HR: 17:10h
AN: B24C-05    [Abstracts]
TI: Estimating Seasonal Changes in Volumetric Soil Water Content at Landscape Scales in a Savanna Ecosystem Using Two-Dimensional Resistivity Profiling
AU: * Garcia-Montiel, D C
EM: dgarcia@uprm.edu
AF: University of Puerto Rico Department of Biology, PO Box 9012, Mayaguez, PR 00681, United States
AU: Coe, M T
EM: mtcoe@whrc.org
AF: The Woods Hole Research Center, 149 Woods Hole Rd, Falmouth, MA 02540, United States
AU: Davidson, E A
EM: edavidson@whrc.org
AF: The Woods Hole Research Center, 149 Woods Hole Rd, Falmouth, MA 02540, United States
AU: Cruz, M P
EM: meyrcruz@gmail.com
AF: University of Brasilia Department of Ecology, Campus Universitario Darcy Ribero, Brasilia, DF CEP 70.919,
AU: Ferreira, J
EM: joice@cpatu.embrapa.br
AF: EMBRAPA, Amazônia Oriental, Belem, Para, Caixa Post, Brazil
AU: da Silva, E M
EM: euzebio@cpac.embrapa.br
AF: EMBRAPA, Planaltina, DF, Brasilia, DF CEP 70.919, Brazil
AB: Water distributed in deep soil reservoirs is an important factor determining ecosystem structure of water-limited environments, such as the seasonal tropical savannas of South America. We employed a two-dimensional (2-D) geoelectrical profiling technique to estimate seasonal dynamics of soil water content to 10m depth along transects of 275-m in savanna vegetation. Resistivity values along these 2-D resistivity profiles were converted into volumetric water content (VWC) by soil depth. These resistivity profiles revealed the following soil and aquifer structure: 0-4m of permanently unsaturated and seasonally droughty soil, less severely dry unsaturated soil at about 4-7m, nearly permanently saturated soil between 7-10m, mostly impermeable saprolite interspaced with fresh bedrock of parent material at about 10-30m, and a region of highly conductive water-saturated material at 30m and below. Temporal dynamics in VWC indicate that the active zone of water uptake is predominantly 0-7m, and follows the seasonal cycles of precipitation and evapotranspiration. Uptake from below 7m may have been critical for a short period near the beginning of the rainy season, although the seasonal variations in VWC in the 7-10m layer are relatively small and lag the surface water recharge for about 6 months. Calculations using a simple 1-box water balance model indicate that average runoff was 15-20 mm/mo in the wet season and about 6 mm/mo in the dry season. Modeled ET was about 85 mm/mo in the wet season and 20-25 mm/mo in the dry season. Variation in basal area and tree density along one transect was positively correlated with VWC of the 0- 3m and 0-7m soil depths, respectively, during the wettest months. These multi-temporal measurements demonstrate that the along-transect spatial differences in soil-moisture are quasi-permanent and influence vegetation structure at the scale of tens to hundred of meters.
DE: 1813 Eco-hydrology
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1865 Soils (0486)
DE: 1878 Water/energy interactions (0495)
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting