Pollutant release from a disturbed urban snowpack in northern Sweden

Water and pollutant release from a disturbed urban snowpack was studied in an experimental plot encompassing a road section and the adjacent grassed boulevard in the city of Lulea, in northern Sweden. Winter road maintenance in this area includes snow ploughing and applications of grit without any road salts. During the study period, 18 snowmelt events were observed. Compared to rural areas and urban areas with extensive use of chloride in winter road maintenance, in the former case, the observed snowmelt quality differed by relatively high and uniform pH (7.7–8.1) and, in the latter case, by low chloride event-mean-concentrations (EMCs) (5.7–123.4 mg/L) and conductivity (11.6–60.7 mS/m). Total suspended solids (TSS) EMCs greatly exceeded those reported for rural snowmelt and urban rainfall runoff and contributed to the high pH buffering capacity of deposited snow. Observed concentrations of total and dissolved heavy metals were compared to water quality guidelines that suggested a high likelihood of biological effects. Chloride was the only pollutant that indicated an early release and all other constituents showed a uniform release with snowmelt from the snowpack. The partitioning of heavy metals between total and dissolved phases indicated the highest dissolved fractions for Cu, followed by Cd, Ni and Zn, and the lowest values were observed for Pb. The urban snowmelt characteristics substantially differed from those reported for undisturbed sites with respect to higher pollutant loads, high pH buffering capacity and a general absence of early or delayed pollutant release from the snowpack.