Snowpack

One of the major effects of acidic deposition is felt by aquatic ecosystems in mountainous terrain, where considerable precipitation occurs due to orographic lifting. The maximum effect is felt where there is little buffering of the acid by soil or rock structures and where steep lakeshore slopes allow little time for precipitation to remain on the ground surface before entering the lake. Maximum fish kills occur in the early spring due to the "acid shock" of the first meltwater, which releases the pollution accumulated in the winter snowpack. This first melt may be 5-10 times more acidic than rainfall. 

Rainfall samples collected in the Great Lakes area of Canada in 1976 and 1977 contained mean concentrations of 1-2 ng/L (parts per trillion) a-endosulfan and 4—5 ng/L P-endosulfan. Endosulfan was detected in spring and summer rainfall samples but not in samples collected during the fall and winter (Strachan et al. 1980). a-Endosulfan has also been detected in snowpack samples obtained from widely distributed sites in the Canadian Arctic. Endosulfan concentrations in samples collected in the spring of 1986 ranged from 0.1 to 1.34 ng/L (Gregor and Gummer 1989). 

Estimates of THg loading (pg/m ) can be determined for a dated snowpack interval by the product of the interval Hg concentration and the snow water equivalent, which is determined from the interval density and thickness. Seasonal and, at many sites, near annual (-90%) loadings can then be estimated by summing the interval loadings (USEPA 2003). 

FIGURE 2.9 Total Hg concentrations (ng/L) in the 2002 snowpacks at snow-sampling sites in the Rocky Mountains of the United States (GP Ingersoll and others, U.S. Geological Survey, written commun., 2003). 

Sea ice is represented in the model as a two-dimensional surface covered with a snowpack. Ice advection, rheology and snow cover are calculated from the sea-ice model embedded in MPIOM [Hibler (1979)]. The only source of pollutants for the ice compartment is deposition from the atmosphere. Once pollutants enter the ice compartment they can diffuse into the snow pore space air, dissolve in the interstitial liquid water or adsorb to the ice surface. Together with the sea ice the pollutants undergo advection. Sinks considered for the ice compartment are volatilisation to the atmosphere and release into the ocean with melt water. 

Fig. 22 Monthly variations in total water storage volumes in Switzerland from 1940 to 1981. Water storage volumes include medium-term changes in soil moisture, groundwater, snowpack, lakes, and reservoirs. Long-term changes in groundwater and glaciers are not taken into account [71]. Minimum and maximum years are indicated...

An obvious correlation between polar and alpine environments is the decrease in temperature with increasing latitude or elevation. This temperature change leads to a shift in environmental phase distribution equilibria - i.e. a chemical moves from the atmosphere to terrestrial surfaces, including direct deposition to surface waters, but also to snowpack and soils from which movement into surface and groundwater is possible. This process has been termed cold condensation but should more correctly be called cold-trapping because the contaminants are not actually condensing. 

Brown LE, Hannah DM, Milner AM (2007) Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks. Global Change Biol 13 958... 

In addition, mechanisms for regeneration of photo-chemically active bromine that involve aerosol particles or reactions on the snowpack have been proposed. For example, McConnell et al. (1992) and Tang and McConnell (1996) proposed that HBr and organobromine compounds could be converted to Br2 through adsorption and reaction on ice and aerosol particles. Fan and Jacob (1992) suggested that HOBr, formed by the reaction of BrO with H02,... 

However, what remains unknown is the source of the original bromine that initiates the chemistry. There have been a number of hypotheses, including the photolysis of bromoform which is generated by biological processes in the ocean (Barrie et al., 1988) or reactions of sea salt, either suspended in the air or deposited on, or associated with, the snowpack. These include photolysis of BrN02 formed from the reaction of sea salt particles with N2Os (Finlayson-Pitts et al., 1990), the... 

As the site is snowbound for about six months of each year, the treatment plant was designed to operate unattended for months on end. Unattended operation over short periods was demonstrated, though after the final inspection before winter the wastewater supply from the mine to the treatment plant was interrupted by rupture of the feed pipe under snow loading, which also crushed two sheds at the site. However, a flume packed with crushed limestone to neutralize mine drainage operated continuously through the winter under snowpack. 

In areas with large snowpacks (e.g., much of the Northeast and all of the mountainous West), ions have been shown to drain from the pack in the early stages of snowmelt. This process leads to concentrations that are much higher than the average concentration of the snowpack itself (82). D ifferential elution of acid anions (like N03") during the initial stages of snowmelt has been shown to be responsible for the elevated N03" concentrations observed in parts of Scandinavia (81), Canada (82), the Adirondack Mountains (181), the Midwest (182), and the Sierra Nevada Mountains (180). Ammonium deposited to the snowpack (either wet or dry deposition) can subsequently... 

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