CHEMICAL FLUXES AND SENSITIVITY TO ACIDIFICATION OF 2 HIGH-ELEVATION CATCHMENTS IN SOUTHERN WYOMING

Hydrological and chemical fluxes were examined for East and West Glaci er Lakes and their adjacent high-elevation (3200-3700 m) catchments in the Snowy Range of southern Wyoming. Both lakes are approximately 3 h a, but the East Glacier catchment (29 ha) is about half the size of We st Glacier. Bedrock is primarily quartzite that has been heavily fract ured and crossed with mafic intrusions. Precipitation pH averages abou t 5.4-5.5, and weighted mean acid neutralizing capacities (ANC) of the discharge are about 50 mu equiv. l(-1) for East Glacier lake and 39 m u equiv.l(-1) for West Glacier, while the respective annual base catio n removals are about 36 mequiv. m(-2) and 73 mequiv.m(-2). Two West Gl acier tributary streams average less than 10 mu equiv.l(-1) ANC, but s olute concentrations during the early snow melt are more than five tim es those found in midsummer. It is inferred that these early high conc entrations primarily are due to early elution of solutes from the snow pack rather than the displacement of high-concentration groundwater, b ut the cations may be substantially affected by exchange reactions. Pr eliminary evaluation suggests that the mean ANC of both lakes would fa ll below zero if precipitation pH were to fall to 4.2-4.3. Episodic ac idity during snowmelt and acidification of tributary streams would lik ely occur at a somewhat higher precipitation pH.