HR: 1340h
AN: H33D-0497    [Abstracts]
TI: Hydrologic and Ecologic Responses to Diminished Spring Discharge; Surface-Water/Groundwater and Vegetation Modeling, Grand Canyon, Arizona
AU: * Kobor, J S
EM: jsk23@dana.ucc.nau.edu
AF: Department of Geology Northern Arizona University, Frier Hall Box 4099, Flagstaff, AZ 86011 United States
AU: Springer, A E
EM: abe.springer@nau.edu
AF: Department of Geology Northern Arizona University, Frier Hall Box 4099, Flagstaff, AZ 86011 United States
AU: Scott, M L
EM: mike_l_scott@usgs.gov
AF: U.S. Geological Survey Biological Resources Discipline, 2150 Centre Ave. Bldg. C, Ft Collins, CO 80526 United States
AU: Shafroth, P
EM: pat_shafroth@usgs.gov
AF: U.S. Geological Survey Biological Resources Discipline, 2150 Centre Ave. Bldg. C, Ft Collins, CO 80526 United States
AB: Numerous springs discharge from the regional Redwall-Muav aquifer of the Coconino Plateau along the South Rim of the Grand Canyon, AZ. Many of these springs provide base flow to Colorado River tributaries, and support stands of native riparian vegetation. Development of the Redwall-Muav aquifer as a water supply began in 1989, with potential abstraction rates up to ~1.1 x 106 m3/yr. Regional groundwater flow models predict that groundwater pumping has the potential to result in diminished discharges at the South Rim Springs, which may result in negative impacts to the associated riparian ecosystems. Management of this regional spring-aquifer system requires an interdisciplinary understanding of the dynamics between the operating hydrologic, ecologic and cultural processes. To aid in this effort, we calibrated a coupled numerical surface-water and groundwater flow model for the riparian aquifer associated with one of the smaller of the South Rim springs, Cottonwood Springs. The model simulated the seasonal variability of surface-water and groundwater flow in the aquifer as observed between March 2003 and January 2004 at a 1-m grid spacing. Surface-water flux and groundwater flux data were extracted from the model at various transects through the riparian area to highlight temporal and spatial variations in water availability to the associated riparian communities. During the winter, the total flux of water was relatively constant throughout the model area and was ~60 m3/d. During the peak of the growing season, the total flux of water in the upstream portion of the model area was ~60 m3/d and decreased progressively down to ~35 m3/d in the downstream portion of the model. The downstream decrease in water availability is manifested in downstream changes in woody riparian vegetation structure and composition. Changes in cottonwood stand and individual tree metrics were examined quantitatively in relation to this moisture availability gradient. An analysis of stream gauging data (1994-2003) from two South Rim springs showed statistically significant decreasing discharge trends over the period of record. These trends, coupled with ongoing groundwater pumping, climatic predictions of continuing drought, and the observed sensitivity of the riparian vegetation to variations in water availability suggests there is a potential for alteration to the riparian ecosystem over relatively short timescales.
DE: 1803 Anthropogenic effects
DE: 1818 Evapotranspiration
DE: 1829 Groundwater hydrology
DE: 1836 Hydrologic budget (1655)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting