HR: 15:25h
AN: H53F-08    [Abstracts]
TI: Geological Control of Physical and Chemical Hydrology in Vernal Pools, Central Valley, California
AU: * Rains, M C
EM: mrains@cas.usf.edu
AF: Department of Geology, University of South Florida, 4202 E. Fowler Avenue, SCA 528, Tampa, FL 33620 United States
AU: Williamson, R J
EM: rjwilliamson@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Fogg, G E
EM: gefogg@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Harter, T
EM: thharter@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Dahlgren, R A
EM: radahlgren@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AB: Vernal pools are seasonally-inundated depressional wetlands with perched water tables due to low-permeability deposits such as bedrock, mudflows, clay-rich soils, or hardpans. Vernal pools on these deposits are morphologically similar and, therefore, are treated similarly by land managers. However, these deposits result in distinct hydrological conditions. In this study, we compared the hydrology of vernal pools formed on clay-rich soils and hardpan soils, the two most common types of vernal pools in the Central Valley, California. The vernal pools on clay-rich soils were formed in fine-textured alluvial deposits that originated from sandstones, siltstones, and mudstones of marine origin. The upper 0.1 m of soil had a clay loam texture and was underlain by a saline-alkaline claypan (Aquic Natrixeralfs). The vernal pools on hardpan soils were formed in alluvial deposits that originated from crystalline bedrock. The upper 0.6 m of soil had a gravelly loam texture and was underlain by a silica-cemented duripan (Abruptic Durixeralfs). The vernal pools on clay-rich soils responded rapidly to rainfall. Rainfall perched on the surface and flowed rapidly overland to the vernal pools. There was little soil moisture or groundwater recharge, with soil saturation limited to the upper few cm after months of inundation. Most surface water evaporated, evapoconcentrating vernal pool water and resulting in high electrical conductivity. Sodium concentrations and clay contents were relatively high, resulting in dispersed clays which contributed to high turbidity. The vernal pools on hardpans responded more slowly to rainfall. Rainfall infiltrated in the uplands, perched on the hardpans, and flowed slowly through the vernal pools, discharging at the upgradient ends and recharging at the downgradient ends. Groundwater flow through the vernal pools provided a continuous source of fresh water that limited evapoconcentration, resulting in low electrical conductivity. Sodium concentrations and clay contents were relatively low, resulting in low turbidity. Though morphologically similar, these vernal pools differ hydrologically and, therefore, should be treated differently by land managers.
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting