Browsing by Subject "Temperature"

Now showing 1 - 20 of 27

Aloha! Is Hitting the Beach Good for your Rheumatoid Arthritis?
(2012-07-24) Newman, Logan
Assessing Hydrologic Connectivity using Water Temperature, Wax Lake Delta, Louisiana
(2018-09) Evans, Nicholas
We take a reduced complexity approach to assessing the advective factors that contribute to the hydrologic connectivity between a primary distributary channel and interdistributary island on the Wax Lake Delta of coastal Louisiana. We deployed a relatively inexpensive, open-source data logging platform to collect high quality continuous water temperature, water depth, air temperature, and shortwave solar radiation from a portion of Wax Lake Delta from February 18 through May 19, 2015. We use this field data to create a reference model of predicted water temperature at the data logging locations at the site. Based on comparison of that model with the water temperature observations, we find that different regions of the island have differing degrees of hydrologic connectivity to the primary distributary channel.
CAD algorithms dealing with process and temperature effects in digital integrated circuits.
(2010-01) Mogal, Hushrav
The aggressive scaling trend of the semiconductor industry to improve integrated circuit performance manifests itself as process, voltage and temperature (PVT) variations which can negatively impact design yield. The aim of this work is to deal with process (P) and temperature (T) effects and to develop software CAD analysis and optimization tools to mitigate their effects on digital integrated circuit performance. In the first part of this thesis, we aim to develop an algorithm to compute the criticality of gates in a circuit with underlying process variations. The timing criticality of a gate indicates its impact on the overall timing performance of a circuit. We propose to use graph-based techniques to linearly traverse the timing graph of a digital circuit to obtain its criticality information. Such information can be useful to a designer or optimization tool in making decisions regarding gate sizing to improve the circuit performance. Our methodology must not only improve the speed of computation but also the accuracy with which we obtain the criticality values of gates in the circuit. In the second part of this thesis, we propose to deal with temperature effects in the presence of increased scaling of devices. The sub-threshold leakage power of a digital chip, which is the wasted power in a digital circuit without doing any useful work, is exponentially dependent on the operating temperature of the chip. We propose to use techniques to exploit this dependence to reduce the sub-threshold leakage power. By rearranging the physical placement we can affect the temperature distribution of various blocks on a digital chip, thereby also affecting the total sub-threshold leakage power. We aim to develop a physical floorplanning tool to alleviate the temperature and sub-threshold leakage power by taking into account their interdependence. This work proposes to use task migration (TM) as a methodology to deal with increasing sub-threshold leakage power in future technology nodes. The main idea is to replicate certain high-power blocks in the design, and migrate tasks at regular intervals from one part of the chip to another, thereby reducing the power density and temperature of the design. We aim to develop a CAD optimization framework using floorplanning to read in a circuit description and produce a physical floorplan layout of the TM-aware design. This involves the selection of the design blocks to replicate, followed by the judicious placement of the blocks and finally the selection of an appropriate migration interval taking into account its negative impact on circuit performance. The traditional semiconductor process technology consists of a single layer of silicon on which various devices like transistors and diodes are fabricated along with several layers of metal. Besides the problems outlined above, increasing device density is forcing larger die footprints. As a result, designers are facing increased congestion of routing wires, limiting the amount of performance benefit with scaling. Three-dimensional or vertical integration technology offers a promising alternative, in which multiple layers of silicon with their associated metal layers are stacked on top of each other. Field-programmable devices are particularly suited to such a technology due to the regular layout of logic and routing elements on the die. As the final part of this thesis, we examine the benefits of vertical integration applied to field programmable logic devices.
Cold Temperature Effects on Stress Laminated Bridge Decks
(Minnesota Department of Transportation, 1997-11) Seavey, Robert T.; Erickson, Robert W.
This study evaluated the thermodynamics of stress-laminated bridges under laboratory conditions. After assembling three timber laminated bridge deck panels of 120" x 43" x 12", high tension rods were used to form "stress-laminated" panels. Researchers placed the panels in a laboratory freezer, with cold temperature settings of 10*, 0*, -10*, -20°, and -300 Fahrenheit and repeated the process three times, each with the wood at a different moisture content--a "green" moisture content greater than 30 percent, a 17 percent moisture content, and a 7 percent moisture content (mc). The results showed that the bar force reduction in the green moisture content sample was significantly greater than in either the 17 percent or 7 percent me tests. The study concluded that the moisture content levels and temperature fluctuations cause variations in rod stressing levels; that the tensioning losses occur within a few hours of the temperature drop; that the green moisture content levels have a severe adverse effect on the stressing levels; and that tensioning levels somewhat stabilize with moisture contents below 17 percent. Based on this study, it would appear that any existing stressed bridge decks should be closely monitored until the moisture content of the members is less than 19 percent. Further study may be needed to determine the behavior of bridge decks with a moisture content above 17 percent and below the fiber saturation point.
Comparison of thermal stress calculated from asphalt binder mixture creep compliance data
(2010-08) Moon, Ki Hoon
Low temperature cracking represents a significant problem in asphalt pavements built in Northern US and Canada. As temperature decreases rapidly, thermal stresses develop in the restrained surface layer and, when the temperature reaches a critical temperature, cracking occurs. In this thesis, statical analyses were used to compare thermal stresses that develop in an idealized asphalt pavement layer calculated from experimental data obtained with three different test methods: 1) Asphalt mixture creep test using Bending Beam Rheometer (BBR) 2) Asphalt mixture testing using Indirect Tensile Test (IDT) 3) Asphalt binder creep test using BBR and an empirical Pavement Constant Thermal stresses calculated using mixture BBR and mixture IDT data were reasonably identical. Thermal stresses calculated using binder BBR data and an empirical Pavement Constant were significantly different than the other calculated thermal stresses. The effect of physical hardening on thermal stress evaluation was investigated for a limited number of materials and it was found that this effect significantly affect thermal stress magnitude.
Consequences of elevated temperature on prairie plants: legumes, nitrogen, and phenology.
(2012-05) Whittington, Heather Renee
Because prairies are often nitrogen (N) limited, prairie legumes can have significant impacts on the nitrogen (N) dynamics of these communities because of their ability to add fixed N to their surroundings through symbiotic biological N2-fixation and their N-rich tissues that can stimulate net nitrogen mineralization. Predicted increases in temperature have the potential to alter legume traits and functioning, which can feedback to affect ecosystem dynamics. The goal of this dissertation was to examine the effect of elevated temperature on the growth, phenology, and N nutrition of four prairie legumes: Amorpha canescens, Dalea purpurea, Lespedeza capitata, and Lupinus perennis, using both a growth chamber experiment and a manipulative field warming experiment. In the growth chamber experiment, seedlings of Lespedeza exhibited higher biomass and shoot N content at 28°C than 25°C, while Lupinus seedlings displayed decreased nodulation and lower shoot N concentration at the higher temperature. In the field warming study, Dalea and Lupinus displayed higher biomass under warming and all species exhibited lower shoot N concentrations under warming. Neither N2-fixation nor net N mineralization were affected by warming. Warming accelerated flowering for several species, including Amorpha and Dalea, and accelerated spring green-up, as evidenced by higher normalized difference vegetation index (NDVI) values in warmed communities in May. These results indicate that prairie legumes are responsive to increases in temperature in a species-specific manner and that warming may alter N-cycling by changing legume abundance and tissue N chemistry. Additionally, significant interannual variation in many variables and in their responses to warming emphasizes the need for long term studies to better understand and predict potential consequences of elevated temperature on plants and their ecosystems.
The Effect Of Climate Change On Mercury In Boreal Peatlands
(2023-09) Pierce, Caroline
Mercury is a ubiquitous pollutant that accumulates in peatlands, an ecosystem highly sensitive to climate change. Methylmercury (MeHg) is a neurotoxin that is capable of biomagnifying in food webs. We examined the effects of increasing temperature and elevated atmospheric carbon dioxide (CO2) on the concentration of total mercury (THg) and MeHg in peatland soil. This research was performed at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, an ecosystem-scale manipulation in an ombrotrophic bog in northern Minnesota, USA, which includes five temperature levels (ambient plus above- and below-ground warming), with ambient or enhanced CO2 concentration. Increased temperature led to decreased MeHg concentrations in peat and increased THg and MeHg in porewaters. This decrease in peat MeHg, and increases in THg and MeHg in porewater could be caused by more rapid decomposition of the peat leading to mercury mobilization, increased methylation/demethylation rates, or increased gaseous mercury emission. The response to elevated atmospheric CO2 was limited to the surface depths of peat. Total mercury and MeHg decreased in the peat and increased in the porewater. There are no known direct effects of CO2 on mercury cycling so this finding is likely due to changes in other response variables such as the lowering of the water table or changes in the proportion of different plant species. Overall, we observed that temperature and CO2 had significant but subtle effects on THg and MeHg retention in peat. Our findings indicate that mercury concentrations in peat may decrease with climate change which may shift the system from a mercury sink to a mercury source.
Effect of Temperature on Prestressed Concrete Bridge Girder Strand Stress During Fabrication
(Center for Transportation Studies, University of Minnesota, 2015-12) Swenson, Tanner W.; French, Catherine E. W.
The Minnesota Department of Transportation has reported erection cambers of many prestressed concrete bridge girders that were much lower than anticipated. A previous University of Minnesota study (O’Neill and French, MnDOT 2012-16) attributed the discrepancies to inaccurate estimates of the concrete strength and stiffness at release and strand force loss due to temperature during fabrication. The objective of this study was to further investigate the effects of temperature on strand force and camber during precast, prestressed girder fabrication and to make recommendations for the design and fabrication processes to reduce the potential loss of prestress due to temperature effects during fabrication and to improve the release camber estimation. A thermal effects analysis was developed based on four key steps in the girder fabrication process: tensioning, concrete-steel bond, release, and normalization. The study included fabricating six short prestressed concrete segments released at early ages to determine the time/temperature associated with bonding the prestressing strand to the concrete. To investigate the non-recoverable prestress losses during girder fabrication, four sets of girders (MN54 and 82MW) were instrumented with thermocouples, strain gages, and in some cases load cells, that were monitored during the fabrication process to separate the thermal and mechanical strain components. Effects investigated included casting during a cold season, casting during a warm season, casting with the free length of strand covered, and casting with different bed occupancy during any season. A recommended procedure for adjusting strand force during tensioning was proposed to account for non-recoverable strand force changes due to temperature changes between tensioning and bond.
The effects of physical variables on zooplankton distributions in stratified lakes.
(2007-10) Spitael, Maria Susan
Zooplankton play a vital role in lake ecosystems. They serve as an important food source for fish, as well as being major consumers of algae, which contributes to greater water clarity. To understand the dynamics in a lake, it is necessary to understand zooplankton and how they are affected by the physical environment around them. The purpose of this research was to address the question of how turbulence and temperature stratification affect zooplankton aggregations in lakes. Laboratory experiments were performed to quantify the effects of temperature and turbulence on zooplankton distributions in a stratified tank. These measurements were designed to measure zooplankton aggregations and to provide detailed information on the physical conditions causing them. Comprehensive field measurements were taken throughout one summer, covering five 24-hour periods, in order to investigate the effects of temperature and turbulence on zooplankton aggregations in the field. A high-frequency sonar measurement device was developed to take the measurements by modifying the output of a commercial fish-finder and calibrating it to match zooplankton net counts. Our results showed that zooplankton distributions are strongly affected by temperature and turbulence, and that these effects are species-specific, and are different between day and night.
The effects of temperature on cardiac paging thresholds.
(2010-05) Marshall, Mark Thomas
Background: Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures due to fluctuations in core body temperature or as caused by interactions between implantable pacing systems and heating caused by MRI scans. This project was designed to assess the effects of temperature on VPCT of the mammalian heart. Methods: Fresh ventricular specimens were obtained from healthy canine, healthy swine, and diseased human hearts. Isolated trabecula were suspended in temperature-controlled tissue baths containing oxygenated Krebs buffer. Small active fixation pacing leads delivered pacing pulses to each specimen. Baseline strength-duration curves were determined at Background: Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures due to fluctuations in core body temperature or as caused by interactions between implantable pacing systems and heating caused by MRI scans. This project was designed to assess the effects of temperature on VPCT of the mammalian heart. Methods: Fresh ventricular specimens were obtained from healthy canine, healthy swine, and diseased human hearts. Isolated trabecula were suspended in temperature-controlled tissue baths containing oxygenated Krebs buffer. Small active fixation pacing leads delivered pacing pulses to each specimen. Baseline strength-duration curves were determined atBackground: Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures due to fluctuations in core body temperature or as caused by interactions between implantable pacing systems and heating caused by MRI scans. This project was designed to assess the effects of temperature on VPCT of the mammalian heart. Methods: Fresh ventricular specimens were obtained from healthy canine, healthy swine, and diseased human hearts. Isolated trabecula were suspended in temperature-controlled tissue baths containing oxygenated Krebs buffer. Small active fixation pacing leads delivered pacing pulses to each specimen. Baseline strength-duration curves were determined at 37°C, then at randomized temperatures ranging from 35°C to 42°C. Final thresholds were repeated at 37°C to confirm baseline responses. All threshold data were normalized to a baseline average. Results: Both canine and swine trabeculae elicited significant decreases in thresholds (10-14%) at pacing stimulus durations (pulsewidths) of 0.02ms (p<0.01) and 0.10ms (p<0.05) between the temperatures of 38°C and 41°C, compared to baseline. Thresholds at 42°C trended back to baseline for both canine (NS) and swine trabeculae (p<0.05 compared to 38-41°C). Human trabeculae thresholds increased > 35% (p<.05) at 42°C relative to baseline with no significant differences at other temperatures. Conclusions: Temperature is a significant factor on pacing thresholds for mammalian ventricular myocardium. This data for the diseased human trabeculae indicates that cases where cardiac heating may occur (e.g. RF energy due to MRI scans), patients with marginal VPCT may lose proper function of an implanted pacing system.
EnergyPlus Energy Simulation Software
(2014) Gerber, Michael; Dave, Eshan V.
Fire and Ice: Thermoluminescent Temperature Sensing in High-Explosive Detonations and Optical Characterization Methods for Glacier Ice Boreholes
(2017-07) Mah, Merlin
The environment around a detonating high explosive is incredibly energetic and dynamic, generating shock waves, turbulent mixing, chemical reactions, and temperature excursions of thousands of Kelvin. Probing this violent but short-lived phenomena requires durable sensors with fast response times. By contrast, the glacier ice sheets of Antarctica and Greenland change on geologic time scales; the accumulation and compression of snow into ice preserves samples of atmospheric gas, dust, and volcanic ash, while the crystal orientations of the ice reflect its conditions and movement over hundreds of thousands of years. Here, difficulty of characterization stems primarily from the location, scale, and depth of the ice sheet. This work describes new sensing technologies for both of these environments. Microparticles of thermoluminescent materials are proposed as high-survivability, bulk-deployable temperature sensors for applications such as assessing bioagent inactivation. A technique to reconstruct thermal history from subsequent thermoluminescence observations is described. MEMS devices were designed and fabricated to assist in non-detonation testing: large-area electrostatic membrane actuators were used to apply mechanical stress to thermoluminescent Y₂O₃:Tb thin film, and microheaters impose rapid temperature excursions upon particles of Mg₂SiO₄:Tb,Co to demonstrate predictable thermoluminescent response. Closed- and open-chamber explosive detonation tests using dosimetric LiF:Mg,Ti and two experimental thermometry materials were performed to test survivability and attempt thermal event reconstruction. Two borehole logging devices are described for optical characterization of glacier ice. For detecting and recording layers of volcanic ash in glacier ice, we developed a lightweight, compact probe which uses optical fibers and purely passive downhole components to detect single-scattered long-wavelength light. To characterize ice fabric orientation, we propose a technique which uses reflection measurements from a small, fixed set of geometries. The design and construction of a borehole logger implementing these techniques is described, and its testing discussed.
Habitat Quality in the Floodplain Following a Channel Reconfiguration Project: Stewart River, MN
(2021-02) Scott, Larissa
Low flows and elevated temperatures threaten many cold-water habitats. Restoration work is commonly implemented to improve a variety of habitat degradations like elevated temperatures and lack of deep pool habitat. However, the influence of restoration work on groundwater storage and connectivity in systems with low human impacts is not well understood, especially restoration projects that involve the installation of off-channel ponds. This study looks at the connectivity and habitat quality of seven floodplain ponds with very different morphology and connectivity with the channel. The ponds were constructed as part of a large channel reconfiguration project to decrease width-to depth ratios, and improve/create coldwater fish habitat in the Stewart River, a trout stream near Two Harbors, Minnesota. During May-September of 2016 and 2017 (one year and two years following the realignment work), I studied the constructed ponds influence on water storage and water temperatures by installing water level and temperature sensors in the ponds, in shallow groundwater wells, and in the main channel. I also measured dissolved oxygen in the channel and ponds and surveyed the locations of thermal refuges between 2016 and 2018. Only one of seven floodplain ponds had suitable low-flow habitat for coldwater fish. This pond (P761) was directly connected to the channel at all flows. Three of six ponds in which temperature was measured throughout the summer were warmer than the channel, and six of seven ponds exhibited low dissolved oxygen levels (≤ 7 mg/L) in summer. Habitat quality in ponds, as measured by temperature and dissolved oxygen, was related to shading, pond morphology, and connectivity with the channel. Sunny locations displayed warmer water temperatures than shaded locations (p = 0.0001). Dissolved oxygen levels increased with pond surface area and connectivity with the channel. This study illustrates that pond geometry, connectivity with the channel, and canopy cover primarily drive temperature and dissolved oxygen levels in constructed ponds. Water elevations in five ponds and several channel locations showed that water levels in the channel peaked earlier and receded slightly quicker than ponds following precipitation events. It took about a day for the channel to reach its peak water elevation following summer precipitation events and two days for constructed ponds to peak. Pond water elevations receded to half their elevation ~3-6 days slower than the channel, but not gradually enough to augment low flows long term. During storm events, channel water elevations peaked earlier and were higher than nearby pond water elevations making the upper part of the realignment behave like a losing reach. Overall, the Stewart River reconfiguration project did not generate substantial long-term water storage or lasting high-quality floodplain fish habitats. This study illustrates the challenges and risks of channel re-meandering in flashy, relatively healthy river systems.
Heat testing methodology comparison.
(2010-08) Bierma, Mark M.
Pre-operative pulpal and periapical diagnosis is critical for effective and appropriate endodontic treatment. Occasionally patients present with a chief complaint involving hypersensitivity to heat – a hallmark sign of irreversible pulpitis. In an attempt to replicate this chief complaint, a variety of clinical methods have been developed to deliver a heat stimulus to a tooth. Friction from a burlew wheel, heated gutta-percha, a heated instrument, and hot water have all been used to warm teeth. Recently, an instrument has been developed which is heated electronically and placed directly against a tooth. The aim of this study was to determine which of these methods produces the most consistent temperature rise within the pulp of a tooth. The value of this consistency is that it allows clinical differentiation between a normal pulp and a pulp demonstrating irreversible pulpitis. The present study used extracted maxillary teeth with thermocouples mounted within the pulp chamber. Four operators applied the following methods to the teeth: heated gutta-percha, heated ball burnisher, hot water, and an electronic probe attached first to a System B™ and then to an Elements™ unit. Each test was performed for 60 seconds, and the temperature recorded every half-second. Analysis of the data revealed the most consistent warming of the pulp was accomplished with the electronic probe attached to the Elements™ unit. The lowest level of consistency was found with hot water. The electronic probe also yielded temperature changes which were more consistent between operators compared to the other three methods.
Lake Superior moored temperature and currents, Sep 2005-May 2015
(University of Minnesota Duluth, Large Lakes Observatory, 2021-07-28) Austin, Jay A; Elmer, Cassandra; jaustin@d.umn.edu; Austin, Jay; University of Minnesota Duluth, Large Lakes Observatory
From 2005 to the present, investigators from the Large Lakes Observatory at the University of Minnesota, Duluth have been deploying sub-surface moorings instrumented with temperature and current sensors at a variety of sites around Lake Superior. Temperature sensors at a range of depths, and profiling current meters were used to characterize the physical properties of the lake's water column. At one site, a nearly continuous time series of temperature throughout the water column exists from 2005 to the present, including winter months. Other sites are occupied for shorter spans. This archival entry covers the period 2005-2015.
Landscape effects on stream temperature in Minnesota Streams of the Lake Superior Basin
(2014-05) Black, Brian Jim
Changes in land use and land cover are known to be important factors causing thermal alterations in small streams. The heating of coldwater and coolwater streams influences aquatic communities that inhabit such environments. We recorded continuous stream temperature data at 50 sites during July - September of 2008 to better understand thermal controls on small streams (1st - 3rd order) within Minnesota's Lake Superior watershed, with specific interest in determining the role of water storage capacity and impervious surface cover. Local and landscape variables were used to predict in-stream temperature using multiple regression analyses. These analyses identify those variables most correlated with stream temperature, and therefore, most likely to influence thermal characteristics. Sites were selected to represent natural gradients of water storage capacity (0-86%) and impervious surface cover (0-26%) within each catchment. Stream habitat data were collected to explain natural temperature variation among sites due to local conditions. Results indicate that geomorphic (stream width and depth), atmospheric (air temperature), and local landscape (riparian shading) variables are all strongly correlated with stream temperature. Thermal characteristics are also influenced by regional landscape variables such as hydraulic conductivity and percent land cover classified as open water or emergent herbaceous wetlands. In contrast, neither impervious surface cover nor water storage capacity were good predictors of the stream temperature metrics summarized in this study. Land cover variables were selected more frequently in best-fit models when they were weighted by distance from the sampling location, indicating that position in the watershed may be an important factor. These trends suggest that changes in land use and land cover have great potential to either mitigate or exacerbate the impacts on stream temperature from climate change, and stress the importance of effective land management.
Metagenomic Survey Of Denitrifying Woodchip Bioreactors: Carbon And Nitrogen Cycling Under Varying Temperature And Flow Regimes
(2020-02) Pauleon, Aaron
The denitrifying woodchip bioreactor (WCBR) is a promising edge of field technology used as a biofilter of nitrate pollutants. These reactors have diminishing performance under low temperature and high flow conditions. In this study the taxonomic, nitrogen metabolism, and glycoside hydrolase profiles of meso-scale biochar-amended denitrifying woodchip bioreactors (WCBRs) are assessed and compared through shotgun metagenomic sequencing with reads aligned to protein coding sequences. Four treatment conditions: 14.5oC+12Hr hydraulic residence time (HRT), 14.5oC+4Hr, 6oC+12Hr, and 6oC+4Hr were analyzed in triplicate for the effects of temperature and flow rate (HRT) on the removal of nitrate from synthetic agricultural runoff water. The experimental design offered greater flow and temperature controls than field scale reactors while offering greater size and realism than most lab-scale reactors. Temperature and flow conditions had significant impacts in every category of analysis. The warm (14.5oC) and slow (12Hr HRT) WCBRs removed the greatest percentage of nitrate (75% of 30mg/L influent), were the most microbially abundant, and the most diverse. These reactors also had greatest average metagenomic potential for plant matter degrading enzymes. The taxonomic and functional analyses indicate bacterial dominance among extracted DNA, although ascomycete fungi were present across all treatments (0.7%-5.2%). By estimates, most bacteria across WCBRs were atypical denitrifiers (>50%) while a minority were typical denitrifiers (<12%). Large portions (78%) of the core nitrogen metabolism were attributed to the creation or assimilation of ammonia with nitrogen fixation appearing unexpectedly enriched (26%). Comparisons to bacteria-dominant midwestern corn soil reveal relatively high fungi representation, low archaea representation, and lower microbial diversity in the WCBR samples. The overall metagenomic commitments to nitrogen cycling and glycoside hydrolases were higher in the WCBRs befitting a concentrated nitrate and polysaccharide environment. The findings of this study highlight the otherwise unreported taxonomic and metabolic patterns of WCBRs, revealing topics for future study and potential avenues for further engineering to inform and enhance the use of denitrifying woodchip bioreactors moving forward.
Modeling Stream Thermal Dynamics: The Influence of Beaver Dams in a Minnesota Watershed
(2020-08) Behar, Hannah
Beaver dams are known to alter the thermal regime of ponds, streams, and adjacent subsurface waters. Downstream of a dam, stream temperature is influenced by increased exchange with the hyporheic zone, which may cool and buffer the stream’s diel temperature cycles. Concurrently, reduced shading in the beaver forage zone is likely to increase heat flux at the stream-atmosphere boundary. The dynamics of these processes can be analyzed to understand how stream temperature is affected on diel time scales, as well as longitudinally at distances downstream from the dam. At two beaver dam-impacted stream sites in the Knife River Watershed in Minnesota, USA, I monitored in-stream and shallow subsurface flow and temperature during low-flow summer conditions. I used a dye tracer test, vertical heat transport modelling, and soil characterization to estimate flux through the streambed at multiple locations. Temperature, stream flow, and atmospheric data were also collected throughout the summer from the two sites. A one-dimensional model of longitudinal stream temperature, calibrated to in-stream temperature measurements, was developed to determine which physical parameters and heat flux components have the greatest influence on stream temperature. The model was then used to demonstrate how these changes persist downstream, as well as to simulate stream temperature under potential future site conditions. These findings increase scientific understanding of stream temperature regime in the context of beaver dam-altered watersheds.
Monitoring Phytoplankton Biomass and Surface Temperatures of Small Inland Lakes by Multispectral and Thermal UAS Imagery
(2021-08) Bartelt, Garrett
Chlorophyll-a is an essential environmental indicator for water quality monitoring, as it is used in photosynthesis by all phytoplankton. Chlorophyll-a concentration in water is correlated to phytoplankton biomass, which is used to monitor harmful algal blooms (HABs). The eutrophication of waters observed during HABs can deplete the water of dissolved oxygen, smother aquatic vegetation, and some species can even release cyanotoxins into the environment. Nutrient pollution and warmer waters caused by climate change are expected to increase the intensity and frequency of HABs. Remote sensing chlorophyll-a concentration for HAB monitoring has been demonstrated with satellite imagery. Satellites effectively monitor temperatures and large algal blooms in oceans and large lakes but lack the spatial resolution to monitor small bodies of water effectively. This study aims to apply remote sensing techniques to multispectral and thermal images captured by an unmanned aerial system (UAS). A UAS survey was conducted on a small freshwater lake, Brownie Lake, in Minneapolis, Minnesota. The collected imagery was then correlated to in-situ chlorophyll-a and temperature measurements. Data was collected using the MicaSense Altum sensor. The Altum is a combination multispectral and thermal camera designed for agricultural data collection. While the multispectral camera attachment is not designed for surface water surveys, this study observed good agreement between measured chlorophyll-a concentrations in a small freshwater lake and the UAS multispectral data. Chlorophyll-a concentration was discovered to be highly correlated with the indexes containing the near-infrared (NIR) band, with a wavelength of 840 nm. Of the multispectral indexes evaluated in this study, the most correlated index was the normalized difference vegetative index (NDVI), with an R2 value of 0.80. Remotely determined water surface temperatures also showed a correlation to manually collected water temperatures. This correlation was not as definitive, with an experimental R2 value of 0.31. This research supports the use case for UAS technologies in measuring water quality indicators important to HAB monitoring, such as temperature and chlorophyll-a concentration.
Moose movement in Minnesota and the use of known moose movement to evaluate the random encounter model
(2021-12) Hinojoza-Rood, Valerie
Abstract. Moose (Alces alces) are cold-adapted ruminants with a relatively low tolerance for warmer temperatures. The movement and activity of free-ranging moose can be recorded simultaneously through GPS locations and activity sensors to analyze the effects of season, temperature, and bout duration on the movement and bedding behavior of moose. Nine adult moose were fitted with GPS collars and dual-axis activity sensors in the Superior National Forest in northern Minnesota. GPS locations were recorded every 20 minutes and synchronized with activity counts. Intervals with activity counts of 0 were considered inactive while intervals with activity counts greater than 0 were considered active. Short 20-minute bouts were the most frequent across all seasons and periods where moose moved less than an average of 0.5 m/minute for an hour were more common in bouts over 2 hours long. Activity and distance moved during each 20-minute interval peaked at the middle of each active bout. This pattern may be caused by the smaller comfort movements that characterize the beginning and end of active bouts or by increasing rumen fill during the latter half of active browsing bouts. The duration of inactive bouts decreased as temperature increased while the duration of active bouts increased until reaching a maximum. The percent of each day spent active varied by season with moose spending more time active from Julian day 100 in spring to Julian day 250 in late summer. The male moose had an additional spike at the beginning of rut lasting from Julian day 215 to Julian day 247. Daily moose movement and activity was crepuscular, peaking about 2 hours after sunrise and sunset. Moose activity also increased slightly 1 to 4 hours before sunset in all seasons except winter. Activity and travel distances during daily maximums were highest during summer when nocturnal activity and movement also increased. The maximum bout duration for female moose occurred at a higher temperature than the maximum for the male. The effect of temperature on distance moved was more pronounced during the warmer months where average travel distance stopped increasing around 12 C during spring and decreased around 18 C in summer. Moose modified their activity and movement during warmer temperatures, suggesting feeding behavior during spring and summer may be affected by higher temperatures brought about by climate change.These frequent recordings of moose locations using GPS telemetry were also used to quantify moose populations. Reliable estimates of animal population densities are vital to many wildlife studies and management recommendations. The random encounter model (REM) uses data from field cameras and concepts from the ideal gas model to estimate population densities with less study effort than traditional mark-recapture studies. REM accuracy and precision was assessed using GPS telemetry from moose recorded at 15-minute and 20-minute intervals since these known movements were more realistic approximations of animal movement than computer simulations. REM estimates of moose density had a 5.1 ± 3.3 percent error on average when using daily velocities calculated from all available moose telemetry data. Estimates of moose density had a 0.95 ± 0.78 percent error when using velocities specific to the times and individual moose used within the camera survey. However, precision was low for both surveys with only about 51.3 ± 32 percent of moose densities calculated using the general velocity and 52.2 ± 33 percent of moose densities calculated using the specific velocities within a 25 percent error of the actual population density. When only cameras from forested habitats were used in the survey, accuracy decreased to a 6.8 ± 4.1 percent error and precision decreased so that only 50 ± 31 percent of calculated densities was within a 25 percent error. For all surveys, accuracy increased with study area size, study duration, and percent of the study area within the camera frame of view of a camera. REM precision was most strongly affected by the percent of a study area covered by a camera view so field studies should either increase the camera coverage within the study area or perform replicate REM surveys to increase the accuracy and precision of calculated population densities.

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