HR: 16:00h
AN: H14E-01 INVITED    [Abstracts]
TI: Options for Monitoring Climate-driven Recharge Changes in Western Mountains
AU: * Dettinger, M
EM: mdettinger@ucsd.edu
AF: US Geological Survey, Scripps Institution of Oceanography UC San Diego, Dept 0224 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Earman, S
EM: searman@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, United States
AB: Ground-water supplies have long been used as fallback supplies during droughts and other lean times, and thus it has been natural to view them as fall backs if deficits develop as a result of long-term climate change. However, ground-water supplies may not be immune to detrimental influences from climate changes of the sort projected under the influence of increasing atmospheric greenhouse-gas concentrations. An example of a possible detrimental influence is the potential for significant reductions in mountain-based recharge in the western USA as mountain snowpacks decline in response to warming trends. Most recharge to western aquifers comes from snowmelt and, as snowpacks diminish, opportunities for recharge are at risk of serious declines. A multidisciplinary workshop, funded by the USGS and California Energy Commission, was held in July 2007 to discuss options for long-term monitoring of mountain recharge variations and changes in California and Nevada. The meeting polled hydrologists, geochemists, geophysicists, and biologists about methods for characterizing western recharge fluctuations. In particular, the meeting asked whether current methods exist for characterizing changing recharge rates and mechanisms that could be used in a geographically distributed, long-term monitoring network. Hydrologic methods, including monitoring wells and streambed methods, have been underutilized in mountain-recharge settings and offer important, but at-present uncommon, views of the influences and timing of recharge in western mountains. Among geophysical methods, repeated microgravity measurements appear to hold the most promise for tracking recharge fluctuations. The method has been used to measure recharge episodes on alluvial fans and basin floors, but has not been applied in mountain settings, so protocols and experience are needed prior to widespread mountain deployment. Biological observations at springs and seeps have the potential to provide important evidence of changing hydrologic conditions associated with recharge fluctuations but, to date, have been used thusly mostly at low-altitude springs. Geochemical methods—including major ions, isotopes and dissolved gases—have been used to characterize recharge mechanisms, rates, and pathways in western mountains. Studies to date have focused on characterizing spatial patterns and differences, but repeated sampling over the course of years has the potential to also characterize temporal variations. Although the general sense was that more research would be necessary to design an operational monitoring network using combinations of these methods, several opportunities were identified. In the Sierra Nevada, a number of extensively instrumented research watersheds were identified that do not yet include observations of ground water and recharge. These watersheds could be augmented with wells, streambed sensors, repeat geophysical surveys, and geochemical censuses to help close their water budgets and as opportunities for learning how to use these methods for recharge-variation monitoring. Elsewhere, historical surveys of hydrology, biology, and geochemistry at mountain springs and selected wells/mines in Nevada and California could be repeated regularly as a foundation for detection of recharge changes and as a complement to the kinds of focused studies that may grow from the research watersheds and basins.
DE: 1655 Water cycles (1836)
DE: 1807 Climate impacts
DE: 1829 Groundwater hydrology
DE: 1848 Monitoring networks
SC: Hydrology [H]
MN: 2007 Fall Meeting