Dissertation/Thesis Abstract

Effects of vegetation-related soil heterogeneity on runoff, infiltration, and redistribution in semi-arid shrubland and grassland landscapes
by Bedford, David Ralph, Ph.D., University of Colorado at Boulder, 2008, 195; 3337180
Abstract (Summary)

Semi-arid landscapes typically consist of patchy vegetation and associated soil heterogeneity. The dynamics of runoff and infiltration have been hypothesized to ecohydrologically link vegetated and un-vegetated areas. We studied small-scale soil heterogeneity and its effect on runoff, infiltration and redistribution of water in two semi-arid shrublands and a grassland landscape. We analyzed heterogeneity of surface soil properties in relation to the vegetation type and pattern, and landforms. Most of the soil properties studied are different under vegetation from the bare-ground intercanopy area. Microtopography and saturated conductivity are almost always higher under plant canopy and decreased with distance away from canopy. The magnitude and scale of spatial variability varies primarily with vegetation type and landform. Geostatistical analysis shows that soil heterogeneity commonly extends 3-4 times the width of plant canopy.

We quantified the effects of microtopography and saturated conductivity variability on runoff in the grassland site. We used runoff observations and a numerical model that couples infiltration and overland flow over detailed maps of heterogeneous soil properties. Microtopography has ∼30 times larger effect than saturated conductivity: omitting microtopography can result in 200% more runoff predicted by the model. The effect of microtopography is due to depression storage, which affects the timing of runoff, hydrograph shape, spatial distribution of overland flow depths, and the location and magnitude of infiltration.

We studied the effects of overland flow on the spatial pattern and magnitude of infiltration, a process dubbed redistribution. Redistribution has been hypothesized to play a key role in the ecohydrologic function of drylands. Redistribution was only detected in alluvial fan shrublands and gently sloping grasslands. Most redistribution occurs near the edges of vegetation canopy rather than underneath. Infiltration of surface water in microtopographic depressions was found to be more important than inundation of more infiltrable plant mounds, even in the case of extreme variations in infiltration capacity.

Soil heterogeneity associated with semi-arid vegetation strongly affects the location and amounts of runoff and infiltration in semi-arid shrublands and grasslands. Microtopography, which is relatively unstudied in dryland ecohydrology, affects runoff, infiltration, and concentration of rainfall more than variability of infiltration capacity at our sites.

Indexing (document details)
Advisor: Small, Eric E.
Commitee: Anderson, Robert S., Beatty, Susan W., Miller, David M., Tucker, Greg E.
School: University of Colorado at Boulder
Department: Geology
School Location: United States -- Colorado
Source: DAI-B 69/11, Dissertation Abstracts International
Subjects: Ecology, Geography, Geology
Keywords: Grasslands, Infiltration, Overland flow, Plant patterns, Redistribution, Runoff, Semiarid, Shrubland, Soil heterogeneity
Publication Number: 3337180
ISBN: 978-0-549-91865-3
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