Browsing by Subject "Lake"
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Item 2015 Lake County Adolescent Sexual Health Report(2015) Teenwise MinnesotaItem 2016 Lake County Adolescent Sexual Health Report(2016) Healthy Youth Development - Prevention Research CenterItem 2017 Lake County Adolescent Sexual Health Report(2017) Healthy Youth Development - Prevention Research CenterItem 2018 Lake County Adolescent Sexual Health Report(2018) Healthy Youth Development - Prevention Research CenterItem 2019 Lake County Adolescent Sexual Health Report(2019) Healthy Youth Development - Prevention Research CenterItem 2020 Lake County Adolescent Sexual Health Report(2020) Healthy Youth Development - Prevention Research CenterItem 2021 Lake County Adolescent Sexual Health Report(2021) Healthy Youth Development - Prevention Research CenterItem 2022 Lake County Adolescent Sexual Health Report(2022) Healthy Youth Development - Prevention Research CenterItem 2023 Lake County Adolescent Sexual Health Report(2023) Healthy Youth Development - Prevention Research CenterItem Effects of Winter Hypoxia on Fish Communities in Northern Wisconsin(2023-07) Ellman, MarkHypoxia is a significant source of winter mortality for freshwater fish in north-temperate lakes and has the potential to alter fish communities. A multi-year dataset on Buckskin Lake, a shallow, productive drainage lake in northern Wisconsin with a history of winterkill, allowed the investigation of the effects of periodic winter hypoxia on fish communities. An aeration system was installed in 1984, which raised winter oxygen levels to levels sufficient for higher fish survival. In the winter of 2007-2008, the aerator system failed, causing an extensive winterkill. The lake was sampled from 2002-2005, before the aerator failure, and in 2008-2009, after the winterkill event. In addition, 16 similar lakes in the area with no winterkill history were sampled using similar methods. Using the combined datasets, two hypotheses were tested with non-metric multidimensional scaling (NMDS) and PERMANOVA analyses. We hypothesized that (1): after 18 years of aeration, the Buckskin Lake fish community from 2002-2005 would be similar to the non-winterkill lakes due to the recolonization of species from connected lakes, and (2): the fish community changed significantly in the lake due to the 2007-2008 winterkill event. The first hypothesis was not supported, as NMDS and PERMANOVA analyses showed that Buckskin Lake retained a fish community distinct from the non-winterkill lakes. Our findings were consistent with the second hypothesis: an incomplete winterkill occurred in 2007-2008 due to lack of aeration, causing changes in fish abundances, including the reduction of game fish species and centrarchids, with no notable extinctions. Together, our findings indicate that winter aeration may improve gamefish survival and allow lakes with winterkill tendency to support sport fish communities with healthy piscivore populations such as walleye and largemouth bass, which would be otherwise greatly reduced.Item Glaciers in the Earth system: an evaluation of the causes and effects of glacier change in southern Patagonia and beyond(2022-04) Van Wyk de Vries, MaximillianGlaciers do not exist in isolation: they interact with the surrounding Earth System across a wide range of temporal and spatial scales. Global glacier recession driven by anthropogenically forced global warming has both intensified many of the interactions between glaciers and their surroundings and highlighted their importance. Glacier-ocean interactions are one well-known and globally important example, considering that unstable marine-terminating portions of Greenland and West Antarctica hold several metres of potential sea-level rise. However, other important interactions, such as between glaciers and ice-contact lakes, remain largely unexplored. Likewise, a wide suite of connections between glaciers and the surrounding Earth System can influence, and are impacted by glacier change. This thesis explores these interactions with the objective of contributing to a new integrated view of glaciers in the Earth System. The twenty-first century has both highlighted the need to understand glacier retreat and provided scientists with powerful new tools to analyze our cryosphere. In this thesis, I assess the drivers of glacier change by combining high-resolution satellite imagery, lake sediment cores, and field data with numerical modelling. Southern Patagonia is an ideal natural laboratory to examine the interactions between glaciers and the surrounding Earth System, due to its extensive glaciation, high relief, large proglacial lake systems, and extreme climate gradients. We also include two other study locations, the Northern Andes and Uttarakhand Himalaya, in which glacier change has created new geohazards and water security challenges for nearby populations. We find that large ice-contact lakes preserve an high-resolution record of climatic and glacial changes. We identify annual-resolution sediment layering ('varves') in Lago Argentino, the world's largest ice-contact lake, and use this to investigate the dominant controls on sedimentation across the lake. We show that, at Lago Argentino, varves are formed due to seasonal variations in glacial and fluvial sediment fluxes along with a seasonal cycle in lake mixing. In addition, we demonstrate that the dominant climatic controls on sedimentation are summer temperature and wind speed. On a larger scale, we use Lago Argentino's sedimentary record to identify a high late-Holocene eruption rate at the nearby Andean Austral Volcanic Zone, and dominant 200, 150, and 85 year periodicities in the high-latitude Southern Hemisphere's dominant mode of climatic variability, the Southern Annular Mode. Next, we investigate the interactions between glaciers and two major natural hazards: landslides and volcanic eruptions. For the former, we show that landslides can induce extensive and long-lasting effects on glaciers, with a 0.25 km^3 landslide reversing the multi-decadal retreat trend of a Patagonian tidewater glacier. For the latter, we identify a ~75% greater eruption rate in times of low ice volume in Southern Patagonia, due to deglaciation-induced tensional upper-crustal stresses. This process may affect other ice-clad volcanoes around the world. Glaciers can also contribute to major disasters, of which the deadly Chamoli rock-ice avalanche in February 2021 is a devastating example. We combine several advanced remote sensing methods to investigate the pre-collapse conditions of this avalanche, and show that the landslide was mobile more than five years prior to its February 2021 collapse. We also use a newly developed glacier velocity-based method to calculate the thickness and volume of all glaciers in the Northern Andes, where volcano-ice interactions initiated the worst volcanic disaster of the past 100 years. These ice-thickness maps will enable future research to identify zones most vulnerable to glacier-related hazards, and map out future water-resource vulnerabilities. Overall, our results highlight the importance of integrative and collaborative studies for forecasting the future of the world's glaciers, and their impacts on nearby populations.Item Minnesota macrophytes: linking aquatic plants, lake health, and human activities(2013-06) Beck, Marcus W.Aquatic plants (macrophytes) are an undervalued but critically important component of Minnesota's lakes. The macrophyte Index of Biotic Integrity (IBI) was developed to evaluate lake health using metrics that describe the condition of the aquatic plants. However, a detailed evaluation to determine whether the index can explicitly link lake condition with activities that negatively impact lake resources has not been conducted. This information is necessary before the IBI can be used to develop biological standards required under the federal Clean Water Act. The goal of this dissertation was to develop and implement a framework for identifying the strengths and weaknesses of the index to inform biological assessment. Four chapters describe research to fulfill this goal. The first chapter identifies comparable groups of lakes using a set of environmental variables that influence macrophyte community composition. The second chapter describes the development and application of semi-automated techniques for quantifying potential stressors of aquatic macrophytes in nearshore areas of lakes, such as docks and boat lifts. The third chapter provides a complementary analysis to chapter two by examining the relationships of shoreline development at different spatial scales with metrics describing macrophyte richness. The fourth and final chapter develops modeling techniques to quantify the relative effects of multiple stressors on the IBI. Specifically, I have used artificial neural network models that can 'learn' inherent data structures and are especially useful for modeling noisy data with non-linear relationships. Outcomes from my dissertation will inform management agencies on the most appropriate use of the index, which will ultimately facilitate the protection and restoration of Minnesota's lakes.Item Minnesota Taconite Workers Health Study: Environmental Study of Airborne Particulate Matter in Mesabi Iron Range Communities and Taconite Processing Plants - Lake Sediment Study(University of Minnesota Duluth, 2019-12) Zanko, Lawrence M; Reavie, Euan D; Post, Sara PAtmospheric deposition of airborne particulate matter such as fugitive dust contributes to sediment that accumulates at the bottom of a lake. Because of this phenomenon, lake sediment can provide an historic mineralogical and chemical record of what may have been in the air at the time of its atmospheric deposition. This point is important, because the NRRI’s role in the Minnesota Taconite Workers Health Study (MTWHS) was to not only help answer the question “What is in the air?” by conducting present-day in-plant and community air sampling, but – and even more challengingly – to potentially answer the question “What was in the air, when?” by collecting and analyzing historic samples. Lake sediment was the only historic sampling medium available that could allow the investigators to make an attempt to assess what might have been present in the air in the past on Minnesota’s Mesabi Iron Range (MIR). The NRRI therefore core-sampled, age-dated, and characterized intervals of sediment from two MIR lakes – Silver Lake in Virginia, on the central MIR, and “North-of-Snort” Lake on the eastern end of the MIR, near Babbitt (Fig. i). The objective was to determine if fugitive mineral dust generated by past iron ore/taconite mining activity could be discerned in mineral particulate matter (PM) deposited and preserved in the sediment of both lakes.Item Particle Tracking in Lake Superior using FVCOM with focus on Apostle Islands(2021-08) Weber, GraceThis 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).Item Quantification of magnetic components in sediments with applications in paleoenvironmental studies.(2011-12) Lascu, IoanThe present dissertation is a collection of papers investigating the magnetic properties of sediments. The main aim of the work presented here is to study the magnetic characteristics of sedimentary deposits by using a methodology that efficiently quantifies the contributions of various ferrimagnetic components in sediments, and to exemplify how this model can be used to make inferences about past climatic and environmental variability. Magnetic minerals in sediments have long been used as indicators of variability in the factors controlling sediment deposition, and sediment-magnetic properties can be interpreted in terms of the processes controlling the fluxes of various magnetic components. Ferrimagnetic minerals, such as magnetite, are strong magnetically, and tend to dominate the signal from bulk measurements. Two sedimentary ferrimagnetic components that play a major role in shaping the magnetic record with time: a detrital component and a biogenic component. The detrital component of magnetic assemblages probably accounts for the greater proportion of the magnetic signal in many records, and therefore has been the focus of most environmental magnetism studies. The processes that control detrital records are mostly tied to local hydrology, climate, and vegetation cover. However, there is strong evidence that many magnetic assemblages are dominated by autochthonous magnetic particles, which in most cases are produced as a result of direct biologic control. Knowing the contribution of each of these components to the total mass of ferrimagnetic material becomes important when making inferences about past climatic or environmental conditions. The theoretical mixing model devised here using the characteristics of detrital and biogenic end members was tested on lake sediments from Minnesota. The analysis incorporates both spatial and temporal effects on magnetic record. We have investigated the history of sediment flux to Deming Lake, Minnesota, for the past 1000 years. Our results reveal several episodes of reduced precipitation, during which less sediment is mobilized from the catchment by overland flow and runoff. The most prominent episode occurred at the end of the Little Ice Age, indicating that this time period was not only cold but might have been drier than previously thought. The spatial control on sediment-magnetic properties was established via a survey of the magnetic properties of surface sediments from several Minnesota lakes. The magnetic properties are controlled by the competing fluxes of detrital and biogenic particles, according to location in the basin, while the position of the oxic-anoxic interface controls whether biogenic magnetite is formed in the sediment or in the water column, with implications in the preservation of intact versus collapsed bacterial chains. The thesis concludes with an incursion into the magnetic properties of chemical sediments from caves, or speleothems. The magnetic recordings preserved in calcite speleothems hold enormous potential for paleomagnetic and paleoenvironmental reconstructions. Speleothems lock in magnetization instantly, are not affected by post-depositional effects, and can be dated with high precision. The natural remanence in speleothems is carried mainly by magnetite, and the main remanence acquisition mechanism is depositional, through physical alignment of detrital magnetic grains parallel to the Earth's magnetic field. Future speleothem magnetism studies should benefit from increasingly sensitive magnetometers, operating at high spatial resolution, that are able to resolve short-term geomagnetic variability, and characterize events such as geomagnetic excursions at an unprecedented scale.