New University of Colorado at Boulder research shows high-altitude aquifers honeycomb parts of the Colorado Rockies, trapping snowmelt and debunking the myth that high mountain valleys act as "Teflon basins" to rush water downstream.
Mark Williams of CU-Boulder's Institute of Arctic and Alpine Research said geochemical and water isotope studies show that less than half of the annual snowmelt in the Green Lakes Valley region in the high mountains west of Boulder arrives at the watershed treatment facility within a year as "new water." He found that most of the water sampled from North Boulder Creek during the runoff months was "old groundwater" that had been stored in subterranean mountain catchments.
Similar studies by Williams and colleagues near Leadville, Colo., show that high-mountain groundwater is dominated by snowmelt that is locked underground for years or decades. The research shows that water from snow pack replenishes high-altitude groundwater reservoirs, pooling underground rather than rushing downstream toward the plains.
"We are seeing that snowmelt is re-charging the hydrologic systems in the mountains, pushing old groundwater from subsurface reservoirs into the rivers and streams," Williams said. "The common perception that water stored in mountain snow packs runs immediately into streams and rivers is probably wrong, and the Teflon basin myth is incorrect."
Williams presented his findings at the annual Geological Society of America meeting held in Denver Nov. 7 to Nov. 10.
The many fault and fracture zones in the Rocky Mountains are the primary portals to the hidden catchments, he said. But the complex geology overlying the mountain aquifers continues to challenge researchers.
"Once we started doing the chemistry and looking at the different water isotopes, it really changed my perspective," Williams said. "The significant delay between the time we saw water entering the system at the top end and the time it showed up in the creeks was surprising."
Groundwater in the Green Lakes Valley on Niwot Ridge -- a National Science Foundation-funded Long Term Ecological Research site administered by INSTAAR -- appears to be stored in a huge catacomb of rock that Williams likened to a tiered cake. Researchers sampled surface snow and rain as well as streams, lakes and springs in the area, primarily at treeline and above.
The team analyzed each sample for specific water isotopes, including oxygen 18, deuterium and tritium, Williams said. They also analyzed water samples for levels and combinations of roughly 40 trace metals ubiquitous to the high mountains -- including cadmium, lead, arsenic and zinc.
"These isotopic and geochemical measurements provide unique fingerprints, allowing a CSI approach to tracing water sources," he said.
The researchers found that just before the peak spring runoff, more than 50 percent of the flow in North Boulder Creek above treeline was determined to be old groundwater. During the weeks immediately following the peak runoff flow, the amount of aging groundwater in the creek jumped to roughly 80 percent, he said.
"We just don't know yet how well connected the high-mountain groundwater is to the large, well-known aquifers on the eastern plains," Williams said. "We need to investigate this possible connection."
Williams has been collaborating with Mike Wireman of the Environmental Protection Agency and the U.S. Geological Survey's Andy Manning and Bob Michel on the research around Leadville. The research at Green Lakes Valley, funded by NSF, also involves INSTAAR fellows Bruce Vaughn and James White.
Five CU-Boulder graduate students are collaborating with Williams, who also is an associate professor of geography.