Abstract
Groundwater, the sub-surface presence of water, comprises about 99% of the world’s liquid freshwater. As a result, some ecosystems require groundwater to sustain their ecological function, structure, and composition and are classified as groundwater-dependent ecosystems (GDE). A growing body of research emphasizes the potential of GDEs to buffer ecological stress associated with intensifying disturbance and climate change since GDEs provide cold and consistent water inputs. Understanding the capacity of GDEs to provide refugia is critical as climate change poses serious risks to ecosystem persistence. In snowmelt-dominated watersheds of the western U.S., interannual snowpack variability is increasing, snow is melting earlier, and precipitation is shifting from snow to rain. On top of baseline shifts in the water cycle, more frequent and severe disturbances, like record high temperatures that increase evaporative demand and large high-severity wildfires, risks pushing ecosystems beyond their historical range of variability. Despite the recognition of GDEs as potential refugia, GDEs are chronically understudied due to a lack of mapping and legal protection and significant gaps remain in understanding the capacity of GDEs to function as refugia. Few studies have quantitatively assessed the stability of GDEs under disturbances such as drought, wildfire, or climate change. Therefore, the goal of this dissertation is to quantify the role of GDEs in buffering the impacts of interannual climate variability, high-severity wildfire, and severe drought through an interdisciplinary ecohydrological approach. Chapter 2 investigates how spring ecosystems, a type of GDE, facilitate forest recovery following high-severity wildfire using field-based measurements of tree density and age. We found that proximity to springs resulted in higher conifer density and earlier establishment after high-severity wildfire when conditions for available seeds and topography were also met. Chapter 3 explores the role of springs as climate refugia in mountainous headwater environments of central Idaho using remote sensing of plant phenology. We show that the vegetation phenology at springs has reduced annual variability and sensitivity to interannual climate conditions relative to the surrounding non-spring environment. Chapter 4 examines the role of groundwater connectivity in buffering springtime drought and interannual snowmelt variability in headwater streams using diel air and water temperature data. Results indicate that groundwater connectivity increased in some streams during the extreme 2021 springtime drought, while others remained stable or declined. Additionally, some streams exhibited stronger groundwater connectivity and reduced atmospheric coupling during low-snow years, while others maintained consistent hydrologic behavior. Each chapter of this dissertation contributes to an improved understanding of the capacity of GDEs to function as refugia in the face of disturbance and climate change.