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Regional groundwater monitoring in the Athabasca region of Alberta, Canada, provides information on groundwater quality and geochemical changes over time, including data useful for evaluating potential impacts of industrial activity such as oil sands mining and in situ operations. Data collected from over 5000 wells from the 1950s to 2014, including 161 wells from government’s monitoring network, were used to develop and apply bootstrap techniques for the detection of changes in groundwater geochemistry over time and at specific points in time. Increasing temporal anomalies were identified in Cl, TDS, B, and naphthenic acids in the McMurray formation across 2003 and 2008, while decreasing anomalies were found for SO4. Temporal variance for 15 indicators was quantified for a smooth bootstrap approach to arrive at stable values representative of the most recent samples taken from wells in the study area. Stable values revealed sampling bias in the Devonian, Grand Rapids, Empress, Channel Beverly, and Muriel Lake formations suggesting expansion of sampling may be necessary. Although temporal anomalies were found in the McMurray formation, sampling bias was not identified. The entropy and relative magnitude of time series were evaluated to identify candidate wells for continued observations, which consist of wells with low measurements and low entropy that are near active industry lease boundaries. Temporal anomalies, stable values, and entropy were combined into type-well information to provide plots for visual inspection and interpretation. Stable values are useful for regional mapping, for detecting future changes and trends, and for identifying areas of interest warranting further investigation.

For a period of 16 months in Sydney, Australia, the variations of 2 H/ 1 H and 18 O/ 16 O in atmospheric vapour ( δ 2 H A and δ 18 O A ) were estimated using an evaporation pan method as well as using the isotopic precipitation-equilibrium approach. These calculations were then compared with δ 2 H A values measured at 10 m above ground surface using a Fourier Transform Infrared Spectrometer (FTIR). As pan isotopic composition was available on a weekly time scale, the evaporation rates were measured daily, and the atmospheric variables were available hourly, the weekly time scale was used to calculate the arithmetic averages of the atmospheric variables that were used in the estimation of the pan-derived δ 2 H A . Good agreement (r=0.7, P-value=0.00) was found between the pan-derived and the FTIR measured δ 2 H A for weekly intervals, although individual differences ranged from −25.0 to 20.4 ‰, with the absolute difference averaging 8.0 ‰. A sensitivity analysis showed that the determination of δ 2 H A is most sensitive to air temperature, relative humidity and the isotopic composition of the pan water . While the precipitation-equilibrium approach only appears to be representative of atmospheric conditions close to times of precipitation events, the pan-derived isotopic composition of atmospheric vapour was found to be closer to the FTIR averages over longer periods including intervals with no precipitation. Overall, this means that the pan method is far more effective for uninterrupted estimation of δ 2 H A and δ 18 O A of atmospheric water vapour, as required for water budget studies, than the precipitation-equilibrium method, and it is more cost effective and robust than continuous measurement.

The analysis of functional trait-habitat relationships has been used to measure the degree to which environmental factors influence the assembly of ecological communities. In the Parkland and Grassland natural regions of Alberta, wetlands are embedded in a matrix of human modified landscapes. The extent and effects of land uses on the condition of these wetlands and plant assemblages remains largely unknown. We used the physico-chemical characteristics and plant functional traits collected in 322 wetlands as indicators of wetland condition. Plant functional traits included origin, life history, and habitat requirements. Physico-chemical characteristics at each wetland site were assessed and the intensity of land use quantified within a 250-meter buffer. Our analyses reveal that functional plant traits are impacted by surrounding land use intensity; the abundance of non-native (exotic), upland, and annual plants tend to increase with degree of agriculture. Wetlands in areas with abundant groundwater input (low isotopic oxygen-18 enrichment) tend to be associated with functional groups preferring stable hydrological conditions including perennials and upland species. This contrasts with wetlands with greater potential for evaporation which were shallower, had higher nutrient levels, and were positively associated with species tolerating higher levels of disturbances, such as annuals. Our study demonstrates how an understanding of plant functional trait-habitat relationship can provide a framework for linking the responses of taxonomically-unrelated plant species to the condition of wetlands, and ultimately be used as indicator of wetland condition.

In the southern Athabasca Oil Sands (SAOS) Region, located in Alberta Canada, individual in-situ oil sands operators have conducted local geochemical and isotope groundwater studies to establish baseline characteristics and to improve understanding of the connectivity of water supply and disposal formations within individual leases. Canada's Oil Sands Innovation Alliance (COSIA) initiated this study to combine the data from these individual studies along with public information into a comprehensive unified dataset to evaluate conceptual models of regional groundwater flow and the degree of interaction and separation between important water supply and disposal aquifers. The unified dataset comprised over 293 groundwater samples from the main water source and disposal hydrostratigraphic units and included geochemical and isotopic tracers that can be used to identify sources (δ18O and δ2H) and age of water (3H) and associated solutes (14CDIC, 36Cl), as well as the sources of salinity and diagenetic processes (δ13CDIC, δ34SSO4, 87Sr/86Sr, δ11B, δ37Cl and δ81Br) and dissolved organics (δ13CDOC). The TDS and stable isotope composition (δ18O and δ2H) of groundwater from several Cretaceous formations were used to identify three main mixing controls. i) Areas where locally recharged groundwater mixes with glaciogenic water were identified by lower δ18O and δ18O values, high TDS, Cl:Br and δ34SSO4, 87Sr/86Sr, and δ37Cl values consistent with dissolution of evaporites. These areas were situated where vertical pathways through otherwise competent formations are likely to occur. ii) Mixing with paleo-waters characterized by high TDS and higher δ18O and δ2H signatures indicating groundwater recharged under warmer climate periods and/or evaporative enrichment were identified in the south, and southwestern portions of the study area. The presence of these paleo-waters indicate slow-moving groundwater zones with limited lateral and vertical connectivity. iii) Areas with potential connectivity to shallow aquifers were identified by their lower TDS values, modern meteoric δ18O and δ2H signatures, HCO3 type waters, and δ34S SO4 and 87Sr/86Sr signatures, consistent with weathering of shallow aquifer material. Geochemical and isotopic indicators suggest that in areas where the Colorado Group aquitard is thin or absent, there is greater connectivity between the Grand Rapids Formation and the shallower aquifers. Interpretation of the new unified dataset has improved understanding of the extent that glacial recharge had on Devonian aquifers, and overlying Cretaceous formations, and identified zones with relatively stagnant groundwater flow, both of which have implications for regional groundwater resource development, monitoring and potential wastewater disposal.

Identifying impacts of oil sands development on aquatic ecosystems requires understanding of the natural background water quality. In the Athabasca Oil Sands Region of Alberta this is challenging because the Athabasca River is incised directly into bitumen saturated sands of the McMurray Formation, and other saline Cretaceous and Devonian formations. This study compares the geochemical and isotopic composition of porewater sampled from the alluvial sediment beneath the Athabasca River with regional groundwater data to identify the geological origin of these saline groundwaters, and improve characterization of natural background sources of solutes entering the Athabasca River. Terrain conductivity surveys conducted along the Athabasca River were used to identify areas with evidence of saline groundwater discharge. Porewater samples were obtained from the alluvial sediment using drive point piezometers installed between 1 and 3 m below the water-sediment interface and were analyzed for δ18O, δ2H, δ34S SO4, δ18O SO4, 87Sr/86Sr, δ13C-DIC, δ13C-DOC, 3H, and 14C. The porewater in the alluvial sediment showed variable degrees of mixing with the overlying Athabasca River water, but the geochemical and isotopic composition in zones 1, 3 and 5 are consistent with discharge of saline groundwater from Cretaceous or Devonian units. The low percentages of modern carbon, and δ18O, δ2H, δ34S SO4, δ18O SO4, and 87Sr/86Sr signatures in the deepest porewater samples from Zones 1, 3 and 5 indicate glaciogenic water with high total dissolved solids originating from Devonian sourced solutes. Theses saline groundwater discharge zones occur where higher horizontal hydraulic gradients coincide with areas of higher salinity in the adjacent Cretaceous and Devonian aquifers, and areas with vertical connectivity with underlying Devonian aquifers. The results of this study demonstrate the influence of groundwater-surface water interactions and saline bedrock formation water discharge to water quality along some reaches of the Athabasca River which need to be considered in monitoring and water management strategies.

Interactions between lakes and groundwater are of increasing concern for freshwater environmental management but are often poorly characterized. Groundwater inflow to lakes, even at low rates, has proven to be a key in both lake nutrient balances and in determining lake vulnerability to pollution. Although difficult to measure using standard hydrometric methods, significant insight into groundwater–lake interactions has been acquired by studies applying geochemical tracers. However, the use of simple steady-state, well-mixed models, and the lack of characterization of lake spatiotemporal variability remain important sources of uncertainty, preventing the characterization of the entire lake hydrological cycle, particularly during ice-covered periods. In this study, a small groundwater-connected lake was monitored to determine the annual dynamics of the natural tracers, water stable isotopes and radon-222, through the implementation of a comprehensive sampling strategy. A multilayer mass balance model was found outperform a well-mixed, one-layer model in terms of quantifying groundwater fluxes and their temporal evolution, as well as characterizing vertical differences. Water stable isotopes and radon-222 were found to provide complementary information on the lake water budget. Radon-222 has a short response time, and highlights rapid and transient increases in groundwater inflow, but requires a thorough characterization of groundwater radon-222 activity. Water stable isotopes follow the hydrological cycle of the lake closely and highlight periods when the lake budget is dominated by evaporation versus groundwater inflow, but continuous monitoring of local meteorological parameters is required. Careful compilation of tracer evolution throughout the water column and over the entire year is also very informative. The developed models, which are suitable for detailed, site-specific studies, allow the quantification of groundwater inflow and internal dynamics during both ice-free and ice-covered periods, providing an improved tool for understanding the annual water cycle of lakes.

Hydrology and geochemistry studies were conducted in the Athabasca Oil Sands region to better understand the water and nitrogen cycles at two selected sites in order to assess the potential for nitrogen transport between adjacent terrain units. A bog—poor fen—upland system was instrumented near Mariana Lakes (ML) (55.899° N, 112.090° W) and a rich fen—upland system was instrumented at JPH (57.122° N, 111.444° W), 100 km south and 45 km north of Fort McMurray, Alberta respectively. LiDAR surveys were initially conducted to delineate the watershed boundaries and topography and to select a range of specific locations for the installation of water table wells and groundwater piezometers. Field work, which included a range of physical measurements as well as water sampling for geochemical and isotopic characterization, was carried out mainly during the thaw seasons of 2011 to 2015. From analysis of the runoff response and nitrogen species abundances we estimate that nitrogen exchange between the wetlands and adjacent terrain units ranged between 2.2 and −3.1 kg/ha/year for rich fens, 0.6 to −1.1 kg/ha/year for poor fens, and between 0.6 and −2.5 kg/ha/year for bogs, predominantly via surface pathways and in the form of dissolved nitrate. A significant storage of dissolved ammonium (and also dissolved organic nitrogen) was found within the pore water of the bog-fen complex at Mariana Lakes, which we attribute to decomposition, although it is likely immobile under current hydrologic conditions, as suggested by tritium distributions. In comparison with the experimental loads of between 5 and 25 kg/ha/year, the potential nitrogen exchange with adjacent terrain units is expected to have only a minor or negligible influence, and is therefore of secondary importance for defining critical loads across the regional landscape. Climate change and development impacts may lead to significant mobilization of nitrogen storages, although more research is required to quantify the potential effects on local ecosystems.

Stable isotopes of water, oxygen-18 and deuterium, were measured in water samples collected from a network of 300 lakes sampled in six ∼100 km 2 blocks (centred at 49.72°N, 91.46°W; 48.49°N, 91.58°W; 50.25°N, 86.62°W; 49.78°N, 83.98°W; 48.24°N, 85.49°W; 47.73, 84.52°W) within Precambrian shield drainages in the vicinity of Lake Superior, northern Ontario, Canada. Additional sampling was also conducted within the Turkey Lakes watershed (47.03°N, 84.38°W), a research basin situated in the Algoma region located 50 km north of Sault Saint Marie, Ontario. The studies were undertaken to gain a better understanding of hydrology and geochemistry of watersheds in the region in order to better predict acid sensitivity of lakes. The main objective of this paper is to describe the hydrologic variations observed based on stable isotope results. Evaporative isotopic enrichment of lake water was found to be systematic across the region, and its deviation from the isotopic composition of precipitation was used to estimate the evaporation/inflow to the lakes as well as runoff (or water yield) based on a simple isotope mass balance model. The analysis illustrates significant variability in the water yield to lakes and reveals a pattern of positively skewed distributions in all six widely spaced blocks, suggesting that a high proportion of lakes have relatively limited runoff whereas relatively few have greater runoff. Such basic information on the drainage structure of an area can be valuable for site-specific hydrologic assessments but also has significant implications for critical loads assessment, as low runoff systems tend to be less buffered and therefore are more sensitive to acidification. Importantly, the Turkey Lakes sampling program also suggests that isotope-based water yield is comparable in magnitude to hydrometric gauging estimates, and also establishes that uncertainty related to stratification can be as high as ±20% or more for individual lakes, although it likely has only a minor influence on regional survey results. While further analysis in gauged lake watersheds would be beneficial to constraining the accuracy of the method or calibrating it for operational use, it is nevertheless a powerful tool in its present form for lake-to-lake and regional runoff inter-comparisons.

In this work, a reversed-phase ultra-HPLC (UHPLC) ultrahigh resolution MS (UHRMS) method was evaluated for the comprehensive profiling of NAs containing two O atoms in each molecule (O2NAs; general formula Cn H2n + z O2 , where n is the number of carbon atoms and z represents hydrogen deficiency). Using a polar cyanopropyl-bonded phase column and negative-ion electrospray ionization mass spectrometric detection at 120,000 FWHM (m/z 400), 187 and 226 O2NA species were found in two naphthenic acid technical mixtures, and 424 and 198 species with molecular formulas corresponding to O2NAs were found in two oil sands process-affected water samples (one from a surface mining operation and the other from a steam-assisted gravity drainage operation), respectively. To our knowledge, these are the highest numbers of molecular compositions of O2NAs that have been profiled thus far in environmental samples. Assignments were based on accurate mass measurements (≤3 ppm) combined with rational molecular formula generation, correlation of chromatographic behavior of O2NA homologues with their elemental compositions, and confirmation with carboxyl group-specific chemical derivatization using 3-nitrophenylhydrazine. Application of this UHPLC-UHRMS method to the quantitation of O2NAs in the surface mining operation-derived water sample showed excellent linearity (R2 = 0.9999) with external calibration, a linear range of 256-fold in concentration, and quantitation accuracies of 64.9 and 69.4% at two "standard substance" spiking levels.

Oil sands mines have large disturbance footprints and contain a range of new landforms constructed from mine waste such as shale overburden and the byproducts of bitumen extraction such as sand and fluid fine tailings. Each of these landforms are a potential source of water and chemical release to adjacent surface and groundwater, and consequently, the development of methods to track water migration through these landforms is of importance. The stable isotopes of water (i.e. 2 H and 18 O) have been widely used in hydrology and hydrogeology to characterize surface water/groundwater interactions but have not been extensively applied in mining applications, or specifically to oil sands mining in northern Alberta. A prerequisite for applying these techniques is the establishment of a Local Meteoric Water Line (LMWL) to characterize precipitation at the mine sites as well as the development of a ‘catalogue’ of the stable water isotope signatures of various mine site waters. This study was undertaken at the Mildred Lake Mine Site, owned and operated by Syncrude Canada Ltd. The LMWL developed from 2 years (2009/2012) of sample collection is shown to be consistent with other LMWLs in western Canada. The results of the study highlight the unique stable water isotope signatures associated with hydraulically placed tailings (sand or fluid fine tailings) and overburden shale dumps relative to natural surface water and groundwater. The signature associated with the snow melt water on reclaimed landscapes was found to be similar to ground water recharge in the region. The isotopic composition of the shale overburden deposits are also distinct and consistent with observations made by other researchers in western Canada on undisturbed shales. The process water associated with the fine and coarse tailings streams has highly enriched 2 H and 18 O signatures. These signatures are developed through the non-equilibrium fractionation of imported fresh river water during evaporation from cooling towers used within the raw water process circuit. This highly fractionated surface water eventually becomes part of the recycled tailings water circuit, and as a consequence it undergoes further non-equilibrium fractionation as a result of surface evaporation, leading to additional enrichment along local evaporation lines.

The theoretical basis for application of stable isotope mass balance of lakes is described for a range of climatic situations including low latitude, high latitude, high altitude, continental and coastal systems, as well as cases where the atmospheric boundary layer is significantly modified by the lake evaporation process. The effects of seasonality on isotopic offset between precipitation and atmospheric vapour and the slope of the local evaporation line are described. Atmospheric feedback and its role in labelling the isotopic composition of the Laurentian Great Lakes and tropical lakes is discussed. Several important considerations are suggested to improve parameterization of quantitative paleoclimatic reconstructions including use of assumptions that are appropriate for the climatic setting, for the atmospheric feedback situation, for salinity, and headwater setting. Potential for use of dual-isotopes to trace past changes in seasonality and input, and a dual-lake index method that can potentially be used to trace connectivity of lakes are presented. In cases where modern or paleo-evaporation systems may be under-defined there are inherent limitations in the degree of quantification that can be attained.

Stable isotopes of oxygen and hydrogen were measured in water samples collected annually from a representative suite of 50 lakes in northeastern Alberta over a 9-year period and are interpreted using a steady-state isotope mass balance model to determine water yield and runoff ratios for the lake watersheds and residence time of the lakes. This isotopic perspective on hydrology of the region provides new insight into the role of land cover, watershed morphometry, climatic drivers and permafrost thaw on lakes. Bog cover, permafrost and presence of thaw features in bogs are found to be the dominant hydrologic drivers, although morphometric properties such as elevation, lake area and drainage basin area are also influential. In addition to quantifying the hydrologic fluxes, the analysis establishes contrasting conditions in more southerly lakes, located in the Stony Mountains and west of Fort McMurray, as compared with more northerly sites in the Birch Mountains, Caribou Mountains and northeast of Fort McMurray, mainly because of contributions from thawing permafrost at the northerly sites. Distinct hydrologic conditions are also noted for Shield systems north of Lake Athabasca where bogs and permafrost are absent. While permafrost thaw is not directly labelled by oxygen and hydrogen isotope composition, isotope mass balance calculations suggest that contributions of up to several hundred millimetres per year are occurring in 14 of the 50 lake watersheds under study. Several of these lakes have water yields in excess of precipitation in some years, and regional groups of lakes display significant correlations between water yield and percentage of bogs that have collapsed. Copyright © 2015 John Wiley & Sons, Ltd.

Summary Stable isotope measurements and isotope mass balance (IMB) calculations are presented in support of an unprecedented 20-year water balance assessment for a tailings pond and a chain of downstream lakes at the Salmita–Tundra mine site, situated near Courageous Lake, Northwest Territories, Canada (65°03′N; 111°11′W). The method is shown to provide a comprehensive annual and interannual perspective of water balance fluxes along a chain of lakes during the period 1991–2010, without the need for continuous streamflow gauging, and reveals important lake-order-dependent patterns of land-surface runoff, discharge accumulation, and several key diagnostic ratios, i.e., evaporation/inflow, evaporation/evapotranspiration, land-surface-runoff/precipitation and discharge/ precipitation. Lake evaporation is found to be a significant component of the water balance, accounting for between 26% and 32% of inflow to natural lakes and between 72% and 100% of inflow to mine-tailings ponds. Evaporation/evapotranspiration averages between 7% and 22% and is found to be higher in low-precipitation years, and in watersheds with a higher proportion of lakes. Runoff ratios for land-surface drainages and runoff ratios for watersheds (including lakes) ranged between 14–47% and 20–47%, respectively, and were higher in low precipitation years, in watersheds with a higher proportion of lakes, and in watersheds less affected by mining development. We propose that in general these two runoff ratios will likely converge as lake order increases and as land cover conditions become regionally representative. Notably, the study demonstrates application of IMB, validated with streamflow measurements, to constrain local water balance in a remote low-arctic region. For IMB chain-of-lakes applications, it underlines the importance of accounting for evaporatively-enriched upstream sources to avoid overestimation of evaporation losses.

An analysis of the relative effects of transpiration and evaporation, which can be distinguished by how they affect isotope ratios in water, shows that transpiration is by far the largest water flux from Earth’s continents, representing 80 to 90 per cent of terrestrial evapotranspiration and using half of all solar energy absorbed by land surfaces. Water fluxes from the land surface to the atmosphere are divided between evaporation, and transpiration from leaf stomata. Although a seemingly basic division between the physical and biological, there is still no consensus on the global partitioning between the two fluxes, resulting in uncertainties as to responses to future climate variations. Now, Scott Jasechko and colleagues use the isotopic signatures of transpiration and evaporation from a global data set of large lakes and reveal that enormous quantities of water — as much as 90% of total terrestrial evapotranspiration — are cycled through vegetation via transpiration. One conclusion to be drawn from this study is that the accuracy of biological — rather than physical — fluxes should be prioritized in work to improve climate models. Renewable fresh water over continents has input from precipitation and losses to the atmosphere through evaporation and transpiration. Global-scale estimates of transpiration from climate models are poorly constrained owing to large uncertainties in stomatal conductance and the lack of catchment-scale measurements required for model calibration, resulting in a range of predictions spanning 20 to 65 per cent of total terrestrial evapotranspiration (14,000 to 41,000 km3 per year) (refs 1, 2, 3, 4, 5). Here we use the distinct isotope effects of transpiration and evaporation to show that transpiration is by far the largest water flux from Earth’s continents, representing 80 to 90 per cent of terrestrial evapotranspiration. On the basis of our analysis of a global data set of large lakes and rivers, we conclude that transpiration recycles 62,000 ± 8,000 km3 of water per year to the atmosphere, using half of all solar energy absorbed by land surfaces in the process. We also calculate CO2 uptake by terrestrial vegetation by connecting transpiration losses to carbon assimilation using water-use efficiency ratios of plants, and show the global gross primary productivity to be 129 ± 32 gigatonnes of carbon per year, which agrees, within the uncertainty, with previous estimates6. The dominance of transpiration water fluxes in continental evapotranspiration suggests that, from the point of view of water resource forecasting, climate model development should prioritize improvements in simulations of biological fluxes rather than physical (evaporation) fluxes.

In this work, a reversed-phase ultra-HPLC (UHPLC) ultrahigh resolution MS (UHRMS) method was evaluated for the comprehensive profiling of NAs containing two O atoms in each molecule (O2NAs; general formula C

Western Canadian oil sands contain over 170 billion barrels of proven unconventional petroleum reserves currently extracted at 1.8 million barrels per day by either surface mining, or by in situ techniques that require subsurface injection of steam and hydrocarbon solvents. Natural high-salinity springs are known to add water and entrained inorganic and organic constituents to the Athabasca River and its tributaries in the region of ongoing bitumen production. However, the magnitude and synoptic distribution of these saline inputs has remained unquantified. Here, a chloride mass balance is used to estimate saline groundwater discharge to the Athabasca River from 1987 to 2010. Results show that the highest saline water discharge rate to the Athabasca River occurs between Ft. McMurray and the Peace-Athabasca Delta, supported by subcrop exposure of lower Cretaceous- and Devonian-aged formations bearing saline waters. Further, the input of saline groundwater is found to be an important control on the chemistry of the lower Athabasca River, despite comprising 10 � 1 to 3% of the Athabasca River’s discharge. The flux of natural saline groundwater entering the Athabasca does not appear to have increased or decreased from 1987 to 2010. The origin of seep salinity is interpreted as relict subglacial meltwater that has dissolved Devonian-aged evaporites, supported by saline Na-Cl type waters with low 18 O/ 16 O and 2 H/ 1 H ratios relative to modern precipitation. The magnitude of groundwater discharge and its impact on the Athabasca River’s chemistry in the area of ongoing bitumen development warrants the incorporation of natural groundwater seepages into surface water quality monitoring networks.

summary We report oxygen and hydrogen isotopic composition of river discharges in the main stem and tributaries in Mackenzie River system, Canada, based upon a synoptic survey and a time-series monitoring program undertaken between 2003 and 2006. The water isotope signals in the Mackenzie River system exhibit distinct geographic variations. Isotopic results from the comprehensive synoptic survey offset from meteoric water lines in d 18 O–d 2 H space, and suggest a snowmelt-driven discharge regime with mixing between heavy-isotope depleted discharge from Liard River and Mackenzie Mountains, and evaporativelyenriched water from Great Slave Lake catchment. Based upon these isotopic data in river discharge, we propose an evaporative-mixing line for the Mackenzie River system (d 2 H = 6.0 � d 18 O � 40.8), which highlights the integrated effects of the two most important hydrologic processes (i.e., evaporation and mixing). Time-series investigation of water isotope signatures and river discharge at three key hydrometric stations demonstrates the isotopic response to the strong seasonality of river discharge in northern Canada. In general, isotopic compositions in river discharge tend to be negatively correlated with discharge amount, which is a typical snowmelt-driven isotope-discharge pattern. However, low flow conditions are found to be noisy with a wide range of isotopic variability. More importantly, we also observe that extreme high flow events, especially in the Liard River, appear to be unexpectedly enriched in heavy isotopes, which indicate contributions from evaporated water that are probably derived from wetland surface storage. This is a situation, which produces a reversal in the isotope-discharge pattern and marks important episodes that may impact chemical and riverine/estuarine biotic processes at times of extremely high runoff.

summary Stable isotopes of water, oxygen-18 and deuterium, were measured at biweekly to monthly intervals during the open-water season in a small, headwater lake (Pocket Lake, 4.8 ha) near Yellowknife Northwest Territories, and concurrently in a nearby string-of-lakes watershed (Baker Creek, 137 km 2 ) situated in the subarctic Precambrian Shield region. As measured in water samples collected over a 12 year period (1997–2008), the levels of evaporative isotopic enrichment in both lake and watershed outflow were differentially offset, and seasonal variations were found in both to be driven by variations in open-water evaporation. Systematic differences measured in the magnitude of the offset between the lake and watershed outflow are interpreted as being caused by changes in the effective drainage area contributing to runoff. Based on the observed and extremely consistent relationship between isotopic compositions of lake water and watershed outflow (r 2 = 0.849, p < 0.001) we extend the analysis of open-water evapora

Various types of ecosystem-based climate proxies have been used to assess past arctic change. Although lotic records are relatively poor because of the constant reworking of riverine material, high-quality lentic data have been assembled back to the end of the Pleistocene and deglaciation of the circumpolar Arctic. In general, climatic variations in the Holocene, partly due to changes in the shrinking effect of glacier coverage, produced significant temporal and spatial variations in arctic hydrology and freshwater ecosystems. Of particular note were the vast expansions of northern peatlands during major protracted periods of wetting. More recent lake biota and sedimentiological data reflect the general warming trend that has occurred over the last one to two centuries and indicate major changes to freshwater characteristics such as ice-cover duration and thermal stratification. Such data provide an excellent baseline against which future effects of climate change can be both projected and measured.

Isotope tracers are widely used to study hydrological processes in small catchments, but their use in continental-scale hydrological modeling has been limited. This paper describes the development of an isotope-enabled global water balance and transport model (iWBM/WTM) capable of simulating key hydrological processes and associated isotopic responses at the large scale. Simulations and comparisons of isotopic signals in precipitation and river discharge from available datasets, particularly the IAEA GNIP global precipitation climatology and the USGS river isotope dataset spanning the contiguous United States, as well as selected predictions of isotopic response in yet unmonitored areas illustrate the potential for isotopes to be applied as a diagnostic tool in water cycle model development. Various realistic and synthetic forcings of the global hydrologic and isotopic signals are discussed. The test runs demonstrate that the primary control on isotope composition of river discharge is the isotope composition of precipitation, with land surface characteristics and precipitation-amount having less impact. Despite limited availability of river isotope data at present, the application of realistic climatic and isotopic inputs in the model also provides a better understanding of the global distribution of isotopic variations in evapotranspiration and runoff, and reveals a plausible approach for constraining the partitioning of surface and subsurface runoff and the size and variability of the effective groundwater pool at the macro-scale.

Summary Water level observations and a daily water balance model are used to build a naturalized water level history for Great Slave Lake dating back to the 1967 completion of the W.A.C. Bennett Dam in the Peace River basin headwaters. Comparison of water level observations dating back to 1938 and water balance scenarios for 1964–1998 assist in constraining the probable magnitude and likely direction of climate and regulation impacts on the water level history of the lake. Overall, the first-order analysis suggests that the effect of flow regulation has been to dampen annual water level variability by about 20 ± 2 cm, to reduce annual maximum water levels by about 14 ± 3 cm and to shift peak water levels earlier in the season by about 30 ± 8 days. Meanwhile, climate forcing has tended to enhance water level variability by 8 ± 2 cm, to enhance maximum water levels by 10 ± 3 cm and to advance the timing of maximum water levels slightly (11 ± 8 days). Climatic and regulation impacts appear to have generally counter-balanced changes in amplitude of water level changes and magnitude of peak levels but have cumulatively contributed to a seasonal shift toward earlier peak water levels in the lake.

The Northern Rivers Ecosystem Initiative (NREI) was established in the late 1990s to address important science questions resulting from previous studies undertaken by the Northern Rivers Basin Study (NRBS). This manuscript summarizes the results from a number of reports on hydrologic research conducted on the Peace-Athabasca-Slave river and lake systems. Specific concerns expressed by the NRBS and subsequent NREI focused on how these systems were being affected by climate change, flow regulation and land-use changes. Issues addressed in this report include: the fate of aquatic perched basins within the Peace-Athabasca Delta under historical and future climate trends; the sources of major floods that replenish these basins and how the frequency, magnitude and source areas of such events have changed over time; the synoptic weather patterns and atmospheric teleconnections that are responsible for the generation of major snowmelt runoff that drive major floods; the potential effect that climate and land-use changes might have on basin runoff and delta lake levels; the specific hydro-climatic conditions required to produce major ice-jam floods on the Peace River and how these may be altered by climate change; remote-sensing methods to document delta flooding and vegetation change; and the dual effect of climate and flow regulation on the water levels of Great Slave Lake and how these may affect other nearshore processes, particularly wind seiches, that influence flooding of the Slave River Delta. A review of the major findings and recommendations for future research concludes the report.

On average, 86% of riverine discharge to Great Slave Lake, Northwest Territories, Canada, was gauged during the period 1964–1998, offering an unprecedented opportunity to study and understand controls on water balance of a large northern lake at the headwaters of the Mackenzie River. A functional daily water balance model, incorporating measurements of riverine inflow, precipitation on the lake surface, evaporation, and riverine outflow was developed, which predicts the amplitude and frequency of annual water level fluctuations, and closes the water balance to within s6% for 28 of 35 years and s11% for the remaining 7 years, with an overall systematic error of C2%. Annual water balance estimates for the period 1964–1998 reveal that about 74% of inflow into Great Slave Lake originates from the Peace-Athabasca catchments that enter the lake via the Slave River, whereas 21% is derived from other catchments bordering Great Slave Lake, and 5% from precipitation on the lake surface. An estimated 94% of water losses occur by riverine outflow to the Mackenzie River and 6% by evaporation from the lake surface. The primary driving force behind water level fluctuations in Great Slave Lake, including the post-regulation period following development of the W.A.C. Bennett Dam, is shown to be climate-driven precipitation variability in the Peace-Athabasca basins. A simple precipitation regression model is developed to simulate water level fluctuations in Great Slave Lake over the past 100 years. Copyright  2006 John Wiley & Sons, Ltd.

The distribution of stable water isotopes provides valuable insight into runoff generation processes in subarctic wetland regions of the Mackenzie River basin, a major freshwater contributor to the Arctic Ocean and the focus of intensive hydrological research as part of Canada's contribution to the Global Energy and Water Cycle Experiment (GEWEX). This article describes a streamfiow hydrograph separation analysis carried out over three complete annual cycles (1997-1999) for five subarctic catchments ranging in size from 202 to 2050 km 2 situated near the confluence of the Liard and Mackenzie rivers. This heterogeneous landscape, characterized by extensive wetlands (fen and bog), shallow lakes and widespread discontinuous permafrost, is representative of vast flow-contributing areas of the upper Mackenzie Valley, and is suspected to be highly sensitive to climate variability and change. We document seasonal patterns and interannual variability in the isotopic composition of local streamflow, attributable to mixing of three distinctly labelled flow sources, namely groundwater, surface water plus rain, and direct snowmelt, and apply these isotopic signals to partition sources and their temporal variability. Although groundwater input is the dominant and most persistent streamflow source in all five catchments throughout the year, direct snowmelt runoff via surface and shallow subsurface pathways (during spring freshet) and surface waters from lakes and wetlands situated in low-lying areas of the basins (during summer and fall) are also significant seasonal contributors. Catchment-specific differences are also apparent, particularly in the generation of snowmelt runoff, which is more attenuated in fen-dominated than in bog-dominated catchments. The data set additionally reveals notable interannual variability in snow isotope signatures and snow water equivalent, apparently enhanced by the 1998 El Nino event.

Monitoring of stable water isotopes (18O and 2H) in precipitation and surface waters in the Mackenzie River basin of northern Canada has created new opportunities for researchers to study the complex hydrology and hydroclimatology of this remote region. A number of prior studies have used stable isotope data to investigate aspects of the hydrological regime of the wetland-dominated terrain near Fort Simpson, Northwest Territories, Canada. The present paper compares estimates of groundwater contributions to streamflow derived using the WATFLOOD distributed hydrological model, equipped with a new water isotope tracer module, with the results of conventional isotope hydrograph separation for five wetland-dominated catchments along the lower Liard River. The comparison reveals highly promising agreement, verifying that the hydrological model is simulating groundwater flow contributions to total streamflow with reasonable fidelity, especially during the crucial snowmelt period. Sensitivity analysis of the WATFLOOD simulations also reveals intriguing features about runoff generation from channelized fens, which may contribute less to streamflow than previously thought.

An overview of current research in isotope hydrology, focusing on recent Canadian contributions, is discussed under the headings: precipitation networks, hydrograph separation and groundwater studies, river basin hydrology, lake and catchment water balance, and isotope palaeohydrology from lake sediment records. Tracer-based techniques, relying primarily on the naturally occurring environmental isotopes, have been integrated into a range of hydrological and biogeochemical research programmes, as they effectively complement physical and chemical techniques. A significant geographic focus of Canadian isotope hydrology research has been on the Mackenzie River basin, forming contributions to programmes such as the Global Energy and Water Cycle Experiment. Canadian research has also directly supported international efforts such as the International Atomic Energy Agency’s (IAEA) Global Network for Isotopes in Precipitation and IAEAs Coordinated Research Project on Large River Basins. One significant trend in Canadian research is toward sustained long-term monitoring of precipitation and river discharge to enable better characterization of spatial and temporal variability in isotope signatures and their underlying causes. One fundamental conclusion drawn from previous studies in Canada is that combined use of υ 18 O and υ 2 H enables the distinction of precipitation variability from evaporation effects, which offers significant advantages over use of the individual tracers alone. The study of hydrological controls on water chemistry is one emerging research trend that stems from the unique ability to integrate isotope sampling within both water quality and water quantity surveys. Copyright  2005 John Wiley & Sons, Ltd.

The hydrology of subarctic, discontinuous permafrost regions is sensitive to the effects of climatic warming, because pronounced changes in water storage and runoff pathways could occur with small additional ground heating. The objective of this study is to understand the hydrologic functions of unique land-cover types in this region (channel fens, flat bogs, and peat plateaus) using isotopic and chemical signatures of surface and subsurface water, as well as hydrometric measurements. The study was conducted in a 152-km 2 basin of Scotty Creek, located in the central part of the Mckenzie River basin in northern Canada. The headwater of Scotty Creek, Goose Lake had a strongly enriched isotopic composition due to evaporation. The stream water composition changed downstream, as the lateral drainage from the active layer of peat plateaus contributed isotopically light and chemically dilute water to channel fens that are part of the drainage network. Flat bogs received drainage from peat plateau in addition to direct precipitation, and were internally drained or drained water to adjacent channel fens. Average evapotranspiration estimated from the chloride-balance method was 280‐ 300 mm/yr, which was consistent with the hydrometric estimate (precipitation minus runoff) of 275 mm/yr indicating a potential applicability of this method to ungauged basins. Tracer-based hydrograph separation showed that the direct snowmelt contribution to spring runoff was less than half of total discharge, suggesting an importance of the water stored over winter in lakes and wetlands. The total amount of water stored over winter in the basin was estimated to be 140‐ 240 mm, which was comparable to the average annual basin discharge (149 mm). q 2004 Elsevier B.V. All rights reserved.

The process of water delivery to a headwater stream in a hypermaritime rainforest was examined using a variety of physical techniques and tracing with dissolved organic carbon (DOC) and the stable isotopes of water. Headwater swamps, often the major discharge zones for water draining off steep forest slopes, strongly affect the physical and chemical character of streamflow in the region. The headwater swamp selected for detailed investigation was sustained by relatively constant groundwater input from the steep colluvial slopes that maintained the water table above the ground surface. During significant storm events the water table rose quickly and the swamp expanded to engulf marginal pools that developed rapidly on the adjacent ground surfaces. The corresponding release of surface water directly to the stream typically comprised up to 95% of total stream discharge. The proportion of groundwater seepage to the stream by matrix flow (

Shallow lakes in a continental, low Arctic setting are found to undergo substantial fluctuations in heavy-isotope content during the annual cycle due to extreme seasonality in water balance processes. Progressive isotope enrichment during the icefree period occurs as a consequence of isotope exchange during evaporation under seasonally arid conditions, while enhanced input and flushing by heavy-isotope depleted precipitation and snowmelt during late fall and spring tend to deplete the lakes in heavy isotopes once again. Time-series sampling surveys in a group of nearby lakes, ranging in volume from 41,000 to 2,250,000 m 3 , was carried out for two consecutive ice-free periods, in conjunction with a comprehensive hydrological measurement program in a detailed study lake, to assess models that describe isotopic enrichment in lakes and to test their suitability for comparing evaporation rates and water balance. From a non-steady isotope balance analysis, it is found that isotope enrichment rates in lakes during the ice-free period are determined primarily by evaporation rates and volume of the lakes, and are less sensitive to water balance variations for short time intervals when evaporation is less than 50 mm or so. A basic assessment of best-fit and step-wise models is presented which suggests that the former are useful only for predicting evaporation and water balance during month-long periods with relatively stable atmospheric and hydrologic conditions. A stepwise isotope balance approach is presented which demonstrates how isotope-based estimates of evaporation rates can be applied to effectively compare short-term (weekly) water balance in nearby lakes. Practical applications in the region include water balance assessments to assist in design and maintenance of tailings ponds for gold and diamond mining operations. q 2002 Elsevier Science B.V. All rights reserved.

An isotope-based approach for water balance assessment is presented and applied to estimate throughflow, residence time and catchment runoff to 70 headwater lakes on the Boreal plain and uplands of northern and north-central Alberta, Canada. The survey reveals a complex hydrologic regime with systematic variability in water balance due to local site characteristics. On average, runoff to lakes in wetland-dominated catchments is found to be significantly higher than runoff to upland-dominated lakes, with generally higher contributions from catchments with low bog/fen ratios. The isotope method, which relies primarily on water sampling and isotopic analysis, can be easily integrated in routine water quality surveys and is shown to be a practical alternative to conventional hydrological modelling for comparative analysis of water balance controls on hydrochemistry and aquatic ecology of lakes, particularly in low-relief wetland-rich terrain.

The process of isotopic fractionation during freezing in the riverine environment is discussed with reference to a multi-year isotope sampling survey conducted in the Liard–Mackenzie River Basins, northwestern Canada. Systematic isotopic patterns are evident in cores of congelation ice (black ice) obtained from rivers and from numerous tributaries that are recognized as primary streamflow signals but with isotope offsets close to the equilibrium ice–water fractionation. The results, including comparisons with the isotopic composition of fall and spring streamflow measured directly in water samples, suggest that isotopic shifts during ice-on occur due to gradual changes in the fraction of flow derived from groundwater, surface water and precipitation sources during the fall to winter recession. Low flow isotopic signatures during ice-on suggest a predominantly groundwater-fed regime during late winter, whereas low flow isotopic signatures during ice-off reflect a mixed groundwater-, surface water- and precipitation-fed regime during late fall. Copyright © 2002 John Wiley & Sons, Ltd.

A review of headwater lakes in undisturbed watersheds on the Boreal Plain, with indirect gradient analyses of chemical data, indicated a clear separation between those in wetland-dominated watersheds (57–100% wetland with variable proportions of bog, fen, swamp, and marsh cover) and those in upland-dominated watersheds (0–44% wetland cover). In the former, percentage wetland cover in the watershed was positively correlated with total phosphorus (TP, r2 = 0.78, primarily bog), total nitrogen (TN, r2 = 0.50), and dissolved organic carbon (DOC, r2 = 0.74) concentrations. Rich fens appeared to sequester both TP and TN. In upland-dominated lakes, the ratio of catchment area to lake volume (CA/LV) was the strongest watershed correlate of TP concentration (r2 = 0.56), whereas most limnetic nitrogen and DOC were generated in situ. Colour concentration, being highest in wetland lakes, was correlated with the ratio of isotopically defined effective drainage basin area to lake volume (eDBA/LV, r2 = 0.63). Drainage basin slope was only weakly associated with water quality, likely because of low topographic relief ([Formula: see text]11%). Higher Chlorophyta and Peridineae biomasses in wetland-dominated systems than in upland-dominated ones may coincide with greater NH4+ availability.

Shallow hillslope groundwater is shown to be a dominant source of streamflow in sloping bog-forest uplands of the North Coast Forest District, British Columbia, based on a three-component isotope hydrograph-separation analysis conducted in July 1998. At peak discharge during a mid-summer rainfall event, new water contributions accounted for only 12% of streamflow, whereas shallow groundwater accounted for 85% of streamflow and bog groundwater and deep hillslope groundwater accounted for the remaining 3% of streamflow. Mean residence time of water is estimated to be about 2 months, and soil storage capacity is roughly 400 mm based on the analysis of the baseflow discharge and isotopic response. Systematic seasonal shifts in deuterium excess of rainfall in the Prince Rupert area are shown to be useful for labelling shallow and deep groundwaters based on their residence time signatures. The potential for using dissolved organic carbon and deuterium excess as hydrological tracers is also discussed.

Isotope stratigraphy of river-ice covers can be applied to reconstruct time-series of the stable isotopic composition of winter streamflow, although careful attention to ice type, morphology and location of sampling is required to obtain useful results. Ice surveys conducted in the Liard River Basin, northwestern Canada, suggest that the isotopic composition of winter streamflow is relatively invariant along the main river stem. However, systematic isotopic enrichment is observed over the course of the winter for small tributaries draining discontinuous-permafrost wetlands, and is attributed to shifts in the isotopic composition of source water. Recommendations for further study required to verify the underlying physical processes associated with this response are outlined.

[1] Regional variations in evaporation losses and water budget are interpreted from systematic isotopic patterns in surface waters across a 275,000 km2 region of northern Canada. Differential heavy isotope enrichment in a set of >255 nonheadwater lakes sampled by floatplane during 1993 and 1994 is strongly correlated to varying hydroclimatic conditions across the region. Calculated catchment-weighted evaporation losses typically range from ∼10–15% in tundra areas draining into the Arctic Ocean to as high as 60% in forested subarctic areas draining to the Mackenzie River via Great Bear or Great Slave Lakes. Because of the diversity in drainage order and the ratio of catchment to surface area, lakes in the region may inherit as little as 30% to as much as 99% of their isotopic enrichment signal from upstream water bodies. Open-water evaporation generally decreases with increasing latitude and accounts for 5–50% of total evapotranspiration. Coupling of meteorological and isotopic data permits a novel assessment of regional evaporation-transpiration flux partitioning in the three major ecoclimatic zones (high-boreal forest, subarctic forest-tundra, and low-arctic shrub tundra), while the differing frequency distributions of lake water balance in these zones provides a new index of landscape-scale hydroclimatology that may have significant potential for investigating ongoing (or past) changes in response to high-latitude climate change.