Matching Items (16)

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Soil moisture availability and energetic controls on belowground network complexity and function in arid ecosystems

Description

The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However,

The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However, much of the research regarding soil biota and soil processes is centered on maintaining soil fertility (e.g., plant nutrient availability) and soil structure in mesic- and agro- ecosystems. Despite the empirical and theoretical strides made in soil ecology over the last few decades, questions regarding ecosystem function and soil processes remain, especially for arid areas. Arid areas have unique ecosystem biogeochemistry, decomposition processes, and soil microbial responses to moisture inputs that deviate from predictions derived using data generated in more mesic systems. For example, current paradigm predicts that soil microbes will respond positively to increasing moisture inputs in a water-limited environment, yet data collected in arid regions are not congruent with this hypothesis. The influence of abiotic factors on litter decomposition rates (e.g., photodegradation), litter quality and availability, soil moisture pulse size, and resulting feedbacks on detrital food web structure must be explicitly considered for advancing our understanding of arid land ecology. However, empirical data coupling arid belowground food webs and ecosystem processes are lacking. My dissertation explores the resource controls (soil organic matter and soil moisture) on food web network structure, size, and presence/absence of expected belowground trophic groups across a variety of sites in Arizona.

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Created

Date Created
  • 2014

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Effects of Water Holding Capacity and Precipitation on Above Ground Net Primary Production

Description

Aboveground net primary production (ANPP) is an important ecosystem process that, in drylands, is most frequently limited by water availability. Water availability for plants is in part controlled by the

Aboveground net primary production (ANPP) is an important ecosystem process that, in drylands, is most frequently limited by water availability. Water availability for plants is in part controlled by the water holding capacity of soils. Available water holding capacity (AWHC) of soils is strongly influenced by soil texture and depth. This study drew upon localized rain gauge data and four data-sets of cover-line and biomass data to estimate ANPP and to determine annual precipitation (PPT). I measured soil depth to caliche and texture by layer of 112 plots across the four landscape units for which estimation of ANPP were available. A pedotransfer function was used to estimate AWHC from soil depth increments to depth of caliche measurements and texture analysis. These data were analyzed using simple and multivariate regression to test the effect of annual precipitation and available water holding capacity on aboveground net primary production. Soil texture remained constant among all plots (sandy loam) and depth to caliche varied from 15.16 cm to 189 cm. AWHC and the interaction term (PPT*AWHC) were insignificant (p=0.142, p=0.838) and annual PPT accounted for 18.4% of the variation in ANPP. The y-intercept was significantly different for ANPP ~ annual PPT when considering AWHC values either above or below 3 cm. Shrub ANPP was insensitive to precipitation regardless of AWHC (R2=-0.012, R2=0.014). Results from this study indicate that a model incorporating annual PPT and AWHC may not serve as a good predictor for ANPP at a site level where there is little variation in soil texture.

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Created

Date Created
  • 2019

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Characterization of Tropical Agricultural Soil Microbiomes After Biochar Amendment

Description

Modern agriculture faces multiple challenges: it must produce more food for a growing global population, adopt more efficient and sustainable management strategies, and adapt to climate change. One potential component

Modern agriculture faces multiple challenges: it must produce more food for a growing global population, adopt more efficient and sustainable management strategies, and adapt to climate change. One potential component of a sustainable management strategy is the application of biochar to agricultural soils. Biochar is the carbon-rich product of biomass pyrolysis, which contains large proportions of aromatic compounds that influence its stability in soil. Concomitant with carbon sequestration, biochar has the potential to increase soil fertility through increasing soil pH, moisture and nutrient retention. Changes in the soil physical and chemical properties can result in shifts in the soil microbiome, which are the proximate drivers of soil processes. This dissertation aims to determine the compositional and functional changes in the soil microbial community in response to the addition of a low-volatile matter biochar. First, the impact of biochar on the bacterial community was investigated in two important agricultural soils (Oxisol and Mollisol) with contrasting fertility under two different cropping systems (conventional sweet corn and zero-tillage napiergrass) one month and one year after the initial addition. This study revealed that the effects of biochar on the bacterial community were most pronounced in the Oxisol under napiergrass cultivation, however soil type was the strongest determinant of the bacterial community. A follow-up study was conducted using shotgun metagenomics to probe the functional community of soil microcosms, which contained Oxisol soil under napiergrass two years after the initial addition of biochar. Biochar significantly increased total carbon in the soils but had little impact on other soil properties. Theses analyses showed that biochar-amended soil microcosms exhibited significant shifts in the functional community and key metabolic pathways related to carbon turnover and denitrification. Given the distinct alterations to the biochar-amended community, deoxyribose nucleic acid (DNA) stable isotope probing was used to target the active populations. These analyses revealed that biochar did not significantly shift the active community in soil microcosms. Overall, these results indicate that the impact of biochar on the active soil community is transient in nature. Yet, biochar may still be a promising strategy for long-term carbon sequestration in agricultural soils.

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Created

Date Created
  • 2020

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Net effect: social media as a catalyst for political reform into the age of cyberspace warfare : exploring the revolutionary narrative of social media

Description

The purpose of this study is to examine if there exists a discrepancy between popular Westernized notions about the role of social media and the notions of those affected by

The purpose of this study is to examine if there exists a discrepancy between popular Westernized notions about the role of social media and the notions of those affected by the Green Revolution in Iran in 2009 and assess how this might change the dominant discourse of cyber-utopia. The internet has most certainly transformed our lives in unforeseeable ways having various and unknown shifting effects but the purpose of this research is to view the dominant discourse of liberation in comparison with the perceived meaning and function of the internet and social media within anti-democratic regimes. The awareness of global misconceptions are imperative to move away from the popular norm and scope of research that uses framing tactics of liberation and democratization because the development, adoption and political consequences of any technological tool within any society will always tell a story. The net effect of social media was silenced soon after the Green Revolution and many Iranians are still experiencing the consequences of their actions. The dark side of internet freedom in authoritative governments will assuredly play a role in forming a more comprehensive understanding of the revolutionary narrative that is social media as well as contributing to the overall relationship of how the internet influences the political realm. Iran represents a unique situation to analyze due to its politically closed landscape and historical global misperception about Iranian society and its citizenry. Through the utilization of personal narratives of individual Iranians directly or indirectly involved within the movement and an overview of global trends of suppression of online speech, this research attempts to show that no i universal framework exists when it comes to the discourse about social media because the characteristics of a society will ultimately drive the forces that influence technological manifestation.

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Agent

Created

Date Created
  • 2012

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Impact of restoration practices on mycorrhizal inoculum potential in a semi-arid riparian ecosystem

Description

Mycorrhizal fungi form symbiotic relationships with plant roots, increasing nutrient and water availability to plants and improving soil stability. Mechanical disturbance of soil has been found to reduce mycorrhizal inoculum

Mycorrhizal fungi form symbiotic relationships with plant roots, increasing nutrient and water availability to plants and improving soil stability. Mechanical disturbance of soil has been found to reduce mycorrhizal inoculum in soils, but findings have been inconsistent. To examine the impact of restoration practices on riparian mycorrhizal inoculum potential, soil samples were collected at the Tres Rios Ecosystem Restoration and Flood Control Project located at the confluence of the Salt, Gila, and Agua Fria rivers in central Arizona. The project involved the mechanical removal of invasive Tamarix spp.( tamarisk, salt cedar) and grading prior to revegetation. Soil samples were collected from three stages of restoration: pre-restoration, soil banks with chipped vegetation, and in areas that had been graded in preparation for revegetation. Bioassay plants were grown in the soil samples and roots analyzed for arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) infection percentages. Vegetations measurements were also taken for woody vegetation at the site. The mean number of AM and EM fungal propagules did not differ between the three treatment area, but inoculum levels did differ between AM and EM fungi with AM fungal propagules detected at moderate levels and EM fungi at very low levels. These differences may have been related to availability of host plants since AM fungi form associations with a variety of desert riparian forbs and grasses and EM fungi only form associations with Populus spp. and Salix spp. which were present at the site but at low density and canopy cover. Prior studies have also found that EM fungi may be more affected by tamarisk invasions than AM fungi. Our results were similar to other restoration projects for AM fungi suggesting that it may not be necessary to add AM fungi to soil prior to planting native vegetation because of the moderate presence of AM fungi even in soils dominated by tamarisk and exposed to soil disturbance during the restoration process. In contrast when planting trees that form EM associations, it may be beneficial to augment soil with EM fungi collected from riparian areas or to pre-inoculate plants prior to planting.

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Created

Date Created
  • 2012

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Characterizations of soil layers artificially deposited on glass and photovoltaic coupons

Description

The deposition of airborne dust, especially in desert conditions, is very problematic as it leads to significant loss of power of photovoltaic (PV) modules on a daily basis during the

The deposition of airborne dust, especially in desert conditions, is very problematic as it leads to significant loss of power of photovoltaic (PV) modules on a daily basis during the dry period. As such, PV testing laboratories around the world have been trying to set up soil deposition stations to artificially deposit soil layers and to simulate outdoor soiling conditions in an accelerated manner. This thesis is a part of a twin thesis. The first thesis, authored by Shanmukha Mantha, is associated with the designing of an artificial soiling station. The second thesis (this thesis), authored by Darshan Choudhary, is associated with the characterization of the deposited soil layers. The soil layers deposited on glass coupons and one-cell laminates are characterized and presented in this thesis. This thesis focuses on the characterizations of the soil layers obtained in several soiling cycles using various techniques including current-voltage (I-V), quantum efficiency (QE), compositional analysis and optical profilometry. The I-V characterization was carried out to determine the impact of soil layer on current and other performance parameters of PV devices. The QE characterization was carried out to determine the impact of wavelength dependent influence of soil type and thickness on the QE curves. The soil type was determined using the compositional analysis. The compositional data of the soil is critical to determine the adhesion properties of the soil layers on the surface of PV modules. The optical profilometry was obtained to determine the particle size and distribution. The soil layers deposited using two different deposition techniques were characterized. The two deposition techniques are designated as “dew” technique and “humidity” technique. For the same deposition time, the humidity method was determined to deposit the soil layer at lower rates as compared to the dew method. Two types of deposited soil layers were characterized. The first type layer was deposited using a reference soil called Arizona (AZ) dust. The second type layer was deposited using the soil which was collected from the surface of the modules installed outdoor in Arizona. The density of the layers deposited using the surface collected soil was determined to be lower than AZ dust based layers for the same number of deposition cycles.

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Agent

Created

Date Created
  • 2016

Design, Fabrication, and Characterization of a Sand Burrowing Robot

Description

Unmanned subsurface investigation technologies for the Moon are of special significance for future exploration when considering the renewed interest of the international community for this interplanetary destination. In precision agriculture,

Unmanned subsurface investigation technologies for the Moon are of special significance for future exploration when considering the renewed interest of the international community for this interplanetary destination. In precision agriculture, farmers demand quasi-real-time sensors and instruments with remote crop and soil detection properties to meet sustainability goals and achieve healthier and higher crop yields. Hence, there is the need for a robot that will be able to travel through the soil and conduct sampling or in-situ analysis of the subsurface materials on earth and in space. This thesis presents the design, fabrication, and characterization of a robot that can travel through the soil. The robot consists of a helical screw design coupled with a fin that acts as an anchor. The fin design is an integral part of the robot, allowing it to travel up and down the medium unaided. Experiments were performed to characterize different designs. It was concluded that the most energy-efficient speed from traveling down the medium is 20 rpm, while 60 rpm was the efficient speed for traveling up the medium. This research provides vital insight into developing subsurface robots enabling us to unearth the valuable knowledge that subsurface environment holds to help the agricultural, construction, and exploration communities.

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Created

Date Created
  • 2020

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Soil Microbial Responses to Different Precipitation Regimes Across a Southwestern United States Elevation Gradient

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

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.

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Created

Date Created
  • 2019

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Methane and nitrous oxide fluxes from water, plants, and soils of a constructed treatment wetland in Phoenix, AZ

Description

Constructed treatment wetlands (CTW) have been a cost-efficient technological solution to treat different types of wastewater but may also be sources of emitters of methane (CH4) and nitrous oxide (N2O).

Constructed treatment wetlands (CTW) have been a cost-efficient technological solution to treat different types of wastewater but may also be sources of emitters of methane (CH4) and nitrous oxide (N2O). Thus, my objective for this dissertation was to investigate CH4 and N2O fluxes via multiple pathways from the Tres Rios CTW located in Phoenix, AZ, USA. I measured gas fluxes from the CTW along a whole-system gradient (from inflow to outflow) and a within-marsh gradient (shoreline, middle, and open water sites). I found higher diffusive CH4 release in the summer compared to spring and winter seasons. Along the whole-system gradient, I found greater CH4 and N2O emission fluxes near the inflow compared to near the outflow. Within the vegetated marsh, I found greater CH4 emission fluxes at the vegetated marsh subsites compared to the open water. In contrast, N2O emissions were greater at the marsh-open water locations compared to interior marsh. To study the plant-mediated pathway, I constructed small gas chambers fitted to Typha spp. leaves. I found plant-mediated CH4 fluxes were greater near the outflow than near the inflow and that CH4 fluxes were higher from lower sections of plants compared to higher sections. Overall, Typha spp. emitted a mean annual daily flux rate of 358.23 mg CH4 m-2 d-1. Third, using a 30-day mesocosm experiment I studied the effects of three different drydown treatments (2, 7, 14 days) on the fluxes of CH4 and N2O from flooded CTW soils. I found that CH4 fluxes were not significantly affected by soil drydown events. Soils that were dry for 7 days shifted from being N2O sources to sinks upon inundation. As a result, the 7-day drydown soils were sinks while the 14-day drydown soils showed significant N2O release. My results emphasize the importance of studying ecological processes in CTWs to improve their design and management strategies so we can better mitigate their greenhouse gas emissions.

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Agent

Created

Date Created
  • 2017

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Development of uniform artificial soil deposition techniques on glass and photovoltaic coupons

Description

Soiling is one of the major environmental factors causing the negative performance of photovoltaic (PV) modules. Dust particles, air pollution particles, pollen, bird droppings and other industrial airborne particles are

Soiling is one of the major environmental factors causing the negative performance of photovoltaic (PV) modules. Dust particles, air pollution particles, pollen, bird droppings and other industrial airborne particles are some natural sources that cause soiling. The thickness of soiling layer has a direct impact on the performance of PV modules. This phenomenon occurs over a period of time with many unpredictable environmental variables indicated above. This situation makes it difficult to calculate or predict the soiling effect on performance. The dust particles vary from one location to the other in terms of particle size, color and chemical composition. These properties influence the extent of performance (current) loss, spectral loss and adhesion of soil particles on the surface of the PV modules. To address this uncontrolled environmental issues, research institutes around the world have started designing indoor artificial soiling stations to deposit soil layers in various controlled environments using reference soil samples and/or soil samples collected from the surface of PV modules installed in the locations of interest. This thesis is part of a twin thesis. The first thesis (this thesis) authored by Shanmukha Mantha is related to the development of soiling stations and the second thesis authored by Darshan Choudhary is associated with the characterization of the soiled samples (glass coupons, one-cell PV coupons and multi-cell PV coupons). This thesis is associated with the development of three types of indoor artificial soiling deposition techniques replicating the outside environmental conditions to achieve required soil density, uniformity and other required properties. The three types of techniques are: gravity deposition method, dew deposition method, and humid deposition method. All the three techniques were applied on glass coupons, single-cell PV laminates containing monocrystalline silicon cells and multi-cell PV laminates containing polycrystalline silicon cells. The density and uniformity for each technique on all targets are determined. In this investigation, both reference soil sample (Arizona road dust, ISO 12103-1) and the soil samples collected from the surface of installed PV modules were used. All the three techniques are compared with each other to determine the best method for uniform deposition at varying thickness levels. The advantages, limitations and improvements made in each technique are discussed.

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Agent

Created

Date Created
  • 2016