Greg Giberson

Chloride (Cl) salts, while an effective de-icing agent, have negative environmental effects on local aquatic ecosystems, especially in urban and urbanizing watersheds. Assessments of Cl retention and transport at the watershed scale require accurate estimates of road salt inputs; however complex jurisdictional control over salt applications makes this task challenging. This study uses a geospatial approach to combine information on road salt application rates, road networks, and watershed characteristics to estimate watershed-scale Cl inputs. Geospatial shapefiles were used to calculate total road “lane-lengths” for each subwatershed, provincial and municipal road salt application data were used to determine rates of salt application, and these were allocated to the relevant road network and summed to the subwatershed of concern. Approximately 60%-70% of the variance in salts/solids distributed for the provincial roadways in each watershed was explained by a combination of meteorological variables, including air temperature and total snowfall. Several watersheds stood out as having higher than normal Cl inputs per unit lane-length that were not explained by meteorological patterns, indicating a potential discrepancy between winter road maintenance guidelines and actual activities. The results of this study will provide watershed-scale inputs for chloride mass balance analyses to assess chloride retention across a range of urbanizing catchments in southern Ontario. Future research will focus on integrating private and commercial salt application into the watershed-scale Cl input estimates.

Keywords: road salt, chloride, geospatial, non-point source pollution, watershed, lane-lengths