Characterizing The Role And Controls Of Snowmelt In Alpine Groundwater Recharge
Hill, Alice 1 ; Shimabuku, Morgan 2 ; Williams, Mark 3 ; Ge, Shemin 4
1 University of Colorado-Boulder
2 University of Colorado-Boulder
3 Institute for Arctic and Alpine Research
4 University of Colorado-Boulder
High altitude mountainous regions are vital source areas of water. Hydrologic processes in these regions are particularly sensitive to climate change because of the presence of glaciers, snow, and permafrost. Yet, basic questions remain about the rate groundwater is replenished, the size of groundwater reservoirs, circulation paths and residence time, as well as the role of permafrost in alpine regions.
Research was conducted at the Niwot Ridge Long Term Ecological Research Site (LTER) in the Colorado Rocky mountains from 2008 to 2012. The study site includes two geologically contrasting adjacent alpine tundra basins sited at about 3,500 m in elevation. Utilizing a unique data set from 14 piezometers installed to monitor alpine groundwater processes, Principal Component Analysis and End Member Mixing Analysis, we confirm that the major annual groundwater recharge event is directly in response to snowmelt. Groundwater levels change on the order of 4-6 m each year and peak groundwater levels lag the SWE peak by a matter of days even in very dry years (eg, 2012). While groundwater is often perceived to be a water vulnerability buffer, the annual response in groundwater to the previous year?s snowpack suggests alpine groundwater reservoirs are small and do not provide the anticipated cushion in water supplies. The magnitude of recharge increases with the size of the snowpack, showing sensitivity of the groundwater reservoir to changes in climate. Changes in the chemistry and isotopes of groundwater within and between catchments identify the spatial variability of groundwater paths and source waters over both small and medium scales. In both basins, groundwater was an important contributor to stream flows but groundwater?s role is influenced by subsurface geology.
The direct effect that climate has on groundwater recharge and the spatial variability of groundwater response over all scales lies at the heart of a central challenge in characterizing the impact groundwater will have on water resources in the context of a changing climate.