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Browsing by Author "Denef, Karolien, committee member"

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    Exposing new compositional coverage of weathered petroleum hydrocarbons through a tiered analytical approach
    (Colorado State University. Libraries, 2019) Bojan, Olivia, author; Blotevogel, Jens, advisor; Sale, Tom, advisor; Denef, Karolien, committee member
    Petroleum hydrocarbon spills are a widespread source of contamination that may threaten ecosystem services and human health, especially due to modern society's dependence on petroleum-based fuels. Remediation mainly relies on natural source zone depletion (NSZD) processes, which may generate partially oxidized transformation products of the spilled hydrocarbons through weathering or biodegradation processes. These byproducts containing one or more heteroatoms (N, S or O) – referred to as "polar hydrocarbons" – have increased water solubility and mobility in the environment. The unknown fate and toxicity of these complex mixtures of polar metabolites are causing growing concern. The objectives of this thesis were (1) to use a tiered analytical approach to investigate polar transformation products from various sources and (2) to identify common marker compounds that can be used for a more focused characterization of weathering processes at petroleum-contaminated sites. Previous studies have shown that the majority of weathered petroleum hydrocarbon compounds could not be detected by the GC-based analyses currently required by the United States Environmental Protection Agency due to their low volatility and high molecular weight. Therefore, standard methods may yield misleading characterizations of plumes and impede effective risk management. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), an emerging analytical technique in the field of "petroleomics" (the characterization of petroleum at the molecular level) offers unrivaled resolving power and mass accuracy; here it was used to determine the elemental composition of highly complex petroleum mixtures present in hydrocarbon-impacted sediment samples collected from field sites with varying redox and hydrogeological conditions. The tiered analysis revealed that GC-based techniques could only detect select nonpolar, low-molecular weight species (
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    Mechanisms and management for soil carbon sequestration
    (Colorado State University. Libraries, 2020) Mosier, Samantha, author; Cotrufo, M. Francesca, advisor; Paustian, Keith, advisor; Davies, Christian, committee member; Denef, Karolien, committee member
    Soil organic matter (SOM) holds more carbon (C) than the atmosphere and terrestrial aboveground biomass combined. SOM also provides many other co-benefits in the form of ecosystem services. The rate at which we lose or sequester more C in soils is of great importance for mitigating the rising atmospheric greenhouse gas concentrations as well as for maintaining the fundamental services that soils provide to humanity. Many of the mechanisms involved in accruing and storing soil C are not entirely clear, and factors like litter chemistry and minerology can all come into play when determining the sequestration potential of a specific ecosystem. Additionally, not all soil C is equal in its turnover time or in its ability to resist disturbance. Therefore it is crucial that we better understand how functionally different soil C pools form and persist in the soil environment. Several "climate smart" soil management practices have been analyzed for their potential to sequester more C. However there are still gaps in our knowledge regarding soil C sequestration and how it can be impacted by land use management. The southeast US is a region with particularly severe soil degradation from poor agricultural management, but also has a high potential for increased soil C sequestration and overall soil health. This dissertation looks at some potential mechanisms and management practices involved with storing more stable soil C in the southeastern US. Mechanisms include how litter chemistry and soil C saturation can enhance or inhibit soil C sequestration. Then, we evaluated management practices from pine plantations and grassland grazing in the southeastern US to evaluate if improved management could increase soil C stocks, their distribution, and overall soil health.