Determining Spatial Controls on Snow Isotopic Signature and Tracing the Snowmelt Pulse as it Moves Through Two Montane Catchments

Author

Jenna K. Rolle, The University Of MontanaFollow

Year of Award

2022

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Other Degree Name/Area of Focus

Hydrogeology

Department or School/College

Geosciences

Committee Chair

W. Payton Gardner

Commitee Members

Joel Harper Zachary Hoylman Kelsey Jencso

Keywords

hydrogeology, snowmelt, stable isotopes, fractured bedrock flow

Subject Categories

Geochemistry | Hydrology

Abstract

In this study, we investigate the spatial and temporal distribution of stable isotopes of oxygen and hydrogen in water across two mountainous catchments in west-central Montana to trace the input of snow to local soil, bedrock aquifers, and streams. Snowpack and snowmelt samples were collected throughout the winter season at ten sites selected to encompass a range of elevation, aspect, slope angle and hillslope position. Soil and bedrock wells at five of the ten sites were sampled after the initial snowmelt pulse and stream samples were collected weekly at the outlets of both catchments to trace the timing and partitioning of the snowmelt pulse as it moves through the two watersheds. Comparison of δ¹⁸O, δ²H and deuterium-excess values revealed that no single spatial factor dominated overall isotopic composition, and that snowpack isotopic signals were controlled by different topographic variables than snowmelt isotopic signals. Snowpack isotopic ratios were most strongly influenced by elevation and slope angle, whereas snowmelt samples were most strongly influenced by aspect and hillslope positions. Temporal trends in snow isotopic signatures were shown to outweigh spatial trends, with all samples showing enrichment over time, and spatial factors affecting signatures differently throughout phases of snow accumulation and melt. Mass balance mixing models using bulk snowpack and bulk snowmelt signatures as end-members were utilized to develop a timeline for snow-derived recharge and streamflow generation processes in our catchments. We found that 1) isotopically light early-season meltwater recharges bedrock aquifers and follows longer pathways to dominate streamflow generation in summer, fall and winter baseflow conditions, and 2) isotopically heavy late-season meltwater infiltrates soil and flows laterally to streams during spring peak flow conditions. These results have implications for understanding the processes controlling snowpack recharge processes by conceptualizing how snowmelt travels throughout the soil, bedrock, and streams of fractured bedrock headwater catchments.

Recommended Citation

Rolle, Jenna K., "Determining Spatial Controls on Snow Isotopic Signature and Tracing the Snowmelt Pulse as it Moves Through Two Montane Catchments" (2022). Graduate Student Theses, Dissertations, & Professional Papers. 11940.
https://scholarworks.umt.edu/etd/11940