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The Chemistry of Snow and Meltwaters Within the Mesostructure of a Boreal Forest Snow Cover
| Content Provider | Semantic Scholar |
|---|---|
| Author | Jones, H. G. |
| Copyright Year | 1985 |
| Abstract | A physical and chemical study of snow mesostructure was carried out in a boreal forest site at Lake Laflamme, Quebec in spring 1983. The concomitant physical observations and 6180%0 data on the upper layers led to the reconstruction of recent snowfall events and meltwater movements which influenced the chemistry of snow at different levels of the snowpack. Correlations between data relating the concentrations of atmospheric pollutants in snow strata were significant (H+, SO!-, r = 0.89; H+, NO;, r = 0.81, P ( 0.001). The grouping of chemical species by factor analysis distinguished clearly between ionic species originating from the long-range transport of atmospheric pollutants and those due to local deposition phenomena and organic debris from the forest canopy. Mesostructural characteristics led to heterogeneous flow patterns of meltwater and rainwater through the snow cover. Both physical and chemical characteristics of the snow mesostructure change rapidly in a non-uniform manner under such conditions. This leads to increased difficulties in the interpretation of data gathered during snow sampling studies on pack decay during the spring run-off period. INTRODUCTION The chemical evolution of snow cover depends both on deposition phenomena (wet and dry deposition of acidic pollutants, local dust and organic debris) and on subsequent ionic and organic transformations in the pack (Jones and Sochanska 1985). Although samples taken by means of snow cores (Jeffries and Snyder 1981) and/ or integrated samples from snow-pits (Adams and others 1982) are used to follow general chemical trends in snowpack evolution, the complex nature of the structural characteristics of the pack such as snow strata, ice lenses, localized debris and voids make it difficult to follow in-pack chemical transformations from the data obtained. This is particularly true for snow cover in boreal forest sites where a large amount of organic debris is continually deposited from the canopy. Its presence is such a dominant feature of snow cover evolution that problems are encountered both in sampling procedures and in the interpretation of the data relating the quality of incident precipitation with that of the snowpack (Jones and Sochanska 1985). In particular, the spatial irregularity in the deposition of large amounts of debris causes variations in the physical nature of the snow cover. This, in turn, can influence meltwater flow and cause spatial variability in the chemical content of the snowpack, particularly during periods when the presence of free water (meltwater and/ or rain) is appreciable. Most of the organic debris falls from the canopy between precipitation episodes and can be removed during the sampling of discrete strata in the snow cover. In contrast, snow cores are often contaminated with large amounts of organic debris collected during the sampling procedure. It was thus thought that data from snow strata could offer more precise information on the possible mechanisms for the transformation of chemical components from atmospheric aerosols in the snowpack. In the spring of 1983, an intensive study on the evolution of chemical species (H+, NH;, Na+, K+, Ca 2 +, Mg 2 +, AI, Mn, CI-, NO;, SO!-, PO~-) in snow cores (168 samples) and snow strata (95 samples) was carried out during spring at the Lake Laflamme watershed (Jones and others 1984). This present article discusses the distribution and evolution of ionic species in the snowpack and its component strata observed before and during the spring melt period of 1983. To define the successive arrangements of strata in the vertical profile of a snowpack, I have adopted the term "mesostructure". The term was used in this sense by Langham (1974); it should be noted, however, that the definition of Langham differs from that of McKay and Gray (1981) for the mesostructure of snow cover in general. METHODOLOGY Study area and sampling sites The watershed Lake Laflamme (0.68 km 2 ) lies between 777 (mean lakewater level) and 884 m altitude at lat 47°19'N and long 71°0'W in the Montmorency Forest, 80 km to the north of the city of Quebec, Canada. The study area, sampling sites and sampling frequency for snow cores are described in Jones and others (1984) . Three snow-profile stations (A and B under intermediate forest canopy cover, C in open area) were sampled once only for the chemical stratigraphy study on 9 April 1983 when all strata were collected. Site A was 4 m to the south-west of site B while site C was II m to the east of site B. Different strata were identified by eye (organic debris and / or morphic sta te of snow grains) or by touch (ice lenses). Although the method is subjective, it works well; cross-checks with three observers in the field showed tha t the mesostructure of the snow cover as recorded by each observer agreed to within 90% of all the snow strata identified (87 samples). This percentage success rate drops (3 75%) and becomes more erratic after spring melt starts. 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 in diameter) (Jeffries and Snyder 1981). Individual snow strata were also cored with the same device by inserting it horizontally into the face of the snow-pit. The snow-pits (Adams and others 1982) were dug to permit a better appreciation of the physi ca l mesostructure of the snow cover and the removal of separate snow strata with large plastic spatulas (26 x 26 cm). As the deposition of organic debris from the canopy is heterogeneous, large particula te material was removed manually from the top of each stratum during the sampling. All samples were placed in plastic bags (polyethylene) and kept at -20°C until melted for analysis. To determine the meltwater flow patterns at different levels of the snowpack structure, small lysimeters constructed from ABS tubing cut lengthwise (10 cm x I m and 12.5 cm x 1 m) were inserted at the interfaces between the different strata at sites A and B on 12 April 1983. The lysimeters were placed in a vertical staggered pattern in the faces of the snow-pits in order to a void in terference of one I ysimeter with another during the movement of meltwater through the pack. |
| Starting Page | 161 |
| Ending Page | 166 |
| Page Count | 6 |
| File Format | PDF HTM / HTML |
| DOI | 10.1017/s0260305500006108 |
| Volume Number | 7 |
| Alternate Webpage(s) | https://www.igsoc.org/annals/7/igs_annals_vol07_year1985_pg161-166.pdf |
| Alternate Webpage(s) | https://doi.org/10.1017/s0260305500006108 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
