Project at a Glance

Title: Survey of soil map unit sensitivity to acid deposition in the Sierra Nevada, California

Principal Investigator / Author(s): Reilly, Timothy A.

Contractor: North State Resources, Inc. and UC Davis

Contract Number: A732-037

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition


A method for classifying soil map units on the basis of relative response to acid deposition is described. Study area boundaries are the crest of the Sierra Nevada west to the interface of the mesic and frigid soil temperature regimes; and from 3545'00" north latitude to 3931 '44" north latitude. The Emerald Lake Integrated Watershed Study Area and seventy-eight sampled Sierran lakes are included in the 2,116,448 acre study area.

A computer program was developed which calculates changes in soil base saturation and pH given soil chemical parameters and an acidification regime. A rate of 0.3 kmol H+ /hectare/year was imposed on soils for 50 years to determine relative capacities to maintain base saturation and pH.

One hundred sixty-seven soil samples from forty-three modal soil profiles were analyzed for relevant chemical characteristics. Extrapolations were made on the basis of soil taxonomic similarities to represent the chemical composition of the one hundred fifty taxonomic components, which occur in the study area.

Soil chemical data and map unit data were organized in a relational database. Taxonomic units were ranked according to the projected base saturation after fifty years of deposition. This ranking was combined with soil hydrologic grouping and map unit slope to rank soil map units in terms of their relative abilities to attenuate additions of strong mineral acids. Map units on less steep slopes containing high percentages of soils with low runoff characteristics and high buffering capacities are termed least sensitive. Other soils are termed moderately sensitive or most sensitive.

The distribution and relative sensitivities of soil map units are presented in a 1:62,500-scale map registered to USGS IS-minute quadrangles. Forty-five IS-inch by 24-inch sheets are required for coverage of the entire study area.

Approximately 25 percent of the study area (527,564 acres) are least sensitive on the basis of the present ranking criteria. Eighteen percent, (380,677 acres) are moderately sensitive; fifty-six percent (1,183,601 acres) are most sensitive. Water bodies occupy 24,586 acres, or 1 percent of the study area.

Soil map unit delineation boundaries are retained on the sensitivity map. Because of this, in addition to its value as an index to relative map unit sensitivity, the document is a source of regional baseline soil survey information.

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

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