Water Resources Research, V 27, p 1563-1574, 1991
Precipitation chemistry in and ionic loading to an alpine basin, Sierra Nevada
Mark W. Williams
Department of Biological Sciences
University of California
Santa Barbara, CA
John Melack
Department of Biological Sciences
University of California
Santa Barbara, CA
Abstract:
Wet deposition of solutes to an alpine catchment
in the southern Sierra Nevada was measured from October,
1984 through March, 1988.
Rainfall had a volume-weighted pH of 4.9 and snowfall had a
volume-weighted pH of 5.3.
Acetic and formic acids
were important components of
all wet deposition,
contributing 25-30% of the measured anions in snowfall,
and through analysis of charge balance deficits
the same percentage in rainfall.
The nitrate to sulfate equivalent ratio for all wet deposition was 1.16.
Ammonium concentration was 10-fold greater than H+ in rainfall;
ammonium nitrate and ammonium sulfate appear to be the principal
nitrate and sulfate containing aerosols in wet deposition.
Snowmelt runoff (1985 and 1986) or snowpack runoff plus rainfall
during the period of snowpack runoff (1987)
supplied 90% of the annual solute flux from wet deposition
to the catchment.
The amount of snow water equivalence (mm/m2)
and H+, SO4, and Cl (equivalents/m2) in
cumulative snowfall measured on snowboards
was similar to the accumulated deposition of these
parameters measured in snowpits at midwinter and maximum snow
accumulation periods,
while about 20% of the @no3@ in snowfall was not stored
in the winter snowpack.
Dry deposition was therefore not an important
contributor of H+, NO3, and SO4 to the winter snowpack.
The source of the ions in snowfall
was air masses that originated over the Pacific Ocean,
while low Cl and Na relative to NO3 and NH4
in rainfall indicate that local urban and agricultural areas
were the major source of the ions in rainfall.