Project at a Glance

Title: Watershed biogeochemical processes affecting surface waters in the Sierra Nevada, with emphasis on snowmelt episodes

Principal Investigator / Author(s): Melack, John & Aaron D. Brown

Contractor: UC Santa Barbara

Contract Number: A032-116

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts, Impacts, Monitoring


Mass balances, mineral weathering and the capacity to neutralize acidic snowmelt inputs were studied during the snowmelt periods of 1992 and 1993 in two small alpine catchments (2957 m) in Sequoia National Park, California. The catchments are 0.5 and 0.2 ha with 10 and 25% soil coverage, respectively, and are dominated by granodiorite rock outcrops. Between-catchment differences in the solute concentrations of both runoff and soil solutions indicate that soils are important factors in determining the chemical composition of surface runoff. Significant relationships of [SO42-] with base cations and Si in runoff, and the reconciliation of Ca2+ residuals in stoichiometric weathering reactions achieved by subtracting Ca2+ in the equivalent amount of SO42- present, indicate that SO42- is partially a product of weathering processes in these catchments. Sulfate flux was not attributed to SO42- desorption processes. An ionic pulse of strong acid anions from the catchments was observed in runoff, but the timing of peak NO3- and SO42- export was sometimes delayed until the late snowmelt period, indicating that soil processes may help regulate the timing of solute export in these alpine catchrnents. Cation exchange processes caused pH to decrease in response to a rain-on-snow event and applications of a LiBr tracer. The retention of LiBr by predominately rock cat&n-rents suggests that acid neutralizing capacity is not compromised in areas with only sparse alpine soil cover, and rock surfaces may contribute to acid neutralization processes.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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