High-frequency observations reveal acute chloride pulses and chloride legacy effects in an urbanizing watershed impacted by road salting
- Ryerson University, Geography and Environmental Studies, Toronto, Canada (coswald@ryerson.ca)
In watersheds impacted by urban growth and road salt usage, increasing stream chloride (Cl-) concentrations are well-documented. Peaks in stream Cl- concentrations that exceed chronic and/or acute water quality guidelines are typical in the winter salting season when Cl- (from Cl--based de-icers) is flushed from the landscape but are not easily measured with grab samples. In some cases, chronic Cl- conditions persist into the summer growing season due to a build-up of Cl- in the subsurface. Estimating the proportion of Cl- loads transported in the salting and non-salting seasons is of interest for tracking the relative role of subsurface Cl- pools to the annual load, as well as the influence of runoff events on loads across the two periods. In this study, we made use of a 6-year record of high-frequency stream Cl- concentrations from an urbanizing watershed in southern Ontario, Canada. High-frequency measurements revealed that the acute and chronic water quality guidelines for Cl- were exceeded for 7 and 97 % of the study period, respectively. Salting season Cl- loads were 2 to 5 times higher than in the non-salting season, but surprisingly, inter-event periods contributed 21 to 56 % of the annual load across years. The results of this study illustrate the utility of high-frequency sensors for identifying water quality extremes that negatively impact aquatic ecosystems, identifying Cl- transport pathways, and tracking the build-up of legacy Cl- in the subsurface.
How to cite: Oswald, C., Ross, C., Moslenko, L., and Wellen, C.: High-frequency observations reveal acute chloride pulses and chloride legacy effects in an urbanizing watershed impacted by road salting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12985, https://doi.org/10.5194/egusphere-egu22-12985, 2022.