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The Chemical Characteristics of Snow Cover in a Northern Boreal Forest During the Spring Run-Off Period
| Content Provider | Semantic Scholar |
|---|---|
| Author | Jones, H. G. Sochanska, Wanda |
| Copyright Year | 1985 |
| Abstract | An intensive snow-cover survey at Lake LafIamme, 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 m2) in the snowpack. Mean values for the daily wet deposition loadings (meq m2 d -1) of ionic species associated with atmospheric aerosols (H+, SO;-, NO;) were of approximately the same magnitude as the daily changes in gains recorded in the snow cover during th e melt period . In contrast, the mean value for the contribution by wet deposition to the total loads of K + and PO~ 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 th e actual losses observed for all ionic species except H +. The increases (%) in the loads for the major anions CI , NO; and SO~ were comparable (25 to 32%). The results sugges ted 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+, NH:, 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 AI3+. Mn2 +, K+ and PO;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 mic robiological degradation of organic debris. It is suggested that ion exchange capacity of both particulate and soluble organic material led to a decrease in pack acidi ty; this phenomenon should thus be co nside red as a major factor in all attempts to model acid rain f1ux es through borea I forest systems. INTRODUCTION The acidity of atmospheric precIpItation in north-eastern North America (Likens and Butler 1981) ha s been identified as the prevailing factor in the acidification of poorly buffered surface waters in both the north-eastern United States and eastern Canada (Wright 1983). In the latter region, snow, which covers the ground for 5 to 9 months of the yea r , accumulates acidic aerosols by both wet and dry deposition during th~ winter period . The subsequent sp ring season is characterized by the rapid release of pollutant loads by the snowpack (Johannessen and Henriksen 1978) lead in g to high acidity values in surface waters and concomitant st ress conditions for the aquatic biota (Driscoll and others 1980). Although the major source of the acidic input to the snow cover is the deposition of SO!and NO; aerosols transported over long distances from the ind ustrial areas of both eastern Canada and eastern and mid-western United States (Altshul!er and McBean unpublished) local characteristics of watersheds also influence the acidity of the snow cover in winter (Jeffries and Snyder 1981, Jones and others 1984). In the Laflamme watershed of Quebec, where conifer stands are predominant, Jones and others ( 1984) found tha t, although the concen tra tions of ionic species (K + excepted) in incident snowfall was, in general , little affected by the canopy , the concentration of some ionic species (H+, K+, PO; , NH:) in the snow on the ground showed unexpected temporal and spatia l variations. It was suggested that organic debri s deposited from the canopy during a nd between individual precipitation events could be the source of some of the changes observed . Dry deposition of micron and submicron acidic aerosols (Ibrahim and others 1983) and larger dust particulates of a local nature (Popp and others 1982) are already known to play a role in the evolution of the chemical composition of snow cover. The local deposition of debris from the canopy, however , can be apprecia ble in the boreal forest; its presence may dominate other deposition to such an extent that problems are enco untered both in sampling procedures and in th e subseque nt in terpretati on of the data relating the quality of incident precipitation with that of the snowpack (Jeffries and Snyder 1981, Jones and others 1984). In the study of the role that snow cover at Lake Laflamme plays in both the retention and the releas e of acidic pollutants into the stream tributaries at springtime, the influence of the local deposition of organic matter on the snow surface cannot be ignored. Thus, during the spring of 1983 we carried out a snow-cover survey at Lake Laflamme, Quebec, with the purpose of determining the impact of the coniferous stands on the chemistry of the snowpack during both premelt and melt periods. The main objective of this study was to establish the relative importance of wet and dry deposition (atmospheric aerosols, dust a nd organic debris) to the total loads of ionic species in the snow cover of boreal forest si tes receiving acid precipitation. METHODOLOGY Study area and sa mpling sit es The watershed of Lake Laflamme (0.68 km 2) li es between 777 (mea n lakewater level) and 884 m a.s .1. altitude at lat 47·19 I , long 71 ·07 I in the Montmorency Forest (mixed spruce, fir and birch) 80 km to the north of the city of Quebec, Canada (Fig.I). The mean annual precipitation is 1400 mm of which 34% is snow. The sampl ing sites for the study of the snow cover (2 1 baseline stations and one main station) were located within an area of 2880 m2 (45 x 64 m). Detailed biophysical charac terist ics of each site are described in lones and others (1984). Precipita tion (snow and rain) was collected on an event basis by means of two Sangamo Type A wet-on ly collectors placed outside the drip zone of conifers . Samples for the chemical analysis of the snow cover were obtained by coring with a clear plastic tube (Plexiglas 2 m long and 7.5 cm internal diameter) (Jeffries and Snyder 1981). No special precautions to remove surface debris from cores were taken except where twigs, lichen |
| Starting Page | 167 |
| Ending Page | 174 |
| Page Count | 8 |
| File Format | PDF HTM / HTML |
| Volume Number | 7 |
| Alternate Webpage(s) | https://www.igsoc.org/annals/7/igs_annals_vol07_year1985_pg167-174.pdf |
| Alternate Webpage(s) | https://doi.org/10.1017/s026030550000611x |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
