Browsing by Subject "Laurentian Great Lakes"

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    Defining the Risk-Release Relationship of Daphnia magna, a Non-native Aquatic Species in the Environment of Duluth-Superior Harbor
    (2015-07) TenEyck, Matthew
    Understanding how inoculation characteristics (propagule pressure) affect establishment outcome of a non-native, invading species in the context of abiotic and biotic factors (ecological resistance) is a recent area of emphasis in ecology given an urgent need to prevent and manage invasive species globally. The overarching objective of this dissertation research is to quantify how a non-native species (Daphnia magna) establishes in response to different levels of propagule pressure in the context of a Laurentian Great Lakes port receiving system. Specifically, I described spatial and temporal patterns in the density and diversity of crustacean zooplankton in the context of abiotic factors of the Duluth-Superior Harbor and St. Louis River Estuary (DSHSLRE) and used those measures to develop establishment criteria for the propagule pressure experiments. Next, I evaluated the ability of a surrogate invader, D. magna to successfully colonize 200-L mesocosm aquaria by manipulating propagule pressure and several components of ecological resistance. Special attention was paid to the density of 10 individuals m-3 as this is the current standard suggested by the International Maritime Organization for density of permissible non-native species in ballast water discharge from oceangoing vessels. Lastly, I re-analyzed the results from the propagule pressure experiments to evaluate how different establishment criteria, which vary in rigor, influence the perceived outcome. Results demonstrate notable spatial and seasonal patterns in the abiotic conditions and zooplankton diversity and density measured at nine locations sampled biweekly during 2007 and 2008 in the DSHSLRE. Abiotic characteristics of upstream sites were indicative of littoral habitats and changed more dramatically within a year and from year to year. Overall 49 distinct taxa were identified, half at the genus level Copepoda and half Cladocera. Colonization of the mesocosm aquariums by D. magna populations ranged from 50-80% in the spring and fall experiments but never achieved success greater than 33% in the summer experiments. Only when the background assemblage of zooplankton was first removed from the tanks in the summer was D. magna able to establish suggesting that ecological resistance related to resource competition was prohibitive. Risk of establishment evaluated by different threshold criteria influenced the perceived outcome of the mesocosm experiments. This study demonstrates the multi-faceted nature of drivers that determine establishment success of a non-native species and the complexities of evaluating standards on permissible biological pollution using an experimental, mesocosm venue.
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    Effects of Water Level Fluctuations and Regulation on Upper Great Lakes Nearshore Ecosystems: An Annotated Bibliography
    (University of Minnesota Duluth, 2009-07) Brady, Valerie; Ruzycki, Elaine
    This is an annotated bibliography of literature relating to the effects of water level fluctuations on ecosystems and biota of the Laurentian Great Lakes. This report was created in support of investigations into the potential ecosystem effects of altering the water level regulation of Lake Superior at the St. Marys River lock and dam system. Because such a change would most affect lakes Superior, Michigan, and Huron, we tried to concentrate on these lakes. However, we have included quite a bit of literature from lakes Erie and Ontario, where there has been more investigation of water level fluctuations (or lack thereof) and water level regulation. We have also included pertinent literature from around the world on effects of water level fluctuations in large lake and reservoir systems, primarily because of the paucity of pertinent literature for the upper Great Lakes.
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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.