Browsing by Subject "Diatom"
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Item A 250-year assessment of human impacts on Lake Superior: an updated paleolimnological perspective(2013-05) Chraibi, Victoria Lindsay ShawTo understand environmental conditions in Lake Superior over the last two centuries, we conducted a paleolimnological study on two sediment cores collected in the eastern and western regions of the lake. We examined the diatom community assemblages, trace metals, sediment characteristics, and GIS-reconstructed human land use to evaluate the historical impacts of human activities. During European settlement and agricultural development, there is clear indication the diatom community reorganized due to nutrient enrichment. Trace metal profiles tracked a period of mining and ore processing which temporarily increased metal loads to the lake in the mid- to late-20th century. In recent decades, more oligotrophic diatom species were favored, suggesting nutrient decreases associated with remedial activities. The diatom community has reorganized to be dominated by Cyclotella species, providing evidence that water quality changes are being influenced by atmospheric nitrogen deposition and changes in the lake's physical and chemical processes associated with climate change.Item Great Lakes Coastal Diatoms(2014-06-13) Reavie, Euan D; Brady, Valerie; akireta@nrri.umn.edu; Kireta, Amy R; Natural Resource Research Institute, University of Minnesota DuluthA Great Lakes Environmental Indicators (GLEI) project. Diatom community data were collected from periphytic substrates at approximately 0.5-3.0 m depths along two different land-use transects from more than 200 wetlands, bays, and high energy sites on the U.S. side of the Great Lakes coastline. Collections included four within-site replicates and approx. 10 percent re-sampling over a three year period. Additionally, approximately 25 offshore, open water samples were collected from surface sediment at depths up to 30 m. The data link with other GLEI datasets to provide water chemistry, site, and landscape information. This study represents the most extensive synoptic diatom dataset of the Great Lakes and includes both undescribed species and species that have not been previously identified in the Great Lakes. The major goal of this GLEI subproject was to develop diatom ecological indicators, and these indicators are presented in a number of publications. The diatom data in this database include the complete raw counts from all samples that were enumerated under the GLEI program, as well as corresponding (condensed) environmental data that were used to develop the indicators.Item Lake Sensitivity To Late-Holocene Climate Change In The Western Great Lakes Region Based On Diatom-Depth Reconstruction(2018-07) Woods, PhillipLake sediments provide an unparalleled source of proxy records of Holocene climate change and landscape response. Existing studies show overall synchrony in the upper Midwest (USA) to major climate periods (e.g., Holocene Thermal Maximum, and cooler/wetter late-Holocene), but less synchrony in response to shorter climate anomalies such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We examined a sediment core from Cheney Lake (northwest Wisconsin, USA), a lake positioned high in the landscape to reconstruct regional hydrologic climate response using diatom records to predict lake depth for the last 3500 years. To reconstruct historical changes in lake depth, a single lake diatom-based model was constructed based on species-depth relationships from 18 modern surface samples collected at depths of 0.5 to 5 m from Cheney Lake. Based on redundancy analysis (RDA), lake depth explained ~27% of the variance in diatom community abundance. A transfer function for reconstructing lake depth was developed using weighted averaging (WA) regression with inverse deshrinking. The transfer function was applied to downcore diatom communities in a 93-cm long 14C-dated core collected from a littoral zone site, to estimate lake level changes over the last 3500 years. Results suggest that Cheney Lake was almost 6 m deeper beginning ~3500 cal. yr BP, nearly twice as deep as the modern lake, a condition that persisted for several thousand years. An abrupt decrease in water depth occurred around 1500 cal. yr BP, reaching minimal depths around 700 cal. yr BP during the Medieval Climate Anomaly. Lake levels then rebounded and remained ~4 m above modern lake level until ~0 cal. yr BP (1950 CE). An abrupt decrease in moisture availability is evident in the last ~60 years, when lake levels fell to current low levels.Item Modern Limnological and Paleolimnological Applications of Diatoms in Minnesota Lakes(2021-05) Burge, DavidThe following chapters represent a continuity of diatom research in Minnesota lakes. In Chapter 2, the study on Upper and Lower Red Lakes demonstrates the use of well-established paleolimnological proxies to assess eco-limnological change in a pair of large shallow lakes and inform management of the lakes by the Red Lake Tribal Department of Natural Resources and the Minnesota Pollution Control Agency. Highlighted here was the use of diatoms using traditional morphological and geochemical approaches to reconstructing limnological history. In Chapter 3, I present a review on resurrection ecology as a new tool in the paleolimnological tool belt. This chapter highlights diatoms as prime candidates for resurrection ecology studies and the use of sediment eDNA to guide such studies. Chapter 4 uses the recommendations in Chapter 3 to leverage diatom microfossils and their DNA to examine the influence of 20th century dust deposition on productivity and community composition. This study highlights the first use of sediment DNA to characterize diatom assemblage changes in a North American lake, and furthermore highlights the beneficial uses of paired microfossil-DNA diatom proxies. In Chapter 5, I used sediment DNA to describe the genomic diversity of diatoms across lakes of Minnesota. The diatom diversity described here corresponds to the distribution of lake types across Minnesota that can be characterized by diatoms observed in light microscopy or by their DNA signatures. Furthermore, the paired use of diatom microfossils and sediment DNA showed similar limnological trends in the paleolimnological record of two lakes.