State Water Resources Research Institute Program (WRRI)
USGS Grant Number: G16AP00193
Start Date: 2016-09-01 End Date: 2019-08-31
Total Federal Funds: $130,381 Total Non-Federal Funds: $130,381
Principal Investigators: Dr. Stephanie Ewing
Abstract: A repeated landscape pattern in the inter-mountain west is relatively steep, actively eroding mountainous headwater streams draining onto more depositional sedimentary environments in intermountain basins. Little is understood about how hydrologic storage changes across this dramatic transition between hydro-geomorphological process domains. This limits our ability to make informed management decisions regarding baseflow water supply, because human infrastructure typically becomes more directly coupled to the hydrosystem within intermountain basins. We propose to study the Gallatin River watershed as a case study in the continuum of watershed hydrologic storage and the coupling between human and natural systems using weathering geochemistry to understand the sources of base flow water supply in rivers acros1s mountain- that are typical for the region. We suggest that geochemical weathering imparts a chemical signal on water quality that is an underutilized source of information about the nature of base flow storage along the mountain-basin continuum. Therefore, we propose to explore spatial and temporal patterns of weathering products dissolved in base flow of the Gallatin River and its network, with the purpose of gaining new insight into the patterns of aquifer storage contributing to surface-water base flow across the mountain-basin continuum. Publications will (1) evaluate baseflow sources by comparing strontium isotope ratios, oxygen isotope ratios, and elemental composition across the mountain-basin continuum with the chemistry of water samples along the associated streams and rivers; (2) expand this assessment to larger scale source and process relationships based on data collected at gages on the Gallatin River and across multiple traversing streams using uranium isotope activity ratios in addition to strontium and oxygen isotope ratios; and (3) develop implications for hydrologic systems traversing this kind of boundary that improve the conceptual basis for local to regional watershed models. More broadly, this work will develop both data and a conceptual framework in support of the USGS National Water Census goal of integrating groundwater and surface water into watershed-level assessments of water availability with links to water quality. By focusing on use of novel tools across this key landscape transition, this work specifically addresses the USGS goal under WaterSMART to invest in the development of new, cutting edge hydrologic tools and assessments to fill the most critical information gaps. This work provides a natural link between these national initiatives and the Montana State Water Plan, which highlights the contribution of “natural storage” to summer water supplies for both human and ecosystem services.