Estimating the fine soil fraction of desert pavements using ground penetrating radar

A reconnaissance tool that can estimate the clay content and saturated hydraulic conductivity (K-s) of well-developed desert pavements has immediate applications for researchers and practitioners who work in arid environments. We examined the use of surface-based ground penetrating radar (GPR) to rapidly approximate these properties on six, 100-m-long transects for two different aged (similar to 100 000 vs. 4000 yr) desert pavement surfaces. We determined early-time amplitudes from GPR transects, ground electrical conductivity, hydraulic properties, clay content, water content, and soil salinity at regular intervals along each transect. Both surfaces were low in water content and salinity; however, the older pavement contained substantial amounts of silt and clay in the surficial soil horizon. Using multivariate linear regression, which included GPR amplitude and a nominal measure of soil structure ascertained by visual field inspection, we show significant correlations between measured and predicted values of both silt plus clay content (r = 0.84, P < 0.0001) and K-s (r = 0.73, P < 0.0001) for the older surface. No significant correlations were found on the younger surface. This is probably due to the low concentrations of clays in the young soil. Including the metric of soil structure improved the predictive capabilities on the older surface. The GPR method provides higher spatial resolution than electromagnetic measurements. The results suggest that, at this location, the approach is not influenced by heterogeneities in lower soil horizons. The method can be used for reconnaissance surveys as a means of estimating the clay content, and in some cases K-s, of surficial soils on certain well-developed desert pavements.