<p>In arid regions, springs are important in many aspects of society due to the scarcity of surface water features. In the Great Basin of the United States, desert springs support the majority of regional biodiversity and are critical for supporting rare, threatened, and endangered organisms. Despite their importance, there are numerous threats to desert springs, with the most ubiquitous being climate change. In contrast to many studies examining potential metrics to describe the vulnerability of streams, wetlands and other surface water features to the effects of climate change, springs are often overlooked. Part of the knowledge gap stems from the complexity of springflow generation and the rarely field-tested connection between groundwater response time and groundwater residence time.</p> <p> This dissertation tests, in a systematic way, different metrics that may help define criteria to evaluate whether a spring is likely to persist or desiccate with increasing regional hydrologic stress due to climate change. Field data was collected over a 4-year period from >80 springs across the topographically and geologically heterogeneous terrain of the southern Great Basin. </p> <p>Throughout this dissertation, I use a variety of different tools (e.g., remote sensing, environmental tracers, geospatial analysis) to “attack” this complicated problem from different angles. I begin by examining factors indicative of hydrogeologic resistance to major drought. After finding a connection between groundwater residence time and hydrogeologic resistance, I examine other factors (e.g., geochemical, topographic, ecological, variability) that are related to groundwater residence time and also identify where these relationships fail. </p>

The availability of water is a limiting resource for many wildlife species in arid and semi- arid environments. Free water is essential for critical life stages for numerous species, including migration, reproduction, survival, and habitat selection. Riparian areas in the desert occur relatively infrequently, but support a disproportionally large percentage of plant and wildlife species found in arid environments. Our study covered two aspects of water use in the west desert of Utah. The first was assessing the impacts of nonnative ungulates (specifically feral horses and cattle) on natural springs, and how they influenced water quality, vegetation, and wildlife diversity at those springs. We found that these ungulates reduced plant cover and plant species richness at our sites. Additionally, we found that the number of plant species positively correlated with wildlife diversity. This indicates that further management of these nonnative ungulates may be warranted. In our second chapter we investigate how Golden Eagles (Aquila chrysaetos) use water by quantifying seasonal use, behavior, and testing a hypothesis that a ‘runway’ with drop in elevation is needed for eagles to have a quick exit. We found that eagle use of water resources was strongly concentrated in the summer months during the hottest temperatures. Adult birds used water features more often than younger birds. The most common behavior exhibited at water features was drinking, followed by bathing and preening. We found that there was a positive relationship between the number of visits and the maximum slope at each site, supporting the idea that the ‘runway’ is not required but is preferred at water sources. Overall, our results indicated that Golden Eagles use water regularly in arid environments, particularly during summer months. This research provides insight into how species are using desert riparian areas and how these species and habitats should be managed in future decades.

No description available.

Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.