Matching Items (2)
Description
In the southwestern United States, water is a precious resource that influences landscapes and their respective ecosystems. Ephemeral lakes, known as playas, are drainage points for closed or endorheic basins and serve as important locations for plant productivity, biogeochemical processes, and groundwater recharge. In this study, I explore the hydrologic dynamics of eighteen (18) instrumented playas in the Jornada Basin of the Chihuahuan Desert with respect to the drivers of playa inundation and how their behaviors vary in space and time. To this end, I combine water level observations in playas with gauge-corrected radar precipitation estimates to determine hydrologic dynamics over the more than 6-year period of June 2016 to October 2022. Results indicate that all playa inundation events are associated with precipitation and that 76% of events occur during the warm season from April to September that is characterized by the North American monsoon. Mean annual runoff ratios in the playa catchments range from 0.01% to 9.28%. I observe precipitation depth and 60-minute intensity thresholds for playa inundation ranging from 16.1 to 71.3 mm and 8.8 to 40.5 mm/hr, respectively. Although playa inundation is typically caused by high rainfall amounts and intensities, other factors such as antecedent wetness conditions and the spatial variability of rainfall within the playa catchment also play a role. The magnitudes, durations, and occurrence of inundation events vary among playas, but their responses to precipitation generally agree with groupings determined based on their geological origin. Logistic and linear regressions across all playas reveal the relative importance of catchment variables, such as area, sand fraction, slope, and the percentage of bare ground. It is shown that larger catchment areas are strongly associated with a lower likelihood of inundation and higher precipitation thresholds for inundation. An analysis of precipitation data from 1916 to 2015 leads to the estimation of historical playa inundation and suggests that an increase has occurred in the frequency of large rainfall events that may be associated with increasing frequency of playa inundation. This study highlights the complex nature of playa inundation in the Jornada Basin, which can change over time in an evolving climate and landscape.
ContributorsKimsal, Charles Robert (Author) / Vivoni, Enrique R (Thesis advisor) / Whipple, Kelin X (Committee member) / Li, Jiwei (Committee member) / Arizona State University (Publisher)
Created2023
Description
Coral reefs provide essential social, economic, and ecological services for millions of people worldwide. Yet, climate change and local anthropogenic stressors are damaging reefs globally, compromising reef-building capacity, and therefore impacting functionality. Growth of coral reefs depends upon the production and maintenance of the reef framework when calcium carbonate production exceeds erosion, and utilization of remote sensing to scale-up estimates of reef carbonate production remains limited. This study provided a first field estimate of net carbonate production on Hawaiʻi Island, in Hōnaunau Bay, and used high-resolution benthic-cover data, derived from Global Airborne Observatory (GAO) airborne imaging spectroscopy, to scale-up estimates. Net carbonate production was, on average, 0.5 kg CaCO3 m-2 y-1 across the depth gradient, with the highest rates of approximately 2.4 kg CaCO3 m-2 y-1 at 6 m. Urchins, especially the abundant Echinometra, suppressed reef-accretion potential in the shallow reef (< 6 m) and urchin bioerosion decreased with depth. Critically, a threshold of ~26% live-coral cover is currently needed to maintain positive net production across depths. Scaling-up estimates were achieved using a 2 m resolution map of live-coral cover collected by the GAO. Overall, field measurements translate to average vertical reef growth of 0.5 mm y-1 across depths, whereas sea level is currently increasing at 3.55 mm y-1, suggesting the reef in its present status is not keeping pace with sea-level rise. This work lays the foundation to enhance monitoring of carbonate production over increased temporal and spatial scales with airborne imaging spectroscopy — to help determine where reefs are potentially keeping up with anthropogenic stressors, ocean warming, and sea-level rise — and to help inform restoration and management decisions that support resilient carbonate budgets of coral reefs.
Contributorsvan Woesik, Kelly Jane (Author) / Asner, Gregory P (Thesis advisor) / Li, Jiwei (Committee member) / Vaughn, Nicholas (Committee member) / Arizona State University (Publisher)
Created2024