Chloride inputs to the North Saskatchewan River watershed: the role of road salts as a potential driver of salinization downstream of North America's northern most major city (Edmonton, Canada)

Abstract

Multiple anthropogenic activities are driving the salinization of freshwater environments threatening water resources worldwide. Accordingly, this research will first examine the spatial and temporal variability of major ions (i.e. Ca2+, Mg2+, Na+, K+, SO42−, CO32−, and HCO3−) upstream and downstream of the northernmost major city in North America (Edmonton, Canada). Second, this research will estimate the relative contributions of the major sources of chloride (Cl), the main constituent of road deicers, to the sub-basin around Edmonton. Monthly water quality data was for three sites on the North Saskatchewan River (NSR): Rocky Mountain House (RMH - downstream of the Rocky Mountain headwaters), Devon Bridge (upstream of Edmonton) and Pakan Bridge (downstream of Edmonton). Change ratios investigate the downstream alterations of major ions at Pakan and Devon, relative to RMH. Seasonal Kendall tests examine temporal trends (1987–2017). A mass-balance approach then quantifies the major sources of Cl in the sub-basin of the NSR between Devon and Pakan. Progressing from the Rocky Mountain headwaters (at RMH) to downstream of Edmonton (at Pakan), Cl− increased by >5.5 times, Na+ by 4.8 times and K by 2.7 times. No significant temporal trends for Cl−, Na+ and K+ were evident at Devon (upstream of Edmonton), whereas all three significantly increased at Pakan (downstream of Edmonton). Deicers (54%), agriculture (20%), along with waste water treatment plant and industrial effluent (15%) were the largest Cl sources in the NSR Devon-Pakan sub-basin. In total, 77 Gg yr−1 of Cl (or 6 t km2 yr−1) is added to the Devon-Pakan sub-basin, of which, 43 Gg yr−1 is retained. Understanding and managing the major drivers of freshwater salinization will be of increasing importance in the 21st century owing to the potential salinization of freshwater resources in the context of a changing climate.