Controls governing active layer thermal hydrology : how predictable subsurface properties influence thaw, groundwater flow, and soil moisture

• Main Author: O'Connor, Michael Thomas, Ph. D.
• Other Authors: Cardenas, Meinhard Bayani, 1977-, Kling, George W, Neilson, Bethany T, Matheney, Ashley M, Rempe, Daniella M, Coon, Ethan T
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Permafrost; Hydrology; Climate change; Arctic; permafrost
• Online Access: https://hdl.handle.net/2152/76207; https://doi.org/10.26153/tsw/3296

The hydrology of near-surface arctic soils above continuous permafrost, known as the ‘active layer’, is controlled by coupled thermal and hydraulic processes that are not well understood. The poorly-quantified spatial variability in active layer soil thermal and hydraulic properties, compounded with continually-migrating aquifer geometries that are not mechanistically understood, cause our current knowledge of arctic hydrology to be limited. Particularly, we do not mechanistically understand which parameters govern arctic groundwater flows, we do not understand how such governing properties vary across the landscape, and we do not understand the ranges that such landscape variability provides on arctic hydrologic processes. This dissertation investigates these open questions through novel field observations and numerical modeling. In Chapter Two, I show how groundwater flows in the active layer are controlled by highly-variable soil permeability within three variable-thickness soil layers using fieldwork and saturated groundwater flow models. In Chapter Three, I identify how those soil layers and properties vary across the commonly-observed land surface slopes, dominant vegetation types, and microtopographic features found on the foothills of the Alaskan North Slope through original fieldwork and terrain analysis. In Chapter Four, I show how the thawing and freezing of the active layer, lateral groundwater flow, and soil moisture storage (i.e., dominant thermal hydrologic processes) are controlled by the commonly-observed patterns in soil stratigraphy and soil properties found across the landscape. Finally, in the Conclusion, I lay out a framework for how this information can be leveraged to inform larger-scale arctic thermal hydrology models. In totality, this dissertation provides insight in the understanding of arctic thermal hydrology because of its grounding in observed soil properties and the use of cutting-edge numerical tools. Geological Sciences