Date of Award

Spring 5-16-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Michael N. Gooseff

Second Advisor

Diane M. McKnight

Third Advisor

Roseanna Neupauer

Fourth Advisor

Ben Livneh

Fifth Advisor

Robert Anderson

Abstract

The McMurdo Dry Valleys (MDV) of Antarctica is an ideal landscape for studying the relationship between hydrologic connectivity and ecosystems. In the MDVs, aquatic and terrestrial ecosystems are controlled by patterns of hydrologic connectivity. It is hypothesized that climate warming in the MDV ecosystem will amplify hydrologic connectivity among landscape units (glaciers, streams, soils, and lakes), causing changes in the structure and function of the MDV ecosystem. This dissertation is devoted to understanding the current and future state of water-mediated mass and energy fluxes in MDV streams and soils.

Chapter 1 synthesizes 20 years of stream gauge observations (discharge, water temperature, and specific conductance) to assess patterns of hydrologic connectivity between glaciers, streams and lakes. Results reveal hydrologic patterns across daily, annual and inter-annual timescales, which together characterize the hydrologic regime of MDV streams. Also, stream gauge data display a relationship between stream length and hydrologic regime. Longer streams are more intermittent, warmer, and saltier than shorter streams. This work provides physical context for understanding biological differences among MDV streams, while providing a methodological template for quantifying hydrologic connectivity.

Chapter 2 investigates the nature of concentration-discharge relationships for weathering-derived solutes in MDV streams. The relative simplicity of MDV “watersheds” permits the use of concentration-discharge relationships to infer hydrologic and chemical mixing dynamics occurring along the river corridor. Long-term stream geochemical data show that weathering derived solutes exhibit chemostatic C-Q relationships. Chemostasis implies that rates of solute production and/or mobilization scale proportionately with stream discharge. A numerical weathering and solute transport model suggests that chemostasis is maintained by a positive relationship between weathering rate and discharge along the stream corridor.

Finally, Chapters 3 and 4 investigate water-mediated energy fluxes within the soil habitat. Nematode communities in MDV are highly sensitive to the thermodynamic regime of active layer soils. Soil moisture and air temperature data were collected across natural wetness gradients adjacent to fluvial features to assess the control of soil moisture on the soil thermal regime. Observations show that wetter soils freeze less frequently and more gradually than drier soils. Also, a numerical soil heat transfer model suggests that increases in soil moisture and air temperature result in warmer average habitat temperature, an extension of the duration of time the soil habitat spends above freezing, and a reduction in the rate and frequency of freezing. The results of this chapter provide a physical context for understanding current and future patterns of ecosystem structure and function in MDV soils.

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