Transformations of snow chemistry in the boreal forest: accumulation and volatilization

This paper examines the processes and dynamics of ecologically-important in organic chemical (primarily NO3-N) accumulation and loss in boreal Forest s now during the cold winter period at a northern and southern location in th e boreal forest of western Canada. Field observations from Inuvik, Northwes t Territories and Waskesiu, Saskatchewan, Canada were used to link chemical transformations and physical processes in boreal forest snow. Data on the disposition and overwinter transformation of snow water equivalent, NO3-, S O42- and other major ions were examined, No evidence of enhanced dry deposi tion of chemical species to intercepted snow was found at either site excep t where high atmospheric aerosol concentrations prevailed. At Inuvik, conce ntrations of SO42- and Cl- were five to six times higher in intercepted sno w than in surface snow away from the trees. SO4-S and Cl loads at Inuvik we re correspondingly enhanced three-fold within the nearest 0.5 m to individu al tree stems. Measurements of snow affected by canopy interception without rapid sublimation provided no evidence of ion volatilization from intercep ted snow. Where intercepted snow sublimation rates were significant, ion lo ads in sub-canopy snow suggested that NO3- volatized with an efficiency of about 62% per snow mass sublimated. Extrapolating this measurement from Was kesiu to sublimation losses observed in other southern boreal environments suggests that 19-25% of snow inputs of NO3- can be lost during intercepted snow sublimation. The amount of N lost during sublimation may be large in h igh-snowfall, high N load southern boreal forests (Quebec) where 0.42 kg NO 3-N ha(-1) is estimated as a possible seasonal NO3- volatilization. The sen sitivity of the N fluxes to climate and forest canopy variation and implica tions of the winter N losses for N budgets in the boreal forest are discuss ed. Copyright (C) 1999 John Wiley & Sons, Ltd.