Matching Items (7)
Description
Drylands (arid and semi-arid grassland ecosystems) cover about 40% of the Earth's surface and support over 40% of the human population, most of which is in emerging economies. Human development of drylands leads to topsoil loss, and over the last 160 years, woody plants have encroached on drylands, both of which have implications for maintaining soil viability. Understanding the spatial variability in erosion and soil organic carbon and total nitrogen under varying geomorphic and biotic forcing in drylands is therefore of paramount importance. This study focuses on how two plants, palo verde (Parkinsonia microphylla, nitrogen-fixing) and jojoba (Simmondsia chinensis, non-nitrogen fixing), affect sediment transport and soil organic carbon and total nitrogen pools in a dryland environment north of Phoenix, Arizona. Bulk samples were systematically collected from the top 10 cm of soil in twelve catenae to control for the existence and type of plants, location to canopy (sub- or intercanopy, up- or downslope), aspect, and distance from the divide. Samples were measured for soil organic carbon and total nitrogen and an unmanned aerial system-derived digital elevation map of the field site was created for spatial analysis. A subset of the samples was measured for the short-lived isotopes 137Cs and 210Pbex, which serve as proxy erosion rates. Erosional soils were found to have less organic carbon and total nitrogen than depositional soils. There were clear differences in the data between the two plant types: jojoba catenae had higher short-lived isotope activity, lower carbon and nitrogen, and smaller canopies than those of palo verde, suggesting lower erosion rates and nutrient contributions from jojoba plants. This research quantifies the importance of biota on influencing hillslope and soil dynamics in a semi-arid field site in central AZ and finishes with a discussion on the global implications for soil sustainability.
ContributorsAlter, Samuel (Author) / Heimsath, Arjun M (Thesis advisor) / Throop, Heather L (Committee member) / Walker, Ian J (Committee member) / Arizona State University (Publisher)
Created2018
Description
Use of off-highway vehicles (OHV) in natural landscapes is a popular outdoor activity around the world. Rapid-growing OHV activity causes impacts on vegetation and land cover within these landscapes and can be an important factor in land degradation and ecosystem change. The Algodones Dunes in southeastern California is one of the largest inland sand dune complexes in the United States and hosts many endangered species. This study examines changes in land cover and OHV activity within two OHV active sites in comparison to an adjoined protected area. The study also investigates potential associations between land cover changes, climate trends, and OHV activity over recent decades. Time-series analysis was used to investigate the spatial-temporal changes and trends in the land cover in the Algodones Dunes from 2001 to 2016. In addition, high-resolution aerial photographs were analyzed to determine spatial patterns of OHV usage in comparison to visitor estimation collected by the Bureau of Land Management and observed changes in land cover composition between the control site and OHVs areas.
A decreasing trend in Normalized Difference Vegetation Index over time indicates a decline in the amount of vegetation cover, which corresponds with an increasing trend in albedo and land surface temperature. Results also show a substantial difference in land cover between the control site and OHVs areas, which typically have a lower amount of vegetation cover, higher exposed sand surface, and increased anthropogenic features. Both climatic variations and OHV activity are statistically associated with land cover change in the dune field, although distinct causal mechanisms for the observed declines in vegetation cover could not be separated. The persistence of drought could inhibit vegetation growth and germination that, in turn, would hinder vegetation recovery in OHV areas. Meanwhile, repeated OHV driving has direct physical impacts on vegetation and landscape morphology, such as canopy destruction, root exposure, and increased aeolian sand transport. Active ecosystem protection and restoration is recommended to mitigate the response of declining vegetation cover and habitat loss to the impacts of OHV activity and climatic variability and allow natural recovery of re-establishement of nebkha dune ecosystems in the Algodones Dunes.
A decreasing trend in Normalized Difference Vegetation Index over time indicates a decline in the amount of vegetation cover, which corresponds with an increasing trend in albedo and land surface temperature. Results also show a substantial difference in land cover between the control site and OHVs areas, which typically have a lower amount of vegetation cover, higher exposed sand surface, and increased anthropogenic features. Both climatic variations and OHV activity are statistically associated with land cover change in the dune field, although distinct causal mechanisms for the observed declines in vegetation cover could not be separated. The persistence of drought could inhibit vegetation growth and germination that, in turn, would hinder vegetation recovery in OHV areas. Meanwhile, repeated OHV driving has direct physical impacts on vegetation and landscape morphology, such as canopy destruction, root exposure, and increased aeolian sand transport. Active ecosystem protection and restoration is recommended to mitigate the response of declining vegetation cover and habitat loss to the impacts of OHV activity and climatic variability and allow natural recovery of re-establishement of nebkha dune ecosystems in the Algodones Dunes.
ContributorsCheung, Suet Yi (Author) / Walker, Ian J (Thesis advisor) / Myint, Soe W (Committee member) / Dorn, Ronald I. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Dryland ecosystems are integral to the global agricultural system and play an important role in soil carbon (C) storage. Despite their importance, drylands are currently facing many challenges including climate-change induced rainfall variability and soil degradation. These challenges are predicted to have effects on the soil microbial communities in drylands. Compost, an organic soil amendment, is a land management strategy that has been proposed to increase soil C storage as well as improve soil conditions in drylands, specifically in restoration and agricultural sites where degradation has affected soil properties like microbial biomass and respiration. Compost additions and rainfall variability may interact to affect soil moisture, an important catalyst for microbial activity. Assessing microbial activity responses under compost applications and variable moisture will aid in understanding how land management strategies will be affected by climate change in the future. This study investigates how soil microbial activity from a degraded dryland restoration site is affected by different compost applications amounts and variable soil moistures. A laboratory incubation study was conducted in a controlled environmental chamber for 60 days. Soils were amended with different treatments of compost (0, 0.35, and 0.70 g cm -2) and water pulses (5, 10, and 15 mm) in a full factorial design. Each treatment received the same cumulative amount of water throughout the incubation, but pulses were administered in different frequencies (every 5, 10, and 15 days). Soil respiration and soil water content were measured daily, and microbial biomass was measured at the end of the incubation to assess treatment effects on microbial activity. Microbial respiration and soil water content increased with increasing compost additions and water pulse sizes. Microbial biomass did not have consistent increases with compost additions or water pulse size. Cumulative microbial respiration was highest with the large-infrequent pulse size and smallest with the small-frequent pulse size. These results suggest that microbial activity and carbon dynamics in soils where compost amendments are used will respond to future changes in precipitation variability. The results of this study can aid in understanding how microbial activity is influenced by compost applications, which will be critical in making informed management decisions in the context of climate change.
ContributorsAmari, Katherine Nicole (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Blankinship, Joseph C (Committee member) / Gherardi, Laureano A (Committee member) / Cueva Rodriguez, Alejandro H (Committee member) / Arizona State University (Publisher)
Created2021
Description
In arid and semiarid areas of the southwestern United States and northwestern México, water availability is the main control on the interactions between the land surface and the atmosphere. Seasonal and interannual variations in water availability regulate the response of water and carbon dioxide fluxes in natural and urban landscapes. However, despite sharing a similar dependance to water availability, landscape characteristics, such as land cover heterogeneity, landscape position, access to groundwater, microclimatic conditions, and vegetation functional traits, among others, can play a fundamental role in modulating the interactions between landscapes and the atmosphere. In this dissertation, I study how different landscape characteristics influence the response of water and carbon dioxide fluxes in arid and semiarid urban and natural settings. The study uses the eddy covariance technique, which calculates the vertical turbulent fluxes within the boundary layer, to quantify water, energy, and carbon dioxide fluxes within local patches. Specifically, the study focused on three main scopes: (1) how vegetation, anthropogenic activity, and water availability influence carbon fluxes in four urban landscapes in Phoenix, Arizona, (2) how access to groundwater and soil-microclimate conditions modulate the flux response of three natural ecosystems in northwestern México during the North American monsoon, and (3) how the seasonal hydrologic partitioning in a watershed with complex terrain regulates the carbon dioxide fluxes of a Chihuahuan Desert shrubland. Results showed a differential response of landscapes according to their land cover composition, access to groundwater or functional traits. In Chapter 2, in urban landscapes with irrigation, vegetation activity can counteract carbon dioxide emissions during the day, but anthropogenic sources from the built environment dominate the carbon dioxide fluxes overall. In Chapter 3, across an elevation-groundwater access gradient, low elevation ecosystems showed intensive water use strategies linked to a dependance to shallow or intermittent access to soil moisture, while a high elevation ecosystem showed extensive water use strategies which depend on a reliable access to groundwater. Finally, in Chapter 4, the mixed shrubland in complex terrain showed an evenly distributed bimodal vegetation productivity which is supported by an abundant water availability during wet seasons and by carry-over moisture in deeper layers of the soil during the dry season. The results from this dissertation highlight how different forms of water availability are responsible for the activity of vegetation which modulates land surface fluxes in arid and semiarid settings. Furthermore, the outcomes of this dissertation help to understand how landscape properties regulate the flux response to water availability in urban and natural areas.
ContributorsPerez Ruiz, Eli Rafael (Author) / Vivoni, Enrique R (Thesis advisor) / Sala, Osvaldo E (Committee member) / Throop, Heather L (Committee member) / Whipple, Kelin X (Committee member) / Yepez, Enrico A (Committee member) / Arizona State University (Publisher)
Created2021
Description
Increasing rates of sea-level rise (SLR) pose a major threat to coastal communities around the world. Evidence of these impacts is found in increased rates of extreme weather, erosion, coastal flooding, high water levels and wave height, altered geomorphology, and more. Coastal dunes act as a buffer for neighboring ecosystems and protect inland communities from increased rates of SLR. The Eureka Littoral Cell (ELC) in Humboldt County, California, which extends from Trinidad Head in the north to Cape Mendocino in the south, experiences extreme wave conditions and higher rates of SLR in comparison to the rest of the Pacific Northwest. This study focuses on assessing the vulnerability of the outer-barrier system of the ELC to SLR and complements previous vulnerability assessments of the inner Humboldt Bay. The study area was partitioned into thirteen (13) representative study reaches based on shoreline change rates and geomorphology. Twenty-two (22) environmental and socio-economic variables were identified to characterize the broader human-environmental connections and exposures that define coastal vulnerability beyond basic physical forcing and exposures. The study first compiled and examined a range of physical, biological, hazardous, socio-cultural, and infrastructure attributes of the outer barrier region of the study site for their inherent vulnerabilities. Second, individual vulnerability scores, based on geographic attributes of each variable, were determined by modifying existing methodologies (e.g., USGS), spanning variable data ranges, and/or with feedback from local representatives and a research advisory team. Aggregations of individual variables were used to provide variable category groupings (e.g., physical, biological, hazards, socio-cultural, and infrastructure). Finally, aggregated values were normalized on a one-to-ten scale to determine two sub-categories of vulnerability (environmental, socio-economic) and an overall comprehensive vulnerability for each study reach. The resulting vulnerability assessments identify which reaches are likely to experience low, moderate, and high levels of vulnerability and, based on variable and sub-grouping values, what factors contribute to this vulnerability. As such, this study addresses the significance of including both environmental and socio-economic variables to examine and characterize vulnerability to SLR and it is anticipated that the results will help inform future adaptation and resilience planning in the region.
ContributorsShinsato, Lara Miyori (Author) / Dorn, Ron I (Thesis advisor) / Walker, Ian J (Thesis advisor) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2023
Description
Anthropogenic activities have had a profound effect on ecosystems, sediment budgets, and dust emissions stemming from widespread changes in land use and land cover and increases in sediment disturbance. Sandy coastal environments are under increasing pressure from the impacts of rising sea levels, coastal flooding, and erosion. Coastal foredunes can serve as a buffer to protect coastal communities from the impacts of coastal erosion, flooding, and sea-level rise. They also serve an important role as an ecosystem service, providing opportunities for recreation (off-highway vehicle, hiking, tourism) and habitat for native and endemic biota. Increased disturbance and pressure by human activity within the beach-dune system can lead to a decoupling of form and function from natural geomorphic and biotic processes. Dune management and restoration is often employed to mitigate some of the aforementioned pressures. Dynamic or ‘nature-based’ restoration aims to restore the form and function of a geomorphic system and improve landform resilience to external pressures by employing complimentary native plant species. This type of approach places emphasis on the ecological and geomorphic interactions within a landscape to improve the overall function and resiliency of the system to external pressures. Two case studies along the coast of California, the Lanphere Dunes and Oceano Dunes, provide uniquely different approaches to foredune restoration and the corresponding issues of landscape management for various goals. The case studies provided employ a suite of close-range remote sensing techniques, including kite aerial photography, uncrewed aerial systems photography, and terrestrial laser scanning, to generate high resolution (< 0.1 m) products (surface models; orthophoto mosaics in red-green-blue (RGB) and multispectral) to quantify and inform on restoration efforts by examining sediment budget and vegetation characteristics over a mesoscale (spatial and temporal). Results were compared to a variety of control sites (e.g., no restoration, natively vegetated, invasively vegetated) to highlight the differences between restored and unrestored landscapes, and the efficacy of restoration efforts for improving the developmental trajectory of a landscape towards a "desired" state.
ContributorsHilgendorf, Zach (Author) / Walker, Ian J (Thesis advisor) / Dorn, Ronald I (Committee member) / Schmeeckle, Mark W (Committee member) / Arizona State University (Publisher)
Created2022
Description
Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change.
ContributorsMonus, Brittney (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Hultine, Kevin R (Committee member) / Munson, Seth M (Committee member) / Arizona State University (Publisher)
Created2019