipales traitées a été l’effet écologique dominant observé pour le cours principal de la rivière Athabasca, associé à l’augmentation de la taille des poissons et aux changements dans les assemblages d’invertébrés, probablement parce que cette source de pollution est rejetée directement dans la rivière. Si le rejet direct des eaux de traitement des sables bitumineux se produit à l’avenir, l’impact écologique potentiel de ces rejets directs de l’industrie devra alors être soigneusement évalué. La méthode d’évaluation des causes écologiques s’est avérée constituer un outil utile pour mieux comprendre comment les sources de stress sont liées aux effets écologiques par des causes immédiates candidates. Les facteurs qui confondent notre capacité à évaluer les effets écologiques de l’exploitation des sables bitumineux se concentrent sur notre incapacité à différencier de manière adéquate les contaminants provenant de sources naturelles et anthropiques. Cette synthèse sur les voies de causalité identifie des options de changements dans la surveillance future afin de mieux anticiper et détecter la dégradation de la santé de l’écosystème du cours inférieur de la rivière Athabasca et de ses affluents. [Traduit par la Rédaction]
1. Introduction
The Canadian oil sands in northeastern Alberta contain approximately 10% of the proven global oil reserves (Natural Resources Canada 2019), with development expanding substantially since 1980 and oil sands production exceeding 2 million barrels per day in 2013 (CERI 2014). Public and scientific concerns, as well as sharply polarized views, regarding perceived effects of oil sands development on environmental health have been raised in Canada and internationally (Hall et al. 2012; Kurek et al. 2013). This is because oil sands development poses potential risks to human and environmental health of this large region, as the Athabasca River provides key ecosystem services to municipalities and indigenous inhabitants and contains an internationally recognized Ramsar Convention wetland of importance (i.e., Peace–Athabasca Delta) (Brook et al. 2019). The primary question surrounding this massive industrial development is whether development of the Alberta oil sands in the Athabasca Oil Sands Region (Fig. 1) has adversely affected the environmental health of the lower Athabasca River watershed and its downstream receiving ecosystems (e.g., Peace–Athabasca Delta) with respect to water, wildlife, and atmosphere integrity. Previous environmental monitoring programs and research activities have generated considerable information on the lower Athabasca system; however, a lack of integration among these efforts was identified in several independent science reviews and journal papers (e.g., Kelly et al. 2009, 2010; Giesy et al. 2010; Schindler 2010) and by expert science panel reviews (e.g., Royal Society of Canada 2010; Federal Oil Sands Advisory Panel 2010; Alberta Water Monitoring Data Review Committee 2011; Alberta Environmental Monitoring Panel 2011). Recommendations from these panels focused on the need for improved monitoring, increased availability of environmental data to assess potential impacts of current developments, and the critical need for an improved scientific approach to monitor and assess the potential cumulative effects of the oil sands industry on freshwater resources (Brook et al. 2019). In response to the identified problems, the Governments of Canada and Alberta developed the Joint Oil Sands Monitoring (JOSM) plan to provide risk‐based assessments of impacts from oil sands activity on environmental health and examinations of cause–effect relationships (Environment Canada and Alberta Environment 2011a, 2011b).
Fig. 1.
The JOSM plan was developed as an adaptive, integrated, multi‐ecosystem monitoring and research program to better understand, predict, and report on status and trends in ecosystem structure, function, and health. This paper focuses only on the principal ecological effects identified by the Water Component of the JOSM plan during the implementation phase (2012–2015), with outcomes from components focusing on wildlife health and atmospheric processes found elsewhere (Harner et al. 2018; Brook et al. 2019). The Water Component included seven integrated subcomponents: atmospheric deposition, water quality of the lower Athabasca River tributaries, water quality of the lower Athabasca River mainstem, groundwater quality and quantity, water quality and quantity modelling, benthic invertebrate condition, and fish health. With such a wide array of themes (seven subcomponents; Table 1), a common challenge across the subcomponents was assessing and integrating the large, complex, and diverse datasets to synthesize and interpret cause–effect relationships and thus better understand possible ecological and cumulative effects. A further complication is the complex interplay between natural environmental conditions and the potential impact of oil sands development and other human activities (e.g., nutrients and contaminants from municipal sewage effluent).
Table 1.
This paper assesses environmental effects, based on known sources and candidate proximal causes provided in the JOSM Water Component reports (Table 1), and then synthesizes these results to provide an overarching causal assessment of ecological effects of oil sands development on the tributaries and mainstem of the lower Athabasca River (Fig. 1). Our approach takes possible environmental effects and rates them based on the strength of available evidence. Such an approach allows for the integration and synthesis of large and diverse data obtained via complex and comprehensive data-intensive monitoring programs (Norton et al. 2015). Further, it allows for improved assessment of environmental and human health risk, support and feedback for modelling, management and policy development, and output to stakeholders. Ultimately, the aim of the JOSM plan was to determine the cumulative impacts of oil sands development on the lower Athabasca River ecosystem, including assessment of the relative importance of natural and anthropogenic contaminant sources on riverine ecosystem health. Here, we broadly define such contaminants as substances (i.e., chemical elements and compounds) or groups of substances that are toxic, persistent, or liable to bioaccumulate and other substances or groups of substances that give rise to an equivalent level of concern (Law et al. 2010). Our objectives are first to review information on the physical dynamics and ecological effects of contaminants and nutrients to these river ecosystems. Second, we outline and apply an ecological causal assessment method to synthesize evidence from JOSM research to produce a multidisciplinary, weight-of-evidence (WOE) assessment of ecological effects of oil sands development on these river ecosystems.
2. Physical dynamics and ecological effects of contaminants and nutrients
2.1. Transport and deposition of contaminants
The physical (water quantity) and chemical (water quality) conditions of aquatic ecosystems in the oil sands region are driven by both natural processes (e.g., atmospheric deposition, runoff, erosion, groundwater flow) and human activities (e.g., contaminant inputs deposited on land, snow cover, or water; alterations to natural landscapes and water flow). Under pre- and post-industrial conditions, natural bitumen in the McMurray Formation (the minable oil sands deposit, Fig. 1) is physically eroded and transported principally by river scour or flow. Under conditions of industrial mining and bitumen processing, the Province of Alberta has mandated a zero release of oil sand process water and sediments to natural river system. While there are circumstances where small releases have been approved by the regulator (RAMP 2015, 2016), they represent less than 1% of receiving river flows. Moreover, although leakage of process water from tailings ponds is known to impact groundwater (Fennell and Arciszewski 2019), there is limited potential for subsequent transport and discharge to nearby rivers (CEC 2020), and any groundwater seepage reaching the river is rapidly diluted (Ferguson et al. 2009; Gibson et al. 2013; Sun et al. 2017; Roy et al. 2016; CEC 2020). As such, the release of contaminants from industrial processes to aquatic ecosystems is currently principally confined to atmospheric release and transport of stack emissions, as well as fugitive dust from open and bare lease areas (e.g., open pits, surface material storage areas, roads, etc.) susceptible to wind entrainment of dust and associated contaminants (Kirk et al. 2014; 2018; Brook et al. 2019). A key component of this dust, pet coke, is of particular concern due to high levels of polycyclic aromatic compounds (PACs) and metals such as vanadium (V) (Zhang et al. 2016). Particulate emissions, in part, deposit on the landscape and to the snowpack and are then transported to adjacent water courses during snowmelt and precipitation events (Kelly et al. 2009, 2010; Kirk et al. 2014; Gopalapillai et al. 2019; Wasiuta et al. 2019; Chibwe et al. 2020). Given that river and lake surfaces represent a fraction of the total surface area in the oil sands region, direct atmospheric deposition to water and ice should be small relative to deposition to land surfaces and snowpack. The surface transport of contaminants via washoff and snowmelt will depend on soil state (e.g., whether frozen or not, and organic carbon content), vegetation cover, and topography. It should be recognized, however, that atmospherically deposited contaminants will accumulate in the soils over long periods of time (particularly when the ground is not frozen) and may represent a large non-point source should an extreme event cause mass erosion over a large surface area. Regardless, contaminants do accumulate in lake and river sediments; however, the lag time in delivery is uncertain (Evans et al. 2016; Emmerton et al. 2018).
Most atmospheric deposition occurs within 30 km of the source as there is a rapid drop-off in deposited compounds (e.g., PACs, mercury (Hg)) with distance from surface mining source (Kelly et al. 2009; Kirk et al. 2014; Harner et al. 2018). Catchment-scale snowpack Hg and methylmercury (MeHg) loads, normalized to watershed area, were found to be highest near oil sands operations, and river water Hg concentrations and loads followed seasonal discharge patterns and tended to be higher downstream of mining operations. Aerial loadings of Hg and MeHg to tributary catchments equaled or exceeded the mass of Hg and MeHg exported during freshet and, in some cases, the entire hydrologic year. In addition, during years of high discharge, these low-relief systems appear to become connected and flush MeHg (and Hg) from the watershed (Wasiuta et al. 2019). Runoff of aerially deposited particles from both land and snow cover is controlled by hillslope angle, extent and type of vegetation, degree of frozen ground, canopy capture, etc., with much of the particulate deposition trapped, stored, and unavailable for river transport until hydrological conditions allow for flushing of contaminants from storage (Droppo et al. 2018a, 2019; Wasiuta et al. 2019). The potential for dissolution, infiltration, and shallow groundwater transport of particulate-derived contaminants to nearby rivers is uncertain, but the presence of soil organic matter would be expected to attenuate the transport of such organic compounds dissolved from airborne deposition to a large extent, though this process likely varies among years.
2.2. Contaminant concentration and loading
Contaminant concentration and loading are highly dependent on river flow regime (e.g., annual peak freshet flows, season rainfall induced peak flows, periods of baseflow, etc.). Historical hydrometric data analyses revealed that mean annual and open-water (after ice breakup) streamflow arriving to the lower Athabasca region declined over the 1958–2009 period (Peters et al. 2013; Bawden et al. 2014). While generally declining, no significant change was discerned for annual peak flow values (Monk et al. 2012); however, a projected increase in precipitation and temperature, leading to an earlier snowmelt period (Eum et al. 2017; Shakibaeinia et al. 2017; Droppo et al. 2018b; Dibike et al. 2018a, 2018b, 2019), may result in an increase in cumulative effects on biota due to the resultant increased mean annual and seasonal peak flows during longer open-water periods. Changes in the seasonality of flows will further affect spatial and temporal erosion and deposition of suspended sediments and groundwater inputs and associated presence of contaminants and nutrients. Notably, a longer open-water period will likely mean a longer period when the major supply of water is from baseflow (groundwater input) and, thus, the possibility of larger contaminant exposure concentrations for invertebrates and other bottom-dwelling organisms (Culp et al. 2018b).
While the hydro-ecological systems differ between the tributaries and Athabasca River mainstem, they exhibit many of the same physicochemical processes determining contaminant concentrations and loads with respect to both natural versus anthropogenic inputs and sediment-bound versus dissolved contaminants. Within the tributaries, contaminant concentrations, including PACs and metals, are strongly influenced by direct water contact, sediment erosion, groundwater inputs, and chemical weathering of the natural bitumen (Birks et al. 2017). Droppo et al. (2018b), Chambers et al. (2018), and Reid et al. (2020) all showed a strong dependence of contaminant concentrations and loads on water discharge and river geomorphology (i.e., direct bitumen outcrop contact). Bitumen-containing sediment, along with contaminant concentrations, increased with distance downstream due to bitumen erosion and increasing exposure time to the natural bitumen outcrops (Droppo and Krishnappan 2016; Droppo et al. 2016). Moreover, the eroded, suspended bitumen sediments were very fine (<10 μm) and found to be buoyant and transportable for long distances by low shear flows (<0.05 Pa (pascal)) (Droppo et al. 2016, 2019). The hydrological regime of the systems also influenced contaminant dynamics, as seasonal and high flow events resulted in the greatest loads (Shakibaeinia et al. 2017; Dibike et al. 2018b).
2.3. Ecological effects on tributary biota
Sediment-bound and dissolved contaminant gradients resulting in temporal and spatial effects on tributary biota have been observed. Reid et al. (2020) characterized the natural, in situ microbial response to increasing hydrocarbon exposure along the river continuum in the downstream direction. Results from both suspended and bed sediments showed clear and significant shifts in microbial metabolic processes within each sediment compartment in response to the elevated PAC concentrations. Specific genes likely responsible for hydrocarbon breakdown (alkane monooxygenase, benzoyl-CoA reductase, etc.) exhibited elevated expression levels, while certain energy metabolism genes (associated with nitrogen, sulfur, and methane) revealed fundamental shifts in their pathway specificity, indicating an adaptive stress response in their basic energy metabolism.
The temporal and spatial effects of terrestrial and aquatic bitumen erosion and transport, along with possible influences of atmospheric deposition (Harner et al. 2018; Kirk et al. 2018) and groundwater discharge (Bickerton et al. 2018), were found to be associated with effects on fish and invertebrate populations. In the lower Steepbank watershed, McMaster et al. (2018) found an increase in PAC tissue levels in a key sentinel species, slimy sculpin (Cottus cognatus). Sculpin collected in 2012 from the lower Steepbank River had nine times higher PACs in their tissues compared with sculpin from upstream sites (Evans et al. 2019). At lower Steepbank River sites, there was also an increase in liver ethoxyresorufin-O-deethylase activity (EROD), an indicator of PAC uptake in fish (McMaster et al. 2018). Moreover, Culp et al. (2018b) found that benthic invertebrate composition was similar at reference sites outside (i.e., upstream in the Clearwater Formation) and inside the upper tributary stream reaches flowing through the McMurray Formation (see Fig. 1). In contrast, lower stream reaches well within the exposed bitumen deposit showed increased sculpin liver EROD activity and increased PAC tissue levels (McMaster et al. 2018; Evans et al. 2019; Tetreault et al. 2020), while benthos composition changed to more pollution-tolerant taxa (Culp et al. 2018b). These results are reflective of the contaminant gradients discussed above and that increase with distance downstream. While undiluted snowmelt water is toxic to larval fish, the overwhelming dilution effect of river-water volume resulted in no measurable toxicity (Parrott et al. 2018).
Biota (particularly sentinel fish, invertebrates, and mussels) can have long residency in the rivers (months to years) with possible concomitant detrimental chronic exposure to contaminants and subsequent ecological effects. This was found for caged mussels, which showed decreased condition in downstream tributary reaches, and for fathead minnow embryos and larvae, which showed decreased survival when exposed to downstream sediments during sediment toxicity tests (McMaster et al. 2018; Vignet et al. 2019). Toxicity tests (embryo–larval survival assay) also showed reduced fathead minnow survival at sites near tailings ponds adjacent to the Athabasca River; however, groundwater collected from sites high in natural bitumen deposits (on the Ells River) showed even greater toxic potency in embryo–larval laboratory bioassay exposures of minnows (McMaster et al. 2018).
2.4. Ecological effects on lower Athabasca River biota
The lower Athabasca River mainstem showed trends similar to those of the tributaries; however, with much higher discharge generated in upstream areas, the mainstem has the propensity to transport large loads of dissolved and particulate-associated contaminants downstream to the Peace–Athabasca Delta and beyond (Conly et al. 2002). Further, it has a higher turbulence structure, which results in a shifting sand bed and mobilization of bed-associated contaminants. The energy of the lower Athabasca mainstem and its capacity to move sediments and associated contaminants is most significant during river ice breakup in the spring (Beltaos 2018, 2019; Beltaos et al. 2018; Droppo et al. 2018b). Bed shear stresses during the passage of highly dynamic waves generated by ice-jam releases were up to 140 Pa, and sediment concentrations were in the order of 10s of grams per litre. It is likely that bed sediment habitats are highly disturbed during this period. Very little information, however, is available on the ecological condition for this period of breakup due to the extremely dangerous nature of the ice flows.
During lower flows on the lower Athabasca, numerical modelling indicated deposition to occur in areas relevant to benthic and fish health (Kashyap et al. 2017; Shakibaeinia et al. 2017; Dibike et al. 2018b; Droppo et al. 2018b). As was observed for the tributaries throughout the oil sands minable area, there was an increase in the proportion of pollution-tolerant invertebrates and a reduction in caged-mussel condition, suggesting an increase in the impact of bitumen exposure (sediment). In contrast, benthic communities in downstream reaches near Wood Buffalo National Park were more similar to reference areas above industrial activity (Culp et al. 2020). Fish (e.g., white sucker) showed increased PAC levels in liver and muscle tissue, as well as increased liver EROD activity, in areas of exposed bitumen deposit and oil sands activity (McMaster et al. 2018). Fish toxicity tests conducted with exposure to groundwater seepage sampled at a location on the Athabasca River proximate to a nearby tailings pond showed reduced fathead minnow survival (McMaster et al. 2018); however, the spatial extent of the impacted benthic zone area is likely minimal due to groundwater dilution (Roy et al. 2016). In situ caged-mussel experiments identified a risk to aquatic life from exposure to contaminants to an unknown proportion of natural versus anthropogenic contaminants (Pilote et al. 2018).
2.5. Confounding effects on aquatic biota
The effects of contaminant exposure on aquatic biota in the lower Athabasca mainstem and tributaries may be masked as a result of confounding inputs from natural bitumen, oil sands activity, and nutrient sources (Culp et al. 2018a, 2020). For example, in situ caged-mussel experiments identified a risk to aquatic life from exposure to contaminants as well as wastewater released from a municipal treatment plant (Pilote et al. 2018). Moreover, tributary research showed that there was no downstream increase in total or particulate phosphorus or organic carbon attributable to natural bitumen erosion. This suggests that the McMurray Formation may be nutrient deficient and that the tributaries likely only receive nutrients from overburden soil and possibly atmospheric deposition (Chambers et al. 2018; Kirk et al. 2018). Although atmospheric deposition to the landscape from oil sands activity includes total phosphorous and particulate organic nitrogen, a change in nutrient concentrations in surface water due to atmospheric deposition was not observed within the footprint of industrial atmospheric deposition (Glozier et al. 2018). This finding is supported by results from Summers et al. (2016), who did not find a pattern of industrial fertilization from atmospheric deposition to lakes in the region affected by emissions from oil sands activity. In sharp contrast to the little or no influence of nutrient input from natural bitumen and atmospheric deposition sources, municipal waste water effluent (MWWE) greatly increased nutrient concentrations below Fort McMurray (Glozier et al. 2018; Culp et al. 2020). This nutrient addition resulted in local enrichment (illustrated by increased fish size and growth rate) (McMaster et al. 2018), greater benthic invertebrate abundance, and compositional change to an increase in pollution-tolerant invertebrate assembly (Culp et al. 2020).
3. Causal assessment of ecological effects
Identifying the ecological impacts associated with a particular cause within a geographic region with multiple stressors requires establishing potential multiple causality links among effects and possible stressors. To aid this process for the JOSM Water Component Program, the Ecological Causality Assessment Method (ECAM) (Cormier et al. 2010; Norton et al. 2015; USEPA 2017) was applied. This framework helps link ecological effects to candidate causes by considering the scientific evidence that best supports the importance of these cause–effect pathways. Cormier et al. (2010) define “ecological effects” as a shift in ecological entities of interest, while “proximate causes” are causal agents that interact directly with ecological entities to cause change. For example, causal agents such as contaminants affect local species, including fish, to cause change, as evidenced by increased tissue concentration of PACs and higher EROD activity with potential consequences for their long-term health. Complicated environmental issues such as oil sands mining require careful inference developed through a weight-of-evidence (WOE) approach that considers all pertinent information to determine which of the candidate causes of ecological effect are most strongly supported. Evidence is assessed based on its relevance, quality, and strength and can include a disparate mixture of information including site-specific observations, regional observations, modelling, laboratory tests, etc. (Norton et al. 2015). The WOE approach incorporates categories of ecological effect, thereby avoiding the disadvantages of numeric systems that attempt to combine weights from very different types of evidence. By establishing such causal linkages, the assessment method also helps to identify critical knowledge gaps that can inform future research priorities and management approaches. The causal assessment models developed for the lower Athabasca ecosystems include effect pathway diagrams (Figs. 2 and 3) supported by evidence on the importance of each causal pathway (Table 2). This material illustrates how ecological effect links to the source stressors through candidate proximate causes, with the strength of the relationship weighted according to the rating system described below.
Fig. 2.
Fig. 3.
Table 2.
An important aspect of the WOE approach is to establish a formal method of assigning importance to causal pathways. Following Norton et al. (2015), evidence is weighed by recording a “0”, “+”, or “++” to indicate the degree to which each pathway is supported as the cause of an observed ecological effect (Figs. 2 and 3). Three primary evidence types were considered when establishing the strength of the linkages between candidate causes and ecological effects in the LAR region. These included (i) spatial or temporal co-occurrence of cause and effect, (ii) laboratory or modelling evidence of a potential effect, and (iii) a defined causal pathway (i.e., a connection made between the cause, an environmental condition, and the effect). Because our assessment was regional in nature and not triggered by a specific event, we did not include preceding causation and time order as evidence types as has been done in other studies (sensu Norton et al. 2015), although we recognize that such time lags may be critical questions for future studies (e.g., atmospheric deposition as noted in our summary and conclusions). Following Painter et al. (2020), evidence was considered of sufficient quality if information had been peer-reviewed or from other high-quality sources (e.g., government agency) that provide detailed protocols and quality assurance – quality control measures. The assignment of “+” (somewhat supports) is based on demonstrated quantitative relationships (e.g., p ≤ 0.05) derived from field, laboratory, or modelling observations; “++” (strongly supports) indicates quantitative relationships from field, laboratory, or modelling observations and strong spatial co-occurrence of stressor and effect; “0” indicates a pathway that has no observed effect (or shows ambiguous results). Pathways for which no supportive evidence exists (e.g., regional near-surface groundwater – surface water interaction) were not included in Figs. 2 and 3. This WOE approach can help to guide future assessment as “+” and “++” level pathways would be the most likely linkages in which more detailed investigation of cause through monitoring and research would yield information that could aid management and potential remedial action.
Besides establishing important ecological effects, the JOSM Water Component Program also produced a considerable amount of new information on temporal and spatial trends in physical and chemical variables, which cannot be directly related to ecological effects at present. For example, flow regime affects sediment deposition and streambed habitat (Droppo et al. 2018b), but the ecological effects of such changes are unknown for the lower Athabasca River. Thus, physical–chemical changes in the ecosystems that could be related to anthropogenic or natural sources (e.g., surface runoff rates) but not to ecological effects are not included in Table 2; however, their potential influence is noted in Figs. 2 and 3. It should also be noted that for many of the contaminants currently being monitored, no guidelines have yet been developed, and therefore it is difficult to address specific risks associated with these compounds. Understanding of the interrelationships among the physical, chemical, and biological variables will improve as future monitoring programs and targeted monitoring and research acquire the additional information required for causal ecological assessments.
4. Using multidisciplinary WOE within ECAM for attribution of ecological effects
As with any large multi-year study or monitoring program, providing an integrated analysis of all sources of contaminants from all seven subcomponents of JOSM Water Component Program, for both tributary and Athabasca mainstem reaches, was a daunting and complex task. By using the ECAM, the structure was able to realize the similarities and differences in source, proximal cause, and ecological effect both within and between the lower Athabasca River mainstem and its tributaries. Table 2 synthesizes the tributary and mainstem cause–effect pathways and the strength of their relationships. The findings in this table, along with additional relevant physical, chemical, and ecological knowledge from key literature, allowed for development of conceptual models for the tributaries and the lower Athabasca mainstem (Figs. 2 and 3, respectively) that illustrate the complex mix of sources and candidate proximal causes leading to possible ecological effects. The aim of this section is, therefore, to highlight the key pathways of effect and their level of importance to the ecological health of rivers in the Athabasca Oil Sands Region.
4.1. Sediments (natural vs. anthropogenic)
Sediments transported by rivers (bed load or suspended particles derived from surface washoff and erosion, scour of riverbeds and banks, groundwater, and direct atmospheric deposition; Droppo et al. 2019) play a primary role in the dynamics (transport and delivery) of nutrients and contaminants and, in essence, have a direct influence on all levels of riverine ecosystem health. Contribution of sediments to the rivers by industrial operations is marginal (infrequent, regulator approved, low-volume releases of principally surface waters (e.g., sedimentation ponds; RAMP 2015, 2016) and during land clearing from pre-mine operations (Alexander and Chambers 2016)) as current provincial government regulations stipulate that no natural waters, oil sands process water (OSPW), or sediment may be released off the development areas once operational. Hence, the principal source of particulates to the rivers from industry operations is via atmospheric deposition (Zhang et al. 2016; Harner et al. 2018; Kirk et al. 2018; Droppo et al. 2018a; Chibwe et al. 2020), which, given the small ratio of aquatic to terrestrial surfaces, is expected to be low given subsequent entrapment of the particles into the soil and vegetation. Snowmelt runoff over frozen ground may provide more particulates to the rivers; however, given topographic irregularities in the stream valley, these relative contributions are logistically challenging to quantify, both spatially and temporally, and to date have not been estimated. Further, while atmospheric particulates retained in the snowpack over the ice were shown to be toxic to fathead minnow larvae (i.e., common native fish that is sensitive to such contaminants; Marentette et al. 2015), the effect was not detectable during freshet, likely due to significant dilution of the snowmelt runoff (McMaster et al. 2018; Parrott et al. 2018). Given the small ratio of water-surface area to terrestrial-surface area and our present inability to quantify atmospheric deposition of particulates on river health, the ECAM rating of “no effect, ambiguous, or insufficient evidence (0)” was applied to this sediment source pathway’s effect on ecosystem health.
Sediment mobilized from the erosion and transport of natural bitumen outcrops, however, has been shown to have a clear cause–effect pathway (Table 2; Figs. 2 and 3) in both tributaries and the mainstem and thus has an ECAM rating of “some effect (+)”. This cause–effect rating is justified by the fact that the majority of contaminants are preferentially attached to sediments (principally fine-grained sediment) and, upon deposition, represent the principal exposure mechanism for macroinvertebrates and other bottom-dwelling animals. Fine sediment, particularly when containing bitumen, demonstrates buoyant and hydrophobic properties resulting in very long transport distances possibly to environmentally sensitive receiving areas such as the Peace–Athabasca Delta. (Note that this does not minimize the importance of bioavailable contaminants and nutrients on ecosystem condition.) Further, sediment and associated contaminant loads are influenced by the hydrology of the system and, thus, provide the highest loads during the spring freshet and large summer rainfall events (Shakibaeinia et al. 2017; Chambers et al. 2018; Droppo et al. 2018b). Beltaos (2019) has shown that shear stresses of up to 140 Pa can occur during the passage of highly dynamic waves caused by ice-jam releases, generating massive quantities of eroded sediment. Further, scour from large ice blocks “tumbling” down rivers during spring ice breakup can result in sediment loads in the 10s of grams per litre (Scrimgeour et al. 1994). Very little ecological information is available on river ice breakup due to the difficulty in obtaining in situ data during this highly dynamic and dangerous period that can be an important ecosystem reset event (Prowse and Culp 2003). Regardless, changes in sediment dynamics (erosion, transport, and fate) influence habitat structure and function as it relates to physical, chemical or nutrient, and biological characteristics that could be advantageous or detrimental in the absence of any chronic or acute toxicological effects. For example, within the tributaries, there is an increasing gradient of fine sediment deposition and PACs as the flow moves downstream through the McMurray Formation, which correlates with a shift in macroinvertebrates, fish health, and microbial consortia (McMaster et al. 2018; Culp et al. 2020; Reid et al. 2020) (see sections 4.2 and 4.3).
4.2. Contaminants (natural vs. anthropogenic)
To some degree, contaminant transport to the aquatic environment is occurring because of the development and operations of the oil sands. Within tributaries, many chemical parameters showed a pattern of increasing concentrations and loads from upstream to downstream of the development (Chambers et al. 2018; Droppo et al. 2018b; Glozier et al. 2018). Historical data (1972–2010) analyzed by Alexander and Chambers (2016) showed, prior to development, no discernible change in concentrations and loads of total vanadium (V), dissolved selenium (Se), and dissolved arsenic (As) when sampled above versus below the McMurray Formation; however, during and following development, concentrations and loads were often greater downstream of the development compared with measurements from upstream (reference) sites. This historical analysis suggests the possible influence of oil sands development on these parameter concentrations and loads, with concentrations being highest during the land-clearing phase of development due to overburden disturbance.
With the extensive spatial footprint of the oil sands industry, contaminant exposure from this source is expected to result in ecological effects (Gerner et al. 2017). This expected effect is shown by McMaster et al. (2018) and Culp et al. (2018b, 2020) in which, for both the mainstem and tributaries downstream of mining activity and in the zone of higher atmospheric deposition, fish, mussels, and macroinvertebrates all showed effects that can be associated with contaminant stressors. In the downstream areas, fish samples showed increased PAC levels, as well as elevated liver EROD activity, while laboratory toxicity tests indicate reduced fathead minnow survival within sediment and groundwater seepage tests. The benthos composition also shifted to more pollutant-tolerant taxa, meaning that stressor exposure was associated with the loss of some invertebrates with apparent replacement by those that can withstand the contaminant concentrations (Culp et al. 2018b, 2020).
Extensive multi-year assessment of impacts on riverine fish and benthos indicate that these ecological effects are confounded because of contamination from natural bitumen versus contaminants derived from human activity (i.e., oil sands development, municipal sewage effluent). For example, ecological changes in fish (McMaster et al. 2018) and benthos (Culp et al. 2018b) from tributaries and the mainstem are likely related to some degree of regionally higher amounts of industry-derived atmospheric deposition (Kirk et al. 2018); however, these habitats (water column and benthic) are also areas of exposure to contaminants derived from naturally occurring bitumen erosion and groundwater discharge. Furthermore, laboratory toxicity tests with groundwater samples affected by oil sands process water and by natural bitumen sands showed reductions in fathead minnow embryo–larval survival for both sets, with the greatest toxicity for a natural sample from along the Ells River in comparison with a reference groundwater (no bitumen influence) (McMaster et al. 2018).
While the WOE assessment suggests that there is indeed some causal effect of contaminants from each of the three sources, particularly organic sources as indicated by EROD responses to PAC-related compounds (Table 2; Figs. 2 and 3), the degree to which these stressors influence ecological health is not fully realized given the confounding effect of natural sources of contaminants. Although recent advances have been made in distinguishing oil sands process water (OSPW) from natural bitumen-influenced groundwaters (Ross et al. 2012; Frank et al. 2014; Hewitt et al. 2020), there is currently an inability to easily and routinely differentiate between industrial and natural contaminant sources to assist complex integrated monitoring programs such as JOSM. Clearly, the identification of effects caused by contaminants derived from natural bitumen deposits (i.e., the McMurray Formation) or industrial activity will remain limited until these natural and industry-derived contaminants can be discriminated and their independent and combined effects examined. Thus, for contaminants associated with natural bitumen and oil sands activity, the ECAM cause–effect pathway rating of “somewhat supports (+)” ecological effects is applied (Figs. 2 and 3).
4.3. Nutrients (natural vs. anthropogenic)
The industrial influence on both tributaries and the Athabasca mainstem was very similar as the primary industrial source and transport mechanisms are atmospheric transport and deposition, with wind direction and particle density being the principal determining factors for deposition (Kirk et al. 2018) (Table 2). Nutrients delivered to the tributaries and Athabasca mainstem are naturally derived from soil erosion and surface washoff and aquatic and terrestrial organic decay (Alexander and Chambers 2016). The observation that the natural bitumen is likely nutrient deficient may explain the lack of spatial gradients in tributary nutrient concentrations (Chambers et al. 2018).
Within the mainstem, however, nutrients from the MWWE represent a main ecological cause–effect pathway (dominating over any other upstream source of nutrients). As nutrients are a limiting factor in the Athabasca River (Chambers et al. 2000), the MWWE supports increased productivity of fish and benthos (McMaster et al. 2018; Culp et al. 2020). This was expressed as shifts in lower Athabasca mainstem benthic invertebrate composition. The shift due to MWWE occurred above the Steepbank River, just downstream of the Clearwater River. The assemblage then changed again in the oil sands development area below the Steepbank River, followed by a return to background composition further downstream in the vicinity of the Peace–Athabasca Delta (Culp et al. 2020). Although there is some evidence of nutrient enrichment as indicated by increased total dissolved phosphorus in the Peace–Athabasca Delta, patterns of diatom communities are more strongly associated with pH gradients rather than oils sands development or contaminants (Connor et al. 2018; Libera et al. 2020).
On the Athabasca mainstem, high nutrient inputs were associated with increased size, age, condition, and fat stores of fish collected proximal to the MWWE outlet (Fig. 3). Nutrient subsidies to freshwaters may offset the stress caused by low-level exposure to contaminants (Alexander et al. 2013), thus possibly attenuating potential chronic toxicity for sentinel species. The consistent and observable strong impact of MWWE nutrients on the near-field ecology dictates an ECAM cause–effect pathway rating of “strongly supports (++)” ecological effects (Fig. 3). In contrast, nutrients derived from industrial operations or natural bitumen sources have been assigned an ECAM cause–effect pathway rating of “no effect (0)” (Table 2; Fig. 2) because, as discussed above: (i) industry introduces a limited amount of nutrients via atmospheric deposition to waterways and (ii) nutrient concentrations did not change within the industrial footprint likely because, with the exception of occasional regulator-approved low-volume releases (e.g., sedimentation ponds; RAMP 2015, 2016), industry does not discharge water or sediments from their leases during operations phases.
5. Summary and conclusions
The assessment of cumulative effects of anthropogenic activities and exposure to natural bitumen geology on riverine ecosystems in the lower Athabasca watershed is particularly difficult because of the overlapping exposure and potentially synergistic or antagonistic environmental impacts associated with these multiple stressor sources. To examine this problem, the JOSM subcomponent reports (Culp et al. 2018a; Table 1) were synthesized to allow a causal assessment of ecological effects that linked effects in tributary and mainstem ecosystems of the lower Athabasca River to candidate causes. Although the JOSM research identified ecological effects that appear to be associated with contaminant exposure, the source of this exposure is confounded by the presence of and inability to easily and routinely differentiate between oil sands operation activity (principally atmospheric emissions and deposition) and contaminant inputs from natural bitumen sands (e.g., erosion, groundwater discharge). Thus, a precursor to improving understanding of the linkages between contaminant exposure and ecological effects will be further development of the ability to routinely differentiate between natural and industry-derived contaminants (e.g., PACs), as well as improved knowledge of their independent and combined ecological impacts (Culp 2018a; Droppo 2018b). Moreover, given the finding of atmospheric deposition as the predominant pathway for contaminant delivery from oil sands activity, it is critical that we quantify atmospheric loadings to the land surfaces and subsequently the load that enters the aquatic environment (Droppo et al. 2018a, 2018b; Kirk et al. 2018). An ability to differentiate between natural and industry-derived contaminants, and their delivery pathways, would allow determination of regional fluxes of contaminants from tributaries to the Athabasca River in relation to mine development (Droppo et al. 2018b). Additionally, it will be important to investigate the relative toxicity of components of surface water, groundwater, and sediments to invertebrates and fish to determine if particular sources of environmental exposure are found to be more directly related to observed ecological effects (Culp et al. 2018a). This toxicity work would be aided by the development of species sensitivity distributions for sentinel microbes (Reid et al. 2020), invertebrates (Culp et al. 2020), and fish (McMaster et al. 2018) when they are exposed to priority oil sands substances identified in Environment Canada and Alberta Environment (2011, appendix B). The development of environmental effects thresholds (i.e., critical effects sizes for fish and invertebrates) and microbial metatranscriptomics to determine possible triggers for oil sands impact will also be important for improved cumulative effects assessment (Kilgour et al. 2019).
Nutrient enrichment from the MWWE was the dominant ecological effect observed for the lower Athabasca mainstem as indicated by increased fish biomass and invertebrate abundance. Such food-web effects, in which nutrient enrichment alleviates conditions of nutrient limitation, have been recorded in the upper Athabasca River (Chambers et al. 2000) and are often observed in rivers (Dodds 2006; Wang et al. 2007). However, contaminant exposure from sewage effluent, industrial operations, tailings pond seepage, and natural exposure to bitumen could also contribute to these ecological trends, and focused investigation-of-cause studies in the field and laboratory are required to better assess the cumulative ecological effects of nutrients and contaminant exposure in rivers. We hypothesize that the primary reason that nutrient enrichment from municipal sewage input is strongly associated with ecological effects is because this pollution source is constantly and directly discharged to the river. In contrast, pollutants from oil sands activity and natural bitumen reach the river largely through atmospheric deposition, overland flow, groundwater transport, and fluvial erosion and transport (Droppo et al. 2018b; Kirk et al. 2018). If governments approve the release of treated oil sands process water to the lower Athabasca ecosystem (Howland et al. 2019a; CEC 2020), a substantial shift in the impact of industrial input sources could occur. Oil sands process-affected waters have elevated concentrations of sodium sulphate, various metals, and naphthenic acids (i.e., oil sands tailings water, acid extractable organics, sensu Grewer et al. (2010)) (Peters et al. 2007; Allen 2008), and research indicates that exposure to such waters has the potential to cause toxicological effects in fish and invertebrates (Peters et al. 2007; Leclair et al. 2013; Howland et al. 2019b). In addition, it would be useful to model the influence of time lags between the deposition of atmospheric materials and the arrival of deposited materials in the tributaries and mainstem. Such transport-fate analysis is highly complicated by physical, chemical, and biological processes; however, an understanding of the possible latency of terrestrial contaminants delivery to the aquatic environment will be important for future monitoring and management of ecological effect. Also, as oil sands mining operations continue to expand northwards towards Wood Buffalo National Park and the Peace–Athabasca Delta, it remains critical to understand the role of sediment transport of all eroded material into this vulnerable ecosystem in terms of the long-term consequences for this wetland of international significance.
In summary, the JOSM plan produced a large, complex dataset, spread across seven subcomponent research themes that present considerable challenges for producing a broad synthesis of results. The ecological causal assessment method applied was a useful tool to help develop a clearer understanding of how stressor sources relate to ecological effects through candidate proximate causes. Such weight-of-evidence approaches can also be linked to risk assessment frameworks for future monitoring through the probability assessment of environmental occurrence and impact. This information on the cumulative environmental effects of anthropogenic and natural stressors to the lower Athabasca River and its tributaries will be important for determining and improving best management strategies for monitoring and assessment of aquatic health in these ecosystems. There are, however, factors that confound our ability to differentiate the ecological effects of natural and anthropogenic contaminant sources, and the causal assessment approach helped to identify these gaps and future areas for focused research. As JOSM was designed to be an adaptive monitoring program with built-in flexibility, our causal synthesis should identify options for changes in monitoring that are grounded upon evidence and for program improvements to better anticipate and detect degradation in the ecosystem health of the lower Athabasca River and its tributaries.
Acknowledgements
Technical support was provided to JOSM Water Component Program projects by the dedicated staff of Environment and Climate Change Canada (ECCC), Alberta Environment and Parks (AEP), and numerous graduate and undergraduate students. Constructive criticism by anonymous reviewers and M. Thompson provided on an earlier draft improved the final manuscript. Research funding was provided by and contributes to the Joint Oil Sands Monitoring Program co-led by the Governments of Canada and Alberta but does not necessarily reflect the position of the Program.
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Published In
Environmental Reviews
Volume 29 • Number 2 • June 2021
Pages: 315 - 327
History
Received: 22 July 2020
Accepted: 18 December 2020
Accepted manuscript online: 4 January 2021
Version of record online: 4 January 2021
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© 2021.
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Joseph M. Culp, Ian G. Droppo, Peter D. di Cenzo, Alexa C. Alexander, Donald J. Baird, Spyros Beltaos, Greg Bickerton, Barrie Bonsal, Robert B. Brua, Patricia A. Chambers, Yonas Dibike, Nancy E. Glozier, Jane L. Kirk, Lucie Levesque, Mark McMaster, Derek C.G. Muir, Joanne L. Parrott, Daniel L. Peters, Kerry Pippy, and James W. Roy. 2021. Ecological effects and causal synthesis of oil sands activity impacts on river ecosystems: water synthesis review. Environmental Reviews.
29(2): 315-327. https://doi.org/10.1139/er-2020-0082
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