HR: 0800h
AN: H21E-1386    [Abstracts]
TI: A Comparison of delO18 Composition of Water Extracted from Suction Lysimeters, Centrifugation, and Azeotropic Distillation
AU: * Figueroa, A
EM: envsengineer@yahoo.es
AF: University of Colorado, Denver, Dept. of Geography and Environmental Science, Campus Box 113, P.O.Box 173364, Denver, CO 80217 United States
AU: Tindall, J A
EM: jtindall@usgs.gov
AF: U.S.G.S., M.S. 413, Box 25046, Denver Federal Center, Denver, CO 80225 United States
AU: Friedel, M J
EM: mfriedel@usgs.gov
AF: U.S.G.S., M.S. 964, Box 25046, Denver Federal Center, Lakewood, CO 80225 United States
AB: Concentration of delO18 in water samples extracted by suction lysimeters is compared to samples obtained by methods of centrifugation and azeotropic distillation. Intact soil cores (30 cm diameter by 40 cm height) were extracted from two different sites. Site 1 was rapid infiltration basin number 50, near Altamonte Springs in Seminole County, Florida on properties belonging to the Walt Disney World Resort Complex. Site 2 was the Missouri Management System Evaluation Area (MSEA) near Centralia in Boone County, Missouri. The delO18 water was analyzed on a mass spectrophotometer. Potassium Bromide (KBr) was also used as a tracer and analyzed by ion chromatography. A portion of the data obtained was modeled using CXTFIT. Water collected by centrifugation and azeotropic distillation data were about 2-5% more negative than that collected by suction lysimeter values from the Florida (sandy) soil and about 5-7 % more negative from the Missouri (well structured clay) soil. Results indicate that the majority of soil water in well structured soil is strongly bound to soil grain surfaces and is not easily sampled by suction lysimeters. Also, it is plausible that evaporation caused some delO18 enrichment in the suction lysimeters. Suction lysimeters preferentially sampled water held at lower matric potentials, which may not represent total soil water. In cases where a sufficient volume of water has passed through the soil profile and displaced all previous pore water, suction lysimeters will however collect a representative sample of all the water at that depth interval. It is suggested that for stable isotope studies monitoring precipitation and soil water, suction lysimeters be installed at shallow depths (10 cm). Samples should also be coordinated with precipitation events. The CXTFIT program worked well for Florida soils (a more homogeneous sand), but gave poor performance for Missouri soils (well structured clays) except for deeper depths where clay structure was less variable. The data also suggest that each extraction method samples a separate component of soil-pore water. Consequently, centrifugation can be used with good success, particularly for efficient sampling of large areas. Azeotropic distillation is more appropriate when strict qualitative and quantitative data for desorption, desorption, and various types of kinetic studies are needed.
DE: 1800 HYDROLOGY
DE: 1831 Groundwater quality
DE: 1846 Model calibration (3333)
DE: 1847 Modeling
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005