This study examines the effect that rainsplash-induced sediment mounds beneath desert shrubs have on sediment flux in semi-arid environments. Mounds form beneath shrubs by differential splash of particles beneath shrub canopies (i.e. a grain activity gradient). Measurements of mounds beneath rabbitbrush and broom snakeweed in New Mexico reveal that mounds range in volume from 1,000 to 16,000 cm3. Mound volume increases with increasing shrub size. A sediment transport model is developed to describe how mound development affects sediment flux by solving the Fokker-Planck Equation. Advection of sediment is determined by the local topographic gradient and mass diffusion is controlled by the activity gradient. Sediment stored in mounds is not available for downslope transport, so a local divergence of flux develops, whereby the land surface downslope of a mound experiences decreasing elevation. A decrease in sediment transport rates is observed up to two meters downslope of a mound during 40 years of shrub growth. After shrub mortality, local sediment flux increases due to the increased hillslope gradient of the mound. Within 100 years of simulated mound development, a mound persists for at least 60 years after shrub mortality, causing elevated local sediment flux. On a hillslope scale with a dynamic shrub population, these changes in sediment flux may lead to significant changes in topography over centuries to millennia. The additive effect of shrubs on sediment flux suggests that modeling larger hillslopes may not involve solving the Fokker-Planck Equation, but may be solved algebraically.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-09092010-133107 |
| Date | 14 September 2010 |
| Creators | Roberts, Andrew Scott |
| Contributors | David Furbish |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-09092010-133107/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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