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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 (it) 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. Key words: oil sands, biomonitoring, cumulative effects, sediments, contaminants, nutrient enrichment. L'exploitation des sables bitumineux dans le cours inferieur du bassin versant de la riviere Athabasca a suscite une grande inquietude chez le public et les scientifiques quant aux effets percus sur la sante environnementale. Afin d'aborder cette question pour les affluents et le cours principal de la riviere Athabasca dans la region des sables bitumineux de l'Athabasca, la composante eau du programme de surveillance conjointe des sables bitumineux (SCSB) a produit des evaluations des surveillances pour sept themes integres : le depot atmospherique, la qualite de l'eau des affluents, la qualite de l'eau du cours principal de la riviere, la qualite et la quantite des eaux souterraines, la modelisation de la qualite et de la quantite de l'eau, la condition des invertebres benthiques et la sante des poissons. La synthese realisee par les auteurs integre et resume les vastes et divers ensembles de donnees rassembles dans les sept evaluations thematiques du programme de SCSB pour (i) evaluer les effets environnementaux possibles sur la base des sources connues et des causes proximales candidates et (it) determiner l'importance des voies de causalite liees aux apports de contaminants, de sediments et de nutriments. Bien que les recherches du programme de SCSB aient identifie des effets ecologiques qui semblent etre associes a l'exposition aux contaminants, la source de cette exposition est confondue par la co-localisation et l'incapacite a differencier entre les operations d'exploitation des sables bitumineux (principalement rejetes par emission atmospherique) et les apports provenant des affleurements naturels de bitume (par exemple, les materiaux formes par 1'erosion transported par le flux des eaux de surface et souterraines). L'enrichissement en nutriments des effluents d'eaux usees municipales traitees a ete l'effet ecologique dominant observe pour le cours principal de la riviere Athabasca, associe a l'augmentation de la taille des poissons et aux changements dans les assemblages d'invertebres, probablement parce que cette source de pollution est rejetee directement dans la riviere. Si le rejet direct des eaux de traitement des sables bitumineux se produit a l'avenir, l'impact ecologique potentiel de ces rejets directs de l'industrie devra alors etre soigneusement evalue. La methode d'evaluation des causes ecologiques s'est averee constituer un outil utile pour mieux comprendre comment les sources de stress sont liees aux effets ecologiques par des causes immediates candidates. Les facteurs qui confondent notre capacite a evaluer les effets ecologiques de l'exploitation des sables bitumineux se concentrent sur notre incapacite a differencier de maniere adequate les contaminants provenant de sources naturelles et anthropiques. Cette synthese sur les voies de causalite identifie des options de changements dans la surveillance future afm de mieux anticiper et detecter la degradation de la sante de l'ecosysteme du cours inferieur de la riviere Athabasca et de ses affluents. [Traduit par la Redaction] Mots-cles: sables bitumineux, biosurveillance, effets cumulatifs, sediments, contaminants, enrichissement en nutriments., 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 [...]

The lower Athabasca River (Canada) has experienced notable declines in streamflow and increasing oil sands development since the 1970s. This study investigates the potential impacts of climate change on navigability using both observed historical and projected future flows derived via hydrological simulations driven by an ensemble of statistically downscaled general circulation model climate data. Our use of proposed indices that form the Aboriginal Navigation Index (ANI) and a new index based on percentage over threshold (POT) occurrences yielded novel insights into anticipated changes to the flow regime. Comparisons of near (2041–2070) and far (2071–2100) future periods with the historical baseline (1981–2010) yielded results that project significant reductions in the 500 m3 s−1 POT during the fall navigability period spanning weeks 34 to 43, as well as reductions in the integrated ANIFall. These results indicate that challenging navigational conditions may become more frequent in the second half of the 21st century, not only during this fall period but also earlier into the summer, due to a shift in the flow regime, with potentially severe impacts on the users of the river channels. Our assessment approach is transferable to other regional study areas and should be considered in water management and environmental flow frameworks. [ABSTRACT FROM AUTHOR]

In cold regions deltas influenced by semi-arid climates, such as the Peace-Athabasca Delta (PAD) in western Canada, surface water connectivity influences aquatic conditions by offsetting evaporative losses that are generally greater than precipitation inputs (Kääb et al., [6]; Lesack & Marsh, [7]; Peters, Prowse, Marsh, et al., [11]). This information is necessary to arrive at key hydrological information for an inland basin in question: (i) total basin area delineation, (ii) runoff contribution areas to the water body, (iii) maximum water surface extent, and (iv) frequency of surface water connectivity. TAKE AWAY MESSAGES We employed a visual and numerical aid to detect ice-jam and open-water condition surface water connectivity points in a sector of the Peace-Athabasca Delta. [Extracted from the article]

The biodiversity–ecosystem function hypothesis postulates that higher biodiversity is correlated with faster ecosystem process rates and increased ecosystem stability in fluctuating environments. Exhibiting high spatiotemporal habitat diversity, floodplains are highly productive ecosystems, supporting communities that are naturally resilient and highly diverse.We examined linkages among floodplain wetland habitats, invertebrate communities and their associated traits, and ecosystem function across 60 sites within the floodplain wetlands of the lower Wolastoq | Saint John River, New Brunswick, using structural equation modelling and Threshold Indicator Taxa ANalysis.We identified key environmental filters structuring invertebrate communities, by linking increased niche differentiation through shoreline change, flood pulse dynamics, and macrophyte bed complexity with increased taxa and functional diversity.Examination of traits linked to ecosystem functions revealed that more resilient wetlands with balance between primary productivity and decomposition as carbon sources were associated with greater functional evenness and richness, while habitat patches with elevated decomposition rates had lower functional richness, reflecting a simplified, more disturbed habitat.While our more complex overarching SEM model was ultimately compromised by an overspecified number of pathways, our results nevertheless are indicative of a divergence between wetland and riverine ecosystems in their relationships linking biodiversity and ecosystem function, illustrating how to define ecosystem health in wetland habitats, and demonstrating how critical functions support healthy wetland habitats by providing increased resilience to disturbance. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Large‐scale, intensive agriculture is a critical activity supporting global food production, yet it has taken a significant toll on the equally critical ecosystem services supplied by global biodiversity. This is particularly true for the planet's most threatened ecosystems: freshwaters. As one of the world's largest agricultural producers, Canada is also home to much of the world's freshwater. As Canada's agricultural capacity expands under climate warming into more northerly latitudes—and in some cases regions with large carbon sinks—it is imperative that this sectoral shift is accompanied by careful management to avoid exacerbating ecosystem service losses. Across Canada, agricultural practices vary in terms of their impact on freshwater ecosystems. Agricultural water extraction, storage behind dams, diversions, dredging and clearing of riparian vegetation can impact more naturalized flow regimes. This review explores the influence of managed low flows on ecosystem functioning in man‐made drainage/irrigation ditch systems. We examine how low flows in these systems can impact ecosystem functions in agricultural watersheds with fragmented natural capital. We provide management options to protect ecosystem functions under a changing climate, recognizing that in agro‐ecosystems, drainage/irrigation ditch systems provide a critical remnant habitat to support biodiversity in otherwise depauperate landscapes. [ABSTRACT FROM AUTHOR]

Abstract: Large-scale comparisons of aquatic bioassessment metrics based on taxonomic composition are currently constrained by the biogeographic limitations of taxon occurrence. The use of species trait patterns offers a possibility [...]

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation. [ABSTRACT FROM AUTHOR]

Rewilding is an ecological restoration concept that promotes the natural recovery of ecosystems, through (initial) active or passive removal of human influence. To support the application of rewilding approaches in rivers and their watersheds, we propose a framework to assess 'rewilding potential' based on measurement of basic river ecosystem functions (e.g. restoring flood and nutrient pulses), including examples of specific indicators for these processes. This includes a discussion of the challenges in implementing rewilding projects, such as lack of spatio-temporal data coverage for certain ecosystem functions or tackling ongoing problems once active management is removed. We aim to stimulate new thinking on the restoration of wild rivers, and also provide an annotated bibliography of rewilding studies to support this. [ABSTRACT FROM AUTHOR]

Background: Benthic macroinvertebrates are common bioindicators used in the assessment of aquatic ecosystems. It is well known that the number of specimens within samples, diversity of taxa, and range in [...]

In freshwater ecosystems, habitat alteration contributes directly to biodiversity loss. Dragonflies are sentinel species that are key invertebrate predators in both aquatic (as larvae) and terrestrial ecosystems (as adults). Understanding the habitat factors affecting dragonfly emergence can inform management practices to conserve habitats supporting these species and the functions they perform. Transitioning from larvae to adults, dragonflies leave behind larval exoskeletons (exuviae), which reveal information about the emergent population without the need for sacrificing living organisms. Capitalizing on Atlantic Canada's largest freshwater wetland, the Grand Lake Meadows (GLM) and the associated Saint John/Wolastoq River (SJWR), we studied the spatial (i.e., across the mainstem, tributary, and wetland sites) and temporal (across 3 years) variation in assemblages of emergent dragonflies (Anisoptera) and assessed the relative contribution of aquatic and terrestrial factors structuring these assemblages. The GLM complex, including the lotic SJWR and its tributaries and associated lentic wetlands, provided a range of riparian and aquatic habitat variability ideal for studying dragonfly emergence patterns across a relatively homogenous climatic region. Emergent dragonfly responses were associated with spatial, but not temporal, variation. Additionally, dragonfly communities were associated with both aquatic and terrestrial factors, while diversity was primarily associated with terrestrial factors. Specific terrestrial factors associated with the emergence of the dragonfly community included canopy cover and slope, while aquatic factors included water temperature, dissolved oxygen, and baseflow. Our results indicate that management of river habitats for dragonfly conservation should incorporate riparian habitat protection while maintaining aquatic habitat and habitat quality. [ABSTRACT FROM AUTHOR]