The Chemical Characteristics of Snow Cover in a Northern Boreal Forest During the Spring Run-Off Period

Abstract

An intensive snow-cover survey at Lake Laflamme, Quebec, during the spring of 1983 showed that wet deposition in the form of rain, which was a dominant phenomenon during the 1983 melt season, gave rise, according to the intensity and chemical quality of the precipitation, to both losses and gains of ion loads (meq m−2) in the snowpack. Mean values for the daily wet deposition loadings (meq m−2 d−1) of ionic species associated with atmospheric aerosols (H+, , ) were of approximately the same magnitude as the daily changes in gains recorded in the snow cover during the melt period. In contrast, the mean value for the contribution by wet deposition to the total loads of K+ and in the snow cover was far outweighed by the gains which were observed at the same time. The expected losses for the snowpack, calculated from the sum of the total loads stocked in the pack at the beginning of the melt period and the total loads in precipitation during the melt period, were lower than the sum of the actual losses observed for all ionic species except H+. The increases (%) in the loads for the major anions Cl−, and were comparable (25 to 32%). The results suggested that dry deposition either directly by aerosol interaction with the snow cover or indirectly by adsorption on organic material followed by leaching during the melt period, or by a combination of both, was a major factor in the increases observed. The values for the increases in loads for Ca2+, , Mg2+ and Na+ (50 to 287%) probably represented, in addition to leaching of local debris, the exudates of cellular material from the cell plasmolysis of detrital organic debris. High rates of in-pack production, however, were characteristic of Al3+. Mn2+, K+ and which showed substantial increases in pack loads (480 to 750%). These increases cannot be accounted for by any local phenomena other than the dissolution or microbiological degradation of organic debris. It is suggested that ion exchange capacity of both particulate and soluble organic material led to a decrease in pack acidity; this phenomenon should thus be considered as a major factor in all attempts to model acid rain fluxes through boreal forest systems.