Article

Site-specific estimates of water yield applied in regional acid sensitivity surveys across western Canada

Authors:
  • InnoTech Alberta
  • InnoTech Alberta (and University of Calgary)
  • Government of Canada, Department of Environment and Climate Change, Burlington, ON, Canada
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Runoff or water yield is an important input to the Steady-State Water Chemistry (SSWC) model for estimating critical loads of acidity. Herein, we present site-specific water yield estimates for a large number of lakes (779) across three provinces of western Canada (Manitoba, Saskatchewan, and British Columbia) using an isotope mass balance (IMB) approach. We explore the impact of applying site-specific hydrology as compared to use of regional runoff estimates derived from gridded datasets in assessing critical loads of acidity to these lakes. In general, the average water yield derived from IMB is similar to the long-term average runoff; however, IMB results suggest a much larger range in hydrological settings of the lakes, attributed to spatial heterogeneity in watershed characteristics and landcover. The comparison of critical loads estimates from the two methods suggests that use of average regional runoff data in the SSWC model may overestimate critical loads for the majority of lakes due to systematic skewness in the actual runoff distributions. Implications for use of site-specific hydrology in regional critical loads assessments across western Canada are discussed.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The method has been successful in characterizing hydrology because of systematic isotopic enrichment that occurs in lakes, largely in response to the amount of lake evaporation compared with throughflow generated from the landscape or connected streams. Recent application of the method has focused in part on developing a better understanding of hydrology in the boreal plains region of Alberta in close proximity to oil sands development (Bennett et al., 2008;Jeffries et al., 2010;Schmidt et al., 2010;Scott et al., 2010;Gibson et al., 2010aGibson et al., ,2010b). Short-term water yields have been compared with interpolated runoff from the Water Survey of Canada hydrometric gauging network for this area (Bennett et al., 2008), critical loads of acidity have been evaluated based on longer-term interannual datasets (Gibson et al., 2010a(Gibson et al., ,2010b and radon-222 has also been applied to examine the fraction of water yield that is derived from subsurface flowpaths for selected lakes (Schmidt et al., 2010). ...
... Recent application of the method has focused in part on developing a better understanding of hydrology in the boreal plains region of Alberta in close proximity to oil sands development (Bennett et al., 2008;Jeffries et al., 2010;Schmidt et al., 2010;Scott et al., 2010;Gibson et al., 2010aGibson et al., ,2010b). Short-term water yields have been compared with interpolated runoff from the Water Survey of Canada hydrometric gauging network for this area (Bennett et al., 2008), critical loads of acidity have been evaluated based on longer-term interannual datasets (Gibson et al., 2010a(Gibson et al., ,2010b and radon-222 has also been applied to examine the fraction of water yield that is derived from subsurface flowpaths for selected lakes (Schmidt et al., 2010). While hydrological conditions in the region have been described, relatively few conclusions have previously been made about the mechanisms that control runoff and water yield. ...
... The lakes are situated in headwater catchments and range in size from small, shallow ponds (1-m depth, <0.5 km 2 ) to large lakes (30-m depth, 0.43 km 2 ; Bennett et al., 2008). They also vary by latitude, morphometry and associated landscape (Gibson et al., 2010a). Lakes north of Lake Athabasca are underlain at shallow depth by Canadian Shield with a thin mantle of Quaternary deposits. ...
Full-text available
Article
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 nine-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 to more northerly sites in the Birch Mountains, Caribou Mountains and northeast of Fort McMurray, due mainly to 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. This article is protected by copyright. All rights reserved.
... First, runoff is needed to convert concentrations into chemical fluxes. Here we used lake specific runoff values estimated by Gibson et al. (2010, ...
... This has also been the case in Canada (e.g., Henriksen et al. 2002; WRS 2004; Dupont et al. 2005; Jeffries & Ouimet 2005). However, we have employed two modifications that distinguish its use here from those previous applications , namely consideration of the influence of DOC through the use of the Lydersen et al. (2004) equation to calculate ANC limit , and substitution of lake-by-lake values for runoff derived using the IMB Model (Gibson et al. 2010, this issue) for long-term regional runoff values . This runoff substitution applied to both our survey lakes and those of SK ENV. ...
... The influence of substituting IMB runoff values for long-term regional values has been evaluated by Gibson et al. (2010, ...
Full-text available
Article
Impacts of sulphur and nitrogen deposition in western Canada J. Limnol., 69(Suppl. 1): 45-55, 2010 -DOI: 10.3274/JL10-69-S1-06 ABSTRACT Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskatchewan (SK) have long been considered unaffected by acid rain. However, emissions of acidifying pollutants from MB smelters and oil sand processing in Alberta (AB) may pose a developing threat. Surveys of 347 lakes located on geologically sensitive terrain in northern MB and SK were conducted to assess their acidification sensitivity and status. The survey domain (~193,000 km 2) contained 81,494 lakes ≥1 ha in area. Small lakes dominated the inventory in terms of numbers, and large lakes dominated in terms of area. Survey lakes were selected using a stratified-random sampling design in 10 sampling blocks within the overall survey domain. Few lakes had pH <6, and only three (all in SK) were acidic, i.e., Gran Alkalinity (Alk) <0 μeq L –1 . A broad range in lake sensitivity was apparent, and very sensitive lakes (low specific conductance, base cations and Alk) were present in all sampling blocks. Dissolved organic carbon (DOC) was an important constituent of many lakes. Critical loads (CL) of acidity calculated using the Steady-State Water Chemistry model (SSWC) revealed extremely low 5th percentile values for every block (range 1.9 to 52.7 eq ha –1 y –1). Block CL exceedances calculated using estimated S and N deposition for 2002 ranged from 54.5 to 909 eq ha –1 y –1 . The largest exceedances were for sampling blocks located near smelter sources or downwind of the oil sands. Lake chemistry revealed by our surveys was compared to others conducted both nearby and outside Canada.
... Site-specific hydrology was characterized using an isotope mass balance (IMB) model developed under the assumption of a well-mixed water body and steady-state conditions, which has been demonstrated previously for shallow lakes in northern Canada (Gibson et al., , 2010a(Gibson et al., ,b, 2015aBennett et al., 2008). The IMB is used to estimate evaporation/inflow based on the isotopic offset between the evaporatively enriched lake water compared to precipitation input. ...
... In general, stratified-randomly selected lake surveys across Canada have revealed negativelyskewed to normal distributions of  18 O and  2 H, but commonly with positively-skewed distributions of evaporation/inflow and water yield (Gibson et al., 2010a;Gibson et al., 2015a). Brooks et al. (2014) show negatively skewed  18 O and  2 H and positively skewed E/I for lakes sampled across the contiguous United States. ...
Article
Stable isotopes of water, oxygen-18 and deuterium, were measured in water samples collected from a network of 300 lakes sampled in six ∼100 km² 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.
... Further, because land-management decisions in agricultural regions are intrinsically linked to system function, there is a need for classifications that can inform decision-makers at a relevant scale. Indeed, stable isotope-based investigations of runoff from small lake catchments in the Boreal Plains (north of the Prairie) emphasize the need for local-scale characterization of watershed behaviour (Gibson et al., 2010(Gibson et al., , 2016, while streamflow dynamics for the Prairie and nearby Boreal Plain are linked to local surface geology and land cover (Devito et al., 2005;Mwale et al., 2011), suggesting an opportunity for a new approach to watershed classification in the region. Another potential advantage of a more comprehensive approach is that by de-emphasizing available hydrometric observations for larger and well-studied or monitored basins and including other environmental characteristics, the risk of overlooking other functions (e.g., ecology, biogeochemistry) that may be equally important to the management of a watershed's natural resources can be reduced. ...
Full-text available
Article
Classification and clustering approaches provide a means to group watersheds according to similar attributes, functions, or behaviours, and can aid in managing natural resources. Although they are widely used, approaches based on hydrological response parameters restrict analyses to regions where well-developed hydrological records exist, and overlook factors contributing to other management concerns, including biogeochemistry and ecology. In the Canadian Prairie, hydrometric gauging is sparse and often seasonal. Moreover, large areas are endorheic and the landscape is highly modified by human activity, complicating classification based solely on hydrological parameters. We compiled climate, geological, topographical, and land-cover data from the Prairie and conducted a classification of watersheds using a hierarchical clustering of principal components. Seven classes were identified based on the clustering of watersheds, including those distinguishing southern Manitoba, the pothole region, river valleys, and grasslands. Important defining variables were climate, elevation, surficial geology, wetland distribution, and land cover. In particular, three classes occur almost exclusively within regions that tend not to contribute to major river systems, and collectively encompass the majority of the study area. The gross difference in key characteristics across the classes suggests that future water management and climate change may carry with them heterogeneous sets of implications for water security across the Prairie. This emphasizes the importance of developing management strategies that target sub-regions expected to behave coherently as current human-induced changes to the landscape will affect how watersheds react to change. The study provides the first classification of watersheds within the Prairie based on climatic and biophysical attributes, with the framework used being applicable to other regions where hydrometric data are sparse. Our findings provide a foundation for addressing questions related to hydrological, biogeochemical, and ecological behaviours at a regional level, enhancing the capacity to address issues of water security.
... Water yields for each yearly survey and for the entire dataset reveal positively skewed distributions in all cases (Fig. 7). Similar skewness has been observed in previous surveys in continental Canada (Gibson et al., 2010a, 2010b, 2015b, 2017. Overall, water yield was found to range from near zero to 5000 mm yr −1 , averaging 656 mm with a standard deviation of 884 mm. ...
Article
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.
... Catchmentspecific (Q imb ) estimates, while often diverging widely from regional estimates of Q (e.g. Q grid ), are understood to be the more reliable estimate (Bennett et al., 2008;Gibson et al., 2010). Nonetheless, while Q imb estimates were available for the study catchments they could not be used with confidence for all lakes. ...
Full-text available
Article
Acid-sensitive ecosystems are found in northern Saskatchewan, which lies downwind of major sulphur (S) and nitrogen (N) emissions sources associated with the oil sands extraction industry. In order to protect these ecosystems against acidification, tolerance to acid deposition must be quantified. The suitability of the central empirical relationship used in the Steady-State Water Chemistry (SSWC) model to predict historical sulphate (SO4) concentrations was investigated, and an alternate approach for determining aquatic critical loads of acidity (CL(A)) was employed for the study lakes (n = 260). Critical loads of acidity were often low, with median values of 12–16 mmolc m−2 yr−1, with the lower value reflecting a region-specific limit for acid-neutralizing capacity identified in this study. Uncertain levels of atmospheric deposition in the region, however, are problematic for characterizing acidification risk. Accurate S and chloride (Cl) deposition are needed to identify catchment sources (and sinks) of these elements in the new approach for CL(A) calculation. Likewise, accurate depiction of atmospheric deposition levels can prove useful for evaluation of lake runoff estimates on which estimates of CL(A) are contingent. While CL(A) are low and exceedance may occur according to projected increases in S deposition in the near-term, S retention appears to be an important feature in many catchments and risk of acidification may be overstated should long-term S retention be occurring in peatlands.
... A comparable evaporation line is estimated from regression of a recent lakewater dataset compiled for the adjacent Athabasca Oil Sands region between 56 and 59 • N, but with a slightly lower ␦ 2 H intercept (ı 2 H = 5.20ı 18 O − 50.6; see Gibson et al., 2015a). Similar evaporation lines have also been reported for lake surveys in nearby Manitoba and Saskatchewan (Gibson et al., 2010b). ...
Article
Study region: This study spans the Prairie/parkland/boreal transition in central Alberta, including lakes in the Athabasca, North Saskatchewan, Battle River and Red Deer Basins. Study focus: Stable isotopes of water, oxygen-18 and deuterium, were measured in a network of 50 lakes during 2008 and 2009. The lakes are the subject of recent concern due to widespread lake level decline and development of eutrophic conditions that have been attributed to climate and land-use impacts. An isotope mass balance method was applied to estimate evaporation/inflow, water yield, and water residence times to assess relationships between water balance and lake status. New hydrological insights: Water yield was found to range from near 0 to 235 mm, evaporation/inflow was found to range from 18 to 136 %, and water residence time ranged from 2.3 to 58 years. The healthiest lakes in terms of trophic status are deep lakes with smaller catchments with long residence times. These lakes may have stable or variable water levels. Distressed lakes are often shallow prairie lakes with limited inflow and shorter residence times, and situated in areas with higher evaporation rates. High conductivity and high sulfate in some eutrophic lakes, attributed to saline groundwater inflow, may inhibit algae and cyanobacterial growth, thereby promoting healthier conditions. Extended drought under climate warming is expected to cause eventual decline of water levels in a greater number of lakes.
... During the warm season, the maximum depths of TL-A and TL-B are approximately 0.8 m and 0.6 m, respectively. They are both classified as shallow lakes, wellmixed, and unstratified (Gibson et al., 2010;Gibson and Reid, 2014). Lake TL-A, is located on a flatland covered by sparse desert steppe, and is a perennially system-closed lake with only minor surface runoff inflow. ...
Article
Considering the widespread distribution of thermokarst lakes and their significant influence on the hydrological cycle in permafrost regions on the Qinghai-Tibet Plateau (QTP), it is necessary to study their hydrological regimes, which are responding to ongoing climate-induced permafrost thaw. In this paper, water isotopic tracers were used to assess the temporal and interannual hydrological variations and the hydrological processes of two thermokarst lakes (TL-A and TL-B) associated with thawing permafrost in Beiluhe Basin on the QTP. The isotopic results revealed significant differences between the two thermokarst lakes: the TL-A showed more positive isotopic values and small fluctuations than TL-B did. This can be attributed to the hydrological discrepancies between them. Based on the water isotopic mass balance (IMB) model and estimated evaporation, the contributions of permafrost melt water and precipitation to the thermokarst lakes were determined. In both 2011 and 2012, the contributions of thawing permafrost water to thermokarst lakes were of significance, as high as 61.3%. The modeled isotopic composition of input water (δI), and the relationships between climatic factors and lake water isotopes were evaluated. Results suggested that the two lakes originated from multiple sources and confirmed the modeling process well. It also indicated that thawing of permafrost significantly affected the development and hydrological regime of thermokarst lakes on the QTP. It is necessary to emphasize the significant impact of thawing permafrost on the thermokarst lakes on the QTP. Findings demonstrate that ongoing permafrost thaw may have major implications for thermokarst landscapes as climate change continues.
Preprint
Gibson, J.J., Barbour, S.L., Bursey, G.G., Isotopic constraints on surface and subsurface water sources and water balance at mine sites. In: Advances in Mine Waste Characterisation, Engineering and Management: A sustainable approach towards mine closure and rehabilitation, A. Parbhakar-Fox, M. Lindsay, M.Moncur, Eds., Springer, in press. Stable isotopes of water (18 O and 2 H) and tritium (3 H) are demonstrated to be useful for characterizing both water sources and water balance at mine sites including origin of water entering underground workings as well as water balance of various mine water circuits including active or inactive tailings ponds, tailings deposits, waste-rock piles, mine pit lakes, and cooling towers. Isotopic data are shown to be valuable and complimentary to physical and geochemical information for assessment of hydrological processes at mine sites, particularly in remote or sparsely monitored regions where basic hydrometric data are limited. Case studies from a decommissioned underground Canadian Shield gold mine, the Giant Mine, located in Yellowknife, Northwest Territories, and an active Oil Sands open-pit surface mine, Mildred Lake, located near Fort McMurray, Alberta, are included to illustrate the potential of the method in typical applications. For the Giant Mine, isotopic variations in sumps and drains at various levels within the mine workings in combination with flow data were used to estimate and map the proportion of water entering from six main sources. These included shallow groundwater derived from recharge of modern precipitation, recharge from natural water bodies and tailings ponds, leakage of the mine water supply, and deep groundwater derived from either precipitation or from shield brines. For the Mildred Lake site, water budgets can be estimated based on systematic evaporative enrichment in active tailings ponds, although it is interesting to note that distinct enrichment patterns are found compared to natural systems in the region as a consequence of mixing between input sources and various mine circuit waters. Notably, cooling tower blowdown is uniquely labelled due to evaporation at relative humidity close to 100%. Other mine circuit waters plotting above the meteoric water line are apparently influenced by H2S exchange. For complex, disturbed areas, quantification of water balance remains useful for estimating evaporation losses, and for constraining water fluxes including seepage. Tailings deposits and waste rock piles also acquire isotopic signatures reflecting water balance conditions during deposition or post-deposition.
Full-text available
Article
Stable isotopic compositions of lake water provide additional information on hydrological, meteorological and paleoclimate processes. In this study, lake water isotopic compositions were measured for more than three years in Lake Taihu, a large and shallow lake in southern China, to investigate the isotopic spatial and seasonal variations. The results indicated that (1) the whole-lake mean δ2H and δ18O values of the lake water varied seasonally from −48.4 ± 5.8 to −25.1 ± 3.2 ‰ and from −6.5 ± 0.9 to −3.5 ± 0.8 ‰, respectively, (2) the spatial pattern of the lake water isotopic compositions was controlled by the direction of water flow and not by local evaporation rate, and (3) using a one-site isotopic measurement to represent the whole-lake mean may result in unreasonable estimates of the isotopic composition of lake evaporation and the lake water residence time in poorly mixed lakes. The original data, documented here as an online supplement, provides a good reference for testing sensitivity of lake water budget to various isotopic sampling strategies. We propose that detailed spatial measurement of lake water isotopic compositions provides a good proxy for water movement and pollutant and alga transports, especially over big lakes.
Full-text available
Article
The expansion of transportation sectors (road vehicles and marine vessels), industry (e.g., oil and gas) and urban centres in western Canada has triggered a growth in research, monitoring and modelling activities investigating the impacts of sulphur and nitrogen deposition On aquatic and terrestrial ecosystems. This special issue presents an overview of related research in British Columbia (Georgia Basin), Alberta (Athabasca Oil Sands Region), Saskatchewan and Manitoba. The research provides a valuable benchmark for future studies across the region awl points the way forward Jar acid rain policies in western Canada.
Article
Abstract The long-term influence of a shallow water cover limiting sulfide-mineral oxidation was examined in tailings deposited near the end of operation in 1951 of the former Sherritt-Gordon Zn-Cu mine (Sherridon, Manitoba, Canada). Surface-water, pore-water and core samples were collected in 2001 and 2009 from above and within tailings deposited into a natural lake. Mineralogical and geochemical characterization focused on two contrasting areas of this deposit: (i) sub-aerial tailings with the water table positioned at a depth of approximately 50 cm; and (ii) sub-aqueous tailings stored under a 100 cm water cover. Mineralogical analyses of the sub-aerial tailings showed a zone of extensive sulfide-mineral alteration extending 40 cm below the tailings surface. Moderate alteration was observed at depths ranging from 40–60 cm and was limited to depths > 60 cm. In contrast, sulfide-mineral alteration within the submerged tailings was confined to a < 6 cm thick zone located immediately below the water-tailings interface. This narrow zone exhibited minimal sulfide-mineral alteration relative to the sub-aerial tailings. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy showed results that were consistent with the mineralogical investigation. Pore-water within the upper 40 cm of the sub-aerial tailings was characterized by low pH (1.9-4.2), depleted alkalinity, and elevated SO4 and metal concentrations. Most-probable number (MPN) enumerations revealed abundant populations of acidophilic sulfur-oxidizing bacteria within these tailings. Conversely, pore-water in the sub-aqueous tailings was characterized by near-neutral pH, moderate alkalinity, and relatively low concentrations of dissolved SO4 and metals. These tailings exhibited signs of dissimilatory sulfate reduction (DSR) including elevated populations of sulfate reducing bacteria (SRB), elevated pore-water H2S concentrations, and strong δ34S-SO4 and δ13C-DIC fractionation. Additionally, mineralogical investigation revealed the presence of secondary coatings on primary sulfide minerals, which may serve as a control on metal mobility within the sub-aqueous tailings. Results from this study provide critical long-term information on the viability of sub-aqueous tailings disposal as a long-term approach for managing sulfide-mineral oxidation.
Full-text available
Article
There has been growing interest in acid rain research in western Canada where sulphur (S) and nitrogen (N) emissions are expected to increase during the next two decades. One region of concern is southern British Columbia, specifically the Georgia Basin, where emissions are expected to increase owing to the expansion of industry and urban centres (Vancouver and Victoria). In the current study, weathering rates and critical loads of acidity (S and N) for forest soils were estimated at nineteen sites located within the Georgia Basin. A base cation to aluminium ratio of 10 was selected as the critical chemical criterion associated with ecosystem damage. The majority of the sites (58%) had low base cation weathering rates (≤50 meq m-2 y-1) based on the PROFILE model. Accordingly, mean critical load for the study sites, estimated using the steady-state mass balance model, ranged between 129-168 meq m-2 y-1. Annual average total (wet and dry) S and N deposition during the period 2005-2006 (estimated by the Community Multiscale Air Quality model), exceeded critical load at five-nine of the study sites (mean exceedance = 32-46 meq m-2 y-1). The high-elevation (>1000 m) study sites had shallow, acid sensitive, soils with low weathering rates; however, critical loads were predominantly exceeded at sites close to Vancouver under higher modelled deposition loads. The extent of exceedance is similar to other industrial regions in western and eastern Canada.
Full-text available
Article
Boreal ecosystems in northwest Saskatchewan may be threatened by acidification as this area is downwind of atmospheric emissions sources from regional oil sands mining operations. To evaluate the status of lakes in this region, a survey of 259 headwater lakes was conducted during 2007–2008 within ~300 km of Fort McMurray, Alberta. Acid sensitivity by ecoregion increased from Mid-Boreal Upland to Churchill River Upland to Athabasca Plain, with 60% of lakes classified as sensitive (50–200 μeq L–1 acid neutralizing capacity (ANC)), and 8% as very sensitive (<50 μeq L–1 ANC) to acid deposition. Organic anions dominated the acidity balance in most lakes, but non-marine sulphate varied positively with lake elevation and % upland cover (r2 = 0.24). Base cation concentrations (Ca, Mg, K, Na) were correlated with % deciduous forest in the catchment area (r2 = 0.33), while dissolved organic carbon (DOC) was related most strongly to % bog and lake flushing variables (r2 = 0.53). Variation in runoff coefficients derived by isotope mass balance corresponded with catchment area attributes that proxy controls on evaporation, infiltration and storage, and showed some ecoregional differences. The findings have implications for assignment of runoff values required to calculate critical loads of acidity. Although acidification appears not to be significantly advanced, many dilute oligotrophic lakes with pH 6.0 to pH 6.5 are vulnerable to acid deposition.
Full-text available
Article
Stable isotopes of water were applied to estimate water yield to fifty lakes in northeastern Alberta as part of an acid sensitivity study underway since 2002 in the Athabasca Oil Sands Region (AOSR). Herein, we apply site-specific water yields for each lake to calculate critical loads of acidity using water chemistry data and a steady-state water chemistry model. The main goal of this research was to improve site-specific critical load estimates and to understand the sensitivity to hydrologic variability across a Boreal Plains region under significant oil sands development pressure. Overall, catchment water yields were found to vary significantly over the seven year monitoring period, with distinct variations among lakes and between different regions, overprinted by inter-annual climate-driven shifts. Analysis of critical load estimates based on site-specific water yields suggests that caution must be applied to establish hydrologic conditions and define extremes at specific sites in order to protect more sensitive ecosystems. In general, lakes with low (high) water yield tended to be more (less) acid sensitive but were typically less (more) affected by inter-annual hydrological variations. While it has been customary to use long-term water yields to define a static critical load for lakes, we find that spatial and temporal variability in water yield may limit effectiveness of this type of assessment in areas of the Boreal Plain characterized by heterogeneous runoff and without a long-term lake-gauging network. Implications for predicting acidification risk are discussed for the AOSR.
Full-text available
Article
Boreal ecosystems in northwest Saskatchewan may be threatened by acidification as this area is downwind of atmospheric emissions sources from regional oil sands mining operations. To evaluate the status of lakes in this region, a survey of 259 headwater lakes was conducted during 2007–2008 within ~300 km of Fort McMurray, Alberta. Acid sensitivity by ecoregion increased from Mid-Boreal Upland to Churchill River Upland to Athabasca Plain, with 60% of lakes classified as sensitive (50–200 μeq L–1 acid neutralizing capacity (ANC)), and 8% as very sensitive (<50 μeq L–1 ANC) to acid deposition. Organic anions dominated the acidity balance in most lakes, but non-marine sulphate varied positively with lake elevation and % upland cover (r2 = 0.24). Base cation concentrations (Ca, Mg, K, Na) were correlated with % deciduous forest in the catchment area (r2 = 0.33), while dissolved organic carbon (DOC) was related most strongly to % bog and lake flushing variables (r2 = 0.53). Variation in runoff coefficients derived by isotope mass balance corresponded with catchment area attributes that proxy controls on evaporation, infiltration and storage, and showed some ecoregional differences. The findings have implications for assignment of runoff values required to calculate critical loads of acidity. Although acidification appears not to be significantly advanced, many dilute oligotrophic lakes with pH 6.0 to pH 6.5 are vulnerable to acid deposition.
Full-text available
Article
Global trends in the δ2H-δ18O enrichment slope of continental lakes and shallow soil water undergoing natural evaporation are predicted on the basis of a steady state isotope balance model using basic monthly climate data (i.e., temperature and humidity), isotopes in precipitation data, and a simple equilibrium liquid-vapor model to estimate isotopes in atmospheric moisture. The approach, which demonstrates the extension of well-known conceptual models in stable isotope hydrology to the global scale, is intended to serve as a baseline reference for evaluating field-based isotope measurements of vapor, surface water, and soil water and as a diagnostic tool for more complex ecosystem models, including isotope-equipped climate models. Our simulations reproduce the observed local evaporation line slopes (4–5 range for lakes and 2–3 range for soil water) for South America, Africa, Australia, and Europe. A systematic increase in slopes (5–8 range for lakes) toward the high latitudes is also predicted for lakes and soil water in northern North America, Asia, and Antarctica illustrating a latitudinal (mainly seasonality-related) control on the evaporation signals that has not been widely reported. The over-riding control on the poleward steepening of the local evaporation lines is found to be the isotopic separation between evaporation-flux-weighted atmospheric moisture and annual precipitation, and to lesser extents temperature and humidity, all of which are influenced by enhanced seasonality in cold regions.
Full-text available
Article
Critical loads of acidity and the amount by which these critical loads are exceeded by atmospheric deposition (termed "exceedances") were estimated for 1469 lakes from five regions in south-central Ontario, Canada, using single lake chemistry measurements and sulphur deposition data for the period 1976-1999. Based on the Steady-State Water Chemistry (SSWC) model, four of the five regions had low critical loads, which is consistent with the underlying geology (silicate bedrock) and the thin glacial soils in these regions. Sulphur deposition in the study area showed a clear downward trend over the time period, with a decrease of approximately 50% to current levels of approximately 44 meq.m(-2).year(-1). As a result of the declining deposition, the portion of lakes with critical load exceedances has dropped substantially, from 74-82% in the four sensitive regions in 1976 to 11-26% in 1999. The pentile critical load is typically used as a regional target to account for uncertainties, but also to ensure that a sufficient percentage of lakes are protected (95%). This suggests that further reductions in emissions are required to reduce depositions to approximately 34 meq.m(-2).year(-1) (11 kg S.ha(-1).year(-1)) to prevent critical load exceedance.
Full-text available
Article
Precipitation in south-central Ontario, with mean pH between 3.95 and 4.38 and frequent event pH's of < 4.0, is more acidic than that in the Sudbury, Ontario, region and in Scandinavia, and as acidic as that in the northeastern USA. As in New England, a major component of the total acidity is strong mineral acid. Because most lakes in south-central Ontario have very low buffering capacities (10–200 μeq∙L−1), high acid loadings are likely to lead to acidification of many lakes and streams in the forseeable future. Although it is not yet possible to estimate the time required for this to happen, there is already some evidence of declining buffering capacity in a few lakes. Key words: acidic rain, buffering capacity, acidic lakes, precipitation, alkalinity
Full-text available
Article
In 1997, during the late stages of production of NCEP-NCAR Global Reanalysis (GR), exploration of a regional reanalysis project was suggested by the GR project's Advisory Committee, “particularly if the RDAS [Regional Data Assimilation System] is significantly better than the global reanalysis at capturing the regional hydrological cycle, the diurnal cycle and other important features of weather and climate variability.” Following a 6-yr development and production effort, NCEP's North American Regional Reanalysis (NARR) project was completed in 2004, and data are now available to the scientific community. Along with the use of the NCEP Eta model and its Data Assimilation System (at 32-km-45-layer resolution with 3-hourly output), the hallmarks of the NARR are the incorporation of hourly assimilation of precipitation, which leverages leverages a comprehensive precipitation analysis effort, the use of a recent version of the Noah land surface model, and the use of numerous other datasets that are additional or improved compared to the GR. Following the practice applied to NCEP's GR, the 25-yr NARR retrospective production period (1979-2003) is augmented by the construction and daily execution of a system for near-real-time continuation of the NARR, known as the Regional Climate Data Assimilation System (R-CDAS). Highlights of the NARR results are presented: precipitation over the continental United States (CONUS), which is seen to be very near the ingested analyzed precipitation; fits of tropospheric temperatures and winds to rawinsonde observations; and fits of 2-m temperatures and 10-m winds to surface station observations. The aforementioned fits are compared to those of the NCEP-Department of Energy (DOE) Global Reanalysis (GR2). Not only have the expectations cited above been fully met, but very substantial improvements in the accuracy of temperatures and winds compared to that of GR2 are achieved throughout the troposphere. Finally, the numerous datasets produced are outlined and information is provided on the data archiving and present data availability.
Full-text available
Article
1] Regional variations in evaporation losses and water budget are interpreted from systematic isotopic patterns in surface waters across a 275,000 km 2 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.
Full-text available
Article
Steady-state isotope balance models have often been applied to estimate long-term average water balance conditions for lakes (Dincer, 1968; Gat 1995). Such studies have commonly employed values for the kinetic isotope fractionations for oxygen and hydrogen determined from wind tunnel experiments (e.g. Vogt, 1976; see also Gonfiantini 1986) and have assumed isotopic equilibrium between atmospheric moisture and precipitation (Rozanski et al. 2001; Gibson et al. 1993). In climates with a pronounced seasonality in evaporation rates, especially in environments where ice cover is present, such models have frequently predicted evaporative enrichment slopes that differ from observations (commonly lower than observed), and have therefore resulted in poor agreement between oxygen-18 and deuterium estimates, or have required use (or fitting) of kinetic fractionation factors that are not in agreement with the experimental studies (Zuber 1983; Gibson et al. 1993). A program of field investigations conducted at a variety of sites in northern Canada over the past decade has focused on development and application of quantitative isotope mass balance methods for water resources assessment in seasonal climates (see Gibson et al. 1994). These studies have included detailed comparisons of weekly to monthly evaporation in small, well instrumented lakes using non-steady isotope balance methods (Gibson et al., 1996a&b; Gibson et al.,1998; Gibson, in press), regional comparisons of long-term water balance in Boreal and Arctic lakes (Gibson, 2001; Gibson et al., 2002; Gibson and Edwards, in press), and application of evaporation pans and cryogenic vapour sampling to characterize isotopic composition of atmospheric moisture near the ground (Gibson et al. 1999). Overall, these studies have shown that application of isotope mass balance using pan-derived atmospheric moisture and laboratory values for kinetic exchange parameters yields consistent results for short time periods as compared to conventional water balance where evaporation is determined using Bowen ratio and aerodynamic profiling methods. Local and regional sampling surveys have also revealed a pronounced latitudinal steepening of the slope of local evaporation lines from about 5 to 7 in δ 2 H-δ 18 O space over the latitude range of 50 to 71°N. A recent sensitivity analysis was conducted to investigate possible seasonality effects on the slope of the local evaporation lines that would explain the steeper slopes at higher latitudes, and the general lack of agreement between predicted evaporation slopes using the previously applied models. The analysis began by fitting atmospheric moisture (δ A) so that predicted values of lake water (δ L) were constrained to fall on the local evaporation line. Notably, the resulting values of δ A were also found to be very close to the values expected if weighted according to the evaporation flux, i.e. when δ A is assumed in equilibrium with δ P but systematically filtered to account for the seasonality of the evaporation flux. Because the local evaporation line is a product of long-term evaporation on multiple lakes with differential throughflow, the use of flux-weighted parameters is apparently a more reasonable assumption than using mean annual values. Operational use of this refined approach has also been found to significantly improve the consistency of the water balance estimates predicted by each tracer, while maintaining the experimental values for the kinetic fractionations for both oxygen and hydrogen. Figure 1. Conceptual models showing isotope composition of major water balance components relative to the meteoric water line (MWL) and local evaporation line (LEL) in δ 2 H-δ 18 O space: (a) original model assuming isotopic equilibrium between atmospheric moisture and precipitation (e.g. Gibson et al. 1993). Predicted slopes fall close to 4 and require fitting of the isotope exchange parameters to obtain good agreement between tracers; (b)refined model assuming equilibrium between flux-weighted precipitation and atmospheric moisture. Predicted slopes are close to the observed LEL and do not require fitting of exchange parameters. δ values denote isotope values where δ P is precipitation, δ A is atmospheric moisture, δ E is evaporating moisture, and δ L are various lakewaters. C K 2 is the kinetic fractionation constant for deuterium, α*(T) and ε*(T) are the equilibrium fractionation and separation factors, respectively for each isotope species, and T is ambient temperature. Superscript "annual" and "evap. fw" denote mean annual and evaporation flux-weighted values.
Full-text available
Article
Impacts of sulphur and nitrogen deposition in western Canada J. Limnol., 69(Suppl. 1): 45-55, 2010 -DOI: 10.3274/JL10-69-S1-06 ABSTRACT Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskatchewan (SK) have long been considered unaffected by acid rain. However, emissions of acidifying pollutants from MB smelters and oil sand processing in Alberta (AB) may pose a developing threat. Surveys of 347 lakes located on geologically sensitive terrain in northern MB and SK were conducted to assess their acidification sensitivity and status. The survey domain (~193,000 km 2) contained 81,494 lakes ≥1 ha in area. Small lakes dominated the inventory in terms of numbers, and large lakes dominated in terms of area. Survey lakes were selected using a stratified-random sampling design in 10 sampling blocks within the overall survey domain. Few lakes had pH <6, and only three (all in SK) were acidic, i.e., Gran Alkalinity (Alk) <0 μeq L –1 . A broad range in lake sensitivity was apparent, and very sensitive lakes (low specific conductance, base cations and Alk) were present in all sampling blocks. Dissolved organic carbon (DOC) was an important constituent of many lakes. Critical loads (CL) of acidity calculated using the Steady-State Water Chemistry model (SSWC) revealed extremely low 5th percentile values for every block (range 1.9 to 52.7 eq ha –1 y –1). Block CL exceedances calculated using estimated S and N deposition for 2002 ranged from 54.5 to 909 eq ha –1 y –1 . The largest exceedances were for sampling blocks located near smelter sources or downwind of the oil sands. Lake chemistry revealed by our surveys was compared to others conducted both nearby and outside Canada.
Full-text available
Article
Stable isotopes of water were applied to estimate water yield to fifty lakes in northeastern Alberta as part of an acid sensitivity study underway since 2002 in the Athabasca Oil Sands Region (AOSR). Herein, we apply site-specific water yields for each lake to calculate critical loads of acidity using water chemistry data and a steady-state water chemistry model. The main goal of this research was to improve site-specific critical load estimates and to understand the sensitivity to hydrologic variability across a Boreal Plains region under significant oil sands development pressure. Overall, catchment water yields were found to vary significantly over the seven year monitoring period, with distinct variations among lakes and between different regions, overprinted by inter-annual climate-driven shifts. Analysis of critical load estimates based on site-specific water yields suggests that caution must be applied to establish hydrologic conditions and define extremes at specific sites in order to protect more sensitive ecosystems. In general, lakes with low (high) water yield tended to be more (less) acid sensitive but were typically less (more) affected by inter-annual hydrological variations. While it has been customary to use long-term water yields to define a static critical load for lakes, we find that spatial and temporal variability in water yield may limit effectiveness of this type of assessment in areas of the Boreal Plain characterized by heterogeneous runoff and without a long-term lake-gauging network. Implications for predicting acidification risk are discussed for the AOSR.
Full-text available
Article
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.
Full-text available
Article
Integrated assessment (IA) is a rapidly evolving field and in recent years the introduction of participatory methods has resulted in the development of a more diverse set of tools. The Georgia Basin Futures Project is presented and reviewed in the context of this expanding portfolio of IA methodologies. The project is an ambitious attempt to combine qualitative scenario methods with a computer-based gaming tool on a regional scale. The paper suggests that the particular combination of methods and the scale of the analysis represent a viable model for the future regional IAs.
Full-text available
Article
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 ice-free 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 m3, 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 step-wise 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.
Full-text available
Article
The authors describe the construction of a 0.5°lat-long gridded dataset of monthly terrestrial surface climate for the period of 1901-96. The dataset comprises a suite of seven climate elements: precipitation, mean temperature, diurnal temperature range, wet-day frequency, vapor pressure, cloud cover, and ground frost frequency. The spatial coverage extends over all land areas, including oceanic islands but excluding Antarctica. Fields of monthly climate anomalies, relative to the 1961-90 mean, were interpolated from surface climate data. The anomaly grids were then combined with a 1961-90 mean monthly climatology (described in Part I) to arrive at grids of monthly climate over the 96-yr period. The primary variables-precipitation, mean temperature, and diurnal temperature range-were interpolated directly from station observations. The resulting time series are compared with other coarser-resolution datasets of similar temporal extent. The remaining climatic elements, termed secondary variables, were interpolated from merged datasets comprising station observations and, in regions where there were no station data, synthetic data estimated using predictive relationships with the primary variables. These predictive relationships are described and evaluated. It is argued that this new dataset represents an advance over other products because (i) it has higher spatial resolution than other datasets of similar temporal extent, (ii) it has longer temporal coverage than other products of similar spatial resolution, (iii) it encompasses a more extensive suite of surface climate variables than available elsewhere, and (iv) the construction method ensures that strict temporal fidelity is maintained. The dataset should be of particular relevance to a number of applications in applied climatology, including large-scale biogeochemical and hydrological modeling, climate change scenario construction, evaluation of regional climate models, and comparison with satellite products. The dataset is available from the Climatic Research Unit and is currently being updated to 1998. The authors describe the construction of a 0.5° lat-long gridded dataset of monthly terrestrial surface climate for the period of 1901-96. The dataset comprises a suite of seven climate elements: precipitation, mean temperature, diurnal temperature range, wet-day frequency, vapor pressure, cloud cover, and ground frost frequency. The spatial coverage extends over all land areas, including oceanic islands but excluding Antarctica. Fields of monthly climate anomalies, relative to the 1961-90 mean, we interpolated from surface climate data. The anomaly grids were then combined with a 1961-90 mean monthly climatology (described in Part I) to arrive at grids of monthly climate over the 96-yr period. The primary variables - precipitation, mean temperature, and diurnal temperature range - were interpolated directly from station observations. The resulting time series are compared with other coarser-resolution datasets of similar temporal extent. The remaining climatic elements, termed secondary variables, were interpolated from merged datasets comprising station observations and, in regions where there were no station data, synthetic data estimated using predictive relationships with the primary variables. These predictive relationships are described and evaluated. It is argued that this new dataset represents an advance over other products because (i) it has higher spatial resolution than other datasets of similar temporal extent, (ii) it has longer temporal coverage than other products of similar spatial resolution, (iii) it encompasses a more extensive suite of surface climate variables than available elsewhere, and (iv) the construction method ensures that strict temporal fidelity is maintained. The dataset should be of particular relevance to a number of applications in applied climatology, including large-scale biogeochemical and hydrological modeling, climate change scenario construction, evaluation of regional climate models, and comparison with satellite products. The dataset is available from the Climatic Research Unit and is currently being updated to 1998.
Chapter
The enrichment of the heavy isotopic species (H2 18O and HDO) in surface waters and lakes was already observed during the early surveys of stable isotope variations in the hydrological cycle (Rankama 1954). Craig (1961a) noted that the isotope compositions of waters from African lakes were displaced in δ-D vs δ-18O space relative to other freshwaters whose composition follows the meteoric water line (MWL).
Article
Five carbonaceous chondrites (including the CI chondrites Orgueil and Ivuna) were analyzed by spark source mass spectrometry (SSMS) for the platinum-group elements Ru, Rh, Os, Ir, Pt, as well as W, Re, An, Th, and U. Conventional photoplate detection and a recently developed multi-ion counting system were used for ion detection. Results obtained for CI chondrites agree with compiled values within 6%. This study contains the first Rh analyses for this chondrite group. Rhodium concentrations for Orgueil and Ivuna agree well, implying a Solar System abundance of 0.140 ± 0.004 ppm and corresponding to 0.359 ± 0.010 atoms relative to 1 × 10 6 Si atoms. Concentrations in CM2, CV3, and CK4 chondrites are enriched compared to those of CI chondrites. However, the abundances of the refractory siderophile elements Re, Os, Ir with condensation temperatures above 1600 K (at 10 -4 atm) are higher by about 15-20% compared to the less refractory elements Ru, Pt, and Rh. Elements with similar condensation temperatures correlate very well resulting in uniform concentration ratios of Rh/Pt = 0.136 ± 0.006, Re/Os = 0.0821 ± 0.0019, and Ir/Os = 0.949 ± 0.039.
Article
The assumption that transpiration is the lesser of an atmospheric demand function and a water supply function was tested by simulation with Federer's (1979) soil-plant-atmosphere model. The best estimate of atmospheric demand is called unstressed transpiration, defined as the transpiration that would occur in ambient conditions if stomata were unaffected by plant-water potential. For practical purposes the Penman equation provides a good estimate of unstressed transpiration for short vegetation but not for forests. Even when atmospheric variables and the Penman estimate are held constant among forest canopies, unstressed transpiration can vary by a factor of two because of variation both in the maximum value of leaf conductance and in the ratio of canopy conductance to leaf conductance. The best water supply function incorporates depth variation of soil water potential and of root and soil properties. A more practical supply function uses the ratio of available water in the root zone, W, to maximum available water WM. The maximum available water is soil water held at potentials less than that at which the hydraulic conductivity is 2 mm/d and greater than the critical leaf water potential at which stomata are completely closed. Using a mature hardwood forest as a standard, various parameters were varied to examine their effects on a water supply function defined as a supply constant times W/WM. The supply constant was found to be independent of soil texture and physical properties. Root density and the internal resistance of the plant to water flow were the most important determinants of the supply constant. Reasonable variation of root density and internal resistance produced variation in the constant from 1.9 mm/h, which implies that supply is less than demand only when soil is very dry, to 0.5 mm/hr, which implies that supply cannot meet the demand even when the soil is wet.
Article
A group of Nordic experts has tried to draw conclusions on critical loads for sulphur and nitrogen. The critical load is defined as “The highest load that will not cause chemical changes leading to long-term harmful effects on most sensitive ecological systems”. Most soils, shallow groundwaters and surface waters would probably not be significantly changed by a load of 10–20 keq H+·km2·yr−1 in areas with a low content of base cations in the deposition. The total deposition of hydrogen ions in southwestern Scandinavia is in the order of 100 keq ·km−2·yr−1. The long-term critical load for nitrogen is in the range of 10–20 kg N·ha·1-yr−1 in most forest ecosystems. In high productive sites it might be as high as 20–45 kg N·ha− yr−1 in southern Sweden, and amounts to 30–40 kg·ha−1·yr−1 and even more over large areas in central Europe. The current deposition of sulphur and nitrogen must be substantially reduced to keep the long-term changes in sensitive ecosystems within acceptable limits.
Article
An isotope mass balance technique is applied to quantify water yield and refine a steady-state critical acid loadings assessment for 49 lakes in hydrologically complex, wetland-rich terrain of northeastern Alberta. The approach uses physical and climatological data combined with site-specific measurements of evaporative isotopic enrichment of 2H and 18O in lake water to measure lake residency and ungauged runoff to lakes. Mean water yields to individual lakes across the region over a 3-year period are estimated to range from 5 to 395 mm·year–1, with a standard deviation of two times the predicted estimates based on interpolation of gauged stream flow from broad-scale watersheds in the area. Comparison of the method with longer-term Water Survey of Canada hydrometric data suggests very similar average water yields for moderate- to large-sized watersheds. However, the isotope-based estimates appear to capture extreme low water yields in flat, disconnected areas and extreme high water yields in other areas thought to be related to stronger connections to regional groundwater flow systems. For aquatic ecosystems of northeastern Alberta, an area expected to be affected by acid deposition from regional oil sands development, continued refinement of the technique is important to accurately assess critical loads for ungauged systems, particularly those in low-yield settings.
Article
To assess the relationships between vapour trajectories and stable water isotopes in the Canadian Rocky Mountains, snow pits were sampled over three accumulation seasons (2004/05, 2005/06 and 2006/07) at two field sites. These sites, the Opabin and Haig Glaciers, are ˜160km apart at similar elevations and represent windward and lee-slope environments respectively. At both sites, snow pits were sampled at one glacier and one forefield location for delta 18O, deltaD, temperature and density. Intra-seasonal changes in delta18O are examined to determine the extent of post-depositional modification of isotope stratigraphies. At forefield sampling locations, vapour transport within the snowpack caused a significant amount of post-depositional modification of the seasonal delta18 O signal. At glacier sites there was minimal temporal change before the onset of spring melt in all years, and the comparative structure of delta 18O profiles from both glacier sites suggests that regional controls govern the isotopic composition of solid-phase precipitation in the Rocky Mountain region. The seasonal stability of isotope profiles at glacier sites enables individual snowfall events to be identified within isotope stratigraphies. A trajectory classification is produced for all events and the key meteorological, synoptic and isotopic characteristics of each trajectory class are investigated using data from alpine field sites and a suite of meteorological records from the region. An analysis of the relative influences of temperature and air-mass trajectory on snow-isotope ratios reveals some separation in mean delta 18O between storm classes, but the separation appears to be primarily driven by the mean temperature of each class rather than being a direct effect of vapour pathway. To further investigate the effect of storm trajectory on stable isotope ratios in this region, the isotopic evolution of precipitation along storm trajectories from 2006/07 is modelled using a single stage Rayleigh distillation model coupled to a simple orographic model. Isotopic data from alpine snow pits, along with an additional dataset from a sampling transect in southern British Columbia, are used to constrain and test the model. The addition of an orographic component is an improvement over a conventional Rayleigh model, and there is a good model fit to alpine isotope data for most storms.
Article
▪ Abstract Changes of the isotopic composition of water within the water cycle provide a recognizable signature, relating such water to the different phases of the cycle. The isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes. As a result, meteoric waters are depleted in the heavy isotopic species of H and O relative to ocean waters, whereas waters in evaporative systems such as lakes, plants, and soilwaters are relatively enriched. During the passage through the aquifers, the isotope composition of water is essentially a conservative property at ambient temperatures, but at elevated temperatures, interaction with the rock matrix may perturb the isotope composition. These changes of the isotope composition in atmospheric waters, surface water, soil, and groundwaters, as well as in the biosphere, are applied in the characterization of hydrological system as well as indicators of paleo-c...
Article
The critical load of acidity for surface waters is based on the concept that the inputs of acids to a catchment do not exceed the weathering less a given amount of ANC. The Steady State Water Chemistry (SSWC) Method is used to calculate critical loads, using present water chemistry. To ensure no damage to biological indicators such as fish species a value for ANClimit of 20 eq/l has been used to date for calculating critical loads. The SSWC-method is sensitive to the choice of the ANClimit. In areas with little acid deposition the probability of acid episodes leading to fish kills is small even if the ANClimit is set to zero, while in areas with high acidic deposition fish kills may occur at this value. Thus, the ANClimit can be a function of the acidifying deposition to the lake, nearing zero at low deposition and increasing to higher values at higher deposition. A formulation for such an ANClimit has been worked out, and we have tested the effect of the ANClimit as a linear function of the deposition, assuming ANClimit = 0 at zero deposition with a linear increase to 50 ueq/l at a deposition of 200 meq.m–2.yr–1. For areas with high deposition the effect of a variable ANClimit is small, while in areas with low deposition the effect is significant. For Norway the exceeded area decreases from 36 to 30% using a variable ANClimit instead of a fixed value of 20 eq/l.
Article
The terrestrial biosphere component of the Integrated Model to Assess the Greenhouse Effect (IMAGE 2.0) uses changes in land cover to compute dynamically the greenhouse gas fluxes between the terrestrial biosphere and the atmosphere. Potential land cover for both natural ecosystems and agrosystems, are determined with the Terrestrial Vegetation Model (TVM). TVM consists of separate submodels for the water-balance, global vegetation patterns, crop distribution and potential rain fed crop yield. All these submodels are based on local climatic, hydrological and soil characteristics and appropriate global data bases for those parameters are collected or compiled. The structure of all models, data bases and linkages between them and other modules of IMAGE 2.0 are described. Although computationally demanding, the models give an adequate description of the global vegetation and agricultural patterns. The only discrepancy occurs in regions where the vegetation and agricultural distribution depends on causes other than climatic, such as additional water storage and supply, anthropogenic influence and natural disturbance. Despite this discrepancy, we conclude that TVM simulates satisfactory global vegetation characteristics and that it can be adequately integrated with other models of IMAGE 2.0.
Article
Forests are likely to show complex transient responses to rapid changes in climate. The model described here simulates the dynamics of forest landscapes in a changing environment with simple phenomenological equations for tree growth processes and local environmental feedbacks. Tree establishment and growth rates are modified by species-specific functions describing the effects of winter and summer temperature limitations, accumulated annual foliage net assimilation and sapwood respiration as functions of temperature, CO2 fertilization, and growing-season drought. These functions provide external conditions for the simulation of patch-scale forest dynamics by a forest succession model, FORSKA, in which all of the trees on each 0.1 ha patch interact by competition for light and nutrients. The landscape is simulated as an array of such patches. The probability of disturbance on a patch is a power function of time since disturbance. Forest structure, composition and biomass simulated for the landscape average in boreal and temperate deciduous forests approach reasonable equilibrium values in 200–400 years. A climatic warning scenario is applied to central Sweden, where temperature and precipitation increases are shown to interact with each other and with soil water capacity in determining the transient and equilibrium responses of the forest landscape to climate change.
Article
Proxy data reflecting the oxygen isotope composition of meteoric precipitation (delta18Oppt) are widely used in reconstructions of continental paleoclimate and paleohydrology. However, actual geographic variation in modern water compositions is difficult to estimate from often sparse data. A first step toward understanding the geologic pattern of change in delta18Oppt is to describe the modern distribution in terms of principal geographic parameters. To this end, we empirically model relationships between 18O in modern precipitation and latitude and altitude. We then identify geographic areas where large-scale vapor transport patterns give rise to significant deviations from model delta18Oppt compositions based on latitude and altitude. Model value and residual grids are combined to derive a high-resolution global map of delta18Oppt that can serve as a spatial reference against which proxy data for paleoprecipitation can be compared. Reiteration of the procedure outlined here, for paleo-delta18Oppt data, may illuminate past changes in the climatic and physiographic parameters controlling the distribution of delta18O regimes.
Article
The relationship between deuterium and oxygen-18 concentrations in natural meteoric waters from many parts of the world has been determined with a mass spectrometer. The isotopic enrichments, relative to ocean water, display a linear correlation over the entire range for waters which have not undergone excessive evaporation.
Article
The Craig-Gordon model (C-G model) [H. Craig, L.I. Gordon. Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperatures, E. Tongiorgi (Ed.), pp. 9-130, Laboratorio di Geologia Nucleare, Pisa (1965).] has been synonymous with the isotope effects associated with the evaporation of water from surface waters, soils, and vegetations, which in turn constitutes a critical component of the global water cycle. On the occasion of the four decades of its successful applications to isotope geochemistry and hydrology, an attempt is made to: (a) examine its physical background within the framework of modern evaporation models, (b) evaluate our current knowledge of the environmental parameters of the C-G model, and (c) comment on a general strategy for the use of these parameters in field applications. Despite its simplistic representation of evaporation processes at the water-air interface, the C-G model appears to be adequate to provide the isotopic composition of the evaporation flux. This is largely due to its nature for representing isotopic compositions (a ratio of two fluxes of different isotopic water molecules) under the same environmental conditions. Among many environmental parameters that are included in the C-G model, accurate description and calculations are still problematic of the kinetic isotope effects that occur in a diffusion-dominated thin layer of air next to the water-air interface. In field applications, it is of importance to accurately evaluate several environmental parameters, particularly the relative humidity and isotopic compositions of the 'free-atmosphere', for a system under investigation over a given time-scale of interest (e.g., hourly to daily to seasonally). With a growing interest in the studies of water cycles of different spatial and temporal scales, including paleoclimate and water resource studies, the importance and utility of the C-G model is also likely to grow in the future.
Re-gional lake surveys in Finland and design
  • A Henriksen
  • B L Skelkvåle
  • L Lien
  • T S Traaen
  • J Man-Nio
  • M Forsius
  • J Kämäri
  • I Mäkinen
  • T Berntell
  • T Wiederholm
  • A Wilander
  • T Moiseenko
  • P Lozovik
  • N Filatov
  • R Niinioja
  • R Harriman
  • J P Jensen
Henriksen, A., B.L. Skelkvåle, L. Lien, T.S. Traaen, J. Man-nio, M. Forsius, J. Kämäri, I. Mäkinen, T. Berntell, T. Wiederholm, A. Wilander, T. Moiseenko, P. Lozovik, N. Filatov, R. Niinioja, R. Harriman & J.P. Jensen. 1996. Re-gional lake surveys in Finland, Norway, Sweden, northern Kola, Russian Karelia, Scotland, Wales 1995: coordina-tion and design. Acid Rain Research Report 40/1996, Nor-wegian Institute for Water Research, Oslo, Norway: 30 pp
Chapter 8: Critical Loads – Are they being exceeded? In: 2004 Canadian acid deposition science assessment
  • D S Jeffries
  • R Ouimet
Jeffries, D.S. & R. Ouimet (Eds). 2005. Chapter 8: Critical Loads – Are they being exceeded? In: 2004 Canadian acid deposition science assessment. Environment Canada, Ottawa, Ontario, 341–368
Canadian acid deposition science assessment. Meteorological Service of Canada
  • Environment Canada
Environment Canada. 2004. Canadian acid deposition science assessment. Meteorological Service of Canada, Toronto, Ontario. www.msc-smc.ec.gc.ca/saib/acid/acid_e.html.
Oxygen and hydrogen isotopes in the hydrological cycle
  • J R Gat
Gat, J. R. 1996. Oxygen and hydrogen isotopes in the hydrological cycle. Ann. Rev. Earth. Planet. Sci., 24: 225–262.
Sensitivity of western and northern Canada soils and geology to acidic input. British Columbia. Ministry of Environment and Parks, Technical Committee for the Long-Range Transport of Atmospheric Pollutants in Western and Northern Canada
  • J H Wiens
Wiens, J. H. 1987. Sensitivity of western and northern Canada soils and geology to acidic input. British Columbia. Ministry of Environment and Parks, Technical Committee for the Long-Range Transport of Atmospheric Pollutants in Western and Northern Canada., Coordinating Committee on Soil and Geology Sensitivity Mapping (Canada).