Monday, November 13, 2006

Impact of Spatial Variability of Soil Properties on Local Water Balance in a Mojave Desert Ecosystem.

Darren Meadows, Michael Young, and Lynn Fenstermaker. Desert Research Institute, 755 E. Flamingo Rd, Las Vegas, NV 89119

The Mojave Global Change Facility (MGCF), located approximately 100 km north of Las Vegas, NV, is comprised of 96 individual 14 m by 14 m test plots.  The site is used as a testing area for understanding the impact of atmospheric inputs (nitrogen and precipitation) and soil disturbance on a variety of ecosystem responses.  Although significant monitoring of plant and soil properties is ongoing, little attention has been given to the spatial variability of soil properties across the facility.  Such variability may explain some of the complex trends that researchers at the MGCF have observed.  In this study, we examined whether and to what extent the spatial variability of soil properties could impact the water balance across the MGCF, and whether these impacts could explain replicate variability.  We collected cores from all 96 plots at two depths from which particle size distribution and bulk density were determined.  We then used pedotransfer functions to estimate the hydraulic properties at the sample locations and created distribution maps of the hydraulic properties.  Variogram analyses showed that the hydraulic properties transition to values more typical of a finer grained texture toward the northeast quadrant of the facility.  We also conducted numerical experiments to examine whether and how soil property variability affects the depth of wetting and soil water content across the MGCF.  The simulations incorporated locally-measured climate data for a period of ~8 years, and included multiple two-dimensional profiles of hydraulic properties estimated from the pedotransfer functions.  We also examined changes in local soil moisture dynamics due to the presence of plants and correlated those changes to soil hydraulic properties.  Results indicate that significant variability in the water balance can be explained by the measured variability in the hydraulic properties, and that further research findings should consider soil property variability as an experimental variable.