Rocky Mountain Snowpack Chemistry at Selected Sites, 2002

During spring 2002, the chemical composition of annual snowpacks in the Rocky
Mountain region of the Western United States was analyzed. Snow samples were
collected at 75 geographically distributed sites extending from New Mexico to
Montana. Near the end of the 2002 snowfall season, the snow-water equivalent
(SWE) in annual snowpacks sampled generally was below average in most of the
region. Regional patterns in the concentrations of major ions (including
ammonium, nitrate, and sulfate), mercury, and stable sulfur isotope ratios are
presented.

The 2002 snowpack chemistry in the region differed from the previous year.
Snowpack ammonium concentrations were higher at 66 percent of sites in Montana
compared to concentrations in the 2001 snowpack but were lower at 74 percent of
sites in Wyoming, Colorado, and New Mexico. Nitrate was lower at all Montana
sites and lower at all but one Wyoming site; nitrate was higher at all but two
Colorado sites and higher at all New Mexico sites. Sulfate was lower across the
region at 77 percent of sites. The range of mercury concentrations for the
region was similar to those of 2001 but showed more variability than ammonium,
nitrate, and sulfate concentrations. Concentrations of stable sulfur isotope
ratios exhibited a strong regional pattern with values increasing northward
from southern Colorado to northern Colorado and Wyoming.

[Summary provided by the USGS.]