HR: 14:10h
AN: H33G-03    [Abstracts]
TI: Using Multiple Natural Tracers to Investigate Groundwater Recharge and Flow in Mountains
AU: * Earman, S
EM: searman@dri.edu
AF: Division of Hydrologic Sciences, Desert Research Institute, 2215 Raggio Parkwy, Reno, NV 89512-1095 United States
AU: Phillips, F M
EM: phillips@nmt.edu
AF: Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801 United States
AB: Because mountain precipitation provides the majority of groundwater recharge in the western USA, an understanding of groundwater recharge and flow in mountain ranges is needed to make informed resource-management decisions.
Natural tracers are excellent tools for studying these systems, but a single tracer can only provide limited information. As a result, using multiple tracers is ideal - by using several tracers, several aspects of mountain groundwater systems can be examined. For instance, groundwater stable-isotope measurements (δD and δ¹⁸O) can reveal the elevation at which the water fell as precipitation, but not the elevation at which the water was recharged. However, concentrations of dissolved gases in groundwater can be used to determine actual recharge elevations. Major-ion chemistry can provide insight into the geologic units through which the water has moved, and may also provide a qualitative indication of residence time; radioisotopes can yield more precise estimates of groundwater age. Other information is helpful for interpreting natural tracer data, including the local and regional geology, the area's climate, and the locations where groundwater recharge ('disappearing' streams) or discharge (springs and seeps) occur.
A study utilizing these tools was conducted in the Chiricahua Mountains (Arizona, USA). Stable-isotope data show that precipitation from near the crest of the range is responsible for the majority of the groundwater recharge. Dissolved-gas data indicate that, while most of this recharge takes place near the crest of the range; some waters recharge in a high-permeability zone near the base of the range. Based on our observations of the range's hydraulics, the majority of this low-elevation recharge appears to be 're-recharge'---water that recharged at higher elevations, flowed underground, discharged, flowed downslope overland, then re-recharged. Major-ion chemistry data show that both volcanic (tuff and rhyolite) and sedimentary (primarily carbonates) units are conduits for groundwater flow in the range, depending on location. Dissolved-gas data demonstrate that the extent of the high-elevation recharge zone is nearly identical to the area of the range that develops snowpack. If snowpack development is a needed condition for recharge in other ranges of the western USA, groundwater recharge could be seriously impacted if current predictions for global-warming-induced changes in precipitation in the western USA (decreased percentage of precipitation falling as snow, and higher snowlines) are accurate.
DE: 1655 Water cycles (1836)
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Hydrology [H]
MN: Fall Meeting 2005