Spanning 750,000 km2 across the Northern Great Plains of North America, the Prairie Potholes Region (PPR) is characterized by millions of shallow wetlands, forming a unique ecosystem that provides habitat for wildlife, carbon storage, and flood control. However, the presence and persistence of Prairie Pothole wetlands is vulnerable to the increasing effects of climate change and land use. Knowledge of northern Great Plains prairie wetland hydrology is based primarily on a few long-term research stations, but generalizing from these intensively monitored areas to the entire PPR requires application of synoptic hydrological approaches across a spatially extensive dataset. The aim of this study is to assess the relative importance of input water sources and evaporative water loss on prairie pothole wetlands of varying permanence class in the Parkland and Grassland Natural Regions in Alberta (Canada). We compare a normal precipitation year (2014) and a relatively dry year (2015), as well as comparing natural sites to 24 restored wetlands. Water samples were collected at intervals during May-August of both years and analyzed for oxygen and hydrogen isotope composition. A combination isotope-mass balance and Bayesian approach was used to generate hydrologic metrics including the isotope composition of input water and evaporation to inflow ratio. Temporal synchrony was tested among the years and site types. We observed little difference in wetland hydrology between the Grassland and Parkland during a normal climate year, but under drier conditions Grassland sites were more vulnerable to evaporation. High synchrony across the study regions indicates that climate change will likely affect wetlands similarly, while restored sites may be less vulnerable to drawdown than natural sites. Interestingly, restored wetlands were more resistant to drawdown than natural wetlands in the Parkland, which will have consequences for wetland biota and climate change adaptation in the northwestern PPR. S'& eacute;tendant sur 750 000 km(2) dans les Grandes Plaines du Nord de l'Am & eacute;rique du Nord, la r & eacute;gion des cuvettes des Prairies (RCP) se caract & eacute;rise par des millions de zones humides peu profondes, formant un & eacute;cosyst & egrave;me unique qui offre un habitat & agrave; la faune, un stockage de carbone et un contr & ocirc;le des inondations. Cependant, la pr & eacute;sence et la persistance de ces zones humides sont vuln & eacute;rables aux effets croissants du changement climatique et de l'utilisation des terres. La connaissance de l'hydrologie des zones humides des prairies des Grandes Plaines du Nord repose principalement sur quelques stations de recherche & agrave; long terme, mais la g & eacute;n & eacute;ralisation de ces zones intens & eacute;ment surveill & eacute;es & agrave; l'ensemble de la RCP n & eacute;cessite l'application d'approches hydrologiques synoptiques sur un ensemble de donn & eacute;es spatialement & eacute;tendu. L'objectif de cette & eacute;tude est d'& eacute;valuer l'importance relative des sources d'eau d'apport et des pertes d'eau par & eacute;vaporation dans les zones humides des cuvettes des Prairies de diff & eacute;rentes classes de permanence dans les r & eacute;gions naturelles des parcs et des prairies de l'Alberta (Canada). Nous comparons une ann & eacute;e de pr & eacute;cipitations normales (2014) et une ann & eacute;e relativement s & egrave;che (2015), ainsi que des sites naturels & agrave; 24 zones humides restaur & eacute;es. Des & eacute;chantillons d'eau ont & eacute;t & eacute; pr & eacute;lev & eacute;s & agrave; intervalles r & eacute;guliers entre mai et ao & ucirc;t des deux ann & eacute;es et analys & eacute;s pour d & eacute;terminer leur composition isotopique en oxyg & egrave;ne et en hydrog & egrave;ne. Une approche combinant bilan isotopique et massique et bay & eacute;sienne a & eacute;t & eacute; utilis & eacute;e pour g & eacute;n & eacute;rer des param & egrave;tres hydrologiques, notamment la composition isotopique de l'eau d'entr & eacute;e et le rapport & eacute;vaporation/apport. La synchronicit & eacute; temporelle a & eacute;t & eacute; test & eacute;e entre les ann & eacute;es et les types de sites. Nous avons observ & eacute; peu de diff & eacute;rences dans l'hydrologie des zones humides entre les prairies et les parcs lors d'une ann & eacute;e climatique normale, mais dans des conditions plus s & egrave;ches, les sites de prairies & eacute;taient plus vuln & eacute;rables & agrave; l'& eacute;vaporation. La forte synchronicit & eacute; entre les r & eacute;gions & eacute;tudi & eacute;es indique que le changement climatique affectera probablement les zones humides de la m & ecirc;me mani & egrave;re, tandis que les sites restaur & eacute;s pourraient & ecirc;tre moins vuln & eacute;rables au rabattement que les sites naturels. Il est int & eacute;ressant de noter que les zones humides restaur & eacute;es & eacute;taient plus r & eacute;sistantes au rabattement que les zones humides naturelles dans les parcs, ce qui aura des cons & eacute;quences sur le biote des zones humides et l'adaptation au changement climatique dans la PPR du nord-ouest.

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.

The Columbia Wetland complex is a rare example of a North American river system with relatively little disturbance from human infrastructure and is the only undammed portion of the main 2000 km stretch of the Columbia River. Declining river flows in western North America, including the upper Columbia River, have reduced the area of open water wetlands in the floodplain and raised concern that the Columbia Wetlands will not remain viable under increasing climate change. In this study we use water isotopes (& delta;O-18 and & delta;H-2) and electrical conductivity to quantify the proportion of groundwater, river water and precipitation contributing to wetland water balance, as well as the role of evaporation, in the Columbia Wetlands through the spring, summer and fall of 2019. We found strong seasonality of water input sources. Groundwater and precipitation were important in spring and fall, while river water was dominant during the summer. An individual wetlands' location in the floodplain as well as relative connectivity to the river channels influenced its seasonal pattern of input sources. Quantifying the relative contributions of the main input water sources to wetlands provides important new understanding of hydrologic connectivity in the Columbia Wetlands.

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.

Study region: The Peace-Athabasca Delta, a Ramsar Wetland of International Importance in northeastern Alberta, is protected within Wood Buffalo National Park and contributes to its UNESCO World Heritage status yet is threatened by climate change and upstream energy projects. Study focus: Recent drawdown of the delta's abundant shallow lakes and rivers has deteriorated vital habitat for wildlife and impaired navigation routes. Here, we report continuous measurements at similar to 50 lakes during open-water seasons of 2018 and 2019 to improve understanding of hydrological processes causing lake-level variation. New hydrological insights for the region: Analyses reveal four patterns of lake-level variation attributable to influential hydrological processes, which provide the basis for a new lake classification scheme: 1) 'Drawdown' (>= 15 cm decline) by evaporation and/or outflow after ice-jam floods, 2) 'Stable' lake levels (<15 cm change) sustained by rainfall, 3) 'Gradual Rise' by inundation from the open-drainage network, and 4) 'Rapid Rise' by input of river floodwater. River flooding during the open-water season is an under-recognized recharge mechanism yet occurred extensively in the Athabasca sector and appears to be a common occurrence based on the Athabasca River hydrometric record. Lake-level loggers show strong ability to track shifts in hydrological processes, and can be integrated with other methods to decipher their causes and ecological consequences across water-rich landscapes.

The oxygen isotope composition (δ18O) of aquatic cellulose extracted from lake sediment cores has long been used to reconstruct past hydrological responses to climate variation and anthropogenic (e.g. mining, agriculture, forestry) disturbance. Application of this method depends upon a constant oxygen isotope fractionation factor between aquatic cellulose and lake water, often reported as α18Ocell-lw = 1.028. Prior field-based assessments of α18Ocell-lw, however, commonly relied on one-time measures of lake water δ18O, which introduces uncertainties because values may not represent lake water δ18O at the time of cellulose synthesis. We field-tested the use of α18Ocell-lw = 1.028 across a broad hydrological gradient of lakes within the Peace-Athabasca Delta (PAD), west-central Canada, where we constrained cellulose production by periphyton on artificial substrates to bracketed measurements of lake water δ18O collected in late May 2015 and late June 2015. Cellulose-inferred lake water δ18O, calculated using α18Ocell-lw of 1.028 ± 0.0015, corresponded with the range of measured lake water δ18O in 36 of 52 (75%) of our study lakes. Agreement improved to 86% for ‘clean cellulose’ samples that appeared to be of higher quality (i.e. those with minimal minerogenic material). Mean apparent α18Ocell-lw calculated for clean cellulose samples, using both May lake water δ18O (1.0286) and the May–June mean lake water δ18O (1.0275), did not differ significantly from 1.028, but was significantly, albeit slightly, below 1.028 using June lake water δ18O (1.0264). Closer correspondence of apparent α18Ocell-lw, calculated using May and May–June average lake water δ18O, suggested rapid and early colonization and cellulose production by periphyton. For samples that were a mixture of cellulose and minerogenic material, mean apparent α18Ocell-lw was significantly below 1.028 for these corresponding lake water δ18O measurements, but differences were small and would potentially lead to under-estimation of cellulose-inferred lake water δ18O by only 1–2‰ in sediment stratigraphic records. Overall, strong agreement observed between the cellulose-inferred and directly measured lake water δ18O supports application of α18Ocell-lw = 1.028 ± 0.0015 and lends confidence to paleohydrological reconstructions using this method in lakes of the PAD and elsewhere.

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.

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.

Well-designed monitoring approaches are needed to assess effects of industrial development on downstream aquatic environments and guide environmental stewardship. Here, we develop and apply a monitoring approach to detect potential enrichment of metals concentrations in surficial lake sediments of the Peace-Athabasca Delta (PAD), northern Alberta, Canada. Since the ecological integrity of the PAD is strongly tied to river floodwaters that replenish lakes in the delta, and the PAD is located downstream of the Alberta oil sands, concerns have been raised over the potential transport of industry-supplied metals to the PAD via the Athabasca River. Surface sediment samples were collected in September 2017 from 61 lakes across the delta, and again in July 2018 from 20 of the same lakes that had received river floodwaters 2 months earlier, to provide snapshots of metals concentrations (Be, Cd, Cr, Cu, Ni, Pb, V, and Zn) that have recently accumulated in these lakes. To assess for anthropogenic enrichment, surficial sediment metals concentrations were normalized to aluminum and compared to pre-industrial baseline (i.e., reference) metal-aluminum linear relations for the Athabasca and Peace sectors of the PAD developed from pre-1920 measurements in lake sediment cores. Numerical analysis demonstrates no marked enrichment of these metals concentrations above pre-1920 baselines despite strong ability (> 99% power) to detect enrichment of 10%. Measurements of river sediment collected by the Regional Aquatics- and Oil Sands-Monitoring Programs (RAMP/OSM) also did not exceed pre-1920 concentrations. Thus, results presented here show no evidence of substantial oil sands-derived metals enrichment of sediment supplied by the Athabasca River to lakes in the PAD and demonstrate the usefulness of these methods as a monitoring framework.

Sustainable approaches capable of tracking status, trends and drivers of lake water balances in complex, remote landscapes are needed to inform ecosystem stewardship and water-security actions. At the Peace-Athabasca Delta (Alberta, Canada), a globally recognized freshwater floodplain landscape, concerns about water-level drawdown and multiple potential stressors have prompted need to improve knowledge of lake water balances and establish a lake monitoring program. Yet, the delta’s remoteness and dynamic nature present challenges to these goals. Here we use over 1000 measurements of water isotope composition at ∼60 lakes and 9 river sites during the spring, summer and fall of five consecutive years (2015–2019) to elucidate patterns in lake water balance over time and space, the influential roles of evaporation and river floodwaters, and relations with meteorological conditions and river water levels. Calculation of evaporation-to-inflow ratios using a coupled-isotope tracer approach, displayed via generalized additive models and geospatial ‘isoscapes’, reveal strongly varying lake water balances. Results identify distinct areas vulnerable to lake-level drawdown, given the likelihood of continued decline in ice-jam flood frequency, longer ice-free season duration and reduced snowmelt runoff. Results also demarcate areas of the delta where lakes are more resilient to factors that cause drawdown. The former defines the Peace sector, which is influenced by floodwaters from the Peace River during episodic ice-jam flood events, whereas the latter describes portions of the active floodplain environment of the Athabasca sector which receives more frequent contributions of Athabasca River floodwaters during both spring ice-jam and open-water seasons. Efficiency of water isotope tracers to capture the marked temporal and spatial heterogeneity in lake water balances during this 5 year time span, and their diagnostic responses to key hydrological processes, serves as a foundation for ongoing lake monitoring, an approach readily transferable to other remote and dynamic lake-rich landscapes.

The need to understand the influence of high-level factors that shape species richness and population size is becoming more important as global biodiversity losses threaten biotic communities. Here we investigate the influence of ecological drift on periphytic diatom community composition in arctic lakes. If community composition is strongly influenced by drift, we hypothesize that (i) alpha diversity will increase with increasing lake size, due to the decreasing influence of drift-mediated local extinction, (ii) beta diversity will be greatest among small lakes and lowest in large lakes, and (iii) relationships between community size and environmental variables will be strongest in large lakes and weakest in small lakes. Analysis was conducted on periphytic diatoms accrued on artificial substrates in 44 shallow, thermokarst lakes over the 2009 growing season. Limnological and hydrological conditions at each site were described and their influence was removed to minimize the confounding effect of environmental heterogeneity. Alpha diversity was not significantly different among the lake sizes. Total beta diversity was significantly higher in the small lakes than the medium lakes. Beta diversity was primarily attributed to turnover, and small lakes had significantly higher turnover than medium and large lakes, while nestedness was not significantly different among lake-size classes. Periphytic diatom community composition and environmental variables were not significantly concordant in any lake-size class. Our results suggest that drift, as related to habitat size, is not a primary driver of periphytic diatom community composition in shallow, thermokarst arctic lakes.

[1] Previous studies of river hydrometric records and Indigenous Knowledge holders claim that flood-induced recharge of ecologically important perched basins decreased across the Peace-Athabasca Delta after 1968 due mainly to hydroelectric regulation of Peace River flow. Natural deltaic processes and climate are acknowledged as additional, lesser contributors, but are challenging to evaluate. We use sediment records spanning ∼115 years from nine perched basins across the Athabasca Delta to test if unidirectional drying coincides with river regulation. Results show bi-directional hydrological changes since the early 1980s, not 1968, to reduced flooding in areas east of the Embarras River confluence with Cree/Mamawi creeks and increased flooding northward along the Cree/Mamawi distributary. The timing and pattern pinpoint the 1982 Embarras Breakthrough, a natural avulsion that diverted flow northward and away from the Athabasca Delta terminus, as the principal cause. The results demonstrate the need to factor natural deltaic processes into impending decisions on the delta's UNESCO World Heritage status and implementation of a federal Action Plan to mitigate widespread drying.

Sediment quality monitoring is widely used to quantify extent of river pollution, but requires knowledge of pre-disturbance conditions in the potentially altered landscape. This has long been identified as a critical aspect to develop for addressing concerns of river pollution in the Alberta Oil Sands Region. Here, we use analyses of sediment cores from eight floodplain lakes spanning a 67 river-km transect across the Athabasca Delta to define pre-1920 (pre-industrial) baseline concentrations for vanadium and five primary pollutants. We then evaluate if sediment metals concentrations have become enriched above baseline since onset of oil sands development and other industrial activities. Results demonstrate no enrichment of metals concentrations (except zinc at one lake) and absence of consistent temporal increases above pre-industrial baselines. Thus, natural processes continue to dominate metal deposition in floodplain lakes of the Athabasca Delta -- an important finding to inform stewardship decisions. The pre-1920 metals concentrations baselines offer a useful tool for ongoing sediment monitoring in aquatic ecosystems of the Athabasca Delta.

Climate-driven decline in freshwater supplied by rivers draining the hydrographic apex of western North America has ramifications for downstream ecosystems and society. For the Peace-Athabasca Delta (PAD), floods from the Peace and Athabasca rivers are critical for sustaining abundant shallow water habitat, but their frequency has been in decline for decades over much of its area. Here, we assess current hydrological and limnological status in the PAD by integrating spatial and temporal data. Analysis of water isotope compositions and water chemistry measured at numerous lakes across the delta shows that hydro-limnological effects of the large-scale ice-jam flood event of 2014 failed to persist beyond the early ice-free season of 2015. Isotope-inferred paleohydrological records from five hydrologically representative lakes in the PAD indicate that periodic desiccation during the Little Ice Age occurred at the most elevated basin in response to locally arid climatic conditions, yet other lower elevation sites were influenced by high water level on Lake Athabasca owing to increased snowmelt- and glacier-derived river discharge. In contrast, water isotope data during the past 15 yr at all five lakes consistently document the strong role of evaporation, a trend which began in the early to mid-20th century according to sediment records and is indicative of widespread aridity unprecedented during the past 400 yr. We suggest that integration of hydrological and limnological approaches over space and time is needed to inform assessment of contemporary lake conditions in large, complex floodplain landscapes.