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No. 94-8 |
| April 1994 | |
| RESEARCH NOTES |
| California Environmental Protection Agency | Brief Reports to the Scientific and Technical |
| Air Resources Board | Community |
| Research Division, John R. Holmes, Ph.D., Chief | P.O. Box 2815, Sacramento CA 98512 |
The objective of this project was to determine whether the Alpine Lake Forecaster could be applied to four watersheds in the Sierra Nevada for data collected between 1986 and 1988. The analysis showed that the Forecaster can be applied to three of the four watersheds. It is also suggested that one of the coefficients in the model can be used to assess the sensitivity of other watersheds in the Sierra to acidic deposition. The results of a multivariate mixing model indicate that two soil environments - the bench meadow and the inlet meadow - may explain most of the observed variation in stream chemistry. This study was performed by the U.S. Geological Survey.
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Background: |
Studies conducted under the Kapiloff Acid Deposition Program showed that there was a significant decrease in the pH and alkalinity during spring snowmelt at Emerald Lake [altitude 2800 m (9,184 ft)] in the Sierra Nevada. To determine whether changes in deposition could cause acidification during snowmelt, a computer simulation model was developed to predict the alkalinity of Emerald Lake and its inlet streams. This model, the Alpine Lake Forecaster, is a coupled hydrologic and chemical model. The chemical formulation includes mineral weathering, the carbonate buffering system, and a simplified representation of the nitrogen cycle.
At the start of the Atmospheric Acidity Protection Program in 1989, studies were planned to regionalize the findings of its predecessor, the Kapiloff Program. Toward this end, this project was proposed to determine whether the Forecaster could be applied to four other watersheds in the Sierra Nevada: Pear [2,904 m (9,528 ft)], Topaz [3,219 m (10,561 ft)], Crystal [2,951 m (9,682 ft)], and Ruby [3,426 m (11,240 ft)] Lakes. In addition, the project included sensitivity analysis of one of the coefficients in the model and the construction of a multivariate mixing model for Emerald Lake. |
| Methods: |
Regression analysis was used to test the applicability of the Forecaster to the four lakes. The intent of this application was to investigate the relevance of the hydrochemical formulation in the Forecaster, which was derived from Emerald Lake data, to the other lake watersheds. Discharge and chemical data used were from work performed under a previous ARB contract.
The multivariate mixing model is based on the premise that streamwater is a mixture of source solutions, which have more extreme concentrations than the stream itself. In this study, samples from the inlets to Emerald Lake and soil solutions from two depths at three sites were analyzed. |
| Results: |
The Forecaster was found to be applicable to Ruby and Topaz Lakes, but not to Pear Lake. The results for Crystal Lake indicated that in-lake processes not included in the model may affect water chemistry.
While the Forecaster was found to be applicable to two, and perhaps three, of the lakes, the relationships among model parameters for those lakes are weaker than for those at Emerald Lake, creating more uncertainty in model predictions. In addition, more information is needed to assure that the reaction constant is appropriate. Sensitivity analysis of the model's stoichiometric coefficient indicates that there is little change in model prediction when this number is decreased from 1.2 to 1.0; but a coefficient of 0.5 or less substantially lowers the alkalinity of the streamwater. The authors suggest that this coefficient can be used to assess the sensitivity to acidification of other watersheds in the Sierra that are hydrologically similar to Emerald Lake. Analysis by the multivariate mixing model showed that deep and shallow soil solutions were similar and that the concentrations of the soil solutions from the inlet and from bench meadows may explain the large variation in streamwater chemistry. In addition, the model showed that there is a source of calcium to the surface water that has not yet been identified. |
| Significance and Application: | For some lakes in the Sierra Nevada the Alpine Lake Forecaster will be useful in predicting short-term changes in alkalinity during spring snowmelt. Given a range of deposition rates, the model can also be used to predict the likelihood of lake acidification. |
| Related Projects: |
In 1989 Board researchers used the Episodic Event Model to assess the regional effect of changes in the deposition of hydrogen ion on short term reductions in alkalinity in lakes in the Sierra.
ARB projects in 1993 and 1994 intensively sampled nine lakes during spring snowmelt to determine the frequency and severity of acidic episodes. |
| This research was conducted under contract with U.S. Geological Survey (ARB Contract No: A932-076). Comments or questions can be directed to the contract manager, Steve Brown, by mail, FAX (916) 322-4357, phone (916) 323-1526, or e-mail: sbrown@arb.ca.gov. For an index of Research Notes, call (916) 445-0753 or FAX (916) 322-4357. |
| Copies of the research report upon which this Note is based can be ordered from: |
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U.S. Geological Survey
Books and Open-File Reports Section Box 25425, Federal Center Denver, CO 80225 Request Water Resources Investigation Report 93-4030 |
| Title: Application of a Hydrochemical Model and a Multivariate Soil-Solution Mixing Model to Alpine Watersheds in the Sierra Nevada, California |
| Author(s): Richard P. Hooper and Norman E. Peters |
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