Browsing by Subject "Superior"

Now showing 1 - 4 of 4
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    Characterizing Terrestrially-Derived Organic Matter in Sediments of Laurentian Great Lakes Superior and Huron
    (2023-08) Zunker, Jake
    While lacustrine systems contain a small fraction of the world’s water, they collectively account for nearly half of the world’s annual total organic matter (OM) burial. Recent years have brought considerable efforts to fully understand the carbon cycle of lacustrine environments with increasing emphasis on anthropogenic impacts. With such an important role in the global carbon cycle, it is critical to fully understand the function of carbon influx and storage in these systems. The carbon cycle and general composition of OM in waters of the Laurentian Great Lakes (LGLs) have been widely studied, yet there remains a large knowledge gap in carbon inputs and the fate and transport of sedimentary organic matter (SOM) in each LGL. To address this, we have characterized the chemical composition and source of OM spatially in the sediments of LGLs Superior and Huron, and temporally in LGL Superior. Surface sediments were collected at 30 sites in LGL Superior and 33 sites in LGL Huron and analyzed for bulk elemental composition (%OC and %N) and δ13C signatures using elemental analysis-isotope ratio mass spectrometry (EA-IRMS), and lignin-phenol biomarkers using gas chromatography-mass spectrometry (GCMS). Additionally, sediment cores were collected at 3 sites in LGL Superior to assess temporal SOM changes. Nearshore sediments exhibited low SOM degradation extent relative to high offshore SOM degradation extent in both lakes suggesting prominent lateral transport mechanisms. High lignin-phenol proxy ratios in offshore SOM may be attributed to airborne pollen as a major contributor of terrestrially-derived SOM into both lakes, suggesting that previously overlooked aeolian influx of pollen into the LGLs may constitute a significant unquantified carbon input. Similar lignin-phenols were measured in sediment cores collected at three of the sample sites in LGL Superior. The temporal degradation extent of terrestrial OM in downcore sediments remained relatively unchanged, while total OM concentrations decreased. These results indicate that terrestrially-derived OM becomes buried and relatively well-preserved in LGL Superior, with an average overall organic carbon burial rate of 2.27 gC m⁻² yr⁻¹. There are also clear temporal changes in lignin-phenol compositions and bulk elemental composition that correspond to changes in productivity, European colonization, and anthropogenic logging activities in the surrounding watershed of LGL Superior. This study advances our understanding of carbon inputs, transport, and storage in LGLs Superior and Huron by characterizing sedimentary OM spatially and temporally.
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    Particle Tracking in Lake Superior using FVCOM with focus on Apostle Islands
    (2021-08) Weber, Grace
    This study explores the movement of simulated neutrally buoyant drifters in far western Lake Superior. It was motivated by a desire to understand the transport and fate of microplastic particles originating near the region’s population centers and their potential impact on the Apostle Islands National Lakeshore. Particle movements were determined using the Finite Volume Coastal Ocean Model (FVCOM) configuration developed by the Large Lakes Observatory at the University of Minnesota Duluth. When exploring vertically averaged monthly output for the years 2015 and 2018, particles (which could include microplastic particles or suspended sediments) were modeled as passive drifters and advected using model output during each month. Exploring month- long and three month-long model runs showed that drifters originating in the St. Louis and Nemadji estuaries move predominantly towards the Apostle Islands. Drifters are also predicted to be more prevalent on the northern side of the Apostle islands. Drifters were also observed to travel faster in the late summer months, with more drifters entering and staying in the Apostle Islands during those months as well. The drifter tracks suggest that if a microplastic or other neutrally-buoyant particle is deposited inside of the estuary, assuming no large wind events, it will most likely end up in the Apostle Islands within 3 months, especially during the late summer months. The results of this analysis will help researchers to better understand the source, transport and fate of microplastics in Lake Superior. Part of this research was intended to aid in further understanding microplastic sampling research done in the Apostle Islands during June through December of 2015 (Whitmire et al 2017), and May and August of 2018 (Minor et al 2020).
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    River Quest: A Programmatic Evaluation
    (2022-03-24) Munshower, Ellen
    The purpose of this evaluative study was to assess to what extent that the River Quest program in Duluth, MN achieves its mission of “enhance[ing] awareness and understanding of the St. Louis River ecosystem and interrelated commercial, industrial, and recreational activities” in participants, and supports local teacher’s curricula (About Us, n.d.). More specifically, the following learning outcomes were investigated through this study: Knowledge regarding water safety; knowledge of the interactions between the river and recreational, commercial, and industrial activities in the region; attitudes regarding water conservation. From a survey of past participants and an interview with an educator that attended in the past, findings showed that the River Quest program is successfully educating students about the subjects, and the program is viewed in an overall positive light.
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    Seasonal Air-Water Exchange of Toxaphene in Lake Michigan and Lake Superior
    (2013-12) Kvale, Dorian
    Studies from the turn of the century reported annual net volatilization of toxaphene from Lake Michigan and Lake Superior to the atmosphere. Net volatilization from Lake Superior was predicted to shift to net absorption before the year 2010. To measure current toxaphene concentrations and calculate instantaneous air-water fluxes, this study collected paired air-water samples in 2004 and 2005 on Lake Michigan and in 2006 on Lake Superior. Average(±SD) dissolved water concentrations were 380(±180) ng/m3 for Lake Michigan and 730(±85) ng/m3 for Lake Superior. Average gas-phase concentrations were 9.4(±4.1) pg/m3 over Lake Michigan and 22(±20) pg/m3 over Lake Superior. Instantaneous air-water fluxes averaged 240(±530) ng/m2-season for Lake Michigan and 370(±1000) ng/m2-season for Lake Superior. Mass budgets estimated a net export of 81(±30) kg/yr of toxaphene from Lake Michigan and 365(±64) kg/yr from Lake Superior. Half-lives were approximately 17 years for both lakes. These long residence times have prolonged toxaphene's elevated concentration in the upper Great Lakes, and will sustain it as a concerning contaminant in Lake Superior for well over 50 years.