Annual maxima in Zn concentrations during spring snowmelt in streams impacted by mine drainage

Long-term hydrochemical monitoring and 2 years of intensive sampling were used to identify annual patterns in Zn export from three neighboring catchments in Summit County, Colorado. These catchments are characterized by a snowmelt-dominated hydrologic cycle, but range in the level of mining impact from little to severe. Zn concentrations increased during snowmelt along stream reaches with a history of mining, but were diluted by snowmelt where metals originated in widely disseminated pyrite in the host rock of the catchment. Inter-site differences in the relationship between Zn and sulfate, together with inter-annual variability in the timing and magnitude of peak Zn concentrations suggest that a portion of the Zn flush is retarded, perhaps through interaction with cation exchange sites in soil. Although Dissolved Organic Carbon (DOC) concentrations also increase during snowmelt, there was no indication that the export of Zn was facilitated by the flush of organic carbon.