Road Salt Movement into Two Toronto Streams

The temporal and spatial pattern of movement of deicing salts from road surfaces to stream channels was investigated in two Metropolitan Toronto stream systems. In the early stages of thaw periods, large increases in stream chloride occurred immediately downstream from road crossing points. As the thaws continued and more heat accumulated, choloride concentrations decreased; and during the latter stages of the thaws, concentration was more uniform throughout the stream systems as the effect of dilution increased. These general patterns occurred in both urban and rural areas, but the urban areas were characterized by a more rapid and complete removal of salt, while in rural areas, the accumulation of snow and ice in roadside ditches may take some time to melt during thaw periods creating a time lag in the movement of deicing salts to watercourses.