Publication Date

8-2023

Date of Final Oral Examination (Defense)

April 2023

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geoscience

Department

Geosciences

Major Advisor

Anna Bergstrom, Ph.D.

Advisor

Joshua Koch, Ph.D.

Advisor

Kendra E. Kaiser, Ph.D.

Advisor

Ellyn Enderlin, Ph.D.

Abstract

Mountain-derived snow and ice melt are essential for global water resources, and over one-sixth of the population depends on melt for freshwater. Rising air temperatures are causing vegetation to replace snow- and ice-covered landscapes and precipitation regimes to change. Collectively, these changes will alter the hydrology of mountain environments, although the exact impacts to hydrologic regimes are poorly understood. The source waters of streamflow (i.e. the proportion of ice melt, snowmelt, rain, and groundwater) dictate the timing and magnitude and affect temperature, sediment, and nutrient fluxes. By examining differences in source waters across basins with varying land covers and precipitation regimes, we can better predict the impact warming temperatures may have on streamflow from both a physical and biogeochemical perspective. Glaciers also physically weather their environment, which increases chemical weathering potential. High chemical weathering rates can impact global carbon cycling, but the extent and net influence of their impact is unknown. This thesis examines shifting source water contributions and chemical weathering patterns in sub-watersheds of the Nellie Juan basin on the Kenai Peninsula in Southcentral Alaska that range in percent glacier cover, elevation, and land cover type. To do so, a variety of geochemical, remote sensing, and modeling techniques were used. I found strong relationships between elevation, source water contributions, and land cover. There were also clear differences in the timing of snow and ice melt contributions to streams between glacierized and non-glacial streams. Groundwater is shown to be a major contributor to streamflow across the basin and may become increasingly important as snowpack and glacier melt decrease. Geochemical analyses show that the main driver of weathering-derived solutes in the region is bedrock type and that the presence of the glacier seems to play only a minor role in weathering. I also find a positive relationship between the proportion of groundwater in streamflow and weathering-derived solutes. This research characterizes the shift from a glacial to a deglaciated landscape through the lens of source water contribution and geochemical weathering regimes. Broadly, these findings can help improve our understanding of how water resources, biogeochemical fluxes, and carbon cycling in glacierized basins are impacted by warming air temperatures.

DOI

https://doi.org/10.18122/td.2129.boisestate

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