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Activities > Soil Compaction

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Dirt roads are common in the Mojave Desert and are a major cause of soil compaction. Photo by David Miller, USGS.

Soil compaction is one consequence of land use practices that involve trampling or off-road vehicular use. Compaction results in decreased rates of water infiltration and increased soil erosion rates. Reestablishment and growth of desert plants may also be adversely affected by compacted soils, both in terms of decreased water availability and the inability of roots to penetrate compacted layers.

The vulnerability of soil to compaction is related to its particle size distribution. Well-sorted soils (which consist of particles of relatively uniform size), such as sand dunes, do not compact significantly, while poorly-sorted soils (containing a wide range of particle sizes ), which typically occur in the desert on alluvial fans, are prone to high levels of compaction.

Soil moisture content is also important, and soils moistened by rainfall are more vulnerable to being compacted than dry soils. Once highly compacted, recovery is a function of wetting and drying cycles, freeze-thaw loosening, and bioturbation as roots and animals penetrate the denser soils.

Defining both vulnerability to and recoverability from soil compaction depends first on an understanding of geomorphic surfaces, including surficial particle size distribution. Definition of compaction recovery also requires knowledge of climatic processes such as rainfall timing and amounts, which are, int turn, strongly affected by elevation.

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General Patton's tank track from more than 50 years ago are still apparent. Measurements under the tracks relative to adjacent soils show that the track soil is still compacted, which likely influences water infiltrations. While small rocks cover the soils in the track, large rocks cover the adjacent surfaces. The tracks still lack vegetation, including lichens. Photo by Jayne Belnap, USGS.

Methodology

For compaction vulnerability, the study includes:

• Collecting representative samples of desert soils for laboratory analysis

• Georeferencing these samples and attempting to correlate with the representative geomorphic surface that they represent

• Performing laboratory compaction analyses on them using a standard ASTM technique (Proctor compaction tests)

• Statistically analyzing the samples to scale between the point measurement and landscapes

• Using geospatial techniques to distribute the resultant vulnerability measures over landscape scales

For compaction recoverability, activities include:

• Identifying representative dated disturbances where soil was highly compacted and disturbance was minimal following abandonment

• Measuring various soil properties indicative of compaction magnitude

• Analyzing the data by type of disturbance and amount of elapsed time since abandonment

• Evaluating whether the variability can be better explained by particle-size distributions, frequency of wetting and drying cycles, or other measures

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Products

Webb, R.H., 2002, Recovery of severely compacted soils in the Mojave Desert, California, USA: Arid Lands Research and Management, v. 16, no. 3, p. 291-305.

Prose, D.V., and Wilshire, H.G., 2000, The lasting effects of tank maneuvers on desert soils and intershrub flora: U.S. Department of the Interior, U.S. Geological Survey Open File Report 00-512, 26 p.

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