HR: 0800h
AN: H51B-1125    [Abstracts]
TI: Groundwater-Surface Water Exchange as a Hydrologic and Water Quality Buffer
AU: * Covino, T P
EM: tcovino@montana.edu
AF: Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall PO Box 173120, Bozeman, MT 59717-3120 United States
AU: McGlynn, B L
EM: bmcglynn@montana.edu
AF: Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall PO Box 173120, Bozeman, MT 59717-3120 United States
AU: Sojda, R S
EM: sojda@usgs.gov
AF: United States Geological Survey, Northern Rocky Mountain Science Center, AJM Johnson Hall Montana State University, Bozeman, MT 59717-3492 United States
AB: The complex interactions of surface water and groundwater are gaining increasing recognition as an outstanding research need. Specifically, the role of transition zones between alpine headwaters and valley bottom river/lake/wetland systems, common across mountain-valley landscapes, in controlling stream flow quantity, timing, and water quality are poorly understood. In many valleys, streams change in both space and time from gaining water from groundwater to losing water to groundwater as they flow toward the valley-bottom. Alpine-valley transition zones play a key role in regulating the amount, timing, and quality of stream water that arrives in the valley bottom. As such, we hypothesize that valley transitions function as hydrologic and biogeochemical buffers, both groundwater recharge and discharge zones, and reflections of integrated local and alpine hydrologic and climatic processes. To investigate these hypotheses we installed a network of 24 wells, 20 nested piezometers, seven stream gauging stations, and recording soil temperature nests (10 depths in each of 12 nests) across a two kilometer reach of Humphrey Creek in southwestern Montana. This network allowed us to investigate the surface water and groundwater hydrology in the study reach and to further understand the spatial and temporal variability in surface-water/groundwater interactions. We collected regular stream and groundwater samples to determine the relative contributions of groundwater and alpine runoff to downstream hydrographs. Salt tracers were injected during various times of the year to further quantify and elucidate areas of groundwater recharge and discharge. Initial results have shown that groundwater recharge and discharge zones across an alpine-valley transition are dynamic. Strong groundwater recharge gradients occurred during snowmelt, but shifted to discharging water into the stream channel when alpine contributions declined. This shift in source water contributions had a marked effect on the chemistry of water found in the stream channel. Furthermore, groundwater table shape and storage were dynamic and responded to alpine snowmelt, yet rain events had little impact on groundwater recharge but caused short pulsed increases in stream flow. These research efforts will provide a better understanding of the role that transition zones play in buffering the quantity, quality, and timing of water delivered from alpine headwaters to rivers, lakes, and wetlands in valley bottoms. This new understanding will be directly relevant to understanding groundwater recharge controls, irrigation withdrawal impacts, irrigation return flow implications, the surface water and groundwater dynamics controlling moisture status in slope wetlands, and the importance of surface-water/groundwater connections in affecting water quality.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting