HR: 0800h
AN: B21A-0047    [Abstracts]
TI: A New Approach to Testing the Fossorial Rodent Hypothesis of Mima Mound Formation Using Airborne-Based LIDAR and a Diffusive Sediment Transport Model
AU: * Reed, S E
EM: sereed@nature.berkeley.edu
AU: Amundson, R
EM: earthy@nature.berkeley.edu
AB: Mima mounds are nearly circular soil mounds, found in grassland landscapes. In California, Mima mounds are often associated with vernal pools, seasonal wetlands that harbor rare and endemic plants and animals. The processes that form and maintain the mound-pool complexes have not yet been conclusively identified, even though such information is necessary to understand the effects that land use and climate change may have on the resilience and longevity of these landscapes. One hypothesis for the origin and persistence of Mima mound- vernal pool systems (termed the Fossorial Rodent Hypothesis) proposes that burrowing organisms such as pocket gophers (Rodentia: Geomyidae) maintain and possibly create the mounds by preferentially translocating soils towards mound centers as an adaptive response to high water tables. In order to investigate this hypothesis, the topographic characteristics and aboveground gopher activity of one of the largest remaining Mima mound-vernal pool systems in California were studied. Detailed topographic information for the mound-pool systems was obtained via an airborne-based LIDAR (Light Detection and Ranging) survey of a 25km2 region near Merced, CA. An object-oriented classification scheme, which combined different scale, shape, and spectral parameters, was employed in order to characterize the mounds. Based on the initial classification results, roughly 275,000 mounds were identified, indicating a mound density of 11,000km-2. Within the larger study area, gopher sediment transport was monitored on a 3507m2 site by conducting periodic surveys of sediment mounds created by gopher activity using a Global Positioning System and mass measurements. Downslope erosion rates (off Mima mounds) were estimated using a mass balance model which incorporates a diffusive sediment transport law. The median calculated net downslope erosion rate was 15 cm of soil per 1000 years, while the measured rate of aboveground gopher sediment movement was approximately 57cm of soil per 1000 years. Assuming that some portion of the gopher sediment movement is in an upslope direction, these results suggest that gopher soil transport may be large enough to compensate for erosion, and this activity may play a dominant role in maintaining Mima mound-vernal pool systems. The results of this study were used to guide the development of a quantitative model of gopher-driven sediment transport on Mima mound-vernal pool landscapes. This model will be used to infer the origin of the landscapes and the rates of processes critical to their continued functioning and will also help to determine, quantitatively, the role of burrowing animals as a "keystone" species on these landscapes.
DE: 0416 Biogeophysics
DE: 0480 Remote sensing
DE: 0486 Soils/pedology (1865)
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting