Mountain Scholar :: Browsing by Author "von Fischer, Joe, committee member"

Browsing by Author "von Fischer, Joe, committee member"

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Open Access
250 years of climate-mediated ecological change in Santa Fe Lake, NM
(Colorado State University. Libraries, 2022) Shampain, Anna, author; Baron, Jill, advisor; Leavitt, Peter, committee member; von Fischer, Joe, committee member; Sibold, Jason, committee member
Mountain lakes are sensitive indicators of anthropogenically driven global change. Lake sediment records in the western United States have documented increased percent carbon and nitrogen and heightened primary productivity indicative of eutrophication in mountain lakes. Recent paleolimnological studies suggest atmospheric nutrient deposition and warming underlie these changes. We analyzed a short sediment core from Santa Fe Lake, NM, the southernmost subalpine lake in the Rocky Mountain Range to investigate patterns in lake biogeochemical and algal biomarkers since 1747. Lake sediments were dated using 210Pb activities and analyzed for percent C and N, δ13C, δ15N, and algal pigments representative of total biomass, chlorophytes, cryptophytes, diatoms, and other primary producers from Santa Fe Lake. Throughout the 250-year sediment record from Santa Fe Lake, we observed changes in algal community composition alongside biogeochemical alterations. During the cold dry conditions of the Little Ice Age, there were greater proportions of cyanobacteria, diatoms, and sulfur bacteria. Total algal biomass increased under increased warming and climate variability with significant increases in chlorophytes and cryptophytes. Significant rates of change occurred concurrently with increases in regional N deposition in the mid-20th century. C, N, δ13C, δ15N remained relatively stable throughout the record, until the mid-20th century when C and N increased exponentially alongside depletions in δ13C, δ15N. Our results suggest climate-driven algal assemblage changes throughout the record with regional N deposition contributing to contemporary productivity increases. The timing and magnitude of these changes differ from other studied lakes. Our findings highlight the heterogeneity of lakes' responses to changing environmental conditions in the Anthropocene and call attention to the role of climate-induced ecological change in the absence of critical N deposition.
Open Access
Autoigntion and flame speed of premixed liquefied petroleum gas in a rapid compression machine: experimental results and reduced chemical kinetic mechanism
(Colorado State University. Libraries, 2023) Slunecka, Colin, author; Olsen, Daniel, advisor; Marchese, Anthony, advisor; Windom, Bret, committee member; von Fischer, Joe, committee member
Liquefied petroleum gas (LPG) has many properties that make it an attractive alternative fuel such as lower cost than conventional fuels and an established distribution infrastructure. The development of high efficiency, spark ignited LPG engines is currently limited by engine knock and misfire. The knock and misfire limits are further complicated by the wide range of chemical reactivity in LPG, particularly in international markets. In this study, a rapid compression machine (RCM) was used to characterize the effects of variation in LPG fuel reactivity, equivalence ratio, and exhaust gas recirculation (EGR) on the autoignition and flame speeds of LPG/oxidizer/inert/EGR blends. Experiments were conducted with 100% propane and blends of propane with propene, ethane, isobutane, or n-butane. EGR was simulated with mixtures of Ar, CO2, CO, and NO at substitution percentages from 0 to 30 mass percent. Equivalence ratio was varied from 0.75 to 1.5. Ignition delay period under homogeneous autoignition conditions was measured at compressed pressures and temperatures of 23 to 25 bar and 701 to 921 K, respectively. Laminar flame speeds and apparent heat release rates (AHRR) at 24 bar with mixture temperatures of 700 K or 867 K were obtained by firing a laser ignition system into the reaction chamber shortly after compression and analyzing the propagating flame with high speed schlieren imaging. Zero-dimensional simulations of published autoignition experiments were performed using Chemkin-Pro with several detailed chemical kinetic mechanisms to determine their suitability at predicting ignition delay periods. Multiple reduced chemical kinetic mechanisms were created from the NUIGMech1.1 mechanism to determine the optimal balance between accuracy and computational efficiency for future three-dimensional, time-dependent spark-ignited engine simulations. The chosen reduction, ALPINE 153, was used to model ignition delay periods and flame speeds measured in the RCM during this study.
Open Access
Development of a plume identification algorithm for optical gas imaging of natural gas emissions that requires no human intervention
(Colorado State University. Libraries, 2020) Martinez, Marcus M., author; Zimmerle, Daniel, advisor; Marchese, Anthony, advisor; von Fischer, Joe, committee member
Recent growth in natural gas production in the United States has increased focus on reducing greenhouse gas emissions from the natural gas supply chain. Methane, the primary constituent of natural gas, is also a potent greenhouse gas. Optical gas imaging (OGI) is frequently used for emission detection in upstream and midstream sectors of the natural gas supply chain. Current OGI methods typically use mid-range infrared video cameras tuned to absorption lines of light hydrocarbons to make natural gas emissions visible to human operators. Prior studies of camera output have used human interpretation to determine if an emission is visible in the video stream, making it difficult to standardize measures of visibility between tests or to automate large test suites. This work presents a signal processing method which separates the background scene from the gas plume when used in controlled test conditions where video is collected in both leaking and non-leaking conditions. The method utilizes a novel frequency-based method that detects the high-frequency motion of the gas plume in the video stream. After background removal, the size of the gas plume can be quantified by thresholding the detected plume and measuring its size relative to the camera's field of view. The resulting metric eliminates the need for human evaluation of video streams. To demonstrate application of the method, multiple cameras were used to develop a relationship between emission rate and plume visibility over a range of viewing distances. Tests were conducted at the Methane Emissions Technology Evaluation Center, on CSU's Foothills Campus, using six identical OGI cameras (FLIR G300a camera cores with 38 mm lenses) to image the emission from multiple directions at a range 1 to 6 m. Gas was released from a mock well head at 17 to 196 g/h, with wind speeds of 1.8 to 3.0 m/s. Comparison with expert evaluation was used to set and validate the threshold levels; a 90% probability of detection requires a plume covering at least 13.8% of the camera's field of view. Testing indicated a linear relationship between emission rate and plume coverage fractions at a distance of 1 to 2 m, regardless of the viewing angle. Beyond 2 m, plume coverage drops rapidly, approaching the noise floor. While test conditions were limited, sufficient data was collected to demonstrate method functionality and its applicability to evaluating OGI emission detection systems.
Open Access
Drought impacts on the microbiome in grasslands across the Great Plains: a story of legacy effects, resistance, and resilience
(Colorado State University. Libraries, 2022) Vilonen, Leena L., author; Smith, Melinda D., advisor; Trivedi, Pankaj, advisor; Cusack, Daniela, committee member; von Fischer, Joe, committee member; Zeglin, Lydia, committee member
Drought is increasing in frequency and severity across the US Great Plains as a direct result of climate change and if nothing is done to remedy climate change, drought will only continue to get worse over the next century. Thus, understanding how drought impacts natural and rangeland systems in the US will be vital to protecting these systems from negative impacts due to drought. Further, there has been a great deal of research on the aboveground response to drought, but little research on how the belowground soil community responds to drought. Lastly, some research exists on how drought impacts systems during the drought, but even less research exists on what happens after the drought. To further complicate this, the terms used to describe the period after drought are variable and inconsistent, leading to difficulty in synthesizing this literature. This dissertation aimed to re-define and make the terms used to describe the post-drought period consistent, understand how belowground communities respond after the drought has ended at one field site, and understand how microbial communities in the greenhouse respond to drought both during and after across several sites in the US Great Plains. The first chapter of this dissertation was a literature review that examined how researchers define the terms used after a drought ends and attempted to synthesize definitions for future use. The second chapter of this dissertation examined whether there were impacts leftover after a four-year drought on nutrient cycling in a mesic grassland. The third chapter examined whether there were leftover impacts from the same drought as chapter two on the microbial community. Lastly, the fourth chapter examined how microbial communities respond during and after the drought across four Great Plains sites when the microbial community was isolated from the plant community.
Open Access
Ecology of bison herbivory in North Rim Grand Canyon grasslands
(Colorado State University. Libraries, 2023) Musto, Dana Theresa, author; Aldridge, Cameron L., advisor; Schoenecker, Kathryn A., advisor; Knapp, Alan K., committee member; von Fischer, Joe, committee member
The American Plains bison (Bison bison bison) is a grassland ungulate herbivore that historically played a keystone role in the structure and function of grasslands throughout North America. The mechanisms by which bison influence grassland characteristics are both direct (i.e., via plant consumption and highly nutrient-rich waste deposition) and indirect (i.e., plant community responses), having the capacity to alter entire ecosystems. The ungulate herbivore-grassland relationship has been studied across the globe in a wide range of ecosystems from the tallgrass prairie, montane temperate, and semi-arid grasslands of North America, to the savannah plains of East Africa. My research aims to contribute to this body of knowledge by exploring the effects of bison grazing on the semi-arid, high elevation grasslands of the Southwestern United States in the southern edge of the historic range of the Plains bison in northern Arizona. With recent expansion of Plains bison into the North Rim area of Grand Canyon National Park, I sought to assess the potential effects of bison on grassland structure and function in an ecosystem where this relationship had yet to be assessed. I used a replicated herbivore exclusion experiment in grassland meadow habitats, employing both long-term grazing exclosures (0.40-ha) and temporary grazing exclusion cages (1-m²) to quantify herbaceous productivity and consumption by free-ranging bison. I established six sites in Grand Canyon National Park (GRCA) in areas with high bison density, and six additional sites in similar meadow habitat in Kaibab National Forest (KNF) with low to no bison density. Chapter 1 is largely composed of literature review exploring the importance of grassland ecosystems, bison populations, and the interactive history of the effect of bison across North America. I also provide relevant information regarding the ecological and historical aspects of my study area within the Kaibab Plateau, northern Arizona, including a summary of significant biological and cultural aspects, its history with grazing, and current research goals that include bison management plans. The goal of Chapter 1 is to provide the context for my research as well as to provide background for my research objectives and how I conducted the research, which are described in the following chapters. In Chapter 2, I conducted an experimental study among meadows of varied bison density to evaluate vegetation offtake, the effect of bison herbivory on aboveground primary productivity and its effect on vegetation ground cover. Using quadrat clipping rings inside and outside of grazing cages, I sampled plant biomass (which I used to calculate offtake and productivity) and measured percent ground cover twice each year in 2021 and 2022, where sampling events occurred in summer and fall to capture peak production of both cool (C3) and warm (C4) season plants. I compared the effects of grazing at various intensities on grassland productivity and plant percent cover by taking measurements between treatments (experimental grazed plots vs. exclosure control plots), stratum (high bison use areas in GRCA vs. low bison use areas in KNF), as well as between years (2021 vs. 2022). I calculated aboveground herbaceous production of grazed treatments (ANPPg) and exclosure treatments (ANPPug), as well as total annual offtake of grazed treatments (Ot) using the Sum of Significant Positive Increments (SSPI) method, where only significant (p<0.1 due to limited sample size) and positive increments of vegetation biomass change between sampling occasions were summed to the total annual productivity (ANPP) value (measured in g/m2). I used a linear mixed model to evaluate the influence of treatment, stratum, and year on annual primary productivity. As expected, GRCA grazed treatments had higher annual offtake and grazing intensity when compared to KNF grazed treatments. Annual aboveground herbaceous production of grazed plots (ANPPg) was significantly higher in GRCA than in KNF and a positive relationship was observed between herbivory utilization and ANPP in GRCA. These results are partially explained by the "Grazing Optimization Hypothesis," which predicts an increase in aboveground production and nitrogen yield of grazed plants compared to ungrazed plants under intermediate grazing; however, my results indicated a continuous increase in aboveground production past intermediate levels of grazing intensity. My results may be better explained by the "Compensatory Continuum Hypothesis," which theorizes that the ability for a plant to tolerate or compensate for losses from herbivory are likely driven by a complex of interactions among the affected plant and its environment (Maschinski and Whitman 1989). Annual herbaceous production inside exclosure plots (ANPPug) was nearly identical between the two ungulate stratum (high density and low density bison herbivory) and no difference could be detected. When evaluating the relative proportion of ground cover classes, I found no differences between treatments, but differences between strata. Sites within GRCA supported significantly higher coverage of forbs and bare ground, whereas sites in KNF supported significantly higher coverage of graminoids and litter. Additionally, I deployed a temperature and precipitation gauge at ten sites to collect local climate information. Climate information obtained from weather stations was organized by temperature and precipitation seasonal windows and used in the linear mixed model as predictor variables, where spring temperature was the single most influential weather variable. Twelve motion sensor wildlife cameras (one at each site) were installed to assess herbivore type (bison vs. cattle) and frequency of visits to sites. Results from photos indicated that 1) bison were observed in high proportions throughout GRCA during the growing season, 2) cattle grazing occurred at three KNF sites at low frequencies, 3) bison were observed several times at only two KNF sites, and 4) the camera data was mostly consistent with the data from GPS collared bison that shows seasonal migratory behaviors. In Chapter 3, I present results of soil conditions between treatments and strata. I took measurements to evaluate soil structure (erodibility) and function (nutrient availability) using soil corers and in-situ soil probes in both grazed and exclosure treatment plots at each of the established twelve sites. Soil condition measurements of stable aggregates and soil nutrients were measured once during the onset of the study in spring of 2021. Additionally, soil probes were deployed after exclosure construction and prior to most bison arriving in my study area, thus, grazing treatment had yet to take effect. Consequentially, soil nutrient measurements were primarily used to assess baseline soil nutrient availability and distribution while also providing insight during the evaluation of spatiotemporal variability in production across the landscape. I used a paired and two-sample t-test to evaluate differences in aggregate stability between treatments and strata, and no difference in the proportion of stable aggregates (erosion potential) was detected at any spatial scale throughout the study area. Soil nutrient analysis using an ANOVA test revealed significantly higher phosphorus concentrations in KNF vs. GRCA and higher nitrate in exclosures vs. grazed plots. When soil nutrients nitrate, ammonium, total nitrogen, and phosphorus (measured in µg/cm2) were included in the linear mixed model, soil ammonium was the most influential nutrient predictor variable on ANPP; however, the lack of treatment effect limited my ability to assess the effect of bison herbivory on soil nutrients, and thus, aboveground productivity. Subsequently, I conducted elemental analysis on aboveground clipped herbaceous biomass. This revealed significantly higher nitrogen yield in grazed plants compared to ungrazed plants, consistent with the Compensatory Continuum Hypothesis. Prior to my research, there was only a single study that explored ecological effects of the bison herd on the Kaibab Plateau; however, that studies' focus was on riparian areas and riparian vegetation. My research provides a novel evaluation of the effect of the Kaibab Plateau bison herd on soil and plant structure and function within grasslands of the North Rim, Grand Canyon. This unique ecosystem has been protected since 1919, when Grand Canyon National Park was established from the surrounding Kaibab National Forest Service lands (Merkle 1962). Its richness in historical, cultural, and biological resources have given this Park its reputation as a natural wonder of the world. With the establishment of Plains bison in this unique ecosystem, my hope is that the results of this study will support resource managers in their efforts to manage and conserve the natural integrity of the Grand Canyon ecosystem while also promoting the welfare and conservation of the American bison, declared the United States' first National Mammal in 2016 (NPS 2016).
Open Access
Evidence for fluid-assisted shear failure in a ductile shear zone: tectonic tremor in the geologic record?
(Colorado State University. Libraries, 2015) Compton, Katharine, author; Kirkpatrick, James, advisor; Magloughlin, Jerry F., committee member; von Fischer, Joe, committee member
Recent direct observations of tectonic tremor below the seismogenic zone of large fault zones have emphasized the significance of coeval ductile and brittle processes at high temperatures. Tectonic tremor is defined as long-duration, low-amplitude, and low-frequency seismic signals produced at depths of 18-40 km. Because the source of tremor is currently unknown, the physical conditions and processes that cause tremor are unknown. This study presents observations of an exhumed shear zone system contained within the Saddlebag Lake pendant of the eastern Sierra Nevada, California. The high-strain rocks in this shear zone exhibit multiple episodes of vein formation, indicating a prolonged migration of hydrothermal fluids through the system. Crosscutting relationships and mineral assemblages define discrete sets of variously oriented veins that are folded and boudinaged. I document foliation-parallel quartz veins that show shear displacement parallel to the foliation. Textural evidence for dynamic recrystallization mechanisms, stable isotope data, and fluid inclusion thermobarometry measurements indicate temperatures between 300-680°C and relatively high fluid pressure conditions, greater than σ₃, during fracture. Conditions of nucleation of shear fractures within this ductile shear zone suggest these structures may record similar processes to those under which tectonic tremor is observed in other continental transform fault zones. I interpret that these veins formed as shear fractures under increasing differential stress and fluctuations in pore pressure, with failure driven by heterogeneous materials within the shear zone.
Open Access
False Bakken' interval- sediment patterns and depositional architecture at the facies boundary between siliciclastic mudstones and carbonates, Lodgepole Formation, Mississippian in the Williston Basin, ND
(Colorado State University. Libraries, 2020) Spansel, Joel, author; Egenhoff, Sven, advisor; Sutton, Sally, committee member; von Fischer, Joe, committee member
The lateral facies transition on deep shelves between carbonates and siliciclastic mudstones is largely enigmatic. Based on detailed facies descriptions and interpretations, this study explores which processes have shaped the sedimentary rocks on both sides of this lithological divide, and adds to our understanding of processes operating on deep shelves in general. Both siliciclastic and carbonate rocks of the 'False Bakken' and 'Scallion' intervals of the lower Lodgepole Formation in the Williston Basin, ND, can be grouped into twelve facies: these facies are graded argillaceous mudstone (F1), massive siliciclastic-argillaceous mudstone (F2a), massive calcareous-argillaceous mudstone (F2b), bioturbated pyrtitized bioclast-bearing mudstone (F3), lenticular mudstone (F4), bioclast-rich wavy mudstone (F5), siliciclastic siltstone (F6), glauconitic siltstone (F7), calcareous siltstone (F8), massive to bioturbated carbonate mudstone (F9), nodular skeletal wackestone (F10), and laminated skeletal packstone (F11). These facies are here presented in order of increasing grain size, carbonate content, and bioturbation from F1 to F11. They are arranged in three fining- and coarsening-upward units that can be identified throughout the basin within the succession. These twelve facies are interpreted to represent distinct processes on a low-inclined shelf system with carbonate occupying the proximal, and siliciclastic mudstones the distal portions of this transect. An overall decrease in energy is reflected from the proximal carbonate to distal siliciclastic facies in this sedimentary system. Nevertheless, most of the mudstone facies still reflect high energy processes operating within the distal portions of the basin; in fact, only one mudstone facies is interpreted to reflect suspension settling under tranquil conditions. Therefore, this study suggests that storm wave base is best placed within the distal siliciclastic mudstones instead of in the proximal carbonates. Carbonate mudstones, deposited above storm wave base but lacking tempestite deposition are therefore interpreted as having been subject to intense degradation of storm-derived bioclasts. A decrease in oxygen concentration is inferred from proximal carbonates to distal siliciclastics as indicated by the decrease in size and type of burrows; yet, the presence of burrows within the most distal facies belt indicates that at least dysoxic conditions prevailed throughout the Williston Basin during the deposition of the 'False Bakken'. Three transgressions and regressions are identified within this succession based on laterally correlated facies patterns and indicate an overall increase in sea level from the beginning to the end of 'False Bakken' times. Sediment starvation occurred in the northeastern and/or southwestern portions of the basin as indicated by the presence of glauconitic siltstones and/or lenticular mudstones at various locations within the succession. However, a source of sediment input is interpreted to be located in the northwestern part of the basin based on a high abundance of detrital silt. In addition, a shift in the basin depocenter southwards from Bakken to lower Lodgepole times is reflected in this succession most likely mirroring an increase in subsidence south of Mountrail County during 'False Bakken' deposition.
Open Access
Influence of co-disposing oil and gas exploration and production waste and municipal solid waste on hydraulic conductivity
(Colorado State University. Libraries, 2022) Karimi, Sajjad, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sharvelle, Sybil, committee member; von Fischer, Joe, committee member
The most common method of municipal solid waste (MSW) disposal in the U.S. is still landfilling. Co-disposal of MSW with other non-MSWs in solid waste landfills requires engineering design to reduce the risks associated with the stability and functionality of solid waste landfills. Hydraulic conductivity is one of the engineering parameters required to assess the stability of a landfill. This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) to municipal solid waste (MSW) landfills on hydraulic behavior of mixed waste. Hydraulic conductivity of solid waste is a function of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods. A series of laboratory experiments were conducted to assess the impacts of these factors on the hydraulic conductivity of solid waste. Exploration and production waste was prepared to two moisture contents for laboratory testing: (i) as-received, which had a dry weight water content of 18%; and (ii) wet, which had a target moisture content of 32% to 36%. Wet E&PW prepared to the water content threshold represented the upper bound of water content for which the HMW met regulations for direct disposal in an MSW landfill. Hydraulic conductivity of the as-received E&PW measured in a large-scale permeameter decreased from 7.3×10-5 m/s to 1.1×10-8 m/s with an increase in vertical stress from 1 kPa to 394 kPa. The ks of as-received E&PW in small scale a small-scale permeameter reduced from 1.2×10-7 to 1×10-9 m/s with increasing stress to 50 kPa, and then ks stabilized at 7.5×10-10 m/s with increasing effective stress to 400 kPa. Although ks of the small-scale E&PW specimen was two to three orders-of-magnitude lower relative to the large-scale specimen as a function of vertical stress, the data align when evaluating ks as a function of dry unit weight. This indicated similar response of small-scale and large-scale specimens to hydraulic conductivity with respect to dry unit weight. The effects of E&PW hydration can be observed via the wet E&PW. The initial dry unit weight of the wet E&PW specimen was approximately 14 kN/m3, with a ks similar to the trend in ks versus dry unit weight for the as-received (dryer) E&PW specimen. However, ks of the wet E&PW specimen reduced two orders of magnitude (6.6×10-6 m/s to 5.4×10-9 m/s) as the effective vertical stress was increased to 17 kPa and dry unit weight increased to 15 kN/m3. Subsequently, ks of the wet E&PW decreased one order of magnitude to 2.8×10-10 m/s as vertical effective stress was increased from 17 kPa to 389 kPa. The ks of the wet E&PW specimen was two orders of magnitude lower than as-received E&PW under 394 kPa effective vertical stress. The overall trends for all E&PW mixture ratios for both the as-received and wet E&PW were similar, and exhibited an as-expected decrease in hydraulic conductivity with increasing vertical effective stress. Hydraulic conductivity for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3×10-5 m/s to 1×10-7 m/s under effective vertical stress ranged from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in ks to 1×10-8 m/s as vertical effective stress increased above 200 kPa. The lowest ks at each stress level was measured for MSW mixed with 80% wet E&PW. Findings from this study indicate that addition of an E&PW did not change the hydraulic behavior of MSW. Mixture of E&PW and MSW creates a waste matrix such that hydraulic behavior still is controlled by MSW components at low stresses (and low dry densities). However, if vertical stress exceeds 50 kPa, mixtures of MSW + 80% (and above) E&PW were observed to produce a low permeability (i.e., ks < 1×10-9 m/s). If the E&PW is disposed in discrete layers without rigorous mixing with MSW, increasing vertical stress may substantially reduce the E&PW hydraulic conductivity producing water and vapor barriers within the landfill. These findings represent the specific E&PW tested in this study, however, when combined with other data in the literature, illustrate the need for establishing mixture ratio thresholds and intentionally co-disposing E&PWs.
Open Access
Investigating the carbonate-shale facies transition and deposition on the Scandinavian Ordovician Shelf – the Arnestad Formation, southern Norway
(Colorado State University. Libraries, 2018) Schuller, Kathryn M., author; Egenhoff, Sven O., advisor; Harazim, Dario, committee member; Schutt, Derek, committee member; von Fischer, Joe, committee member
The Upper Ordovician Arnestad Formation was located on the northwestern edge of Baltica in the region near modern day Oslo, Norway. This formation was found to be 60 m thick and consists of intercalated siliciclastic mudstones and thin, nodular carbonate beds. Six outcrops and 38 thin sections were used to describe the Arnestad Formation in detail and divide the formation into six key facies. Dark grey silicilastic mudstones dominate the succession and contain lenses of fossil fragments. Interbedded nodular carbonates are mud- to wackestones, contain lenses of fossil fragments, and often form continuous beds. All facies show varying amounts of bioturbation from Chondrites, and Phycosiphon-like fecal strings can be found in the siliciclastic mudstone facies. The Arnestad Formation can be divided stratigraphically into a lower portion with siliciclastic mudstones and continuous carbonate beds, a central part dominated by siliciclastic mudstones with local ash and carbonate beds, and an upper portion containing both thick siliciclastic mudstone beds and intercalated stacks of siliciclastic and carbonate mudstones. The Arnestad Formation is interpreted as representing sedimentation on a ramp-like shelf with carbonate facies deposited proximally to siliciclastic mudstone facies, below normal wave base with sediment and bioclasts being transported basinward due to bed load processes. Fair-weather and storm generated deposits are found in all facies, with storms eroding the sediment and producing shell lenses throughout the formation, but increasing in frequency upwards independent of sea-level. In the lower part of the succession, the Arnestad Formation records a relatively low sea-level stand, shifting to an overall high sea-level position during the middle part, and back to another low sea-level position in the upper portion. Ash beds are found almost exclusively in the middle portion and seem to have higher preservation potential during high versus low sea-level positions. There were likely more ash beds deposited than were found that were later biogenitically homogenized, rendering the beds mostly unrecognizable from the surrounding sediment. The frequent intercalation of the siliciclastic mudstones with carbonate beds most likely shows the influence of climate cycles on deposition. Based on dividing the length of deposition (~3.5 my) by the estimated cycle count (215 – 220), these small-scale cycles were found to have periods between 15,900 and 16,300 years and are interpreted as precessional Milankovitch cycles.
Open Access
Microbial and biogeochemical responses to changing precipitation patterns in grassland ecosystems
(Colorado State University. Libraries, 2012) Evans, Sarah E., author; Wallenstein, Matt, advisor; Burke, Indy, advisor; Lauenroth, Bill, committee member; von Fischer, Joe, committee member
Global circulation models predict that precipitation patterns in grasslands will both intensify and be characterized by more severe drought in the future. In these systems, the availability of water strongly controls ecosystem function, so changes in precipitation are likely to significantly alter biological communities and biogeochemical dynamics. Since these biogeochemical changes could feed back on climate drivers by influencing regional to global scale energy and water balance, predicted changes in grassland precipitation call for a better understanding of relationships between water availability and grassland biogeochemical dynamics. My dissertation aimed to address how changing rainfall patterns affect biogeochemical cycling and soil microbial communities in grasslands. I first tested the generality of controls over soil organic matter storage in temperate grasslands by studying existing spatial gradients in soil carbon and nitrogen, as they relate to the spatial variation in average precipitation and temperature, and soil texture. I found that statistical models developed in US grasslands overestimated soil organic carbon and underestimated soil organic nitrogen in Chinese grasslands. However, when I incorporated nitrogen deposition and historical land use using a simulation model, it resulted in more accurate model estimates for this region. This work suggests that nitrogen deposition and historical land use legacies may need to be considered to accurately describe biogeochemical dynamics in Chinese grasslands and better predict the vulnerability of global carbon stocks to loss. Responses of ecosystems to changes through time are often somewhat different than relationships gleaned from large-scale spatial gradients. At the local scale, I found that an 11-year drought can significantly alter biogeochemical and ecosystem dynamics in the highly drought-resistant shortgrass steppe. Here, soil inorganic nitrogen availability increased up to 4-fold in plots receiving 25% of summer precipitation. This accumulation of nitrogen under drought may explain the higher plant tissue nitrogen and N2 flux observed under recovery. A more "open" nitrogen cycle that I observed following severe drought could affect the impact of drought on grassland ecosystems, as well as the timescale of recovery. Soil microbial community composition was also altered by this 11-year drought manipulation in the shortgrass steppe, and these differences persisted even after communities were subject to the same moisture conditions for 36 hours in the lab. In this lab experiment, I also identified specific microbial groups that grew under a certain moisture levels, presenting evidence of moisture niche partitioning in microbial communities. However, this niche differentiation wasn't realized in the field; communities that grew under dry conditions in the lab were not similar to those that emerged under long-term drought plots. Overall, this work suggests that contrary to previous assumptions, microbial communities display legacies from long-term field treatments, and that although soil moisture has the potential to drive microbial community composition through niche partitioning, this factor may not always be the primary driver of long-term community composition. Microbial communities were also sensitive to altered precipitation timing in the tallgrass prairie. In addition, communities that were subject to intensified precipitation patterns in the field respired less than control soils after laboratory rewetting events, but respiration rates of the different field treatments converged after 100 days under the same conditions. Surprisingly, species composition of these communities was more sensitive to drying and rewetting pulses in the lab than those from the control. Together, these results show that microbial communities display legacies to altered precipitation timing, in addition to drought, but community composition is not necessarily tightly linked to respiration. Overall, my dissertation work suggests that grasslands will be sensitive to extreme shifts in precipitation, and that biogeochemical and microbial responses could influence how grasslands are altered under future precipitation regimes. However, my work also shows that precipitation is not the only factor controlling biogeochemical and microbial community dynamics in grasslands, even under rainfall manipulations and across precipitation gradients. Therefore, the response of grasslands to other environmental factors - that shift with precipitation changes or are predicted to change independently - should not be overlooked.
Open Access
Modeling bioenergy agroecosystems for climate change mitigation and vulnerability assessment
(Colorado State University. Libraries, 2017) Kent, Jeffrey, author; Paustian, Keith, advisor; Ogle, Stephen, committee member; McMaster, Greg, committee member; von Fischer, Joe, committee member
Agriculture is a major driver of anthropogenic climate change while also directly bearing its impacts. In addition to emissions related to farm operations and inputs, substantial greenhouse gases are released from cropland soils. These include carbon dioxide (CO2) fluxes due to long-term changes in soil organic carbon pools, and nitrous oxide (N2O) produced by soil microbes primarily from excess nitrogen (N) fertilizer not assimilated by crops. Agricultural bioenergy systems are expected to produce liquid fuels with lower life-cycle emissions than gasoline. Current US policy specifies several emissions reduction tiers for biomass-derived liquid fuels, ranging from 20% lower than gasoline for corn grain ethanol to 60% lower for ethanol made from perennial grasses or agricultural residues. While these tiers are based on detailed life-cycle assessments of "average" production conditions, they fail to convey the potentially large variability in emissions arising from farm management and biophysical factors. The first half of this dissertation uses a survey of management practices from suppliers of corn grain to a biorefinery in the US Midwest to explore the magnitude and sources of this variability. The first phase of that study finds that feedstock from most of the farms would achieve the statutory threshold of 20%, but that best-performing farms may be producing grain that would lead to fuel with 50% lower life-cycle emissions than gasoline. Key management practices identified are tillage intensity, efficient N fertilizer use and application of livestock manure. Crop residues, such as corn stover, can also be converted to ethanol. The second part of this study explore the sustainability of corn stover collection for ethanol production by a hypothetical dual-feedstock biorefinery. Stover collection presents a tradeoff: when used to produce ethanol, it displaces emissions from gasoline, but at the cost of less soil organic carbon (SOC) accumulation. Still, soils on these farms could sustain relatively high stover collection rates without net SOC losses or erosion, especially in the context of manure application and reduced tillage intensity. Climate change entails two major phenomena – increasing atmospheric [CO2] and increasing extreme high temperatures – likely to have opposing impacts on agricultural productivity, and these impacts will tend to increase over the course of the 21st Century. Chapter 4 of this work reviews the current understanding of crop responses to elevated atmospheric [CO2] and extreme heat as determined from agronomic studies and analyses of historical climate-yield data. It summarizes consensus findings and presents emerging topics in need of further research, and compares the state of knowledge with the simulation approaches employed by several major crop models. The increasing atmospheric [CO2] that largely drives climate change supports increased rates of photosynthesis in C3 plants and improved water use efficiency in all plant types. The magnitude of this fertilization effect is uncertain, however, and recent free atmospheric CO2 enrichment (FACE) experiments appear to show reduced gains relative to earlier enclosure experiments. Chapter 5 tests the hypothesis that the algorithm designed to simulate the CO2 effect in the DayCent ecosystem model overestimates crop responses to elevated [CO2] as observed under FACE conditions.
Open Access
Nonlinear dynamics and machine learning classification of plant pigment patterns
(Colorado State University. Libraries, 2023) Wong Dolloff, Kaylee, author; Shipman, Patrick, advisor; Mueller, 6Jennifer, committee member; von Fischer, Joe, committee member
Plants exhibit a variety of vibrant colors that are both beautiful and functional. They owe their reds, purples, and blues to a class of pigments called anthocyanins. Many plants possess spatial variation in their anthocyanin concentration and color, which manifest as diverse patterns on their leaves and flowers. Flower patterns can influence interactions with pollinators, who may have innate preferences for certain patterns and can learn to distinguish between them. Recent work has identified the genes and proteins involved in activation and inhibition of anthocyanin synthesis in some species of Mimulus and showed that their dynamics can be described with a two-component diffusion model. In this thesis, we combine numerical simulations of this model with machine-learning algorithms to classify patterns based on a parameter value that influences the pattern spot size and density. A key challenge is to successfully classify using 2-dimensional spot data, which would permit the classification of real petal data from photos. Our approach makes use of the Voronoi mountain function to construct a 3-dimensional surface from the 2-dimensional data. Classification is very successful with simulated data, and it produces plausible results for real Mimulus petals.
Open Access
Novel water-use strategies of Colorado wetland plants: implications for wetland water loss
(Colorado State University. Libraries, 2023) Wright, Anna, author; Ocheltree, Troy, advisor; Sueltenfuss, Jeremy, advisor; von Fischer, Joe, committee member
In the arid west, there is a tension between wetland restoration and water rights. Wetlands, relied upon by humans and wildlife alike, also contribute significantly to evapotranspiration (ET) due to higher water tables and dense vegetation. It is therefore critical to understand how much water wetlands lose to evaporation and transpiration, and what affects wetland water loss. This paper quantifies the transpiration of five abundant wetland species and investigates physiological mechanisms that drive transpiration rates for each species. The focal species transpire significantly different amounts at the leaf-level and when scaled to ground area. Stomatal response to environmental stimuli differed from upland stomatal responses, which suggests that wetland plants prioritize carbon uptake over hydraulic safety and do not align with current paradigms for stomatal responses to vapor pressure deficit, leaf water potential, or turgor loss point. Understanding species' stomatal responses to extreme environmental conditions is key to managing this rare and critical ecosystem as the climate changes.
Open Access
Paleozoic facies architecture in low-inclined mixed carbonate-siliciclastic sedimentary systems: depositional and tectonic signatures
(Colorado State University. Libraries, 2019) Novak, Aleksandra, author; Egenhoff, Sven, advisor; Stright, Lisa, committee member; Schutt, Derek, committee member; von Fischer, Joe, committee member
To view the abstract, please see the full text of the document.
Open Access
Plant-microbe interactions of selenium hyperaccumulators: effects on plant growth and selenium metabolism
(Colorado State University. Libraries, 2012) Lindblom, Stormy Dawn, author; Pilon-Smits, Elizabeth, advisor; Leach, Jan, committee member; Wangeline, Ami, committee member; von Fischer, Joe, committee member
To view the abstract, please see the full text of the document.
Open Access
Sedimentology of an Upper Ordovician (late Katian-Hirnantian) deep shelf mudstone exposure preceding massive sea level drop - Mount Ålleberg, Västergötland, Sweden
(Colorado State University. Libraries, 2021) Thomas, Russell, author; Egenhoff, Sven, advisor; Ronayne, Michael, committee member; von Fischer, Joe, committee member
The deposition of siliciclastic mudstones in a passive margin deep shelf environment has not been explored well in literature. The upper Ordovician succession at Mt. Ålleberg, Västergötland (southern Sweden) is such a succession mirroring sedimentation on Baltica's deep shelf just prior to a catastrophic sea-level draw-down during the Hirnantian Ice Age. The here presented only exposed section is 6.3 meter thick and consists mostly of siliciclastic mudstones interspersed with carbonates. Siliciclastic mudstones are subdivided by dominant clast material and size into four facies, namely fine- to medium-grained (1), carbonate-rich (2), silt- to sand-rich (3), and bioclastic-rich (4). The carbonates are divided into two facies; a carbonate mud- to wackestone (facies 5) seen throughout the section and a lithoclastic fossiliferous carbonate rudstone (facies 6) only observed at the top of the section. Facies 6 carbonate rudstone clasts are poorly sorted and the matrix contains geopetal cement. The idealized succession coarsens upward from facies 1 to facies 5 and excludes facies 6; this idealized succession is observed only once in the section. Siliciclastic mudstones as well as one carbonate (facies 5) contain sediment features and trace fossils of round mud-filled burrows, randomly oriented shells, Phycosiphon-like fecal strings, and generally massive texture. Siliciclastic mudstones are observed with irregular, non-continuous, normally graded laminae. The succession is interpreted as deposition on the low-inclined Baltica shelf reflecting a ramp-like setting mostly an outer shelf environment reaching into a mid-shelf setting. Sediment features and trace fossils are a result of bioturbating organisms and suggest the entire water column was at least suboxic to support benthic life. The irregular laminae observed in all mudstones are interpreted as storm beds and counters the notion that the carbonate-siliciclastic transition is a product of storm wave base interaction. Rounded clasts in the carbonate rudstone (facies 6) reflect significant transport of those grains, likely from more proximal settings, and also indicate up-slope erosion. The geopetal cements are interpreted as indicating subaerial exposure following deposition. The exposure is likely the result of a glacioeustatic sea-level drop associated with the Gondwana glaciation during the late Hirnantian or at the Ordovician-Silurian boundary.
Open Access
Tertiary lake sedimentation in the Elko Formation, Nevada -- the evolution of a small lake system in an extensional setting
(Colorado State University. Libraries, 2015) Horner, William H., author; Egenhoff, Sven O., advisor; Harry, Dennis, committee member; von Fischer, Joe, committee member; Amerman, Robert, committee member
The Lower to Middle Eocene Elko Formation of northeastern Nevada consists of basal coarse-grained siliciclastics and carbonates which are overlain by an organic-rich succession consisting of fine-grained siliciclastics, in places with fine-grained carbonates, and fine- to coarse-grained volcaniclastics at the top. Based on lithological and sedimentological characteristics in four documented localities arranged along a north-south transect, the succession shows fourteen facies, which are grouped into five facies associations (FAs): Siliciclastic mudstones and conglomerates (FA1); Massive coal-rich mudstones (FA2); Microbial-mat-bearing mudstones and carbonates (FA3); Microbial-mat-bearing mudstones and volcaniclastics (FA4); Carbonates and volcaniclastics (FA5). The succession is interpreted to reflect deposition in a broad continental-lacustrine setting. FA1 rocks record sedimentation in the most proximal environment, consisting of alluvial-fluvial sedimentation. FA2 rocks reflect deposition in a marginal low-energy swamp environment, while FA3 rocks denote "open-water" lacustrine sedimentation in a limnetic setting that was highly sensitive to lake-level fluctuations. FA4 rocks record the onset of extrabasinal airfall tuff in the limnetic portion of the lake, and FA5 rocks record volcaniclastic sedimentation outpacing subsidence in the lake, ultimately "filling" up available accommodation space and ending lacustrine sedimentation. The studied succession is subdivided into four vaguely chronostratigraphic intervals referred to as Stratigraphic Intervals 1 to 4, which record a lake system with significant lateral changes in accommodation space and resulting facies patterns in a north to south progression through time. Based on two recent 40Ar/39Ar dates and four previous radiometric age dates, the northern outcrop, which is significantly older than the central and southern ones, records initial subsidence and the onset of lake sedimentation (Stratigraphic Interval 1). Subsidence varied over time causing the lacustrine depocenter and limnetic depozone to progressively shift southwards (Stratigraphic Intervals 2 through 4). Black shale source rocks in the measured sections therefore occur along the entire north-south transect of the studied lacustrine system, yet they represent rocks of different ages not correlatable throughout the Elko Formation. Coeval volcanism, which led to increased volcaniclastic sediment supply, followed black shale deposition and contributed to the north-south "filling in" of the lake system, ultimately culminating with the end of lacustrine sedimentation around 37.5 Ma. The Elko Formation black shales have high source rock potential as an unconventional resource play, as their organic content consists almost entirely of Type-I (oil prone) kerogen. Contrary to deep-water, thermally-stratified anoxic-lake source rock models, long considered to be the only environments in which significant organic-matter preservation may have occurred, this study provides evidence for black shale deposition in the Elko lake to have occurred within a "shallow," mostly oxic environment in the photic zone. Further, this research indicates that depositional environments in lacustrine settings may be scale-dependent. The Elko Formation is not merely a scaled-down version of large-lake systems, such as that in which the Green River Formation formed, but a unique type of system with its own set of controls. With increased industry attention being placed on this potential lacustrine petroleum system, this study provides a new source rock model, as well as a temporal and spatial framework to be used as a predictive tool for the identification of rich source rock intervals in the Elko Basin.
Open Access
The impacts of long-term cultivation on soil degradation in the San Luis Valley, Colorado
(Colorado State University. Libraries, 2016) Daniels, Judith Marie, author; Kelly, Eugene F., advisor; Butters, Gregory, committee member; Melzer, Susan E., committee member; von Fischer, Joe, committee member
Essentially all agricultural lands globally are under pressure to meet the food demands of an additional 2 billion people over the next 20 years. All of the agroecosystems possess limitations that constrain their ability to optimize production, however, these limitations are magnified in semi-arid regions where permanent, seasonal or periodic moisture deficiency results in evaporation and transpiration rates that exceed precipitation. Traditional cultivation practices that utilize modern technology have resulted in substantial amounts of soil loss through wind and water erosion, decreased soil organic matter, reduction in soil water-holding capacity, and alterations to the microbial community composition. Cultivation also affects soil chemical processes and conditions (e.g., pH, cation exchange complexes, electric conductivity, and sodium adsorption ratio) that can lead to further soil degradation. Changes in one or more of these properties often have direct or indirect effects on the fertility of soils, which influence resiliency and soil health. While research has clearly established the most common modifications to soil systems from cultivation, further investigation is needed in semi-arid regions to identify the critical links between physical, chemical, and biological properties that regulate resiliency and soil degradation. In establishing these critical links, I evaluated the importance of parent material (basalt versus granite) in assessing the impacts on the physical, chemical, and biogeochemical soil properties as a function of cultivation, specifically sprinkler and flood irrigation. I also distinguished microbial community composition by parent material and land use and identified key soil properties that regulate changes in microbial community structure by sampling native and cultivated soils in the San Luis Valley (SLV), located in the South Central part of Colorado. The SLV is a high elevation semi-arid agroecosystem with basalt and granite substrates, that receives 177 mm of precipitation annually and the potential evapotranspiration that exceeds 1016 mm. The SLV has also has a 150-year history of irrigated agriculture practices, which add an additional 153 to 1226 mm of water during the growing season. This alters the natural climate and possibly results in some degree of land degradation. Overall, the results indicate the importance of parent material (basalt vs. granite), as a soil forming factor in assessing the impact of cultivation on soil degradation processes. The initial clay percent in the native soils was 20% for basalt and 18% for granite. The additional accumulation of clay from irrigation was slightly higher for basalt soil, (22%) and 20% for granite soils. Soils derived from basalt have greater quantities of the major cations while soils derived from granite have lower quantities and a poor nutrient status. Soils derived from basalt have greater percentage of soil organic carbon in the soil surface horizons than soils derived from granite. The uncultivated soils derived from basalt classify as saline-sodic while those derived from granite were consistently non-saline, non-sodic. As a function of irrigation, the nutrient concentrations of calcium, magnesium, sodium, potassium, chloride and sulfate were reduced in basalt soils while concentrations increased in granite. In addition, the greatest accumulation of clay and soil organic carbon occurred in granite soils with flood irrigation which resulted in similar concentrations as the basalt soils. Also, basalt soils re-classified as non-saline and non-sodic while those derived from granite remain consistently non-saline non-sodic. These results demonstrate a convergence among the basalt and granite soil properties as a function of land use. Using the ester-linked fatty acid methyl ester (EL-FAMEs), which evaluates differences among soil microbial community composition based on the condition variables of parent material (granite and basalt) and treatments (control, sprinkler, and flood). The results indicated that total microbial biomass and the stress ratios differed between basalt and granite with flood irrigation and the most variation was observed in the basalt-flooded soils. The fungi-to-bacteria ratios were the same in basalt and granite soils and both irrigation types (sprinkler and flood). Arbuscular Mycorrhizal (AM) Fungi did not differ between basalt and granite, however, the concentrations of AM fungi increased in irrigated soils, suggesting alfalfa and pasture hay grasses nurture root biomass. The correlations analysis identified pH, magnesium, sodium, potassium, chloride, and organic carbon as being the primary soil properties associated with the microbial communities in both soils and treatment types. The results from the sensitivity model for microbial communities in granite soils indicated changes in these soil properties were more pronounced pH, magnesium, sodium, potassium, chloride, and soil organic carbon in both sprinkler and flood irrigation. While the microbial communities in basalt soils were sensitive to pH and soil organic carbon in both irrigation practices; the responses were negligible compared to granite soils. Physical soil properties were not significant in determining correlations or sensitivities among the microbial communities. Overall, my data revealed the importance of communally evaluating the physical, chemical, and biological properties in determining the key properties that collectively regulate resiliency and indicate soil degradation. The key indicators in this study are soil texture, bulk density, clay, soil organic matter, sodium, chloride, sulfate, and AM Fungi microbial communities, which provide a benchmark for quantifying the magnitude and directional change of soils in cultivated systems with respect to their native counterparts. The findings revealed that long-term cultivation in the SLV has not degraded the soils according to the indices used. The parameters used this study improve the understanding of long-term irrigation impacts on agroecosystems in arid and semi-arid regions by linking the substrate properties with the soil-forming factors and irrigated water quality. This study provides the key information that can be used as a matrix by which to evaluate the impacts of climate change and a growing global population in other water-limited regions.
Open Access
The influence of hydrologic regime, vegetation, and land use on carbon fluxes of northern Sierra Nevada fens
(Colorado State University. Libraries, 2018) Flett, Dana Anne, author; Cooper, David J., advisor; von Fischer, Joe, committee member; Chimner, Rodney A., committee member
Peatlands serve as significant carbon storage reservoirs relative to their abundance on the landscape yet impacts to these important ecosystems are numerous. Studies on the effects of cattle grazing on these systems are few. I measured water table dynamics, vegetation composition, CO2 fluxes, and impacts due to cattle hoof punching at four fens in the northern Sierra Nevada of California to understand the natural functioning of these peatlands and the effects of cattle grazing on the ecosystem. I compared areas with and without cattle hoof punching and contrasted impacts from cattle to the effects of erosion gully-induced water table drawdown on the potential for CO2 sequestration. I found that areas without hoof punching are generally carbon accumulating while cattle hoof punching had a negative effect on potential carbon sequestration. Areas with high amounts of hoof punching indicated carbon loss. Areas hoof punched by cattle had 10% the potential for carbon storage as areas without hoof punching in the Oreostemma alpigenum vegetation type (p < 0.0001) and 20% the potential for carbon storage in Sphagnum subsecundum (p = 0.0009). While intact fens demonstrate carbon storage potential, my analysis indicates that even small amounts of cattle hoof punching negatively affects this process and greater disturbance results in greater potential for carbon losses. Soil temperature in hoof punched areas was not significantly different than temperatures in areas without hoof punching and CO2 emissions did not depend on variations in the water table. Results suggest that cattle hoof punching has a greater negative effect on carbon sequestration than water table drawdown resulting from gully incision in these fens.
Open Access
The journey begins: a narrative inquiry into the mentorship and support of novice principals
(Colorado State University. Libraries, 2013) Waido, Anna Colleen, author; Lucero, Rodrick, advisor; Cooner, Donna, committee member; McKelfresh, David, committee member; von Fischer, Joe, committee member
The purpose of this narrative inquiry was to understand the novice principals' experiences in the principalship and the support they received from their district to make recommendations for principal mentorship programs. The study reported on qualitative interview methods with three novice principals and two mentors to determine essential elements for mentorship programs and leadership development. The retelling of the stories validated the personal experiences the researcher had as a novice principal. The collective responses from the leaders provided new possibilities for the mentorship and support of novice principals. The study investigated the relationships between the mentor/mentee, the structures of different mentorship programs, and the components that were delivered for training new principals. The key findings from the analysis constructed what novice principals and mentors determined were effective methods to better support school leaders. The following themes emerged to support novice principals: 1. Mentor with meaning and purpose 2. Prepare novice principals for the realities of the position 3. Leadership skills and professional growth 4. Students are the priority The mutual benefits and support for the mentors and novice principals were used to design a Principal Mentorship Program. The program proposal is meant to have an effective leader in every school, create professional development and learning for principals, and align expectations for administrators across the district. The Principal Mentorship Program is designed for school districts to provide a systematic approach and structure to support new principals and mentors.