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Description
Phosphorus (P), an essential element for life, is becoming increasingly scarce, and its global management presents a serious challenge. As urban environments dominate the landscape, we need to elucidate how P cycles in urban ecosystems to better understand how cities contribute to — and provide opportunities to solve — problems of P management. The goal of my research was to increase our understanding of urban P cycling in the context of urban resource management through analysis of existing ecological and socio-economic data supplemented with expert interviews in order to facilitate a transition to sustainable P management. Study objectives were to: I) Quantify and map P stocks and flows in the Phoenix metropolitan area and analyze the drivers of spatial distribution and dynamics of P flows; II) examine changes in P-flow dynamics at the urban agricultural interface (UAI), and the drivers of those changes, between 1978 and 2008; III) compare the UAI's average annual P budget to the global agricultural P budget; and IV) explore opportunities for more sustainable P management in Phoenix. Results showed that Phoenix is a sink for P, and that agriculture played a primary role in the dynamics of P cycling. Internal P dynamics at the UAI shifted over the 30-year study period, with alfalfa replacing cotton as the main locus of agricultural P cycling. Results also suggest that the extent of P recycling in Phoenix is proportionally larger than comparable estimates available at the global scale due to the biophysical characteristics of the region and the proximity of various land uses. Uncertainty remains about the effectiveness of current recycling strategies and about best management strategies for the future because we do not have sufficient data to use as basis for evaluation and decision-making. By working in collaboration with practitioners, researchers can overcome some of these data limitations to develop a deeper understanding of the complexities of P dynamics and the range of options available to sustainably manage P. There is also a need to better connect P management with that of other resources, notably water and other nutrients, in order to sustainably manage cities.
ContributorsMetson, Genevieve (Author) / Childers, Daniel (Thesis advisor) / Aggarwal, Rimjhim (Thesis advisor) / Redman, Charles (Committee member) / Arizona State University (Publisher)
Created2011
Description
There are two main sections of this thesis: Codebook development and case coding. Over the course of my two years of involvement with the collaborative governance lab with Drs. Schoon and Carr Kelman, I worked on helping to complete the coding manual built by the lab to test variables from the literature using case studies. My main deliverable was building a Qualtrics survey to collect case studies. Using this Qualtrics survey, the lab will be able to collect coded cases by distributing the survey link through research networks. My thesis project included building the interface for the survey, participating in testing the intercoder reliability of the codebook, and coding one case, the Four Forest Restoration Initiative (4FRI), to provide insight on the collaborative governance strategies of this collaboration. Coding 4FRI also acted as a preliminary test of the survey, helping to provide further information on how users of the codebook might interact with the survey, and allowing the lab to generate a test report of survey results.
ContributorsGoddard, Kevin W (Author) / Carr Kelman, Candice (Thesis director) / Childers, Daniel (Committee member) / School of Sustainability (Contributor, Contributor) / School of Geographical Sciences and Urban Planning (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Elevated nitrate (NO3-) concentration in streams and rivers has contributed to environmental problems such as downstream eutrophication and loss of biodiversity. Sycamore Creek in Arizona is nitrogen limited, but previous studies have demonstrated high potential for denitrification, a microbial process in which biologically active NO3- is reduced to relatively inert dinitrogen (N2) gas. Oak Creek is similarly nitrogen limited, but NO3- concentration in reaches surrounded by agriculture can be double that of other reaches. We employed a denitrification enzyme assay (DEA) to compare potential denitrification rate between differing land uses in Oak Creek and measured whole system N2 flux using a membrane inlet mass spectrometer to compare differences in actual denitrification rates at Sycamore and Oak Creek. We anticipated that NO3- would be an important limiting factor for denitrifiers; consequentially, agricultural land use reaches within Oak Creek would have the highest potential denitrification rate. We expected in situ denitrification rate to be higher in Oak Creek than Sycamore Creek due to elevated NO3- concentration, higher discharge, and larger streambed surface area. DEA results are forthcoming, but analysis of potassium chloride (KCl) extraction data showed that there were no significant differences between sites in sediment extractable NO3- on either a dry mass or organic mass basis. Whole-reach denitrification rate was inconclusive in Oak Creek, and though a significant positive flux in N2 from upstream to downstream was measured in Sycamore Creek, the denitrification rate was not significantly different from 0 after accounting for reaeration, suggesting that denitrification does not account for a significant portion of the NO3- uptake in Sycamore Creek. Future work is needed to address the specific factors limiting denitrification in this system.
ContributorsCaulkins, Corey Robert (Author) / Grimm, Nancy (Thesis director) / Childers, Daniel (Committee member) / School of Sustainability (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn, influence whether it is retained and processed in the stream reach or exported downstream. I examined the composition of DOM from vascular wetland plants, filamentous algae, and riparian tree leaf litter in Sonoran Desert streams and its decomposition by stream microbes. I used a combination of field observations, in-situ experiments, and a manipulative laboratory incubation to test (1) how dominant primary producers influence DOM chemical composition and ecosystem metabolism at the reach scale and (2) how DOM composition and nitrogen (N) content control microbial decomposition and stream uptake of DOM. I found that differences in streamwater DOM composition between two distinct reaches of Sycamore Creek did not affect in-situ stream respiration and gross primary production rates. Stream sediment microbial respiration rates did not differ significantly when incubated in the laboratory with DOM from wetland plants, algae, and leaf litter, thus all sources were similarly labile. However, whole-stream uptake of DOM increased from leaf to algal to wetland plant leachate. Desert streams have the potential to process DOM from leaf, wetland, and algal sources, though algal and wetland DOM, due to their more labile composition, can be more readily retained and mineralized.
ContributorsKemmitt, Kathrine (Author) / Grimm, Nancy (Thesis advisor) / Hartnett, Hilairy (Committee member) / Throop, Heather (Committee member) / Arizona State University (Publisher)
Created2018
Description
Phosphorus (P) is an essential resource for global food security, but global supplies are limited and demand is growing. Demand reductions are critical for achieving P sustainability, but recovery and re-use is also required. Wastewater treatment plants and livestock manures receive considerable attention for their P content, but municipal organic waste is another important source of P to address. Previous research identified the importance of diverting this waste stream from landfills for recovering P, but little has been done to identify the collection and processing mechanisms required, or address the existing economic barriers. In my research, I conducted a current state assessment of organic waste management by creating case studies in Phoenix, Arizona and New Delhi, India, and surveyed biomass energy facilities throughout the United States. With participation from waste management professionals I also envisioned an organic waste management system that contributes to sustainable P while improving environmental, social, and economic outcomes.
The results of my research indicated a number of important leverage points, including landfill fees, diversion mandates for organic waste, and renewable energy credits. Source separation of organic waste improves the range of uses, decreases processing costs, and facilitates P recovery, while creating jobs and contributing to a circular economy. Food is a significant component of the waste stream, and edible food is best diverted to food banks, while scraps are best given to livestock. Biomass energy systems produce multiple revenue streams, have high processing capacities, and concentrate P and other minerals to a greater extent than composting. Using recovered P in urban agriculture and native landscaping results in additional benefits to social-ecological systems by improving food security, reducing the urban heat island effect, sequestering carbon, and enhancing urban ecosystems.
The results of my research indicated a number of important leverage points, including landfill fees, diversion mandates for organic waste, and renewable energy credits. Source separation of organic waste improves the range of uses, decreases processing costs, and facilitates P recovery, while creating jobs and contributing to a circular economy. Food is a significant component of the waste stream, and edible food is best diverted to food banks, while scraps are best given to livestock. Biomass energy systems produce multiple revenue streams, have high processing capacities, and concentrate P and other minerals to a greater extent than composting. Using recovered P in urban agriculture and native landscaping results in additional benefits to social-ecological systems by improving food security, reducing the urban heat island effect, sequestering carbon, and enhancing urban ecosystems.
ContributorsStoltzfus, Jared Thomas Yoder (Author) / Childers, Daniel (Thesis advisor) / Basile, George (Committee member) / Abbott, Joshua (Committee member) / Arizona State University (Publisher)
Created2016