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Characterization of DOC in "Accidental" Urban Wetlands in Phoenix, AZ

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Accidental wetlands have been created on the bed of the Salt River and are fed by storm-water outfalls discharging at various sections of the Phoenix Metropolitan Area. Water discharges from

Accidental wetlands have been created on the bed of the Salt River and are fed by storm-water outfalls discharging at various sections of the Phoenix Metropolitan Area. Water discharges from these outfalls throughout the year, during both dry conditions (base flow) and during rain events (storm flow). In this study, DOC content and composition was studied during these two flow conditions, in the outfalls and along the wetland flow path. The importance of DOC lies in its role in transporting carbon via water movement, between different parts of a landscape, and therefore between pools in the ecosystem. Urbanization has influenced content and composition of DOC entering the accidental urban wetland via outfalls as they represent watersheds from different areas in Phoenix. First, DOC load exhibited higher quantities during stormflow compared to baseflow conditions. Second, DOC load and fluorescence analysis outcomes concluded the outfalls are different from each other. The inputs of water on the north side of the channel represent City of Phoenix watersheds were similar to each other and had high DOC load. The northern outfalls are both different in load and composition from the outfall pipe on the southern bank of the wetland as it represents South Mountain watershed. Fluorescence analysis results also concluded compositional changes occurred along the wetland flow path during both stormflow and baseflow conditions. In this study, it was explored how urbanization and the associated changes in hydrology and geomorphology have affected a desert wetland's carbon content.

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  • 2016-05

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Analysis of Nitrogen Uptake in a Duckponics System

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Duckponics is an unconventional form of aquaponics that has recently been implemented by a small community in Washington State as an experiment in sustainable methods of food production. The community

Duckponics is an unconventional form of aquaponics that has recently been implemented by a small community in Washington State as an experiment in sustainable methods of food production. The community created the Duckponics system to test the possibility of using the waste of ducks present on the farm to fertilize crop plants. This research paper examines aspects of the nitrogen cycle within this system to determine the efficacy of nitrogen removal by plants and microbes. More specifically, the research examines (1) the microbial activity occurring in selected beds of the system, (2) the ability of hydroponic grow beds to retain inorganic nitrogen, and (3) how periodic flushing of the system affects nitrogen retention. Water data was collected in all system tanks using aquarium test strips, but water samples were collected for flow injection analysis in (1) one of the grow beds, (2) the duck pond, and (3) a control bed with no plants but filled with gravel and inoculated with the same bacteria from the grow bed. Samples were then analyzed for ammonia (NH4+-N) and combined nitrite and nitrate (NOx-N) concentrations. The results show that the treatment type (control, duck pond, or grow bed) was a significant (p<0.05) predictor of NH4+-N, NOx-N, and total inorganic nitrogen (TIN) in the porewater of the treatment beds. The grow bed was found to have 100% removal of TIN, whereas the control had 0% TIN removal (195% increase). Timing of the sample in relation to the flushing events was a moderately significant predictor of TIN, NH4+-N and NOx-N in the duck pond (p = 0.07 for TIN, p = 0.12 for NH4+-N, p = 0.11 for NOx-N), with an overall decrease in TIN after flood pulses. NH4+-N concentrations at the inlet and outlet were found to be significantly different in the grow bed (p=0.037), but not the control, and moderately significantly different (p<0.15) for NOx-N and TIN in the grow bed (p=0.072 for NOx-N, p=0.075 for TIN), but significant for the control (p=0.043). These findings show evidence of nitrification in the grow bed and control, plant presence significantly contributing to nitrogen removal in the grow bed, and some hydrologic flushing of NOx-N out of the duck pond during pump cycles.

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  • 2016-05

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A Study of Soil Characteristics across an Arid, Urban Landscape and their Relationship with Greenhouse Gas Emissions

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The heterogeneous nature of urban systems is a documented phenomenon that can potentially cause widespread changes in soil characteristics across urban habitat type. These differences in soil characteristics may be

The heterogeneous nature of urban systems is a documented phenomenon that can potentially cause widespread changes in soil characteristics across urban habitat type. These differences in soil characteristics may be linked to hot spots within the city of greenhouse gas (N2O, CO2, CH4) emissions, which have the potential to affect global climate. The purpose of this study was to take an in depth look at how soil characteristics (i.e. soil moisture, organic matter, and inorganic nitrogen) vary across the urban Phoenix landscape and how these differing landscape characteristics can potentially create hot spots of greenhouse gas emissions. We measured greenhouse gas emissions and soil characteristics from ten different landscape types during the summer and fall of 2013 and included a wetting experiment to simulate flooding events in the desert. Using statistical analyses we found that all soil characteristics varied significantly based on both season and land-use type. In addition, land-use types could be clustered into recognizable groups based on their soil characteristics, with the presence of irrigation being a strong deciding factor in how the groups were arranged. However, N2O emissions did not vary significantly based on season, land-use type, or the presence of a wetting experiment. Patterns reinforce the heterogeneous nature of the Phoenix urban area and suggest that N2O emissions may not relate to soil characteristics and habitat designations (i.e. human land use) in the way that we originally predicted.

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  • 2015-05