Alexa C. Alexander

Global pesticide use has resulted in widespread environmental degradation, persistent contamination of surface and ground waters, bioaccumulation of these contaminants in food webs, and unintended impacts on non-target species (e.g., fish kills). Mixtures of multiple pesticides are commonly found in the environment, yet these chemicals are rarely studied in combination. Insecticides are of particular concern as these chemicals are designed to target terrestrial insect pests but also impact aquatic macroinvertebrates. In the following study, we explore the regional context of surface water concentrations of four insecticides in 10 study watersheds over a 20-year period (2002 to 2022) in Prince Edward Island, a region of Canada with continuous agricultural activity since the 1720s. These agroecosystems have been subject to generations of restoration, conservation, and more recently, implementation of various beneficial or best management practices (BMPs). The changing climate significantly adds to the complexity of monitoring these systems as the regional rate of change is exceptionally high (e.g., a 0.70°C to 1.14°C increase in air temperature and 5–8% decrease in precipitation in the last 3 decades). The results of this study highlight that efforts in this area would benefit from a more collaborative, transdisciplinary approach that integrates local, regional, national, and global perspectives while respecting the needs of growers, consumers, and the immense natural capital in the aquatic ecosystems draining these landscapes - such as Atlantic salmon, that can draw both anglers and ecotourists alike. A pivot toward a One-Health Framework is a logical next step for the province as, at present, efforts to integrate observational and monitoring efforts are already conducted by multiple federal, provincial, Indigenous rightsholders, as well as non-government stakeholders. Finally, in recognition that financial resources for these efforts are finite, we would recommend the implementation of a standardized, seasonal water quality sampling scheme that includes flow-weighted sampling and automated samplers to better capture and predict rapidly changing conditions in the region in response to climate change.

Mesocosms are outdoor experimental systems designed to separate and test environmental responses, in this case, cumulative effects to field-collected periphyton and macroinvertebrate communities from multiple stressors. This experimental system produces valuable, highly reproducible data, and along with field monitoring, laboratory bioassays and modeling results, provides a strong weight-of-evidence approach for aquatic risk assessment. Through the control of confounding environmental variables, this type of experiment permits the separation of interactions between multiple stressors in complex effluents or due to shifting ambient conditions. The system described is modular and was originally developed to facilitate transport of the entire system to remote or industrial test sites (e.g., for in situ 21-d chronic level testing). However, this setup is also appropriate for long term installations with suitable provision for routine maintenance and losses associated with regular wear-and-tear on equipment. The following protocol details a basic stream mesocosm system setup (e.g., 4 replicate streams per treatment-level) which is the foundation for the more than a dozen stream mesocosm experiments conducted by the authors since the 1990s.

Bitumen mining and upgrading in northeastern Alberta, Canada, releases toxic pollutants into the atmosphere, including mercury (Hg) and methylmercury (MeHg). This Hg and MeHg is then deposited to the surrounding landscape; however, the fate of these contaminants remains unknown. Here, we compare snowpack chemistry to high-frequency measurements of river water quality across six watersheds (five impacted by oil sands development and one unimpacted). Catchment scale snowpack Hg and MeHg loads normalized to watershed area were highest near oil sands operations. River water Hg concentrations and loads tracked discharge and tended to be higher downstream of mining operations, while MeHg concentrations and loads increased through the summer, reflecting peak summer MeHg production rates. Except in the reference watershed, snowpack Hg and MeHg loads equaled or exceeded the amount of Hg and MeHg exported during freshet and, in some cases, the entire hydrologic year. This suggests landscapes across the oil sands region, which are dominated by low-relief wetlands and other shallow-water systems, are accumulating Hg and MeHg. Importantly, during years of high discharge, these low-relief systems appear to become better connected and flush MeHg (and Hg) from the watershed. Thus, these watersheds may act as temporary, rather than as permanent, natural repositories of oil sands contaminants.

Tailings ponds in northeastern Alberta, Canada contain massive amounts of oil sands process water (OSPW) that cannot currently be released due to the toxicity of some components. Limited space and the need for reclamation of oil sands operation sites will necessitate the release of OSPW in the near future. Knowledge of the composition and toxicity of OSPW is lacking yet is crucial for both risk assessment and management planning. This study examines chronic toxicity of a mixture of OSPW components sodium naphthenate and naphthenic acid (NA) to nymphs of the mayfly Hexagenia spp. in control and polycyclic aromatic hydrocarbons (PAH)-spiked sediment treatments. The objective of this study was to determine whether the addition of the PAH-spiked sediment significantly contributed to or masked responses of these sensitive mayflies to mixtures of NA. Mean survival in nymphs exposed to NA and PAH-spiked sediment treatments was reduced by 48% compared to those exposed to the NA mixture alone. Lethal responses were observed in all of the PAH-spiked sediment treatments. However, within PAH-spiked and control sediment treatments, there was no significant difference in nymph survival due to NA concentration, indicating that changes in survivorship were predominantly a reflection of increased mortality associated with sediment PAHs and not to the NA mixture treatment. Sublethal effects on body segment ratios suggest that mayflies exposed to NA and PAH-spiked sediment, as well as those exposed to the highest NA concentration tested (1 mg/L) and control sediment, made developmental trade-offs in order to emerge faster and escape a stressful environment. These results reveal that the release of OSPW to the surrounding environment could cause a reduction in mayfly populations. Mayflies provide ecosystem services and are an important food source for higher trophic levels in both the aquatic and terrestrial communities.

Extraction of Canada’s oil sands has created 1 billion m³ of tailings, which are stored in on-site tailings ponds. Due to limited storage capacity, the planned release of tailings into the surrounding environment may be required. This represents an environmental management challenge, as the tailings contain contaminants that are known toxins to aquatic communities. Of particular concern are naphthenic acids and their metallic counterparts, as they are the principal toxic components of tailings, are relatively soluble, and are persistent in aquatic environments. This study examines the acute toxicity of environmentally relevant 10:1 mixtures of two process water components: naphthenic acid and sodium naphthenate. We assess the effects of these simplified oil sands process water (OSPW) mixtures under planned and unplanned tailings release scenarios, using traditional and cutting-edge bioindicators for aquatic invertebrate taxa. We found that safe concentrations for mayflies and other aquatic macroinvertebrates were less than 1 mg/l, as no mayfly taxa survived repeated exposure to this dose in either the 48-h or 72-h acute toxicity test. In the 72-h test, no mayflies survived treatment levels greater than 0.5 mg sodium naphthenate/l. In the mesocosm study, even a 90% dilution of the OSPW mixture was not sufficient to protect sensitive macroinvertebrate communities. The results of this study highlight the potential environmental damage that will occur if OSPW is not carefully managed. This information will aid with the development of a management plan for oil sands tailings ponds, which will provide insight into the potential for process water release into the surrounding environment while conserving unique ecosystems downstream of development in the oil sands region.

Habitat degradation associated with resource development is a major ecological concern, particularly in Canada’s boreal zone where limited information on biodiversity is available. Habitat degradation can lead to reductions in biodiversity and ecosystem function, especially when drivers of variability and diversity patterns have not been identified for a region of interest. In this study, the distribution of diatom genera in the Peace–Athabasca Delta in northeastern Alberta was examined in relation to seasonal, geographic, and alkalinity gradients. Grab samples of six abiotic variables (total dissolved nitrogen, total dissolved phosphorus, dissolved iron, turbidity, pH, and specific conductance (SPC)) were taken from 12 remote wetlands over three sampling periods, and regressed against an ordination of diatom community composition to identify key environmental drivers of diatom community variation. Indirect gradient analysis identified two major gradients among sites. First, separation of sites among sampling periods showed successional seasonal changes in diatom community composition. Second, separation of sites from the Peace sub-delta and Birch sub-delta showed a gradient of geographic separation. Direct gradient analysis failed to explain the underlying drivers of these two gradients, but did show that alkalinity is a key driver of diatom community composition in the Embarras sub-delta, and that these sites could be particularly vulnerable to community changes associated with acidification.

In the scientific literature, there is a considerable consensus that working toward evaluating multiple stressors is worthwhile. Unfortunately, our means to evaluate the combined effects of multiple stressors on species is limited. In agricultural systems, the relative threat posed to aquatic insect communities due to individual stressors (e.g., individual insecticides) is relatively well understood. However, understanding mixtures of pesticides, let alone the addition of complex and potentially interacting, natural gradients (e.g., nutrients and predation), is far harder. The objective of the following review was to evaluate the individual and combined effects of a range of multiple agricultural stressors on aquatic insect communities using a series of seven outdoor mesocosm experiments conducted since 2003. The mesocosm studies show that macroinvertebrate community responses can be similar, subtle, or even opposing depending on the stressors investigated and the mechanistic or ecological focus of the study. The current focus on individual chemicals and responses to treatment is misleading. Cumulative effects and multiple sublethal stressors are the norm in impacted ecosystems. A simple, holistic approach to environmental risk assessment is needed.