Colin J. Whitfield

University of Saskatchewan, Saskatoon, Saskatchewan, Canada

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Publications (14)36.55 Total impact

  • Shaun A Watmough, Colin J Whitfield, Mark E Fenn
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    ABSTRACT: Industrial activities in the oil sands region of Alberta, Canada have resulted in greatly elevated emissions of SO2 and N (NOx and NH3) and there are concerns over possible widespread ecosystem acidification. Acid sensitive soils in the region are common and have very low base cation weathering rates: the median base cation weathering rate estimated for 63 sites using PROFILE was just 17mmolcm(-2)yr(-1). Deposition of S and N in throughfall was approximately twice as high as deposition measured with open collectors and could be as high as 360mmolcm(-2)yr(-1) within 20km of the main industrial center, although deposition declined logarithmically with distance from the industrial activities. Base cation deposition however, mostly exceeded the combined inputs of S and N in bulk deposition and throughfall, particularly during the summer months. The potential for soil acidification at a site close (<3km) to the largest mine was assessed using the dynamic ecosystem acidification model, MAGIC (Model of Acidification of Groundwater in Catchments). Despite very low base cation weathering rates (~6mmolcm(-2)yr(-1)) and high (~250mmolcm(-2)yr(-1)) acid (S+N) deposition at the site, soil base saturation and soil solution pH and molar Ca:Al ratio were predicted to increase in the future assuming acid and base cation deposition constant at current rates. This work shows that despite extremely low soil base cation weathering rates in the region, the risk of soil acidification is mitigated to a large extent by high base cation deposition, which in contrast to S emissions is derived from fugitive dust sources in the mines, and is poorly quantified for regional modeling studies.
    Science of The Total Environment 06/2014; 493C:1-11. · 3.26 Impact Factor
  • Shaun A. Watmough, Colin J. Whitfield, Mark E. Fenn
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    ABSTRACT: Industrial activities in the oil sands region of Alberta, Canada have resulted in greatly elevated emissions of SO2 and N (NOx and NH3) and there are concerns over possible widespread ecosystem acidification. Acid sensitive soils in the region are common and have very low base cation weathering rates: the median base cation weathering rate estimated for 63 sites using PROFILE was just 17 mmolc m− 2 yr− 1. Deposition of S and N in throughfall was approximately twice as high as deposition measured with open collectors and could be as high as 360 mmolc m− 2 yr− 1 within 20 km of the main industrial center, although deposition declined logarithmically with distance from the industrial activities. Base cation deposition however, mostly exceeded the combined inputs of S and N in bulk deposition and throughfall, particularly during the summer months. The potential for soil acidification at a site close (< 3 km) to the largest mine was assessed using the dynamic ecosystem acidification model, MAGIC (Model of Acidification of Groundwater in Catchments). Despite very low base cation weathering rates (~ 6 mmolc m− 2 yr− 1) and high (~ 250 mmolc m− 2 yr− 1) acid (S + N) deposition at the site, soil base saturation and soil solution pH and molar Ca:Al ratio were predicted to increase in the future assuming acid and base cation deposition constant at current rates. This work shows that despite extremely low soil base cation weathering rates in the region, the risk of soil acidification is mitigated to a large extent by high base cation deposition, which in contrast to S emissions is derived from fugitive dust sources in the mines, and is poorly quantified for regional modeling studies.
    Science of The Total Environment 01/2014; 493:1–11. · 3.26 Impact Factor
  • Colin J Whitfield, Shaun A Watmough
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    ABSTRACT: In boreal regions of the province of Saskatchewan, Canada, there is concern over emerging acid precursor emission sources associated with the oil sands industry. Base cation weathering rates (BC(w)) and steady-state critical loads of sulfur (CL(S)) were identified for upland forest soil plots (n=107) in 45 ecodistricts according to a new method for approximation of BC(w) in the region. This method was developed by regression of simple soil and site properties with BC(w) calculated through application of a soil chemical model (PROFILE). PROFILE was parameterized using detailed physicochemical data for a subset (n=35) of the sites. Sand content, soil moisture and latitude emerged as important predictive variables in this empirical regression approximation. Base cation weathering varied widely (0.1-8000mmol(c)m(-3)yr(-1)) across the study sites, consistent with their contrasting soil properties. Several sites had lower rates than observed in other acid-sensitive regions of Canada owing to quartz dominated mineralogy and coarse-textured soils with very low surface area. Weathering was variable within ecodistricts, although rates were consistently low among ecodistricts located in the northwest of the province. Overall, half of the forest plots demonstrated CL(S) less than 45mmol(c)m(-2)yr(-1). Historically, the acidification risk in this region has been considered low and monitoring has been limited. Given the very low CL(S) in many northern ecodistricts and the potential for increased acid deposition as oil sands activities expand, soil acidification in these regions warrants further study.
    Science of The Total Environment 08/2012; 437:165-72. · 3.26 Impact Factor
  • Colin J Whitfield, Julian Aherne, Helen M Baulch
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    ABSTRACT: Freshwater lakes are known to release carbon dioxide (CO(2)) and methane (CH(4)) to the atmosphere; however, the importance of lakes in global nitrous oxide (N(2)O) budgets is not yet known. Further, despite the abundance of small lakes on the landscape, neither emissions of these gases nor their drivers are well described. Dissolved concentrations of CO(2), CH(4) and N(2)O greenhouse gases were related to water chemistry, hydrology and catchment characteristics in order to identify factors controlling gas concentrations for 121 small Irish headwater lakes (median area: 2.0ha) in relatively undisturbed catchments; lake-atmosphere gas fluxes were also calculated. The majority of lakes were supersaturated (relative to the atmosphere) with CO(2) and N(2)O while CH(4) was above saturation in all lakes. Dissolved gas concentrations were correlated with land cover (rock, forest and grassland), deuterium excess (an indicator of hydrologic character) and lake organic carbon concentrations, although dissolved CO(2) exhibited few significant relationships. Principal components analysis indicated that higher levels of CH(4) and N(2)O supersaturation were exhibited under different conditions. Methane supersaturation was highest in low elevation catchments with an evaporative hydrologic character and high organic carbon concentrations. In contrast, lakes characteristic of N(2)O supersaturation were low in carbon and located in more rapidly flushed higher elevation catchments. Estimated fluxes of CO(2), CH(4) and N(2)O to the atmosphere averaged 14, 0.36 and 1.3×10(-3)mmolm(-2)d(-1), respectively.
    Science of The Total Environment 12/2011; 410-411:217-25. · 3.26 Impact Factor
  • Colin J. Whitfield, Shaun A. Watmough, Julian Aherne
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    ABSTRACT: Immobile element-based weathering estimation methods assume that Zr (or Ti) is an immobile element, and that weathering rates of other elements can be estimated according to the enrichment of Zr in weathered horizons relative to an unweathered parent material. This approach was used to estimate base cation weathering rates for 33 soil profiles on acid-sensitive terrain in north-eastern Alberta. Zirconium generally showed enrichment within the rooting zone, but the deepest (subsoil) samples were not always associated with the lowest Zr concentrations. Weathering rates estimated with the Zr depletion and Pedological Mass Balance (PMB) methods were generally low (ranges: 0–51 and 0–58mmolcm−2yr−1, respectively); however, low base cation oxide concentrations and heterogeneity within soil profiles complicated weathering rate calculations and net base cation gains were calculated for several (six) sites. Evaluation of the Zr depletion and PMB weathering estimates against those calculated with the process-oriented PROFILE model at a subset (n=9) of the sites indicated the estimates were poorly related, with PROFILE rates typically being higher. The effects-based emissions management strategy for acid precursors in this region requires spatial coverage of soil properties (including weathering rates) across a large area, but the apparent limitations associated with the immobile element based methods in this region: identifying representative parent soils and deriving weathering rate estimates comparable to more robust methods are arguments against their candidacy for future use.
    Geoderma 01/2011; 166(1):189-197. · 2.35 Impact Factor
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    ABSTRACT: Spatial and temporal variability in surface water chemistry, organic soil chemistry and hydrologic indicators were investigated at three poor-fen complexes in two boreal catchments in Northern Alberta to provide insight into the dominant controls on surface water chemistry. Improved understanding of these controls is required to enable prediction of runoff chemistry in the region under changing atmospheric deposition conditions. Surface water chemistry exhibited considerable variability; within each fen conductivity, dissolved organic carbon (DOC), and Cl− tended to decrease and pH tended to increase with increasing distance from the lake edge. Variations in evaporative isotopic enrichment in 2H and 18O, expressed as deuterium excess, were used to distinguish between throughflow waters and those that were more evaporatively enriched. Throughflow surface waters were more acidic primarily due to higher concentrations of DOC and NO3−. Exchangeable base saturation and pH of organic soils were strongly related to surface water chemistry at two of the fen complexes, demonstrating the capacity for cation exchange to influence surface water chemistry. Fen surface water concentrations of most elements and DOC increased during the summer period (between June and August), while pH of water decreased. Evaporative concentration of the surface waters was a dominant driver, with surface water temperature increasing at both catchments. Localized groundwater discharge was an important contributor of base cations to the fens, while the organic soils are sinks for atmospherically deposited SO42−, N and Cl−. Copyright © 2010 John Wiley & Sons, Ltd.
    Hydrological Processes 03/2010; 24(15):2143 - 2155. · 2.50 Impact Factor
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    ABSTRACT: Mineral soil and fibric peat from acid-sensitive western boreal catchments in the Athabasca Oil Sands Region of Alberta, Canada were evaluated for their ability to adsorb and release SO(4)(2-). Laboratory batch studies indicated that SO(4)(2-) adsorption in mineral soil from both the A and B horizons exhibits a limited response to elevated SO(4)(2-) concentrations, with the slope of initial mass isotherms <0.2 for all soils, likely due to low iron and aluminum oxide content. Although S retention is the dominant process in peat soils in the region, drought simulations in the lab using fibric peat collected from a poor fen exhibited as much as a five-fold increase in SO(4)(2-) concentration after drying and rewetting. Given the limited SO(4)(2-) adsorption capacity of mineral soils and the potential drought-induced S release from peatlands in this region where increased S deposition is expected, further investigation of acidification impacts is warranted.
    Journal of Environmental Quality 01/2010; 39(3):1108-12. · 2.35 Impact Factor
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    ABSTRACT: Carbon fluxes at two boreal peatland-dominated catchments in northeastern Alberta were investigated through the analysis of fen and lake water chemistry and the measurement of partial pressure of carbon dioxide (pCO2) using headspace gas analysis. All waters had low pH (
    Journal of Geophysical Research 01/2010; 115. · 3.17 Impact Factor
  • Colin J Whitfield, Julian Aherne, Shaun A Watmough
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    ABSTRACT: Industrial activities have proliferated across Canada's Athabasca Oil Sands Region in recent years, stimulating concerns over the impact of atmospheric sulfur dioxide (SO2) emissions on acid-sensitive terrain. Upland jack pine forests have been identified as possibly the most sensitive ecosystem in the region but despite high emissions of SO2, sulfur (S) deposition is relatively low across much of the region. The response of forest soils at 11 locations that exhibit low estimated weathering rates (< 10 mmol(c) x m(-2) x yr(-1)) was simulated for the period 1900-2100 using a dynamic hydrogeochemical model assuming no change or doubling of S deposition. The model predicted minimal impact on soil base saturation (BS), but a decline in soil solution base cation (BC) to aluminum (Al) ratio (BC:Al). The regional effects-based emissions management framework uses modeled changes in these two parameters relative to site-specific chemical thresholds to trigger actions to reduce S emissions. Modeled changes in BS are insufficient to invoke a response. Under base case conditions, modeled BC:Al reaches the chemical threshold at two and three sites within 15 and 30 years, respectively. Under conditions of double S deposition, seven sites are simulated to reach the threshold within 30 years. Nonetheless, the chemical thresholds are stringent relative to critical chemical criteria used elsewhere and the impacts of acidic deposition in the region are anticipated to be limited.
    Environmental Science and Technology 08/2009; 43(15):5844-50. · 5.26 Impact Factor
  • Colin Whitfield, Julian Aherne, Shaun Watmough
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    ABSTRACT: Sixteen boreal lakes in northern Alberta were sampled for a suite of water chemistry parameters, including dissolved carbon dioxide (CO2), using a headspace gas analysis technique. The lakes encompassed a wide range of pH and alkalinity but had very high dissolved organic carbon (DOC) levels (11–36 mg L−1) and were supersaturated in CO2 with respect to the atmosphere. While the partial pressure of carbon dioxide (pCO2) is regularly estimated from pH and dissolved inorganic carbon (DIC), pH was related to pCO2 at only 13 of 16 lakes and overall pH in combination with DIC was a poor predictor of pCO2. Similarly, despite very high DOC levels, pCO2 was unrelated to the DOC concentration of the lakes. Stepwise multiple linear regressions improved the prediction capability for the entire data set, when compared to simple regressions. Both physicochemical (alkalinity, temperature) and landscape descriptors (lake area, peatland relative area) were important predictors of pCO2. The best regression model included lake area, peatland relative area, and water temperature, and was better able to predict pCO2 than relationships based on DOC, and pH and alkalinity, but lakes with high pCO2 (> 1000 µatm) remain under-predicted and are likely subject to additional factors controlling pCO2 that were not considered in this analysis.
    Canadian Water Resources Journal - CAN WATER RESOUR J. 01/2009; 34(4):415-426.
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    ABSTRACT: In contrast to other lakes studied in Cape Breton Highlands National Park (Nova Scotia, Canada), our paleolimnological results indicated that Glasgow Lake has been impacted by acidic deposition starting in the early 1900s. Based on analysis of diatom assemblages, the lake experienced a decrease in diatom-inferred lakewater pH from a pre-industrial pH of ~5.8 to a current pH of 5.3 (2000–2002 measured mean pH=5.0) as well as a decrease in diatom-inferred Gran-alkalinity. In this study, diatom-based paleolimnological techniques were used in conjunction with a dynamic biogeochemical model (MAGIC) to assess both the timing and extent of the acidification trend, as well as determine a probable explanation as to why this lake, and none of the other 15 Cape Breton Highlands lakes studied for paleolimnology thus far, acidified under a peak non-marine sulphate deposition load of 43.6 mmolc m−2 year−1 in the mid-1970s. Steady-state models estimate that Glasgow Lake had the lowest buffering capacity of six study lakes and estimated critical sulphate loading of <1 mmolc m−2 year−1. MAGIC also estimated a loss of charge balance alkalinity from a pre-1850 value of 38 μmolc l−1 to a low of 12 μmolc l−1. While no evidence of biological recovery has been recorded, MAGIC estimates an increase in charge balance alkalinity to 27 μmolc l−1 in 2002 in response to decreased SO2 emissions. Of the five other lakes that were modelled, all showed trends towards more acidic states and subsequent increases in charge balance alkalinity; however, the empirical paleo-diatom approach applied to these lakes showed no evidence of acidification. Thus, Glasgow Lake has the lowest buffering capacity among the Cape Breton Highland study lakes and serves as a sentinel of potential acidification trends and recovery in this region.
    Hydrobiologia 01/2008; 614(1):299-307. · 1.99 Impact Factor
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    ABSTRACT: The response of twenty acid-sensitive headwater catchments in Nova Scotia to acidic deposition was investigated for the period 1850?2100 using a dynamic hydrochemical model (MAGIC: Model of Acidification of Groundwater in Catchments). To ensure robust model simulation, MAGIC was calibrated to the long-term chemical trend in annual lake observations (13?20 years). Model simulations indicated that the surface waters of all twenty catchments acidified to the 1970s but showed subsequent recovery (increases in acid neutralising capacity (ANC) and pH) as sulphate deposition decreased. However, under proposed future emissions reductions (approximately 50% of current deposition) simulated ANC and pH will not return to estimated pre-industrial levels by 2100. An ANC of 20 ?mol<sub>c</sub> L<sup>?1</sup> and pH of 5.4 were defined as acceptable chemical thresholds (or critical chemical limits) for aquatic organisms in the current study. Under the proposed emissions reductions only one catchment is predicted to remain below the critical limit for ANC by 2100; three additional catchments are predicted to remain below the critical limit for pH. Dynamic models may be used to estimate target loads, i.e., the required deposition reductions to achieve recovery within a given time. Setting target loads at approximately 30% of current depositions would allow three of the four lakes to reach the chemical criteria by 2030. In contrast to the generally good prognosis for surface waters, soils lost an average of 32% of estimated initial base saturation and recovery is estimated to be very slow, averaging 23% lower than pre-acidification levels in 2100.
    Hydrology and Earth System Sciences 01/2007; · 3.59 Impact Factor
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    C.J. Whitfield, S.A. Watmough, J. Aherne, P.J. Dillon
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    ABSTRACT: Critical loads are strongly dependent on the rate of release of base cations from the soil matrix. This study compares five commonly used methods for estimating weathering rates at five acid-sensitive catchments across Nova Scotia, Canada. Three of the methods (Zr Depletion, Clay Content, and the PROFILE model) are based on soil profiles and consider only the rooting zone, whereas the two remaining methods (the soil acidification model MAGIC and catchment Mass Balance Deficit) are catchment-based, and account for contributions from all soils within a catchment. Each weathering estimate method resulted in similar values among the five catchments, indicating similar sensitivity to acidic deposition among the study areas. Base cation weathering estimates were very low using the three soil profile-based methods, with rates varying from 3 to 13 mmolc m− 2 a− 1. In contrast, catchment-based methods predicted base cation weathering rates an order of magnitude higher (60 to 155 mmolc m− 2 a− 1), possibly due to spatial heterogeneity of the soil deposits, and contributions from deeper soil (till). Critical load (sulphur and nitrogen) estimates using the profile-based weathering rates indicate that critical loads for forest soils are currently exceeded at all catchments by 23 to 61 mmolc m− 2 a− 1. Predicted future reductions in acidic deposition should reduce the magnitude of critical load exceedance, but will not result in the catchments reaching a non-exceeded state.
    Geoderma. 01/2006;
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    ABSTRACT: The chemical response of 20 headwater lakes in Nova Scotia to reduced acid deposition was investigated using trend analysis, and the need for further reductions was assessed using two steady-state, critical load models. Significant decreases were observed in the concentration of nonmarine sulphate (SO42–) and hydrogen (H+) at four wet deposition monitoring stations across Atlantic Canada since 1984. Dominant trends in surface water were decreasing SO42– concentrations, with little improvement in alkalinity and H+. Based on the Steady State Water Chemistry (SSWC) and First-order Acidity Balance (FAB) models, and using a critical chemical limit for acid-neutralizing capacity of 20 µmolc·L–1, critical load is exceeded at 9 and 13 of the 20 study lakes, respectively. Application of the SSWC model suggests that sulphur (S) deposition must be reduced by 37.3 mmolc·m–2·year–1 from 1997 levels to prevent critical load exceedance at 95% of the study lakes. Using the FAB model, the minimum reductions in nitrogen and S deposition necessary to protect 95% of the study lakes are 32.7 and 42.1 mmolc·m–2·year–1, respectively. Additional reductions beyond those proposed for 2030 are required to minimize critical load exceedance and promote recovery in alkalinity and pH of surface waters at the study catchments.Nous étudions la réaction chimique de 20 lacs de sommet de bassin versant en Nouvelle-Écosse à une diminution des précipitations acides à l'aide d'analyses des tendances; nous évaluons aussi la nécessité de réductions additionnelles à l'aide de deux modèles de charge critique à l'état d'équilibre. On observe depuis 1984 des réductions significatives des concentrations de sulfates (SO42–) d'origine non marine et d'hydrogène (H+) à quatre stations de surveillance des précipitations humides réparties dans le Canada atlantique. Les tendances dominantes dans les eaux de surface montrent une diminution des concentrations de SO42– avec peu d'amélioration de l'alcalinité ou de l'H+. D'après les modèles SSWC (chimie des eaux à l'état d'équilibre) et FAB (bilan d'acidité du premier ordre) et avec une limite chimique critique de capacité à neutraliser les acides de 20 µmolc·L–1, la charge critique est dépassée respectivement à 9 et 13 des 20 lacs étudiés. L'application du modèle SSWC indique que les précipitations de soufre (S) doivent être réduites de 37,3 mmolc·m–2·an–1 à partir des niveaux de 1997 afin d'empêcher le dépassement des charges critiques dans 95 % des lacs étudiés. Selon le modèle FAB, les réductions minimales de précipitations d'azote et de S nécessaires pour protéger 95 % des lacs étudiés sont respectivement de 32,7 mmolc·m–2·an–1 et de 42,1 mmolc·m–2·an–1. Des réductions plus importantes que celles proposées pour 2030 sont donc nécessaires afin de minimiser les dépassements de charge critique et de favoriser la récupération de l'alcalinité et du pH des eaux de surface dans les bassins versants étudiés.[Traduit par la Rédaction]
    Canadian Journal of Fisheries and Aquatic Sciences 01/2006; 63(7):1504-1514. · 2.32 Impact Factor