Project at a Glance

Title: Assessing the response of Emerald Lake, an alpine watershed in Sequoia National Park, California, to acidification during snow melt by using a simple hydrochemical model

Principal Investigator / Author(s): Hooper, Richard P

Contractor: US Geological Survey

Contract Number: A732-034

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts


A sparsely parameterized hydrochemical model has been developed by using data from Emerald Lake watershed, which is a 120-hectare alpine catchment in Sequoia National Park, California. Greater than 90 percent of the precipitation to this watershed is snow; hence, snowmelt is the dominant hydrologic event. A model which uses a single alkalinity-generating mechanism, primary mineral weathering, was able to capture the pattern of solute concentrations in surface waters during snowmelt. An empirical representation of the weathering reaction, which is based on rock weathering stoichiometry and which uses discharge as a measure of residence time, was included in the model. Results of the model indicate that current deposition levels would have to be increased between three- and eight-fold to exhaust the alkalinity of the lake during snowmelt if there is a mild acidic pulse in the stream at the beginning of snowmelt as was observed during the study period. The acidic pulse in the inflow stream at the onset of snowmelt was less pronounced than acidic pulses observed in the meltwater draining the snowpack at a point using snow lysimeters or in the laboratory. Sulfate concentrations in the streamwater were the most constant; chloride and nitrate concentrations increased slightly at the beginning of snowmelt. Additional field work is required to resolve whether the an acidic meltwater pulse occurs over a large area as well as at a point (implying sulfate-regulating mechanisms in the soil) or whether, due to physical and chemical processes within the snowpack, the acidic meltwater pulse is attenuated at the catchment scale. The modest data requirements of the model permit its applications to other alpine watersheds that are much less intensively studied than Emerald Lake watershed.

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

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