Tuesday, November 6, 2007
184-6

Small-Scale Heterogeneity of Soil Hydraulic Properties on Large-Scale Water Balance Simulations.

Todd Caldwell1, Michael Young2, Jianting Zhu2, and Eric V. McDonald1. (1) Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Pkwy, Reno, NV 89512, (2) Division of Hydrologic Sciences, Desert Research Institute, 755 E. Flamingo Rd., Las Vegas, NV 89119

Desert piedmonts are a mosaic of interspersed vegetation and open soil or interspaces. The distribution of perennial plants in arid regions is ultimately tied to available soil moisture. Surface soil morphological features, including desert pavement and Av horizon formation are known to affect infiltration and runoff processes. Bioturbation and the accumulation of aeolian material as well as organic matter around plant canopies result in a mound-like formation around perennial plant canopies. These micro-topographies have a significant influence on a variety of environmental factors that affect ecologic, hydrologic and pedologic development. We show that these processes control the spatial distribution of soil moisture, and how spatial heterogeneity of these linkages affects our ability to upscale or downscale the observed processes to other scales of interest. In a companion study, we characterized gradients in soil physical and hydraulic properties from canopy to interspace in the Mojave Desert using a 1.5m long array of mini-disk tension infiltrometers (MDTI) and typical physical characterization techniques. In this study, we use different averaging techniques to upscale the point-scale measurements to the field scale, including arithmetic, areal weighting, and inverse modeling. The effective parameters are then tested in larger-scale water balance simulations to examine water and nutrient movement and uptake, as functions of proximity to shrubs. The study was conducted under typical environmental conditions at the Mojave Global Change Facility (MGCF), located at the Nevada Test Site.