Browsing by Author "Gue, Anita"

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    Influence of saline groundwater discharge on river water chemistry in the Athabasca oil sands region – A chloride stable isotope and mass balance approach
    (Elsevier, 2017-12-01) Gue, Anita; Grasby, Stephen E.; Mayer, Bernhard
    A chloride mass and stable isotope (δ37Cl) balance approach was employed to calculate the effect of saline groundwater discharge into the Athabasca and Clearwater rivers in the Athabasca Oil Sands Region (AOSR) in north-eastern Alberta, Canada. Saline groundwater affected by halite, carbonate, and anhydrite dissolution discharges Na-Cl type water with total dissolved solids (TDS) up to 51,700 mg/L from exposed Devonian and Cretaceous units in the river valleys in this area. In this study, nine springs discharging groundwater with a median Cl concentration of 9800 mg/L were sampled and chloride stable isotope ratios were determined, with δ37Cl values ranging from 0.2 to 1.0‰. In contrast, river waters had historical monthly median Cl concentrations between 5.9 and 49.5 mg/L and δ37Cl values between −2.2 and −1.4‰. The discharge rate of saline groundwater was calculated to be 100 ± 20 L/s into the Clearwater River and 134 ± 68 L/s into the Athabasca River. The chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions, metals, and PAHs in the Athabasca and Clearwater rivers. Overall, saline groundwater contributed less than 0.2% of river discharge, but 0.04–39% of major ion concentrations in the rivers, with highest contributions under winter low-flow conditions. In the Clearwater River, saline groundwater contributed 23–39% of average monthly Cl flux and 18–32% of average monthly Na flux. For the same major ion fluxes in the Athabasca River, saline groundwater contributed 12–18% and 6–12%, respectively. The influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible, contributing less than 1% of river fluxes of Cu, Ni, Pb, and Zn. Similarly, the influence on mass flux of PAHs in the rivers was found to be negligible (<0.03%) but quantifiable. These results provide important insights on the natural contributions of saline groundwater discharge to river chemistry in the AOSR, a necessary factor to consider when monitoring for anthropogenic effects of oil sands development on river water quality.
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    The geochemistry of saline springs in the Athabasca oil sands region and their impact on the Clearwater and Athabasca rivers
    (2013-01-08) Gue, Anita; Mayer, Bernhard; Grasby, Stephen
    The geochemistry of saline springs discharging from Devonian carbonate rocks into the Clearwater and Athabasca rivers in northeastern Alberta was characterized using major ions, trace elements, dissolved gases, and PAHs. In addition, stable isotope analyses of H2O, SO4, DIC, Sr, and Cl were used to trace the provenance of spring waters, dissolved solutes, and subsurface processes affecting water chemistry. Spring waters were found to contain Laurentide glacial meltwater, which was supported by radioisotope analyses. The high salinity of the springs was found to be mainly due to evaporite and carbonate dissolution in the subsurface. Spring waters have been affected by bacterial sulfate reduction, methanogenesis, and methane oxidation. Trace elements and some PAHs were present in low concentrations, the origins of which did not seem to be weathering of bitumen. The total discharge of saline groundwater into the rivers over the study reach was estimated using a Cl isotope mass balance approach, which revealed that saline groundwater accounts for only a very small proportion of the annual mass flux in the rivers of trace elements and PAHs, but accounts for a higher proportion of major ions, particularly in the Clearwater River.