In a multistressor world, evidence-based stewardship of aquatic ecosystems requires long-term monitoring data to understand the timing and magnitude of environmental change and potential causes. At the Peace-Athabasca Delta (PAD; northeastern Alberta, Canada), concern for aquatic ecosystem degradation has triggered renewed and urgent calls by Indigenous, national, and international governance bodies for implementation of a long-term lake monitoring program capable of tracking changes in hydrological conditions and contaminant deposition attributable to major energy projects located upstream, climate change, and other unnatural and natural processes. Challenges imposed by the delta's size, hydrological complexity, inaccessibility of lakes, and other factors, however, have long impeded implementation of a delta-wide lake monitoring program. To address this pressing need, here we review and synthesize results obtained during 7 years (2015–2021) of intensive, multifaceted research at 60 shallow lakes spanning the delta's broad hydroecological gradients to inform an integrated hydrology, water chemistry, and contaminants monitoring program. The research involved systematic, repeated measurements of water isotope composition, water depth variation, water chemistry and turbidity, and metal(loid) concentrations in lake surface sediment and periphytic biofilm. Results reveal marked spatial and temporal variation of hydrological processes and their affects on lake water balance and depth, strong association between hydrological processes and lake water chemistry, and that concentrations of nickel and vanadium (key oil sands indicators) remain within the range of natural variation. Correspondence of generalized additive model trendlines for isotope-derived lake evaporation-to-inflow ratios and water chemistry with climate indices (Pacific Decadal Oscillation, Oceanic Niño Index) demonstrates the sensitivity, and predictability, of lake ecosystem processes in the delta to large-scale climatic patterns. We provide recommendations for field sampling, sample analysis, data display, and integration of information for ongoing monitoring at the PAD. These approaches are readily transferable to other complex landscapes with abundant shallow waterbodies threatened by multiple stressors that may alter hydrological regimes and contaminant delivery.

Proliferation of Nitellopsis obtusa (starry stonewort), an aquatic invasive macroalga, is an emerging water quality concern in North America, but disentangling its effects is complicated by multiple stressors and a lack of long-term data. In this study, we investigated the potential impacts of N. obtusa on benthic oxygen depletion and the lower food web of Lake Scugog (southern Ontario, Canada) in a multiple-stressor context through a paleolimnological assessment of ecosystem changes up to the invasion and proliferation of N. obtusa. Results reveal that myxoxanthophyll, a pigment produced by colonial cyanobacteria, was no longer detected in the sediments after the early 1990s despite being prevalent throughout the earlier history of Lake Scugog. This indicates that recently documented blooms of Microcystis, which have been hypothesized to be unprecedented and facilitated by N. obtusa, are not a new phenomenon but instead may represent a resurgence in cyanobacteria production following a period of water quality improvement. Sediment cores also documented increased relative abundance of Chironomidae taxa associated with low benthic oxygen availability after about 1920, while changes in subfossil diatom assemblage provided evidence of increased frequency and/or duration of thermal stratification indicative of climate warming effects. This suggests that N. obtusa may be acting synergistically with existing stressors on Lake Scugog to exacerbate challenges with benthic hypoxia.

Systematic and sustainable monitoring approaches capable of tracking the status and trends of keystone characteristics are critical for detecting aquatic ecosystem degradation, identifying the influence of multiple potential stressors, informing environmental protection policy and anticipating future change. At remote lake-rich landscapes, ability to implement and maintain long-term monitoring is often challenged by logistical and financial constraints. At the Peace-Athabasca Delta (PAD; northeastern Alberta, Canada), an internationally recognized remote freshwater landscape threatened by climate change and upstream industrial development (hydroelectric regulation of river flow, oil sands mining and processing), the need for an integrated aquatic ecosystem monitoring program has long been recognized to track changes to the flood regime, water balance, water quality, and contaminant deposition in the abundant shallow lakes. The remoteness and hydrological complexity of the landscape, among other factors, have hindered the implementation of such a program. In recent years, concern over aquatic ecosystem degradation has led to renewed and urgent calls by international and national governance agencies for implementation of a long-term monitoring program. Here, we report on intensive, multi-faceted research performed during 2015-2021 at 60 lakes spanning the delta’s broad hydroecological gradients to develop, evaluate, and apply a framework for integrated assessment of status and trends in water balance, water chemistry and contaminant enrichment. We present the design and approaches used, synthesize the knowledge gained from data collected during the 7-year-long research phase, and provide a foundation for a long-term aquatic ecosystem monitoring program that addresses several recommendations stemming from assessments by UNESCO and key priorities within the Wood Buffalo National Park Action Plan. We suggest the monitoring framework is readily transferable to other remote shallow lake- and pond-rich landscapes threatened by multiple potential stressors.

Deltas are hydrologically dynamic landscapes where river floodwaters create a mosaic of productive ecosystems that provide important services. The flood regime, however, is vulnerable to upstream anthropogenic activities, climate change and geomorphic processes. Deciphering the roles of multiple potential stressors on flood regime change is critical for developing appropriate adaptive and mitigative strategies but requires knowledge of hydrological variability at broader scales of space and time than is typically available from instrumental and observational records. At the globally recognized Peace-Athabasca Delta (Canada), the timing, magnitude and causes of reduced flooding and drawdown of perched basin water levels remain an intense focus of investigation. Here we employ novel 'paleofloodscapes', generated from geospatial interpolation of Bayesian mixing model fingerprinting of sediment elemental concentrations, to quantify variation in the delta's flood regime during the past ~140 years. Results reveal that flooding of the delta began to decline several decades before hydroelectric regulation of Peace River flow, not coincident with it, and the influence of floodwaters from the unregulated Athabasca River has declined more than the regulated Peace River. A key discovery is that widespread flooding of perched basins occurs when ice-jam events on the river(s) coincide with a relatively high water-plane in the delta's open-drainage network. Without knowledge of open-drainage water levels, inferred change to the flood regime of perched basins may be inaccurate when derived solely from analyses of Peace River hydrometric data and climatic records. The paleofloodscapes illustrate that rising sediment delivery caused by a natural river avulsion in 1982 may undermine the intended purpose of a proposed weir installation. The most recent paleofloodscape, developed from lake surface sediment sampling shortly after widespread flooding, demonstrates the value of the approach as a landscape hydrological monitoring tool, and is readily transferrable to other floodplains to track flood regime change.

Abundant reserves of metals and oil have spurred large-scale mining developments across northwestern Canada during the past 80 years. Historically, the associated emissions footprint of hazardous metal(loid)s has been difficult to identify, in part, because monitoring records are too short and sparse to have characterized their natural concentrations before mining began. Stratigraphic analysis of lake sediment cores has been employed where concerns of pollution exist to determine pre-disturbance metal(loid) concentrations and quantify the degree of enrichment since mining began. Here, we synthesize the current state of knowledge via systematic re-analysis of temporal variation in sediment metal(loid) concentrations from 51 lakes across four key regions spanning 670 km from bitumen mining in the Alberta Oil Sands Region (AOSR) to gold mining (Giant and Con mines) at Yellowknife in central Northwest Territories. Our compilation includes upland and floodplain lakes at varying distances from the mines to evaluate dispersal of pollution-indicator metal(loid)s from bitumen (vana-dium and nickel) and gold mining (arsenic and antimony) via atmospheric and fluvial pathways. Results demonstrate 'severe' enrichment of vanadium and nickel at near-field sites (<= 20 km) within the AOSR and 'severe' (near-field; <= 40 km) to 'considerable' (far-field; 40-80 km) enrichment of arsenic and antimony due to gold mining at Yellowknife via atmospheric pathways, but no evidence of enrichment of vanadium or nickel via atmospheric or fluvial pathways at the Peace-Athabasca Delta and Slave River Delta. Findings can be used by decision makers to evaluate risks associated with contaminant dispersal by the large-scale mining activities. In addition, we reflect upon methodological approaches to be considered when evaluating paleolimnological data for evidence of anthropogenic contributions to metal(loid) deposition and advocate for proactive inclusion of paleolimnology in the early design stage of environmental contaminant monitoring programs.

Sediment core and water quality data, together with historical information on land use/land cover (LULC), were used to reconstruct changes in phosphorus (P) loading and cycling in Lake Wilcox, Ontario, Canada, since the early 1920s. After first being cleared for farming, the originally forested watershed subsequently underwent urbanization. The large increase in P loading accompanying agricultural intensification after World War II caused the eutrophication of the lake. However, improved soil conservation since the 1980s and urban stormwater management since the 1990s have brought watershed P loading and sediment accumulation down to levels comparable to the early 1900s. Yet, the lake continues to exhibit eutrophication-like symptoms, especially the intensification of hypoxia in the hypolimnion. Post-2000 water quality data indicate that the latter is not driven by external P loading from the watershed, but rather by rapid salinization that strengthens the lake's summer stratification and enhances internal P loading. Salinization is caused by the increasing application of deicing agents in the expanding urban area. Curbing salt inputs will therefore be essential to restore the lake. Overall, our results provide new insights into the shifts in lake biogeochemistry associated with LULC changes and the implementation of best management practices. The approaches and findings of our case study have broad applicability for the large number of freshwater ecosystems worldwide that are experiencing salinization.

Exploitation of bitumen-rich deposits in the Alberta Oil Sands Region (AOSR) by large-scale mining and processing activities has generated widespread concern about the potential for dispersal of harmful contaminants to aquatic ecosystems via fluvial and atmospheric pathways. The release of mercury has received attention because it is a potent neurotoxin for wildlife and humans. However, knowledge of baseline mercury concentration prior to disturbance is required to evaluate the extent to which oil sands development has contributed mercury to aquatic ecosystems. Here, we use stratigraphic analysis of total mercury concentration ([THg]) in radiometrically dated sediment cores from nine floodplain lakes in the AOSR and downstream Peace-Athabasca Delta (PAD) and two upland lakes in the PAD region to establish pre-1900 baseline [THg] and evaluate if [THg] has become enriched via fluvial and atmospheric pathways since oil sands mining and processing began in 1967. Concentrations of THg in sediment cores from the study lakes range from 0.022–0.096 mg/kg (dry wt.) and are below the Canadian interim sediment quality guidelines for freshwater (0.17 mg/kg). Results demonstrate no enrichment of [THg] above pre-1900 baseline via fluvial pathways at floodplain lakes in the AOSR or PAD. Enrichment of [THg] was detected via atmospheric pathways at upland lakes in the PAD region, but this occurred prior to oil sands development and aligns with long-range transport of emissions from coal combustion and other anthropogenic sources across the northern hemisphere recognized in many other lake sediment records. The inventory of anthropogenic [THg] in the upland lakes in the AOSR is less than at the Experimental Lakes Area of northwestern Ontario (Canada), widely regarded as a “pristine” area. The absence of enrichment of [THg] in lake sediment via fluvial pathways is a critical finding for stakeholders, and we recommend that monitoring at the floodplain lakes be used to inform stewardship as oil sands operators prepare to discharge treated oil sands process waters directly into the Athabasca River upstream of the PAD.

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.

We are developing liposome-encapsulated hemoglobin (LEH) as an artificial oxygen carrier for resuscitation in indications, such as acute blood loss and surgery. Earlier attempts to formulate a viable LEH met with constraints of scale up and limited hemoglobin content. In this work, we report an LEH formulation containing novel anionic non-phospholipid (CHHDA) that enhances the encapsulation efficiency of hemoglobin inside the liposome bilayer. CHHDA was synthesized from inexpensive ingredients in high yields. The formulation was evaluated in vitro to investigate the cytotoxic effects on RAW 264.7 macrophages and HUVEC endothelial cells in culture by LDH, MTT and hexosaminidase assays. Under optimal conditions of manufacturing, the presence of 28mol% of CHHDA enhanced the hemoglobin content to over 4g/dl. The LEH containing CHHDA shows some cytotoxicity in HUVEC and RAW cells in vitro, especially by LDH assay. MTT assay was negative for cytotoxicity in both cells lines. By hexosaminidase assay, the proliferation of RAW cells, but not HUVEC cells, was inhibited. When CHHDA-LEH was incubated with isolated human platelets in vitro, no platelet activation was observed. The LEH formulation with novel anionic lipid and high hemoglobin content reported in this article is an improvement from the past preparations.

Mercury (Hg) is a pollutant of concern across Canada and transboundary anthropogenic Hg sources presently account for over 95% of national anthropogenic Hg deposition. This study applies novel statistical analyses of 82 high-resolution dated lake sediment cores collected from 19 regions across Canada, including nearby point sources and in remote regions and spanning a full west-east geographical range of ∼4900 km (south of 60°N and between 132 and 64°W) to quantify the recent (1990-2018) spatial and temporal trends in anthropogenic atmospheric Hg deposition. Temporal trend analysis shows significant synchronous decreasing trends in post-1990 anthropogenic Hg fluxes in western Canada in contrast to increasing trends in the east, with spatial patterns largely driven by longitude and proximity to known point source(s). Recent sediment-derived Hg fluxes agreed well with the available wet deposition monitoring. Sediment-derived atmospheric Hg deposition rates also compared well to the modeled values derived from the Hg model, when lake sites located nearby (<100 km) point sources were omitted due to difficulties in comparison between the sediment-derived and modeled values at deposition "hot spots". This highlights the applicability of multi-core approaches to quantify spatio-temporal changes in Hg deposition over broad geographic ranges and assess the effectiveness of regional and global Hg emission reductions to address global Hg pollution concerns.

Evidence from remote sensing studies suggests that the frequency of thermokarst lake drainage events is increasing in response to climate change, but the consequences of these changes on the limnology of remaining waterbodies remain unknown. Here, we utilize a multiparameter paleolimnological record and post-drainage water isotope and chemistry monitoring to characterize the limnological evolution of Zelma Lake in Old Crow Flats, Yukon. During the early part of the record (~1678 to 1900 CE), analysis of geochemical variables and algal pigments indicate relatively stable limnological conditions. Abruptly beginning at ~1900, Zelma Lake experienced a 40 year phase of reduced production, likely resulting from thermokarst shoreline expansion and associated increases in turbidity and low light availability. This was followed by ~70 years of increasing production, likely from the stabilization of shorelines combined with a warming climate. Zelma Lake catastrophically drained in June 2007. Post-drainage conditions were characterized by intense eutrophication marked by increases in nutrient and major ion concentrations and the unprecedented occurrence of okenone and diatoxanthin pigments. Comparison to the post-drainage paleolimnological record from another thermokarst lake in Old Crow Flats indicates that a sharp increase of production is likely a common outcome of thermokarst lake drainage, yet intensity differs owing to site-specific catchment characteristics.

Urbanization is an important modifier of nutrient and contaminant inputs to aquatic environments due to increases in anthropogenic sources in urban areas compared to rural land use types, and due to the increase in impervious area and runoff potential. Lake Wilcox is a natural kettle lake in the greater Toronto metropolitan area whose watershed has progressively become more sub-urban and urban since the 1940s, resulting in increased eutrophic conditions within the lake. Initial management in the 1980s focussed on replacing septic tank usage by expanding the city sewage system, whereas more targeted management efforts within the lake and watershed began in the 1990s. To assess the impact of land use changes on the loadings of the limiting nutrient phosphorus (P) and other elements to the lake, we collected a 76 cm-long sediment core. Radioisotope dating indicates that the deepest sediments of the core were deposited around 1920. For each 1 cm core segment, we measured the total 1 M HCl-extractable P, Fe, S, Mn, Na, K and Al, along with organic carbon, nitrogen and sulfur content. We also extracted a subset of the core samples using a sequential extraction procedure that differentiates the various sediment P pools, including the redox-labile, humic-bound, organic, and exchangeable P. The increase in eutrophication, including the influence of septic system discharge by cottages along the lakeshore, are clearly marked by an increase in total and organic P concentrations with time. Total Na concentrations also record the increase in urban land coverage in the watershed, which have

Episodic flood events are critical for recharging water balance of floodplain lakes and maintaining their ecological integrity, yet are subject to alteration in frequency and magnitude by natural and anthropogenic processes that operate over a range of spatial and temporal scales. To evaluate roles of potential stressors, paleolimnological reconstructions are used to obtain insights into hydrological variability of dynamic floodplain lakes. However, spatial and temporal integration is often underdeveloped because different paleolimnological measurements must be applied across lakes due to the wide range of energy conditions that impart marked differences in sediment composition. Here, we use a linear discriminant analysis to identify 10 significant elemental concentrations in surveyed sediment from multiple sampling campaigns that distinguish the geochemical fingerprints of three end-member sources in lakes at the Peace-Athabasca Delta (PAD; Canada): the Athabasca River, the Peace River and local catchment runoff. Over 90% of the sediment samples were correctly classified into the original groups after cross-validation due to the distinctiveness of the three end members, which permits development of a robust Bayesian mixing model to discern the relative contributions of sediment from the three sources. We evaluate the mixing model at two adjacent lakes in the Athabasca sector of the PAD and demonstrate its effectiveness to discriminate three known hydrological phases during the past 300 years. Notably, the model infers ~60% of the sediment originated from the Peace River during the largest ice-jam flood event on record (1974), which was unrecognized by other methods. We then applied our model to sediment records from 18 lakes spanning the hydrological gradients across the 6000 km2 PAD to further probe the hydrological evolution during the past ~150 years. Results demonstrate decline in frequency of flooding from both the Athabasca and Peace rivers and lake-level drawdown since the early 20th century and align remarkably well with prior interpretation of conventional paleohydrological records of individual lakes. We advocate our approach provides a universal method that can be applied across the full range of sediment composition to quantify change in source, frequency and magnitude of river floodwaters to lakes and is transferable to other dynamic floodplain landscapes where variation of sediment composition challenges efficacy of other approaches.

Gold mining operations near Yellowknife (Northwest Territories, Canada) released vast quantities of arsenic trioxide during the 1950s, which dispersed across the landscape. Contemporary measurements of arsenic concentrations in lake water and surficial sediment identify enrichment within a 30 km radius. However, paleolimnological studies have identified possible evidence of mining influence during the 1950s at a lake beyond this distance, suggesting a more expansive legacy footprint may exist. Here, we analyze spatiotemporal patterns of arsenic, antimony, and lead deposition from sediment cores at lakes located 10-40 km (near-field) and 50-80 km (far-field) from the mines along the prevailing northwesterly wind direction (NW) and 20-40 km to the northeast (NE) of the mines to improve characterization of the legacy footprint of emissions. We build upon previous findings to determine if: 1) there is evidence of mine-related pollutants beyond the well-established 30 km radius and 2) enrichment is greatest in the prevailing wind direction, as expected for aerial dispersion from a point source of emissions. Results demonstrate enrichment since the 1950s for arsenic and antimony at least as far as 80 km to the NW and 40 km to the NE, thus legacy deposition extended beyond the currently defined 30 km radius 'zone of immediate influence'. Concentrations, enrichment factors, and total excess inventories of arsenic and antimony decline with distance from the mines and are greater along the prevailing (NW) than orthogonal (NE) wind direction. Peak concentrations in uppermost sediment strata at near-field lakes in the prevailing wind direction suggest supply of arsenic and antimony remains high from legacy stores in the catchment and lake sediment profiles >60 years after emissions were released. Such lasting influence of legacy emissions likely is not limited to mines in the Yellowknife region, and paleolimnological approaches can effectively delineate zones of past and ongoing pollution from legacy sources elsewhere.

Hydrological monitoring in complex, dynamic northern floodplain landscapes is challenging, but increasingly important as a consequence of multiple stressors. The Peace-Athabasca Delta in northern Alberta, Canada, is a Ramsar Wetland of International Importance reliant on episodic river ice-jam flood events to recharge abundant perched lakes and wetlands. Improved and systematic monitoring of landscape-scale hydrological connectivity among freshwater ecosystems (rivers, channels, wetlands, and lakes) is needed to guide stewardship decisions in the face of climate change and upstream industrial development. Here, we use water isotope compositions, supplemented by measurements of specific conductivity and field observations, from 68 lakes and 9 river sites in May 2018 to delineate the extent and magnitude of spring ice-jam induced flooding along the Peace and Athabasca rivers. Lake-specific estimates of input water isotope composition (delta(I)) were modelled after accounting for influence of evaporative isotopic enrichment. Then, using the distinct isotopic signature of input water sources, we develop a set of binary mixing models and estimate the proportion of input to flooded lakes attributable to river floodwater and precipitation (snow or rain). This approach allowed identification of areas and magnitude of flooding that were not captured by other methods, including direct observations from flyovers, and to demarcate flow pathways in the delta. We demonstrate water isotope tracers as an efficient and effective monitoring tool for delineating spatial extent and magnitude of an important hydrological process and elucidating connectivity in the Peace-Athabasca Delta, an approach that can be readily adopted at other floodplain landscapes.

In rock grouting, idealized 2D-radial laminar flow of yield stress fluids (YSF) is a fundamental flow configuration that is used for cement grout spread estimation. A limited amount of works have presented analytical and numerical solutions on the radial velocity profiles between parallel disks. However, to the best of our knowledge, there has been no experimental work that has presented measured velocity profiles for this geometry. In this paper, we present velocity profiles of Carbopol (a simple YSF), measured by pulsed ultrasound velocimetry within a radial flow model. We describe the design of the physical model and then present the measured velocity profiles while highlighting the plug-flow region and slip effects observed for three different apertures and volumetric flow rates. Although the measured velocity profiles exhibited wall slip, there was a reasonably good agreement with the analytical solution. We then discuss the major implications of our work on radial flow.