NSF Graduate Fellow
Determining dominant source waters of Salmon River tributaries through stable isotope analysis: δD and δ18O.
Dr. Glen Thackray
University Department and/or Lab:
Fluvial geomorphology/hydrology; environmental and climate change sciences; Quaternary geology
Description of Research:
The use of hydrogen and oxygen stable isotopes in hydrologic research is becoming an increasingly popular way to understand the movement of water through a system. Measurements of the isotopic composition of water from each domain of the hydrologic cycle has enabled the identification of different water masses and the tracing of their interrelationships. Isotopic fractionation results in waters and solutes developing unique δD and δ18 O signatures related to source and process of formation. Within a watershed, rivers act as a mixing point for all hydrologic inputs upslope. In addition to the amount and composition of input waters, numerous variables contribute to the isotopic composition of a lake. Local weather, regional climate, watershed area, groundwater influence, residence time, vegetation and mixing all contribute to the resulting δD and δ18O signature of a given river. The purpose of this project is to relate the isotope signature of a river to the source waters dominating discharge. Within a single small watershed, what is the dominating input(s) controlling the isotopic signature of river water?
The Salmon River watershed is the ideal study area for conducting a stable isotope based study of river water composition. Still considered pristine, the Salmon River Basin drains much of central Idaho flowing freely from Galena Summit to its confluence with the Snake River. Similar to the main stem, tributaries to the Salmon River experience nominal manmade diversions and relatively minimal infrastructure. Twelve Salmon River tributaries were chosen for this study based on their near perfect state, elevation within the Salmon watershed and relative accessibility and include: Salmon River headwaters, Frenchman’s, Smiley, Beaver, Carmen, Little Goose, Boulder, Little Slate, Slate, Gregory, Rock and Rice Creeks. It is hypothesized that fractionation due to precipitation phase (snow vs. rain) in a single, small basin provides a more powerful control on the δD and δ18O values at the outflow than internal fractionation processes. The greater goal of this research is to establish an isotope mass balance for multiple river watersheds and understand how, why to what extent isotopic fractionation occurs throughout the hydrologic cycle within a single, small watershed.
One example of how you integrate your research into your GK-12 experience:
My teacher, Mr. Simpson, and myself are going to integrate into the curriculum a year-long project studying the Portneuf River. Since my own research is focused on rivers this will be a great opportunity to share what I know best. Though we will not be doing isotopic analyses, I will still be able to share my knowledge on hydrology and fluvial geomorphology in addition to learning new ecological techniques for evaluating the dynamics of the Portneuf River throughout the coming school year.