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Published June 15, 2002 | public
Journal Article

Comparative characterization of volcanic ash soils exposed to decade-long elevated carbon dioxide concentrations at Mammoth Mountain, California


Elevated concentrations of soil CO_2, ranging from 20% to 90%, from a magmatic source have been killing coniferous trees in the last decade in several distinct areas on the flanks of Mammoth Mountain, California. These areas of elevated soil CO_2 provide a natural laboratory to examine how chemical weathering in soils responds to extremely high-CO_2 concentrations in conjunction with possible changes in organic acids resulting from vegetation mortality. These volcanic ash soils have a particularly low resistance to chemical weathering due to the predominance of volcanic glass and other noncrystalline phases. Thus, decade-long exposure to anomalous conditions may result in differences in soil characteristics. Soil samples from within the high-CO_2 region have been analyzed and compared to samples from outside the anomalous area in the adjacent healthy forest areas where background CO_2 concentrations are less than 1%. Compared to the control soil, the high-CO_2 soil has lower pH values (5.0 compared to 5.6), higher soil moisture content, and higher surface area. Dithionite-citrate and acid-oxalate extractants were less effective in leaching Al and Si from the high CO_2 than from the control soil, indicating a distinct difference in the mineralogy of these soils. The observed differences between the high-CO_2 and control soils are consistent with an enhancement of weathering intensity in the soil exposed to elevated CO_2 concentrations.

Additional Information

© 2002 Elsevier Science B.V. Accepted 18 January 2002, Available online 21 February 2002. We thank the reviewers, Oliver Chadwick and Paul Schroeder, for their comments and helpful criticisms which improved the manuscript. We thank Dr. Robert C. Graham of UC Riverside for his suggestions, Dr. Chi Ma for help in interpreting our XRD diffractograms, John Rogie for sharing his knowledge of the field site and Johnny Lam for his assistance with the analysis of organic acids. Financial support from the American Chemical Society Petroleum Research Fund (Grant # 34558-AC2), the ARCS Foundation, an EPA STAR Graduate Fellowship, and an NSF Graduate Fellowship is gratefully acknowledged

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