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Browsing by Author "Hanson, Bennett"

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    An Investigation into the Biomarker Potential of Highly Branched Isoprenoids in Northern Minnesota Lacustrine Sediments
    (2022-08) Hanson, Bennett
    Highly Branched Isoprenoids (HBIs) are isoprene-based lipids synthesized by diatoms. HBIs are commonly used as sea-ice proxies in marine environments where their presence is indicative of marginal ice zones. Historical data on Ice cover in the Laurentian Great Lakes is sparse and only spans from the mid 1960’s to present day. This study aims to expand the biomarker potential of HBIs to apply them as a proxy for ice cover on Lake Superior. Seven study sites around Lake Superior were selected and studied to determine which freshwater HBIs were present, and at what concentration they were found. Each site was sampled twice, in the summer and in the winter to determine if seasonal conditions affect HBI production of diatom communities. The HBI suite at each site is characterized by gas chromatography mass spectrometry (GC-MS) analysis of the nonpolar extractable fraction of the sediments and the genera of diatoms present at each site are characterized by visual identification. In addition, microcosm studies of Nitzschia and Fragilaria are isolated from the Two Harbors study site and are analyzed to determine the HBI suites produced by them. Overall, eight distinct HBIs were identified from the seven study sites, in concentrations ranging from 0.1-0.9 µg g-1 dry sediment. Four distinct HBIs were identified from the microcosm cultures including three distinct C30 and one distinct C25 HBIs. HBIs show a potential to be correlated to environmental conditions, though future experiments must be conducted to develop this relationship.
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    An Investigation into the Biomarker Potential of Highly Branched Isoprenoids in Northern Minnesota Lake Sediments (2022-03-25)
    (2022) Hanson, Bennett; University of Minnesota Duluth. Department of Chemistry and Biochemistry
    Highly Branched Isoprenoids (HBIs) are isoprene-based lipids synthesized by diatoms. HBIs are often used as sea-ice proxies in marine environments where certain HBIs indicate the presence of sea ice diatoms. However, few studies have focused on HBIs produced by freshwater diatoms. The goal of this study is to expand the knowledge of the types of HBIs produced in freshwater environments through the identification and quantification of HBIs in surface sediment and periphyton samples containing HBI- producing freshwater diatoms collected from small lakes, the St. Louis River estuary, and Lake Superior. Each of the seven study sites was sampled twice, once in the summer and once in the winter to determine if seasonal conditions affect HBI production of diatom communities. At each site, the entire HBI suite is characterized by gas chromatography-mass spectrometry (GC-MS) analysis of the nonpolar extractable fraction, and the genera of diatoms present are characterized by visual identification. Additionally, single strains of Nitzschia frustulum and Fragilaria capucina have been isolated and are being grown in liquid media over a range of temperatures. Eight distinct HBIs have been identified from the seven sites with concentrations ranging from 0.1-0.9 ?g g-1 dry sediment, only one of which has been previously identified in the literature. One distinct C30:6 and two distinct C30:4 HBIs have been identified from the single-strain studies.