Swenson College of Science and Engineering

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https://hdl.handle.net/11299/226844

Historical note: The Swenson College of Science and Engineering was previously called the College of Science and Engineering (1984-2007). Before that it was part of the College of Letters and Science (1974-1984).

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Groundwater Flow Modeling and the Delineation of Wellhead Protection Areas, Cass County, Minnesota
(2002-09) Bertsch, Benjamin Robert
Minnesota Rules define wellhead protection as "a method of preventing well contamination by effectively managing potential contaminant sources in all or a portion of a well's recharge area". They further state that this recharge area, or wellhead protection area is the "surface and subsurface area surrounding a well or well field that supplies a public water system, through which contaminants are likely to move toward and reach the well or well field". 1986 Amendments to the Safe Drinking Water Act mandated States to prepare a Wellhead Protection Program and submit it to the Environmental Protection Agency by 1989. Whereas the EPA allows flexibility in each State's specific Wellhead Protection Plan Program, the programs must address certain criteria. Through legislation, the Minnesota Department of Health has established guidance for communities to follow in developing their Wellhead Protection Programs. This guidance provides for ample involvement at the community level, but relies on scientific investigation for the delineation of the wellhead protection area. Using four communities in Cass County, Minnesota, this study demonstrates the value of published data and local expertise in creating groundwater flow models for use in delineating wellhead protection areas. The guidelines established by the Minnesota Department of Health for delineation of wellhead protection areas requires that five criteria must be addressed. These criteria are: Time of travel: The time of travel must be at least ten years. Flow boundaries: The location and influence of flow boundaries must be identified using existing information. Daily volume of water pumped: The daily volume of water pumped must be calculated for each well in the public water supply system. Groundwater flow field: The groundwater flow field must be identified for the aquifer used by the public water supply. Aquifer transmissivity: The aquifer transmissivity must be calculated. Using MODFLOW, a modular three-dimensional finite-difference groundwater flow model, steady state flow models of the four areas were created and calibrated. MODPATH, a particle tracking post-processing package for MODFLOW, was used to determine the well capture zone. Landform assemblages provided a framework for data entry into the model. Minnesota Department of Health Water Well Records supplied stratigraphic information. USGS 1:24,000 quadrangle topographic maps provided calibration data. Assistance from State and County employees and local well drillers addressed specific local geologic and hydrogeologic variables. The resultant flow models and particle traces established wellhead protection areas for the communities studied. These wellhead protection area delineation's address State guidelines and were accomplished in an economic, efficient manner.
Holocene Climate and Environmental Change from White Owl Lake Sediments, White River Plateau, Colorado
(2009-06) Kramer, Marian Esther
This Masters project investigates the Holocene lacustrine sedimentary record of White Owl Lake (3,270 m), a small alpine lake located on the White River Plateau in west-central Colorado. Past changes in the watershed and within the lake are reflected in the sedimentary geochemical record; timing is constrained by radiocarbon ages. The combined data have been used to develop an age model and compare paleoclimatic and paleoenvironmental interpretations with findings from other nearby studies. Processes reflected in the geochemical record include development of terrestrial vegetation, lake basin evolution, changes in primary productivity, preservation of carbonates, changes in hydrology, and shifts in silicate provenance. Seismic-reflection profiles were used to select a site for sediment coring and to create a bathymetric map of White Owl Lake. Lithological changes in the White Owl Lake sedimentary record provide a unique opportunity to develop and calibrate a method to estimate the abundances of the major components of a typical lake sediment (carbonates, organic matter, and the residual mineral fraction) using scanning x-ray fluorescence (XRF) analysis and geochemical data from the core. The purpose of developing this method is to allow estimation of major components to guide decisions for other detailed analytical work. This research project is a part of a larger USGS project aimed at reconstructing changes in the Holocene hydrology and climate (hydroclimate) of the Upper Colorado River Basin, including the White River Plateau, using lake sediments. Interpretations from this project will add to the ongoing USGS study, and our understanding of millennial-scale Holocene climate variability on the plateau.
Landscape Evolution and a Relict Fish Community, North Slope, Alaska
(2005-04) Rantala, Heidi Marie
The North Slope of the Brooks Range in arctic Alaska has a complex glacial history, having been glaciated several times since the late Tertiary. As a result of these glaciations, a complex arrangement of glacial sediments is exposed on the tundra. It is the presence of the youngest glacial sediments, and their abundant lakes, which allows communities of fish to persist in this harsh environment. Although the importance of the lakes is known, the timing at which fish entered and become land-locked in specific lakes is not. The purpose of this study was to use paleolimnological information in an arctic lake, Fog Lake 3, to reconstruct the fish community dynamics in the lake, resulting from glacial and geomorphic processes on the landscape. Information about past conditions in the lake was inferred from biotic evidence and sediment characteristics in a lake sediment core. Grain size, lithology, and carbon chemistry were used as proxies for processes occurring in the lake and its watershed. The chironomid community structure was recreated throughout the length of the core by identification of fossil remains. The core was dated using 14C techniques to determine total age and sedimentation rates throughout the length of the core. The core was divided into two zones based on constrained incremental sum of squares cluster (CONISS) analysis of the grain size data. Although the CONISS analysis created zones, the only differences in grain size characteristics between zones were marginally significant. There was little difference in the carbon chemistry in the two zones. There appeared to be a significant decrease in the mass lost on ignition at 1000°C, but that mass is likely related to water in the mineral structure of clays and not proportion of carbonate rock. Zones in the core were also developed using the CONISS method on the chironomid community composition data. While Tanytarsini (Tanytarsus and Paratanytarsus) dominated the chironomid community throughout the core, the upper zone had higher community diversity, as determined using the Shannon index. The upper zone (Zone 2) was further broken down using the CONISS results into Zones 2a and 2b. Comparison of the two zones showed an increase in chironomid diversity, an increase in Heterotrissocladius relative abundance, and a decrease in the proportion Tanytarsini through time. The evidence presented by this study suggests that the chironomid community composition was controlled by some factor or factors, possibly including fish community structure, which changed through time. The changes seen in the chironomid community are inconsistent with those expected if they were due to climate dynamics or major changes in lake levels. Increasing diversity of the chironomid community would be expected with increased predation pressures, such as those imposed on invertebrates by fish or with increased organic matter input to the lake sediments. The initial presence of fish in the lake possibly are related to changes in the diversity of the chironomid community which occurred between 7973±50 14C YBP and 7344±45 14C YBP. Based on an increase in the chironomid community diversity, the best estimate of fish becoming landlocked in Fog Lake 3 is between 4230 and 4600 14C YBP.
Stratigraphic Correlation and Geochronology of Varved Sediments from Lake Malawi, East Africa
(2001-01-29) Barry, Sylvia Lee
Five nine-m long piston cores and 16 multi-cores less than 60 cm long were obtained for a paleoclimate study from Lake Malawi in East Africa, and have provided the first high-resolution geochronology of varved lake sediments from the southern tropics. The establishment of this 22,000-year sedimentation chronology is essential to the construction of a paleoenvironmental history of Lake Malawi, and so that results obtained from subsequent work on sediment chemistry and diatom content of the cores can be expressed on a well-dated basis. The cores were stratigraphically correlated using volcanic ash beds and magnetic susceptibility measurements, and were dated using lead-210 assay, radiocarbon and varve counts. Interpretation of the stratigraphy and geochemistry suggests that Lake Malawi experienced a lowstand during the Last Glacial Maximum (LGM); however, the presence or absence of varves does not seem to be dependent on lake level. Thickness was measured on varves spanning the last 600 years on one of the cores. Spectral analysis of a time series constructed from these measurements exhibit periodicities in the 3-4 yr, 8 yr and 17 yr range, suggesting an El Nino/Southern Oscillation (ENSO) type signal or some as yet unknown forcing mechanism. Trace element from discrete ash layers within the cores provided a unique geochemical fingerprint for each tephra, which is useful for correlation of other cores in the absence of varves or other stratigraphic markers.