Matching Items (17)
Description
The aboveground surfaces of plants (i.e. the phyllosphere) comprise the largest biological interface on Earth (over 108 km2). The phyllosphere is a diverse microbial environment where bacterial inhabitants have been shown to sequester and degrade airborne pollutants (i.e. phylloremediation). However, phyllosphere dynamics are not well understood in urban environments, and this environment has never been studied in the City of Phoenix, which maintains roughly 92,000 city trees. The phyllosphere will grow if the City of Phoenix is able to achieve its goal of 25% canopy coverage by 2030, but this begs the question: How and where should the urban canopy expand? I addressed this question from a phyllosphere perspective by sampling city trees of two species, Ulmus parvifolia (Chinese Elm) and Dalbergia sissoo (Indian Rosewood) in parks and on roadsides. I identified characteristics of the bacterial community structure and interpreted the ecosystem service potential of trees in these two settings. I used culture-independent methods to compare the abundance of each unique bacterial lineage (i.e. ontological taxonomic units or OTUs) on the leaves of park trees versus on roadside tree leaves. I found numerous bacteria (81 OTUs) that were significantly more abundant on park trees than on roadside trees. Many of these OTUs are ubiquitous to bacterial phyllosphere communities, are known to promote the health of the host tree, or have been shown to degrade airborne pollutants. Roadside trees had fewer bacteria (10 OTUs) that were significantly more abundant when compared to park trees, but several have been linked to the remediation of petroleum combustion by-products. These findings, that were not available prior to this study, may inform the City of Phoenix as it is designing its future urban forests.
ContributorsMacNeille, Benjamin C (Author) / Childers, Daniel L. (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Cease, Arianne J (Committee member) / Arizona State University (Publisher)
Created2016
Description
The Basin and Range province of southwestern USA are composed of different grassland and shrubland ecosystems. Particularly understudied ecosystems in this region are playas, which are ephemerally-flooded wetlands located in topographic low areas of hydrologically-closed dryland catchments. There is not much known about the ecological functioning of playas and the role of playas within desert basins. Even less is known about how global change drivers may affect playas in the future. The main objective of this thesis was to better understand the ecological functioning and the impact of climate change on desert playa wetlands. I collected new data, used existing long-term data, and used simulation modelling techniques to address this objective. I compared playa soils to upland soils and found that playas were hotspots of soil organic carbon and nutrient storage within a desert basin. I also used existing data to analyze the response of above-ground net primary productivity (ANPP) to annual precipitation in playas and upland ecosystems. I found that playa ANPP responded in a non-linear concave-down relationship with annual precipitation amount. Playa ANPP peaked in moderately wet years and declined in very wet years, which was most likely due to flooding; whereas, upland ANPP increased linearly with precipitation. I measured soil organic carbon and nitrogen concentrations in a representative subset of playas and measured the biophysical characteristics of the upland catchments associated with each playa. I found that both catchment geomorphology and vegetation cover were correlated to differences in soil organic carbon and nitrogen among playas. These results showed the importance external soil-inputs delivered via surface runon to playas. Finally, I empirically measured groundwater recharge beneath playas and combined these empirical data with modelling data to forecast how playa groundwater recharge may change in the future. I concluded that playas contribute to groundwater recharge in desert aquifers, playa runon is a strong predictor of playa groundwater recharge, and climate change will have a net-positive impact on groundwater recharge beneath playas. Overall, my thesis research increased the understanding of the role of desert playas on the functioning of dryland ecosystems.
ContributorsMcKenna, Philip (Author) / Sala, Osvaldo E. (Thesis advisor) / Monger, H. Curtis (Committee member) / Hall, Sharon J (Committee member) / Childers, Daniel L. (Committee member) / Arizona State University (Publisher)
Created2016
Description
Cities can be sources of nitrate to downstream ecosystems resulting in eutrophication, harmful algal blooms, and hypoxia that can have negative impacts on economies and human health. One potential solution to this problem is to increase nitrate removal in cities by providing locations where denitrification¬— a microbial process in which nitrate is reduced to N2 gas permanently removing nitrate from systems— can occur. Accidental urban wetlands– wetlands that results from human activities, but are not designed or managed for any specific outcome¬– are one such feature in the urban landscape that could help mitigate nitrate pollution through denitrification.
The overarching question of this dissertation is: how do hydrology, soil conditions, and plant patches affect patterns of denitrification in accidental urban wetlands? To answer this question, I took a three-pronged approach using a combination of field and greenhouse studies. First, I examined drivers of broad patterns of denitrification in accidental urban wetlands. Second, I used a field study to test if plant traits influence denitrification indirectly by modifying soil resources. Finally, I examined how species richness and interactions between species influence nitrate retention and patterns of denitrification using both a field study and greenhouse experiment.
Hydroperiod of accidental urban wetlands mediated patterns of denitrification in response to monsoon floods and plant patches. Specifically, ephemeral wetlands had patterns of denitrification that were largely unexplained by monsoon floods or plant patches, which are common drivers of patterns of denitrification in non-urban wetlands. Several plant traits including belowground biomass, above- and belowground tissue chemistry and rooting depth influenced denitrification indirectly by changing soil organic matter or soil nitrate. However, several other plant traits also had significant direct relationships with denitrification, (i.e. not through the hypothesized indirect relationships through soil organic matter or soil nitrate). This means these plant traits were affecting another aspect of soil conditions not included in the analysis, highlighting the need to improve our understanding of how plant traits influence denitrification. Finally, increasing species richness did not increase nitrate retention or denitrification, but rather individual species had the greatest effects on nitrate retention and denitrification.
The overarching question of this dissertation is: how do hydrology, soil conditions, and plant patches affect patterns of denitrification in accidental urban wetlands? To answer this question, I took a three-pronged approach using a combination of field and greenhouse studies. First, I examined drivers of broad patterns of denitrification in accidental urban wetlands. Second, I used a field study to test if plant traits influence denitrification indirectly by modifying soil resources. Finally, I examined how species richness and interactions between species influence nitrate retention and patterns of denitrification using both a field study and greenhouse experiment.
Hydroperiod of accidental urban wetlands mediated patterns of denitrification in response to monsoon floods and plant patches. Specifically, ephemeral wetlands had patterns of denitrification that were largely unexplained by monsoon floods or plant patches, which are common drivers of patterns of denitrification in non-urban wetlands. Several plant traits including belowground biomass, above- and belowground tissue chemistry and rooting depth influenced denitrification indirectly by changing soil organic matter or soil nitrate. However, several other plant traits also had significant direct relationships with denitrification, (i.e. not through the hypothesized indirect relationships through soil organic matter or soil nitrate). This means these plant traits were affecting another aspect of soil conditions not included in the analysis, highlighting the need to improve our understanding of how plant traits influence denitrification. Finally, increasing species richness did not increase nitrate retention or denitrification, but rather individual species had the greatest effects on nitrate retention and denitrification.
ContributorsSuchy, Amanda Klara (Author) / Childers, Daniel L. (Thesis advisor) / Stromberg, Juliet C. (Thesis advisor) / Grimm, Nancy (Committee member) / Hall, Sharon (Committee member) / Sabo, John (Committee member) / Arizona State University (Publisher)
Created2016
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). 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.
ContributorsRamos, Jorge, 1984- (Author) / Childers, Daniel L. (Thesis advisor) / Grimm, Nancy (Committee member) / Sala, Osvaldo E. (Committee member) / Vivoni, Enrique R (Committee member) / Arizona State University (Publisher)
Created2017
Description
Sustainability research and action in communities should be holistic, integrating sociocultural, biogeophysical, and spiritual components and their temporal and spatial dynamics toward the aim of co-creating thriving living systems. Yet scientists and practitioners still struggle with such integration. Regenerative development (RD) offers a way forward. RD focuses on shifting the consciousness and thinking underlying (un)sustainability as well as their manifestation in the physical world, creating increasingly higher levels of health and vitality for all life across scales. However, tools are nascent and relatively insular. Until recently, no empirical scientific research studies had been published on RD processes and outcomes.
My dissertation fills this gap in three complementary studies. The first is an integrative review that contextualizes regenerative development within the fields of sustainability, sustainable design and development, and ecology by identifying its conceptual elements and introducing a regenerative landscape development paradigm. The second study integrates complex adaptive systems science, ecology, sustainability, and regenerative development to construct and pilot the first iteration of a holistic sustainable development evaluation tool—the Regenerative Development Evaluation Tool—in two river restoration projects. The third study builds upon the first two, integrating scientific knowledge with existing RD and sustainable community design and development practices and theory to construct and pilot a Regenerative Community Development (RCD) Framework. Results indicate that the RCD Framework and Tools, when used within a regenerative landscape development paradigm, can facilitate: (1) shifts in thinking and development and design outcomes to holistic and regenerative ones; (2) identification of areas where development and design projects can become more regenerative and ways to do so; and (3) identification of factors that potentially facilitate and impede RCD processes. Overall, this research provides a direction and tools for holistic sustainable development as well as foundational studies for further research.
My dissertation fills this gap in three complementary studies. The first is an integrative review that contextualizes regenerative development within the fields of sustainability, sustainable design and development, and ecology by identifying its conceptual elements and introducing a regenerative landscape development paradigm. The second study integrates complex adaptive systems science, ecology, sustainability, and regenerative development to construct and pilot the first iteration of a holistic sustainable development evaluation tool—the Regenerative Development Evaluation Tool—in two river restoration projects. The third study builds upon the first two, integrating scientific knowledge with existing RD and sustainable community design and development practices and theory to construct and pilot a Regenerative Community Development (RCD) Framework. Results indicate that the RCD Framework and Tools, when used within a regenerative landscape development paradigm, can facilitate: (1) shifts in thinking and development and design outcomes to holistic and regenerative ones; (2) identification of areas where development and design projects can become more regenerative and ways to do so; and (3) identification of factors that potentially facilitate and impede RCD processes. Overall, this research provides a direction and tools for holistic sustainable development as well as foundational studies for further research.
ContributorsGibbons, Leah Veronica (Author) / Cloutier, Scott A (Thesis advisor) / Coseo, Paul J (Committee member) / Childers, Daniel L. (Committee member) / Arizona State University (Publisher)
Created2019
Description
Participatory approaches to policy-making and research are thought to “open up” technical decision-making to broader considerations, empower diverse public audiences, and inform policies that address pluralistic public goods. Many studies of participatory efforts focus on specific features or outcomes of those efforts, such as the format of a participatory event or the opinions of participants. While valuable, such research has not resolved conceptual problems and critiques of participatory efforts regarding, for example, their reinforcement of expert perspectives or their inability to impact policy- and decision-making. I studied two participatory efforts using survey data collected from participants, interviews with policy makers and experts associated with each project, and an analysis of project notes, meeting minutes, and my own personal reflections about each project. Both projects were based one type of participatory effort called Participatory Technology Assessment (pTA). I examined how project goals, materials, and the values, past experiences, and judgments of practitioners influenced decisions that shaped two participatory efforts to better understand how practitioners approached the challenges associated with participatory efforts.
I found four major themes that influenced decisions about these projects: Promoting learning; building capacity to host pTA events; fostering good deliberation; and policy relevance. Project organizers engaged in iterative discussions to negotiate how learning goals related to dominant ideas from policy and expert communities and frequently reflected on the impact of participatory efforts on participants and on broader socio-political systems. Practitioners chose to emphasize criteria for deliberation that were flexible and encompassing. They relied heavily on internal discussions about materials and format, and on feedback collected from participants, policy makers, and other stakeholders, to shape both projects, though some decisions resulted in unexpected and undesirable outcomes for participant discussions and policy relevance. Past experience played a heavy role in many decisions about participatory format and concerns about deliberative or participatory theory were only nominally present. My emphasis on understanding the practice of participatory efforts offers a way to reframe research on participatory efforts away from studying ‘moments’ of participation to studying the larger role participatory efforts play in socio-political systems.
I found four major themes that influenced decisions about these projects: Promoting learning; building capacity to host pTA events; fostering good deliberation; and policy relevance. Project organizers engaged in iterative discussions to negotiate how learning goals related to dominant ideas from policy and expert communities and frequently reflected on the impact of participatory efforts on participants and on broader socio-political systems. Practitioners chose to emphasize criteria for deliberation that were flexible and encompassing. They relied heavily on internal discussions about materials and format, and on feedback collected from participants, policy makers, and other stakeholders, to shape both projects, though some decisions resulted in unexpected and undesirable outcomes for participant discussions and policy relevance. Past experience played a heavy role in many decisions about participatory format and concerns about deliberative or participatory theory were only nominally present. My emphasis on understanding the practice of participatory efforts offers a way to reframe research on participatory efforts away from studying ‘moments’ of participation to studying the larger role participatory efforts play in socio-political systems.
ContributorsWeller, Nicholas, Ph.D (Author) / Childers, Daniel L. (Thesis advisor) / Bennett, Ira (Committee member) / Coseo, Paul (Committee member) / Klinsky, Sonja (Committee member) / Arizona State University (Publisher)
Created2019
Description
The rise in urban populations is encouraging cities to pursue sustainable water treatment services implementing constructed treatment wetlands (CTW). This is especially important in arid climates where water resources are scarce; however, research regarding aridland CTWs is limited. The Tres Rios CTW in Phoenix, Arizona, USA, presents the tradeoff between greater water loss and enhanced nitrogen (N) removal. Previous research has suggested that water loss due to transpiration is replaced by a phenomenon termed the Biological Tide. This trend has been documented since 2011 by combining transpiration values with a nitrogen budget. Calculations were made at both the marsh and whole-system scale. The purpose of this paper is to demonstrate how the Biological Tide enhances N uptake throughout the CTW. Results indicate that about half of the nitrogen taken up by the vegetated marsh is associated with new water entering the marsh via the Biological Tide with even higher values during warmer months. Furthermore, it is this phenomenon that enhances N uptake throughout the year, on average, by 25.9% for nitrite, 9.54% for nitrate, and 4.84% for ammonium at the whole-system scale and 95.5%, 147%, and 118% within the marsh. This paper demonstrates the Biological Tide’s significant impact on enhanced N removal in an aridland CTW.
ContributorsTreese, Sawyer Matthew (Author) / Childers, Daniel L. (Thesis director) / Grimm, Nancy (Committee member) / School of Geographical Sciences and Urban Planning (Contributor) / School of Sustainability (Contributor) / School of Public Affairs (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05