The salinity of motorway soils. I. Variation in time and between regions in the salinity of soils on central reserves.
Sodium chloride is used as the standard de-icing agent on motorways in England at annual application rates varying from 2 to 20 tonnes per lane km. Soil sodium concentrations in the central reserves in April were correlated with salt usage rates during the previous winter and showed regional and altitudinal variability. In the 0-50 mm layer of soil, sodium levels varied from < 500 μg g-1 to several thousand μg g-1. Sodium was more persistent in the soil than chloride. In April the highest concentration of sodium, and often also of chloride, was found in the 0-50 mm layer of the soil profile. By October much of the sodium had been transported to greater depth, and much of the chloride had disappeared from the soil. Observations extending over 6 years suggested that there was no consistent annual increase in the salinity of the soils of central reserves.