Browsing by Author "O'Brien, Peter"

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    Plant Community Composition of Camp Grafton Training Center (South Unit) from 1998-2013
    (North Dakota State University, 2014) O'Brien, Peter
    A vegetation monitoring study was conducted from 1998 to 2013 at Camp Grafton South (CGS) in Eddy County, North Dakota to assess how climatic, grazing, and military training disturbance affects plant community composition. The objectives of this study were to 1) describe the prairie vegetation at CGS across three topographic positions and 2) explore any shifts in plant community composition in correlation with time. Frequency data was collected at 45 randomly selected transects on lowland, midland, and upland grassland plant communities on native prairie. Plant communities were compared using non-metric multidimensional scaling (NMS) ordination. NMS ordination showed that the three plant communities were distinct from one another, and that the frequency of the invasive graminoids Kentucky bluegrass (Poa pratensis L.) and smooth brome (Bromus inermis Leyss.) increased. Increases in precipitation, temperature, and growing season days appear to be the primary influence on the changes in plant communities from 1998-2013.
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    Soil Function Following Remediation Using Ex Situ Thermal Desorption
    (North Dakota State University, 2017) O'Brien, Peter
    Soils perform many functions essential to human and ecosystem health, and contamination by organic compounds diminishes the ability of the soil to perform those functions. One method for remediating contaminated soils is ex situ thermal desorption (TD). This process involves excavating contaminated soil material and heating it to encourage contaminant vaporization. Gaseous contaminants are combusted in a thermal oxidizer, while the treated soil is available for reuse. While TD is a fast, reliable way to remediate contaminated soil, the ability of the soil to function after treatment is unknown. The aim of this research was to determine the viability of using TD-treated soil for agricultural production. Laboratory, greenhouse, and field experiments were conducted to compare soil properties of TD-treated soil to non-contaminated topsoil, as well as to explore the effects of mixing TD-treated soil with topsoil. Laboratory experiments found that soil organic carbon was diminished following treatment, which corresponded with an increase in saturated hydraulic conductivity and a decrease in aggregate stability. Despite these alterations, a greenhouse study found that wheat grown in TD-treated soils matched topsoil in producing mature wheat grain, but the grain was lower quality than that grown in topsoil. Further, the soil mixtures produced less grain than either material alone. These findings suggest that microorganism interactions affected the pool of nutrients available to the wheat, especially plant-available nitrogen. Under field conditions, the surface energy balance of TD-treated soils was similar to native topsoil, although the soil heat flux was slightly elevated. These findings indicated that soil temperature dynamics and evaporative fluxes are not different between TD-treated and native topsoil. Overall, this research suggests that TD-treated soils can be viable for agricultural production, but they are unlikely to match native topsoil in either production quantity or quality. Mixing TD-treated soil may mitigate some of the negative impacts of TD-treatment by reintroducing soil organic matter and biological communities, which could further enhance the rate of recovery of soil function.