[Show abstract][Hide abstract] ABSTRACT: The Boreal Plains Ecozone (BPE) in Western Canada is expected to be an area of maximum ecological sensitivity in the 21st century. Successful climate adaptation and sustainable forest management require a better understanding of the interactions between hydrology, climate, and vegetation. This paper provides a perspective on the changing water cycle in the BPE from an interdisciplinary team of researchers, seeking to identify the critical knowledge gaps. Our review suggests the BPE will likely become drier and undergo more frequent disturbance and shifts in vegetation. The forest will contract to the north, though the southern boundary of the ecotone will remain in place. We expect detrimental impacts on carbon sequestration, water quality, wildlife, and water supplies. Ecosystem interactions are complex, and many processes are affected differently by warming and drying, thus the degree and direction of change is often uncertain. However, in the short term at least, human activities are the dominant source of change and are unpredictable but likely decisive. Current climate, hydrological, and ecological monitoring in the BPE are limited and inadequate to understand and predict the complex responses of the BPE to human activities and climate change. This paper provides a case study of how hydrological processes critically determine ecosystem functioning, and how our ability to predict system response is limited by our ability to predict changing hydrology.
[Show abstract][Hide abstract] ABSTRACT: Globally, greenhouse gas budgets are dominated by natural sources, and aquatic ecosystems are a prominent source of methane (CH4) to the atmosphere. Beaver (Castor canadensis and Castor fiber) populations have experienced human-driven change, and CH4 emissions associated with their habitat remain uncertain. This study reports the effect of near extinction and recovery of beavers globally on aquatic CH4 emissions and habitat. Resurgence of native beaver populations and their introduction in other regions accounts for emission of 0.18–0.80 Tg CH4 year−1 (year 2000). This flux is approximately 200 times larger than emissions from the same systems (ponds and flowing waters that became ponds) circa 1900. Beaver population recovery was estimated to have led to the creation of 9500–42 000 km2 of ponded water, and increased riparian interface length of >200 000 km. Continued range expansion and population growth in South America and Europe could further increase CH4 emissions.
AMBIO A Journal of the Human Environment 12/2014; 44(1). DOI:10.1007/s13280-014-0575-y · 2.29 Impact Factor
[Show abstract][Hide abstract] 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. DOI:10.1016/j.scitotenv.2014.05.110 · 4.10 Impact Factor
[Show abstract][Hide abstract] 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. · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The surface area of soil is an important determinant of mineral weathering rates, but is infrequently measured. Simple texture-based pedotransfer functions (PTFs) have been used to predict the specific surface area (SSA) of coarse-textured soils. Detailed physicochemical properties of 40 upland forest mineral soils from northeastern Alberta were used to evaluate three texture-based PTFs and to calculate weathering rates using a process-oriented soil chemical model. Evaluation of the PTFs demonstrated that these equations predict only across a limited range of (low) surface areas. Moreover, the fit between predicted and measured SSA was generally poor for soils in this region of Alberta. Improved prediction of SSA was possible using a texture-based PTF calibrated for the region, although differences between measured and predicted values were often large. Mineralogy terms were used in a more comprehensive PTF to account for mineral-specific differences in surface area. This approach proved superior to texture-only approaches; however, it could not be used reliably for site-specific predictions (NRMSE = 0.41). Soil-chemical model-generated weathering rates were strongly influenced by the SSA method used in parameterization; weathering estimates and corresponding critical load assessments based on measured SSA (and to a lesser extent SSA derived from the regional PTF) were the most robust. Methods for SSA prediction should be used with caution, particularly in cases where they are applied to soils with different character than those for which they were developed.
Canadian Journal of Soil Science 11/2013; 93(5):621-630. DOI:10.4141/cjss2012-009 · 1.38 Impact Factor
[Show abstract][Hide abstract] 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. DOI:10.1016/j.scitotenv.2012.08.046 · 4.10 Impact Factor
[Show abstract][Hide abstract] 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. DOI:10.1016/j.scitotenv.2011.09.045 · 4.10 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 (<5.3) and Gran alkalinity (<2.3 mg L-1), high DOC (>15 mg L-1), and were supersaturated with carbon dioxide (CO2) with respect to the atmosphere (CO2: 1.2-54 times atmospheric). Nonetheless, CO 2 concentrations in the study lakes were significantly lower compared with surface water pools in associated fen systems. Average atmospheric flux of CO2 from the two lakes were 0.18 and 0.48 g C m-2 d -1, while potential fluxes from small surficial pools on the fen complexes were an order of magnitude higher. The higher average efflux estimated at one of the lakes (relative to the other) was attributed to shorter lake residence time and smaller relative lake area (i.e., higher relative carbon loading). Carbon mass balances for the lakes suggest that they act as conduits for dissolved CO2 from surrounding fen complexes to the atmosphere. In one of the two study catchments (with negligible groundwater sources), inputs of dissolved CO2 from fen surface waters supported a substantial component (∼30%) of the lake atmospheric CO2 efflux.
Journal of Geophysical Research Atmospheres 12/2010; 115(G4). DOI:10.1029/2010JG001364 · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A dynamic hydrogeochemical model of water acidification (MAGIC.: Model of Acidification of Groundwater in Catchments) was applied 10 two catchments with contrasting hydrological influences in the Athabasca Oil Sands Region of Alberta 10 predict catchment response to elevated levels of acidic deposition. Key processes that determine catchment response to atmospheric deposition, including groundwater base cation inputs and retention of (S) in peatland complexes were parameterized in the model. Although deposition of S and nitrogen (N) the region has increased over the last 40 years, levels ore law at the study sites relative to impacted areas of eastern North America. Model forecasts for the period 2005 2100 were run under constant 2005 deposition levels (base ease) and at acid deposition double this level. Simulated past and future soil base saturation was constant over die course of the 200 year (1900-2100) modelled period. At the lake with high charge balance acid neutralizing capacity (ANC(CB)), where large base cation sources dominate lake chemistry. little change in surf ace water chemistry was predicted under either forecast scenario. Under the double acid forecast scenario at the low lake, simulated lake ANC(CB), decreased in response to elected S deposition. but the magnitude of was comparable to the range in observational data. The simulations suggest limited risk of acidification primarily due to S retention vi the catchments, but the potential Jar drought-induced episodic depression of ANC(CB) may be important on this landscape.
[Show abstract][Hide abstract] ABSTRACT: The effects-based acid emissions management framework (EMF) for determining the need for emission control policies in the Athabasca Oil Sands Region. Canada is dependent on model simulations of future soil and surface water chemistry. An approach for regional application of the Model of Acidification of Groundwater in Catchments (MAGIC) was developed that addresses the differential sensitivity of forest soils and lakes. The approach used was a dual application wherein a plot-scale cabin-anon to forest soils and a catchment-based calibration to lake chemistry were used to account for poorly understood hydrologic connections between uplands and lakes. key processes including sulphur (S) and nitrogen (N) retention as well as groundwater sources of base cations to the lakes. The regional application was carried out at 50 lake catchments currently monitored for response to acid deposition. Simulated forest soil chemistry (Modelled at 28 catchments) exhibited small changes in base saturation under future conditions of elevated acid deposition, while in general molar BC:Al exhibited considerable change but remained well above critical chemical limits used to protect acid-sensitive forest soils. Similarly. simulations of charge balance acid neutralizing capacity (ANC(CB)) for the lakes suggested very small decreases since industrialization, and forecast projections under acid deposition double the current level suggested that only. one lake will reach the critical threshold ANC(CB) (75 mu eq L(-1)) specified by the EMF. There is limited potential for acidification impacts at the study sites.
[Show abstract][Hide abstract] ABSTRACT: The Athabasca Oil Sands Region of northern Alberta is home to the largest source of S emissions in Canada, and some of the surrounding upland forests are located on acid-sensitive soils. The relative sensitivity of these ecosystems to acidic deposition is largely dependent upon the mineral weathering rate. Weathering rates were evaluated across a range of soils (n = 43) typical of the region using a soil texture approximation (STA) and the PROFILE model. The STA was recalibrated for use in the region, and the weathering rates calculated with this method were used to calculate steady-state critical loads of acidity at 333 sites using the Simple Mass Balance (SMB) Model and a critical chemical criterion for molar base cation (Ca2+, Mg2+, K+) to aluminium ratio of 10. Soils are dominated by quartz, with small quantities of slowly weatherable minerals, and consequently weathering rates are among the lowest in Canada (median = 11.5 meq m-2 y-1), resulting in very low critical loads. Atmospheric acid (S and N) deposition varies considerably across the region, but in general is much lower than impacted areas of central Canada. Under conditions of complete N retention, 34% of the sites receive acid deposition in excess of their critical load; if all N deposition is leached, 62% of the sites are currently exceeded. Acid-sensitive soils in the region are at risk of acidifying due to pressures from industrialization associated with extraction of fossil fuels.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 12/2009; 34(4):415-426. DOI:10.4296/cwrj3404415 · 1.33 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 03/2007; 11(2). DOI:10.5194/hess-11-951-2007 · 3.54 Impact Factor
[Show abstract][Hide abstract] 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.