Major iron and stable isotope geochemistry of the Bow River, Alberta, Canada

Abstract

Natural and anthropogenic impacts on the major ion and isotope geochemistry of the Bow River were evaluated between 2007 and 2008 using integrated hydrometric, chemical and isotopic analyses. Under the influence of mineral dissolution, calcite­gypsum solubility, and wastewater and prairie tributary discharges, the river water evolved from a Ca-Mg-HCO3 type in the Rocky Mountain headwaters towards compositions elevated in Na, SO4, Cl and NO3 with downstream distance. Mass loads of SO4 and NO3 increased with flow distance, and concentrations of SO4 and NO3 were highest throughout the river during baseflow periods in fall and early spring. Isotope mass balances using two end-member mixing models demonstrated that riverine SO4 is a mixture of 53-63% of mainly evaporite derived sources from the Rocky Mountains, 27-37% of oxidized S and wastewater SO4 sources from the prairies, and 10% of wastewater derived SO4 from Calgary. Riverine NO3 is mainly derived from nitrification in forest soil and wastewater effluents, and is more impacted by anthropogenic sources than S04. Wastewater derived NO3 accounted for 84-92% of the NO3 load downstream of Calgary as opposed to :S50% in the upstream reaches. This study demonstrates that sources of SO4 and NO3 in the Bow River can be effectively differentiated and apportioned via integrated isotopic techniques.