Graduate Defense: Hannah Richardson

Thesis Information

Title: Hydrologic Impacts Of Rapidly Changing Glacial And Alpine Environments In Southcentral Alaska.

Program: Master of Science in Geophysics

Advisor: Dr. Anna Bergstrom, Geosciences

Committee Members: Dr. Kendra Kaiser, Geosciences; Dr. Ellyn Enderlin, Geosciences; and Dr. Joshua Koch, Geosciences

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. Meltwater additionally regulates stream temperature and provides nutrients for downstream ecosystems. Increasing temperatures are causing alpine glaciers to recede. Landscapes are becoming less dominated by ice and more dominated by high mountain terrain. Changes in glacier melt contribution, precipitation regimes, and vegetation cover all impact streamflow from a physical and chemical perspective. Changing source waters impact the timing and magnitude of streamflow as well as the temperature, sediment, and nutrient fluxes. Glaciers also impact global carbon cycling due to the high rates of physical and chemical erosion, but the extent and net influence of their impact is unknown. This thesis examines shifting source water contributions and chemical weathering patterns in watersheds that range in percent glacier cover, elevation, and land cover type. To do so, I collected stream and source water samples, measured isotope values and ion and nutrient concentrations, classified land cover using remote sensing techniques, modeled source water contribution, and analyzed geochemical weathering relationships. I find clear elevationally-driven relationships between source water contributions and land cover. I also find clear differences in source water contributions 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 decreases. 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 describes a gradient of glacial, precipitation, and vegetation regimes. It better characterizes the shift from a glacial to a de-glaciated landscape through the lens of source water contribution and weathering regimes. Broadly, these findings can help improve our understanding of how water resources, biogeochemical fluxes, and carbon cycling are impacted by receding alpine glaciers.