Research on the eects of vegetation manipulation on snowpack, soil water, and streamwater chemistry and ¯ux has been underway at the Fraser Experimental Forest (FEF), CO, since 1982. Greater than 95% of FEF snowmelt passes through watersheds as subsurface ¯ow where soil processes signi®cantly alter meltwater chemistry. To better understand the mechanisms accounting for annual variation in watershed streamwater ion concentration and ¯ux with snowmelt, we studied subsurface water ¯ow, its ion concentration, and ¯ux in conterminous forested and clear cut plots. Repetitive patterns in subsurface ¯ow and chemistry were apparent. Control plot subsurface ¯ow chemistry had the highest ion concentrations in late winter and fall. When shallow subsurface ¯ow occurred, its Ca 2 , SO 4 2À , and HCO 3 À concentrations were lower and K higher than deep ¯ow. The percentage of Ca 2 , NO 3 À , SO 4 2À , and HCO 3 À ¯ux in shallow depths was less and K slightly greater than the percentage of total ¯ow. Canopy removal increased precipitation reaching the forest ¯oor by about 40%, increased peak snowpack water equivalent (SWE) 4 35%, increased the average snowpack Ca 2 , NO 3 À , and NH 4 content, reduced the snowpack K content, and increased the runo four-fold. Clear cutting doubled the percentage of subsurface ¯ow at shallow depths, and increased K concentration in shallow subsurface ¯ow and NO 3 À concentrations in both shallow and deep ¯ow. The percentage change in total Ca 2 , SO 4 2À , and HCO 3 À ¯ux in shallow depths was less than the change in water ¯ux, while that of K and NO 3 À ¯ux was greater. Relative to the control, in the clear cut the percentage of total Ca 2 ¯ux at shallow depths increased from 5 to 12%, SO 4 2À 5 . 4 to 12%, HCO 3 À from 5 . 6 to 8 . 7%, K from 6 to 35%, and NO 3 À from 2 . 7 to 17%. The increases in Ca 2 and SO 4 2À ¯ux were proportional to the increase in water ¯ux, the ¯ux of HCO 3 À increased proportionally less than water ¯ux, and NO 3 À and K were proportionally greater than water ¯ux. Increased subsurface ¯ow accounted for most of the increase in non-limiting nutrient loss. For limiting nutrients, loss of plant uptake and increased shallow subsurface ¯ow accounted for the greater loss. Seasonal ion concentration patterns in streamwater and subsurface ¯ow were similar .