HR: 0800h
AN: H31C-1318    [Abstracts]
TI: A Geochemical Dataset for Improved Conceptual and Numerical Modeling of Mountain System Recharge in the Upper San Pedro Basin, Southeast Arizona
AU: * Wahi, A K
EM: awahi@dbstephens.com
AF: Daniel B. Stephens & Associates, Inc., 6020 Academy NE, Suite 100, Albuquerque, NM 87109
AU: * Wahi, A K
EM: awahi@dbstephens.com
AF: Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721
AU: * Wahi, A K
EM: awahi@dbstephens.com
AF: SAHRA, University of Arizona, Tucson, AZ 85721
AU: Ekwurzel, B
H31C-1318 AF: Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721
AU: Ekwurzel, B
H31C-1318 AF: SAHRA, University of Arizona, Tucson, AZ 85721
AU: Ekwurzel, B
H31C-1318 AF: Geosciences, University of Arizona, Tucson, AZ 85721
AU: Hogan, J F
H31C-1318 AF: Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721
AU: Hogan, J F
H31C-1318 AF: SAHRA, University of Arizona, Tucson, AZ 85721
AU: Eastoe, C J
H31C-1318 AF: SAHRA, University of Arizona, Tucson, AZ 85721
AU: Eastoe, C J
H31C-1318 AF: Geosciences, University of Arizona, Tucson, AZ 85721
AU: Baillie, M N
H31C-1318 AF: Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721
AU: Baillie, M N
H31C-1318 AF: SAHRA, University of Arizona, Tucson, AZ 85721
AB: Research to date on water resources in the Upper San Pedro Basin has not taken full advantage of geochemical methods that constrain sources and rates of recharge plus groundwater flowpaths and residence times. A recent investigation gathered data from isotopic tracers, major anions, and noble gases in groundwater to enhance conceptual and quantitative understanding of recharge processes in a semi-arid region with growing demand on limited water resources. Chemical and isotopic species potentially address flow model non-uniqueness, because including additional species reduces degrees of freedom, and radionuclides yield groundwater residence times useful for calibration of local and average regional fluxes. But the utility of these tracers extended beyond model calibration to mechanistic insights. Noble gases and stable isotopes distinguished high-elevation mountain block recharge (fracture flow) from diffuse, low-elevation mountain front recharge. Given the large uncertainties involved, few other studies have attempted to use dissolved gases to determine unknown recharge elevations, but with high topographic relief, the errors were acceptable. Stable isotopic signatures also revealed that winter precipitation contributes 40% to 90% of mountain system recharge (even though more than 50% of annual precipitation occurs in the summer) and established transpiration as the heavily dominant component of basin evapotranspiration. Multiple radionuclides traced fast and slow components of groundwater flow and thus revealed residence times ranging from annual and decadal scales above the mountain front to greater than 10,000 years for groundwater entering the San Pedro River riparian area. An independent estimate of the mountain system recharge rate obtained from the radiocarbon dataset is less than previously suggested estimates from hydraulic-conductivity-based models.
DE: 1040 Radiogenic isotope geochemistry
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1884 Water supply
SC: Hydrology [H]
MN: Fall Meeting 2005