Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $14,973 Total Non-Federal Funds: $29,946
Principal Investigators: Jeff Langman
Abstract: Abstract: Resolving recharge flowpaths to heterogeneous, fractured-rock aquifers, such as the fractured-basalt aquifers of Idaho, can be very difficult, but the stable isotopes of water (2H and 18O) are a powerful tool for discriminating tortuous flowpaths. Fractionation of the stable isotopes of water in the hydrologic cycle allows for separation of rain and snow sources and how source waters evolve with travel through the local terrain, such as the evolution from snowfall to snowpack to snowmelt to aquifer recharge. The evolution of the isotope signals with aging of a snowpack is a critical factor for tracing the snow-to-recharge flowpath. Snowpack isotope evolution is determined by sublimation/evaporation that enriches the isotopic signal of snowpack and resulting snowmelt, which is derived within multiple layers of a snowpack. The isotope fractionation processes are relatively well understood, but the evolution of the isotope signal of snowpacks from snowfall to snowmelt is not well understood but paramount for tracing snowmelt recharge to groundwater systems.A snowpack aging study is proposed to enhance the application of a novel recharge estimator along a mountain-front interface in a northerly climate. This study will define the isotope evolution of a mountain snowpack that is the primary recharge source for a complex, fractured-basalt aquifer system in the Palouse region of north-central Idaho. Identification of the isotope evolution of the snowpack and resulting snowmelt will be integrated with ongoing studies to estimate recharge through seasonal fluctuation of groundwater isotope signals and perturbations in the ambient seismic field. Integration of these studies will highlight our ability to understand the temporal trends of snowpack aging and resulting isotope signal of snowmelt that can be traced to groundwater recharge. The product of this study will be a high resolution view of recharge flowpath(s) from snowfall to deep aquifer in a complex, fractured-rock aquifer system, which will aid in defining groundwater model parameters for managing the resource.The proposed study will generate an understanding of snowpack isotope evolution for discriminating snowmelt and groundwater recharge flowpaths. Results of the study will contribute to the ongoing discussion of isotope fractionation of snowpacks because of the difficulty in discriminating sublimating/evaporating surface areas and isotope fractionation between water vapor/water and snow in these multi-layer systems. The research goal is a contribution to the water isotope fractionation discussion derived from the Craig and Gordon isotope evaporation model that has produced models such as the Hydrocalculator and Soil-Water Isotope Estimator. The isotope evaporation model is adequate for estimating the flux ratios of the stable isotopes of water with evaporation from a surface water layer, but such a model is difficult to apply to a layered system such as snowpack. The atmospheric penetration in a snowpack differentiates isotope signals at multiple layers, which can produce a variable snowmelt isotope signal throughout the melt. Results of our study will differentiate isotope evolution from upper, middle, and lower layers of a mountain snowpack and the isotope signal of the snowpack discharge (snowmelt). Analysis of the results will allow for correlation of snowmelt recharge to groundwater isotope fluctuations and tracing of the recharge to a multi-aquifer system.