Browsing by Author "Myrbo, Amy"
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Item Estimating the abundance of iron sulfide minerals in Minnesota freshwater sediments in relation to pore water and sediment chemistry and wild rice growth(2013-10) Cheah, Darren; Myrbo, Amy; Bilardello, Dario; Feinberg, JoshuaEmpirical observations of growth of wild rice (Zizania sp.) in wetlands, lakes, and rivers appear to indicate that higher sulfate concentrations lead to a growth deficiency in wild rice. Many growth locations of wild rice in Northern Minnesota freshwater systems have been affected by sulfate leakage, and are within the vicinity of the Mesabi and Cuyuna Iron Ranges (historic and current iron mining) and the Duluth Complex (proposed copper and nickel mining). The dissolved sulfate is reduced to sulfide by microbes in the sediment, and may be sequestered as iron sulfide minerals (e.g., greigite, Fe3S4, and pyrite, FeS2). These minerals are likely to be concentrated where iron is common in local terrestrial geology; pore water pH, as well as organic matter and water content of bottom sediments, are probably also significant. Samples were collected from over 100 research sites spread widely across Minnesota, including water bodies that are naturally high and low in sulfate and iron, as well as water bodies that display recent sulfate increases due to local mine drainage. Petrographic microscopy was used to identify and qualitatively estimate pyrite abundance, while scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) was employed to determine sediment mineralogy at high magnification. Environmental magnetic analyses were conducted on samples selected based on qualitative abundance of pyrite. Preliminary results reveal that samples associated with mining drainage have elevated magnetic grain concentrations with a larger proportion of high-coercivity minerals (e.g., hematite, Fe2O3, and goethite, FeO(OH)) than those from non-mining sites. These minerals are common products of acid mine drainage, and are formed as Fe-bearing silicate minerals are hydrolyzed during acid leaching. The grain size distributions of magnetic minerals were similar for mining and non-mining sites, although lake samples with higher sulfate concentrations appear to correlate with coarser magnetic minerals. Results from this investigation and previously determined chemical analyses data were statistically compared through simple regression analysis, correlation matrix analysis, and Pearson correlation coefficient calculations.Item Minnesota Pollution Control Agency Wild Rice Sulfate Standard Field Study: water, sediment, porewater, and observational data collected across Minnesota 2011-2013(2017-04-10) Myrbo, Amy; amyrbo@umn.edu; Myrbo, AmyThis study was undertaken by the Minnesota Pollution Control Agency (MPCA) and University of Minnesota to improve the understanding of why wild rice (Zizania palustris, manoomin, psin) is observed to thrive only in waters with low sulfate (SO4), and to contribute to evaluation of Minnesota Rules 7050.0224, promulgated in 1973, which seeks to limit the exposure of wild rice to sulfate concentrations exceeding 10 mg/L. The dataset is now released as manuscripts using it are being published.Item Minnesota Pollution Control Agency Wild Rice Sulfate Standard Mesocosm Study: Water, Sediment, and Porewater "Synoptic" Sampling 2013 and 2015(2017-05-30) Myrbo, Amy; amyrbo@umn.edu; Myrbo, AmyThis dataset represents opportunistic, "synoptic" sampling of 30 experimental mesocosms for chemical parameters. The mesocosm experiments were undertaken by Dr. John Pastor (UMN-Duluth) and the Minnesota Pollution Control Agency (MPCA) to improve the understanding of why wild rice (Zizania palustris, manoomin, psin) is observed to thrive only in waters with low sulfate (SO4), and to contribute to evaluation of Minnesota Rules 7050.0224, promulgated in 1973, which seeks to limit the exposure of wild rice to sulfate concentrations exceeding 10 mg/L.The dataset is now released as manuscripts using it are being published.Item Reconstructing Past Sulfur Loading and Wild Rice Abundance in Twin Sandy Lake "Bingwi"(2013-04-19) Mayer, Stefanie; Myrbo, AmyItem Twentieth century varve formation in urban Twin Lake, Golden Valley, MN: Evidence for deposition of multiple laminae per year(Geological Society of America, 2011-10-11) Ustipak, Kelsi; Myrbo, AmyLakes in urban settings are subject to a suite of environmental perturbations from the surrounding cityscape, such as increased flux of nutrients, input of road salts, and erosion of shoreline from housing and recreation. High-resolution lamination studies of a small, deep lake in central Minnesota suggest that the lake experiences unusually high sedimentation rates as a result of urbanization in the basin. Twin Lake is located in Golden Valley, Minnesota, five miles from downtown Minneapolis. It is a small, deep lake with a surface area of 8.5 hectares and a maximum depth of 16.6 meters. Twin Lake is relatively isolated from urban development due to its steeply sloped shoreline and remains sheltered from wind-driven mixing by its steep banks and tree cover on the hills surrounding the lake; the lake is bordered on the east by Wirth Park with luxury housing developments on the northern and western shores. In order to understand the impact of twentieth century urban sprawl and construction on the sediment lithology, a freeze core was collected for high-resolution color analysis, thin section preparation, and smear slide analysis. Lamina counting and lead-210 dating provide contrasting age models for Twin Lake, suggesting multiple laminae are deposited annually, with up to 1 cm per year of sediment deposition. Mass accumulation rates reach 0.4 g/cm2 yr (over 10 times the background rate) during the late 1970s and early 1980s, when historical water quality monitoring data indicate poor conditions. Such extraordinary sedimentation rates are due to high rates of authigenic calcite precipitation, diatom deposition, and wash-in of terrigenous material from the steep banks surrounding the lake. Diverse diatom assemblages and diagenetic iron phosphate minerals in the sediment indicate high levels of nutrient flux to the lake and support the hypothesis that Twin Lake has experienced unusually high sedimentation rates in the past 100 years.