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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.

Distinguishing municipal wastewater effluent (MWWE) from other industrial effluents or through an urbanized watershed can be challenging. In complex receiving environments, linking environmental responses to specific compounds or effluents is not always straight forward. In order to characterize the inherent complexity of tracing MWWE in aquatic systems influenced by multiple stressors, a proposed multi-tracer suite is intended to highlight areas of potential biological concern. Characterization and quantification of effluent exposure to aquatic biota in this manner is essential to shape policies intended to encourage wastewater infrastructure development (i.e. treatment plant upgrade) and broader environmental management. This paper describes the use of a comprehensive suite of tracers that includes isotopes in support of a core surveillance program, demonstrating its effectiveness both empirically and with respect to diagnostic value contributed to monitoring programs.

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.

On the Qinghai-Tibet Plateau, permafrost degradation and associated release of permafrost meltwater has undoubtedly modified the annual and seasonal streamflow patterns and influenced groundwater conditions. However, it is still unclear how extensively permafrost degradation has influenced surface and subsurface water systems due to very sparse observations. Isotope mass models combining tritium and 222Rn measurements are developed here to quantify the contributions of groundwater discharge and thawing permafrost to rivers and lakes in the Source Area of the Yellow River. Results demonstrate the spatial variability of permafrost thaw impacts and confirm significant influence on surface and subsurface runoff processes including effects on water yield capacity and water drainage connectivity. While results to date are conclusive, further work to refine the method and extend observations is warranted.

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.

Study region: Surveys of stable isotopes of water in 121 lakes were conducted between 2007 and 2009 to assist in characterizing baseline hydrology of the South Athabasca Oil Sands area, Alberta, a 35,000 km2 boreal forest region with subdued relief, about 70% wetland cover, and a mosaic of lakes, rivers and buried channel networks. The region, currently under rapid development for in-situ oil sands, was close to baseline conditions at the time of survey. Study focus: Using an isotope mass balance approach, isotope data were applied to estimate water yield to lakes across the region. High-resolution maps were created to illustrate the spatial distribution of water yield and to compare observed patterns to geologic and physiographic features. New hydrological insights for the region: Site-specific differences in water yield were found in relation to geologic and physiographic features. Notably, high water yields were found in lakes underlain by Colorado shale, lower runoff was found in proximity to incised and buried channels. Consistent patterns from year-to-year reveal zones of low runoff which may be more susceptible to development-related impacts including changes in surface/groundwater interaction and pressurization or depressurization of aquifers or formations. The approach may be helpful for informing design of new monitoring programs to ensure runoff variability is considered. Periodic reassessments are recommended to capture potential development and/or climatic change impacts on the water cycle. Keywords: Isotopes, Lakes, Water balance, Evaporation, Runoff, Boreal, Oil sands

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.

Interactions between groundwater and surface water are often overlooked in lake water budgets, even though groundwater can significantly contribute to the total annual water inputs to a lake. Isotope mass balance models have seen significant developments in the last decade for assessing the spatial and temporal variability of hydrological processes in lakes but are generally applied assuming steady-state. While this assumption is generally acceptable for long-term water balances of large lakes, it may be less appropriate for lakes which undergo strong seasonality of hydrological processes and meteorological conditions. In this study, a volume-dependent transient isotopic mass balance model was developed for an artificial lake (named Lake A) in Canada, and in a context where direct measurement of surface water fluxes is difficult, if not impossible. This lake typically receives important inputs of flood-water during the spring freshet period, as a hydraulic connection with a large watershed establishes each year. Quantification of the water fluxes to Lake A allowed to highlight the impacts of flood-water inputs over the annual water budget. The isotopic mass balance model revealed that groundwater and surface water inputs respectively account for 71 % and 28 % of the total annual water inputs to Lake A, which demonstrates its dependence on groundwater. An important part of these groundwater inputs is likely to correspond to flood-derived surface water due to bank storage. On an annual timescale, Lake A was found to be resilient to surface water pollution and sensitive to groundwater quantity and quality changes. There is however a likelihood that the resilience to surface water pollution is lower from April to August, as important water inputs originating from Lake DM contribute to the water balance via direct and indirect inputs (i.e., from bank storage). This suggests that the surface water fluxes between Lake DM and Lake A did not only have an impact on the dynamic of Lake A during springtime but also significantly influenced the long-term dynamics of Lake A. These findings can help anticipating the impacts of variation in the intensity and/or duration of future flooding events on lakes' water quality. From a more global perspective, this knowledge is useful for establishing regional-scale management strategies for maintaining water quality at flood-affected lakes in a context of land-use and climate changes.

Study region: Water samples for isotopic analysis were collected during 2013–2019 at 331 gauging stations across Canada in representative watersheds ranging from the Atlantic to the Pacific to the Arctic Oceans. Drainage area coverage of the network included 56 % of Canada’s landmass (9,984,670 km2) and was representative of 91 % of Canada’s annual water yield. Study focus: Baseline data, including 4603 18O and 2H analyses, are described to assess potential for process studies and predictive model calibration. New hydrological insights for the region: While similar patterns are noted between isotopes in streamflow and precipitation across Canada, systematic evaporative enrichment in streamflow occurs in lake- and wetland-rich areas, and systematic depletion occurs in some mountainous and/or cold-regions watersheds. The latter are attributed to uncertainty in precipitation isotope records, glacial melt and/or permafrost thaw. In δ18O-δ2H space, streamflow characteristically plotted on or below the Canadian Meteoric Water Line (CMWL) (δ2H = 8∙δ18O+8.5) along imbricated Regional River Lines (RRL) displaying a range of regression slopes (4.34–9.31) and intercepts (-54 to +24), reflecting regional variations in isotopic composition of input sources, evaporative enrichment, and tributary mixing. We define the Canadian Rivers Line (CRL) based on the linear regression of flow-weighted mean values of station data (δ2H = 7.89∙δ18O+0.45, r2 = 0.962; n = 161).

Oxygen-18 and deuterium analyses of water samples are provided from a regional survey of lakes, wetlands, soil waters, groundwaters, and snowpack samples collected in the Southern Athabasca Oil Sands (SAOS) region, Alberta, Canada, mainly during 2007–2009. Lake, wetland, and river sampling were conducted by helicopter during late summer, capturing conditions close to peak evaporative enrichment. Shallow soil water from the unsaturated zone was also collected in late summer, whereas deeper groundwaters from Quaternary aquifers, Quaternary channels, and uppermost Cretaceous strata, were collected primarily as part of winter drilling programs by industrial partners. Snowpack samples were collected in late March/early April, prior to significant spring melt. This dataset includes 1576 isotopic analyses made on 788 water samples as well as selected isotope mass balance model outputs (lake evaporation/inflow and water yield to lakes). These basic model data are provided to facilitate evaluation of the method as a tool for spatial mapping of water yield and its interannual variability. Details and further discussion on the isotope mass balance approach are provided in “Mapping water yield distribution across the southern Athabasca Oil Sands area: baseline surveys applying isotope mass balance of lakes” (Gibson et al., 2019). Overall, the data are expected to be useful, in comparison with local and regional datasets, for water resource management and planning, including design of monitoring networks and environmental impact assessments for oil sands projects.

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.

Study region This study was conducted within a 100,000 km2 area of British Columbia, (B.C.) Canada including Vancouver Island, the Georgia Basin, and the Pacific and Kitimat mountain ranges rising from the Pacific Ocean. Study focus A stable isotope mass balance method is applied to estimate evaporation loss and water yield from a remote network of 560 lakes on Vancouver Island and coastal B.C., based on helicopter sampling surveys conducted between 2008 and 2015. Spatial patterns in derived hydrological parameters are compared to water quality indicators and watershed characteristics to provide insight into water quantity and water quality relationships in the region, to be incorporated within a future critical loads assessment. New hydrological insights for the region Regional trends in lake water balance, underlying physical drivers, and geochemical processes potentially influencing critical loads of acidity are described. Dominant non-anthropogenic regional drivers of geochemistry include sea spray, lithology, weathering and elevation. Significant contrast is noted in alkalinity between the sedimentary and volcanic substrates on Vancouver Island and igneous intrusive substrates of the Pacific and Kitimat ranges. A positive correlation is found between elevation and water yield to lakes, while the opposite is observed for rivers, which is interpreted to reflect disconnection of low elevation lakes from regional drainage networks. This may invalidate use of river gauge data for critical loads assessment in this or similar regions.

Study region During 2013–2019, we conducted a Canada-wide program of streamflow sampling for the analysis of stable isotopic composition (18O/16O and 2H/1H), providing the first comprehensive survey for gauged watersheds across Canada ranging from 10 to 10,000 km2. A watershed-based assessment of vapour and runoff partitioning is presented for 103 watersheds across a diverse range of climate and land cover types, spanning 25° latitude and 86° longitude. Study focus An isotope-based methodology is applied to estimate evaporation/inflow (E/I) and transpiration/evapotranspiration (T/ET) utilizing offset between isotope values in streamflow and precipitation, augmented by regional climate reanalysis data. Isotopic enrichment in streamflow serves to differentiate direct, abiotic evaporation, mainly arising from open water evaporation from lakes and wetlands, from transpiration by natural vegetation and cropland, which has previously been recognized as principally non-fractionating. Sensitivity analysis suggests only a minor influence of interception losses on T/ET. New hydrological insights for the region Systematic variations in evaporation losses, transpiration losses and gauged runoff are revealed across the major hydrometric regions of Canada. Calculations suggest that E/I ranged from 2 to 60 %, while T/ET ranged from 25 to greater than 95 % across the watersheds. A new water loss classification is introduced which reveals that 19 of 103 watersheds were runoff-dominated, 54 were transpiration-dominated, 5 were evaporation-dominated, and 27 had more than one dominant water loss mechanism.

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.

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.

Study region: Surveys of stable isotopes of water in 50 boreal lakes were conducted during 2002–2017 as a component of Alberta’s Oil Sands acid sensitivity program in northeastern Alberta. Study focus: Using an isotope mass balance approach, watershed, climatic and isotopic data were applied to estimate evaporation losses and residence time of lakes, as well as to estimate water yield from watersheds. New hydrological insights for the region: Site-specific differences in water yield to 50 lakes over 16 years were found to be controlled by latitudinal gradients in climate, wetland type, lake/watershed configuration and permafrost. 19 plateau watersheds located northeast of Fort McMurray and in the Birch and Caribou Mountains which contained significant permafrost were found to have similar water yield to permafrost-poor watersheds if fen-dominated (159 mm/yr: n = 5 vs. 166 mm/yr; n = 31), and enhanced water yield (405 mm/yr; n = 14) if bog-dominated. Water yield was found to be systematically dependent on permafrost extent, yielding up to several hundred millimetres of additional runoff in bog-dominated systems. Temporal trend analysis indicates systemic momentum of change in hydrologic drivers over the 16-year period, although few are statistically significant. A new conceptual framework is proposed for classification of site-to-site permafrost thaw stage to improve water yield prediction, which is expected to influence lake water quality including observed pH increases noted previously for many lakes in the region. Keywords: Isotopes, Lakes, Water balance, Evaporation, Boreal, Bog, Fen, Permafrost thaw

Oxygen-18 and deuterium were measured in streamflow samples collected from 331 gauging stations across Canada during 2013 to 2019. This dataset includes 9206 isotopic analyses made on 4603 individual water samples, and an additional 1259 analysis repeats for quality assurance/quality control. We also include arithmetic and flow-weighted averages, and other basic statistics for stations where adequate data were available. Station data are provided including station code, name, province, latitude, longitude and drainage area. Flow data were extracted from the historical database of the Water Survey of Canada. Details on the preliminary application of these data are provided in “18O and 2H in streamflow across Canada” [1] . Overall, these data are expected to be useful when combined with precipitation datasets and analytical or numerical models for water resource management and planning, including tracing streamflow source, water balance, evapotranspiration partitioning, residence time analysis, and early detection of climate and land use changes in Canada.

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.

Study region: This study is based on the rapidly developing Athabasca Oil Sands region, northeastern Alberta. Study focus: Hydrograph separation using stable isotopes of water is applied to partition streamflow sources in the Athabasca River and its tributaries. Distinct isotopic labelling of snow, rain, groundwater and surface water are applied to estimate the contribution of these sources to streamflow from analysis of multi-year records of isotopes in streamflow. New hydrological insights for the region: The results provide new insight into runoff generation mechanisms operating in six tributaries and at four stations along the Athabasca River. Groundwater, found to be an important flow source at all stations, is the dominant component of the hydrograph in three tributaries (Steepbank R., Muskeg R., Firebag R.), accounting for 39–50% of annual streamflow. Surface water, mainly drainage from peatlands, is also found to be widely important, and dominant in three tributaries (Clearwater R., Mackay R., Ells R.), accounting for 45–81% of annual streamflow. Fairly limited contributions from direct precipitation illustrate that most snow and rain events result in indirect displacement of pre-event water by fill and spill mechanisms. Systematic shifts in regional groundwater to surface-water ratios are expected to be an important control on spatial and temporal distribution of water quality parameters and useful for evaluating the susceptibility of rivers to climate and development impacts. Keywords: Stable isotopes, Hydrograph separation, Groundwater, Surface water, Snowmelt, Oil sands

Widespread permafrost degradation in Canada's western Arctic has led to formation of shoreline retrogressive thaw slumps (SRTS), a process influential in modifying water and biogeochemical balances of tundra lakes. To investigate hydrological effects of SRTS, water sampling campaigns were conducted in 2004, 2005, and 2008 for paired lakes (undisturbed vs SRTS) in the upland region adjacent to the Mackenzie Delta, Northwest Territories, Canada. An isotope mass balance model to estimate evaporation/inflow, precipitation/inflow, water yield, and runoff ratio was developed incorporating seasonal evaporative drawdown effects and a mixing model to simulate gradients in marine-continental atmospheric moisture. Site-specific water balance results revealed systematically higher evaporation/inflow and precipitation/inflow for lakes with active SRTS compared to undisturbed lakes, and typically higher ratios of these indicators associated with stabilized versus active SRTS. Water yields were higher for active SRTS sites compared to undisturbed and stabilized SRTS sites, suggesting that slumping is an initial but not a sustained source of water delivery to lakes. Catchments with wildfire history were found to have lower water yields, attributed to reduced permafrost influence on runoff generation. Conceptually, we define a permafrost thaw trajectory whereby undisturbed sites, active SRTS, stabilized SRTS, and ancient SRTS represent progressive stages of permafrost thaw. We postulate that release of additional runoff is mainly due to permafrost thaw in active SRTS, which also promotes lake expansion, talik formation, and subsurface connectivity. Eventual stabilization of slumps and reduced runoff is expected once permafrost thaw sources are exhausted, at which time lakes may become more reliant on replenishment by direct precipitation. The effect of snow catch in slumps appears to be subordinate to permafrost thaw sources based on eventual decline in runoff once thaw slumps stabilize. Improved, site-specific hydrologic understanding is expected to assist with ongoing research into carbon cycling and biogeochemical feedbacks in the region.

Watershed data, climate and stable data collected over a 16-year period from a network of 50 lakes in northeastern Alberta, are provided to allow for broader incorporation into regional assessments of environmental impacts, particularly hydrologic and geochemical processes under changing climate and land use development. Oxygen-18 and deuterium analyses of water samples are provided from late summer surveys of 50 lakes with varying land cover and permafrost conditions. Six sub-groups of lakes are represented, including Stony Mountains, West Fort McMurray, Northeast Fort McMurray, Birch Mountains, Caribou Mountains and Shield. This dataset includes 1582 isotopic analyses made on 791 water samples and 3164 isotope mass balance model outputs, as well as 800 lake/watershed parameters, 5600 climate parameters, and 800 modelled values for isotopic composition of precipitation used in the computations. Model data are provided to facilitate evaluation of transferability of the model for other applications, and to permit more sophisticated spatial analysis and intercomparison with geochemical and biological datasets. Details and further discussion on the isotope mass balance approach are provided in “Regional trends in water balance and runoff to fifty boreal lakes: a 16-year isotope mass balance assessment including evaluation of hydrologic drivers” [1]. Overall, the data are expected to be useful, in comparison with local and regional datasets, for water resource management and planning, including design of monitoring networks and environmental impact assessments for oil sands projects. Keywords: Stable isotopes, Lakes, Water balance, Boreal wetlands, Oil sands environment, Permafrost thaw

Lakes are under increasing pressure due to widespread anthropogenic impacts related to rapid development and population growth. Accordingly, many lakes are currently undergoing a systematic decline in water quality. Recent studies have highlighted that global warming and the subsequent changes in water use may further exacerbate eutrophication in lakes. Lake evolution depends strongly on hydrologic balance, and therefore on groundwater connectivity. Groundwater also influences the sensitivity of lacustrine ecosystems to climate and environmental changes, and governs their resilience. Improved characterization of groundwater exchange with lakes is needed today for lake preservation, lake restoration, and sustainable management of lake water quality into the future. In this context, the aim of the present paper is to determine if the future evolution of the climate, the population, and the recharge could modify the geochemistry of lakes (mainly isotopic signature and quality via phosphorous load) and if the isotopic monitoring of lakes could be an efficient tool to highlight the variability of the water budget and quality. Small groundwater-connected lakes were chosen to simulate changes in water balance and water quality expected under future climate change scenarios, namely representative concentration pathways (RCPs) 4.5 and 8.5. Contemporary baseline conditions, including isotope mass balance and geochemical characteristics, were determined through an intensive field-based research program prior to the simulations. Results highlight that future lake geochemistry and isotopic composition trends will depend on four main parameters: location (and therefore climate conditions), lake catchment size (which impacts the intensity of the flux change), lake volume (which impacts the range of variation), and lake G index (i.e., the percentage of groundwater that makes up total lake inflows), the latter being the dominant control on water balance conditions, as revealed by the sensitivity of lake isotopic composition. Based on these model simulations, stable isotopes appear to be especially useful for detecting changes in recharge to lakes with a G index of between 50 and 80 %, but response is non-linear. Simulated monthly trends reveal that evolution of annual lake isotopic composition can be dampened by opposing monthly recharge fluctuations. It is also shown that changes in water quality in groundwater-connected lakes depend significantly on lake location and on the intensity of recharge change.

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.

Here we examine the arrangement of plant species across an oligotrophic bog/poor fen peatland complex in the North American boreal plain and the relationships of these species to their physical and chemical environment. A semi-uniform spatial sampling approach was utilized to describe the species assemblages, pore-water chemistry and physical condition of 100 plots throughout a single peatland complex. Regardless of sharing the same ground cover of Sphagnum mosses, the remaining species separated into four distinct assemblages, each with unique indicators. These species groups along with associated chemical and physical factors are organized into four ecosites: bog, margin (edge) and two poor fen ecosites. The plant assemblages of this peatland have a complex relationship with numerous gradients, both physical and chemical, including depth to water table, shade, pH, nutrient and base cation. Rather than being homogenous across the landscape, most environmental variables exhibit distinct spatial patterns and do so in relationship to the plant assemblages, forming spatially distinct ecosites across the complex. Base cation concentrations play a smaller role than previously thought in differentiating these ecosites, and in addition to shade and depth to water table, nitrogen in the form of dissolved organic nitrogen was highly related to the placement of these ecosites. Many significant chemical factors appear related to evaporative water loss within the peatland complex, and these chemical factors are used to differentiate the ecosites. However, the mediation of evaporative water loss is due largely to self-generated responses of the plant assemblages related to shade through plant morphology and peat acrotelm development related to depth to water table. We conclude that plant species and associated environmental gradients act together to form spatially distinct ecosites. The distribution of these ecosites within this large, environmentally complex peatland is largely controlled by differing self-generated responses along the hydrotopographical gradient of differential water loss.

Tritium concentrations were measured in a survey of 24 lakes, 15 wetlands, and 133 groundwaters in the oil sands region of northeastern Alberta and compared with both recent precipitation and precipitation sampled during the 1960s tritium peak caused by atmospheric thermonuclear weapons testing. Water samples from lakes included a group of 14 thaw lakes that had higher runoff attributed to melting of permafrost in peat plateaus within their watersheds. While tritium in all lakes was found to be intermediate between recent and 1960s concentrations, the thaw lakes were found to be significantly enriched in tritium compared with other lakes, as were unfrozen wetlands characterized by a thick sequence of low-hydraulic conductivity peat. The results provide further evidence of different water sources to the thaw lakes and may indicate that melting of modern permafrost in part formed since the 1950s is occurring in these systems. Copyright © 2015 John Wiley & Sons, Ltd.

article i nfo This study was conducted to characterize the composition of dissolved organic compounds present in snow and surface waters in the Athabasca Oil Sands Region (AOSR) with the goal of identifying whether atmospherically- derived organic compounds present in snow are a significant contributor to the compounds detected in surface waters (i.e., rivers and lakes). We used electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) to characterize the dissolved organic compound compositions of snow and surface water samples. The organic profiles obtained for the snow samples show compositional differences between samples from near-field sites (b5 km from oil sands activities) and those from more distant locations (i.e., far- field sites). There are also significant compositional differences between samples collected in near-field sites and surface water samples in the AOSR. The composition of dissolved organic compounds at the upstream Ath- abasca River site (i.e., Athabasca River at Athabasca) is found to be different from samples obtained from down- stream sites in the vicinity of oil sands operations (i.e., Athabasca River at Fort McMurray and Athabasca River at Firebag confluence). The upstream Athabasca River sites tended to share some compositional similarities with far-field snow deposition, while the downstream Athabasca River sites are more similar to local lakes and tribu- taries. Thiscontrast likelyindicatesthe relative role of regional snowmelt contributions to the Athabasca River vs inputs from local catchments in the reach downstream of Fort McMurray.

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.

Understanding and characterizing organics in aquatic environments is a great challenge for environmental monitoring, especially for the oil sands industry due to the complexity and potential toxicity of dissolved organics in water. To date, significant efforts have been made in investigating the toxicity of naphthenic acids, although other compounds may also contribute to the toxicity of oil sands process-affected water (OSPW). Here, we present a case study showing a systematic approach for profiling the organic composition of OSPW and environmental water samples by concentrating and separating dissolved organics through complementary liquid–liquid extractions followed by positive- or negative-ion mode ultrahigh resolution mass detection. Our comparative investigation shows clear differences in the composition of dissolved organics (homologues particularly) not only between OSPW samples and environmental water samples, but also differences among oil sands operators. Sulfur-containing compounds (especially the SO n classes) appear to have great potential to be used for evaluating the impact of OSPW, while our understanding of oxygen-only containing compounds should not be limited to O2 (i.e., classic naphthenic acids), but rather can be broadened to include many other compound classes (for instance O n , n = 1–9). Systematic profiling of water samples should be more widely implemented for monitoring the origin and transport of organics in aquatic ecosystems of the oil sands development region, northeastern Alberta, Canada.

The composition of polycyclic aromatic hydrocarbons present in snow and surface waters in the Athabasca Oil Sands Region (AOSR) was characterized in order to identify major contributors to the organics detected in rivers and lakes in the region. PAH concentrations, measured by three monitoring programs in 2011, were used to compare the PAH compositions of snow and surface waters across the AOSR. The 2011 dataset includes total (dissolved + particulate) concentrations of thirty-four parent and alkylated PAH compounds in 105 snow, 272 river, and 3 lake samples. The concentration of PAHs in rivers varies seasonally, with the highest values observed in July. The timing of increases in PAH concentrations in rivers coincides with the high river discharge during the spring freshet, indicating that this major hydrological event may play an important role in delivering PAHs to rivers. However, the composition of PAHs present in rivers during this period differs from the composition of PAHs present in snow, suggesting that direct runoff and release of PAHs accumulated on snow may not be the major source of PAHs to the Athabasca River and its tributaries. Instead, snowmelt may contribute indirectly to increases in PAHs due to hydrological processes such as erosion of stream channels, remobilization of PAH-containing sediments, increased catchment runoff, and snowmelt-induced groundwater inputs during this dynamic hydrologic period. Better understanding of transformations of PAH profiles during transport along surface and subsurface flow paths in wetland-dominated boreal catchments would improve identification of potential sources and pathways in the region. The compositional differences highlight the challenges in identifying the origins of PAHs in a region with multiple potential natural and anthropogenic sources particularly when the potential transport pathways include air, soil and water.

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.

It is well accepted that the breakage of wastewater suspended particles (flocs) can lead to better disinfection of effluent, especially when utilizing ultraviolet irradiation as the disinfection method. In this work, the breakage of wastewater flocs in orifice flow was investigated through numerical simulations. The strain rate along particle paths was estimated using computational fluid dynamics. Assuming that particle breakage occurs if the maximum strain rate experienced by the particle exceeds a critical threshold value, breakage of wastewater particles was predicted. The effectiveness of the model was supported by simple experiments. Based on the numerical simulations, under the same nominal orifice strain rate, particle breakage was higher in single-orifice systems compared to that of multi-orifice systems. This finding was further confirmed through experimentation. Furthermore, simulation results revealed that while single-orifice systems were the preferred choice for the breakage of strong particles, multi-orifice systems might be more effective in breaking ‘weak’ particles.

We used water d2H and d18O from ca. 1000 lakes sampled in the 2007 U.S. Environmental Protection Agency’s National Lakes Assessment (NLA) to assess two hydrological variables—evaporation as a percentage of inflow (E:I) and water residence time (t) for summer 2007. Using a population survey design, sampled lakes were distributed across the conterminous U.S., and results were scaled to the inference population (,50,000 U.S. lakes). These hydrologic variables were related to lake nutrients and biological condition to illustrate their usefulness in national water quality monitoring efforts. For 50% of lakes, evaporation was , 25% of inflow, with values ranging up to 113% during the 2007 summer. Residence time was , 0.52 yr for half of the lakes and , 1.12 yr for 75% of lakes. Categorizing lakes by flow regime, 66.1% of lakes were flow-though lakes (60% or more of the water flows through the lake, E:I , 0.4), 33.6% were restricted-basin lakes (40% or more of the lake inflow evaporates, 0.4 , E:I , 1), and , 0.3% were closed basin (all water entering the lake leaves through evaporation, E:I . 1). While climate patterns drove some of the spatial patterns of E:I and t, variation in lake depth and watershed size (influencing precipitation volume) were also significant drivers. Lake hydrochemistry was strongly correlated to E:I and more weakly related to t. Lakes in poor biological condition (based on a predictive model of planktonic taxa) were significantly more evaporated than lakes in good biological condition.

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.

Given increasing anthropogenic and climatic pressures on water resources, groundwater and surface water need to be better managed and preserved. As these two water stocks can be connected to each other, their evolutions are linked and need to be considered as such. However, interactions between lakes and groundwater are not well understood and, most of the time, are not taken into account. Therefore, establishing a comprehensive approach to quantify groundwater and lakes’ hydrogeochemical interactions in various settings is of foremost importance for assessing the sensitivity of lakes to groundwater evolution. In this study, small kettle lakes set in fluvioglacial deposits and that are most likely well connected to shallow unconfined aquifers are specifically targeted. Geochemistry and isotopic results highlight that groundwater flux to the lakes is generally the dominant parameter of the lake water budget. The 222Rn results in particular suggest that 38% of the studied lakes have a high proportion of groundwater in their balances. It appears that the different tracers are complementary: geochemistry is influenced by groundwater inflows, reflecting its quality and the local geology, whereas water stable isotopes correspond directly to the volumetric lake water budget, and both of these tracers are impacted by in-lake processes. Moreover, the third tracer considered, 222Rn, highlights the location of groundwater inputs in space and time. Finally, the studied kettle lakes are characterized by a short to medium flushing time by groundwater. As a result, these lakes can be highly sensitive to environmental and climate changes affecting groundwater.