Graduate Student Defense Presentations

Soil Microbial Community Dynamics in Response to Prescribed Extreme Burns of Juniperus virginiana Invasive to the Loess Canyons of Nebraska - Julie Fowler

  • Thesis Defense
  • 11/30/2021
In Nebraska and other regions of the Great Plains, the conifer Juniperus virginiana (J. virginiana, eastern redcedar) is converting grasslands to dense woodlands. This is driven by the interacting drivers of fire suppression, altered grazing regimes, climate change and other anthropogenic factors, impacting the provisioning of ecosystem services. This vegetation regime shift modifies water resource regulation and biogeochemical cycles leading to altered edaphic properties including soil microbial community composition. To restore these grasslands and control J. virginiana spread, prescribed extreme burns are implemented as a management tool through local prescribed burn associations. We hypothesized that the alternative stable state shift to dense J. virginiana woodlands leads to a corresponding stable state shift below-ground that persists post-extreme burn and may facilitate J. virginiana re-establishment. To address this hypothesis, paired grasslands and J. virginiana woodlands in the Loess Canyons of Central Nebraska were subjected to one prescribed extreme burn between 2005 and 2019 to provide a natural burn chronosequence. We quantified J. virginiana re-establishment, soil chemistry, soil microbial biomass and microbial community composition in these paired sites across the chronosequence. Our results partially supported our hypothesis where differences in edaphic variables between J. virginiana sites and grassland sites observed post-burn were largely temporary; however, differences in soil magnesium and microbial community composition were more persistent (> 14 years post-burn). Soil magnesium values were significantly higher in the J. virginiana sites both pre-burn and post-burn across the 14 year chronosequence. Microbial communities were also distinct between J. virginiana and grassland sites pre-burn and across the burn chronosequence. Rapid recovery and/or persistence of specific edaphic factors and soil microbial communities in J. virginiana woodlands post-burn may facilitate early J. virginiana re-establishment. Management at intervals less than 14 years is needed to prevent long term changes to soil function that may facilitate J. virginiana re-establishment.

Comparison of Vadose Zone Nitrate-N to 50-Year Record of Nitrogen Fertilizer Inputs on Nebraska Cropland - Kobi Benao

  • Thesis Defense
  • 11/29/2021
Nitrogen (N) fertilizer is an essential nutrient for agricultural production worldwide, especially in Nebraska where corn requires a large amount. Historical N fertilizer input and poor environmental management practices resulted in unintended consequences in the ecosystem and environment. Lack of spatially complete N fertilizer application time series data in the US, in particular, the state of Nebraska makes N fertilizer quantification in the vadose zone challenging. The state of Nebraska needs spatial time series fertilizer maps to better address its N fertilizer input and potential nitrate-N (NO3--N) migration and storage in the vadose zone (VZ). This thesis assesses 50 years of Nebraska's spatial N fertilizer inputs on cropland, cropping patterns, timings of application, and soil type impact to NO3--N leaching and compares it with the estimated VZ NO3--N mass stored in the Bazile area and the Lower Platte South Natural Resources Districts (LPSNRD).

Extraction and Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Wastewater Matrices to Determine Environmental Loading in the Midwest - Justin Caniglia

  • Thesis Defense
  • 11/22/2021
Per- and polyfluoroalkyl substances (PFAS) are a recalcitrant suite of chemicals that are environmentally persistent and have been detected worldwide in numerous human and environmental matrices. Human exposure to PFAS has been associated with a myriad of human health impacts due to their carcinogenic nature. A better understanding of various transportation routes that instigate human and environmental exposure in the Midwest will assist communities in making management decisions regarding PFAS usage and treatment. However, current PFAS research is limited due to existing analytical constraints and limitations. This thesis focuses on assessing current extraction methodologies for PFAS for four environmental matrices (POCIS, non-potable water, solids, plant tissue) and a study looking at the transportation of PFAS within a wastewater treatment plant, adjacent surface waters, and agricultural ecosystem land applied with municipal biosolids for a better assessment of PFAS within the Midwest.

Assessment and Visualization of Controls on Groundwater Transport and Nitrate Contamination - Mikaela Cherry

  • Dissertation Defense
  • 11/03/2021
Groundwater is an essential resource throughout Nebraska. Land use and climate change can impact groundwater quality and quantity, both of which are necessary for sustaining agriculture, industry, and human consumption. A better understanding of various factors that influence groundwater movement and contamination will assist water managers in making management decisions. However, since groundwater is not as easily visualized as surface water, it can be difficult and costly to create a complete picture of the subsurface environment and different factors impacting groundwater quality and quantity. This dissertation focuses on groundwater seasonality (when groundwater infiltrates below the root zone), a novel remote sensing approach for assessing groundwater quality, and a case study looking at groundwater recharge and nitrate movement around a groundwater mound and how these different methods can come together to form a more cohesive understanding of the subsurface to assist groundwater managers in decision making.

Application of Proximal and Remote Sensing Methods for Estimating Important Morphological and Ecophysiological Plant Traits - Tasos Mazis

  • Dissertation Defense
  • 07/29/2021

Monitoring vegetation dynamics in an efficient and non-invasive way has become increasingly more important for assessing and modeling their responses to the environment and mitigating for climate change. Vegetation optical properties can be used to derive vegetation indices (VIs) which can be used as proxy measures for plants’ biophysical traits. The goal of this dissertation is to use proximal and remote sensing techniques to identify scalable indices and indicators that can be used efficiently to assess vegetation health and performance. The dissertation consists of four studies, each of which tackles different ecological questions utilizing proximal and/or remote sensing methods.

Results from this study are important for the ability to monitor vegetation shifts across multiple scales, important for predicting directional changes of these ecosystems in the face of anthropogenic management and climate change, and the development of effective mitigation plans.

Rancher preferences for payment for ecosystem services program in Nebraska's grasslands - Kyle Martens

  • Thesis Defense
  • 07/19/2021

The idea of "working landscapes" has received considerable notoriety as a tool to better engage with private landowners for the purposes of conservation. These frameworks often rely on top-down approaches that do not account for the socioeconomic conditions of rural areas nor elicit feedback about program design or implementation from its participants. Through a discrete choice analysis, we asked ranchers across Nebraska's remaining grassland ecoregions to assess a series of program offerings that would compensate participants for an array of conservation and environmental objectives. Using an ecosystem services framework, adapted to Nebraska’s statewide wildlife management plan (Nebraska Natural Legacy Project), we explore what attributes of "conservation ranching" are most preferable and why such an approach is necessary for both public and private interests.

Social and Ecological Correlates of Avian Infection by Haemosporidian Blood Parasites - Ian Hoppe

  • Thesis Defense
  • 07/19/2021

Haemosporidian parasites are a significant source of morbidity and mortality for birds. However, factors influencing haemosporidian transmission, especially transmission between species, are poorly understood. To gain insight into these influences, we compared prevalence and diversity of haemosporidian blood parasite infections among avian species in a behaviorally and ecologically diverse host assemblage. We studied whether interspecific associations could explain community-wide trends in infection by pairing molecular diagnostics with direct observations of species interactions. Haemosporidian prevalence in the community was low (8.6%), but varied substantially with host phylogeny. Most (94.8% of all infections) infections were identified as Haemoproteus spp. Few Plasmodium spp. infections were detected, and no Leucocytozoon spp. infections were found. We found no evidence for an effect of interspecific sociality on Haemoproteus infections, but we did find evidence for an effect of intraspecific sociality. Individuals of species that had smaller average conspecific group sizes were more likely to be infected than those of species with larger groups. We also found that species with relatively long lifespans had higher prevalences than species with shorter lifespans. No other individual- or species-level traits were associated with Haemoproteus infection. We identified 7 Haemoproteus mitochondrial cytochrome b lineages, which clustered at the host family level. Two Plasmodium lineages were also identified, each of which was previously detected in different host species in the region. The apparent host-family specificity of the parasite lineages may partly explain the lack of effect of interspecific sociality on Haemoproteus infection probability, and implies the presence of barriers to transmission that are associated with host phylogeny.

A Biological and Chemical Approach to Restoring Water Quality in an Urban Eutrophic Pond - Levi McKercher

  • Thesis Defense
  • 07/16/2021

Efforts to improve water quality in eutrophic ponds often involve implementing changes to watershed management practices to reduce external nutrient loads. While this is required for long-term recovery and prevention, eutrophic conditions are often sustained by the recycling of internal nutrients already present within the water body. In particular, internal phosphorus loads have been shown to delay lake recovery for decades. Thus, in-situ pond management techniques are needed that not only reduce external nutrient loading over the long-term but also mitigate the effects of internal nutrients already present. Our objective was to demonstrate a biological and chemical approach to remove and sequester nutrients present or entering a eutrophic pond. We designed a novel biological and chemical management technique by constructing a 37 m2 (6.1 m x 6.1 m) floating treatment wetland (FTW) coupled with a slow-release lanthanum composite inserted inside an airlift pump. The FTW promoted microbial denitrification and plant uptake of N and P, while the airlift pump slowly delivered lanthanum to the water column over the season to adsorb and precipitate soluble reactive phosphorus (SRP). The design was tested at the microcosm and field scales, where N and P removal was significant (α=0.05) at the microcosm scale and validated at the field scale. The proposed treatment provides a unique and effective technology to address internal phosphorus loads and minimize the effects of nutrient runoff entering urban retention ponds.

Understanding and Contextualizing Foraging among Recreational Opportunities in the North Central United States - Iris McFarlin

  • Thesis Defense
  • 07/14/2021

Over the past few decades, there has been a resurgence in the popularity of foraging for wild products and foods. Despite the cultural importance and ubiquity of foraging, there have been relatively few scientific investigations of social factors influencing foraging behavior, landscape preferences, and the types of materials foraged in the United States. As such, there is a fundamental need to better understand more about those who participate and their foraging behaviors. Two surveys were conducted to gather information on foragers’ motivations and characteristics and to contextualize foraging within the larger recreation landscape. The first survey used snowball sampling to reach foragers throughout the United States and collected information on motivations, types of land foraged, and the type of taxa foraged. Results indicated that respondents were motivated to relax and escape, to feel self-empowered and know about food sourcing, and for the social benefits of participation. We grouped respondents into four clusters based on motivations: 1) self-empowered foragers, 2) multimotivation foragers, 3) casual foragers, and 4) social foragers. While there were differences in in the reasons why individuals forage, there was little difference among the socio-demographic variables as well as where and what they forage.

A second survey was used to estimate the recreational demand among 16 recreational activities among the general population of Nebraska. The results indicated that approximately 13% of the Nebraska population engaged in at least one day of foraging. While activities such as recreational sports, spectator sports, culture and arts were more preferred than foraging, other outdoor activities such as hunting & shooting sports, fishing, and wildlife viewing were less preferred than foraging. Older Nebraskans gained more utility from foraging than their younger counterparts, but there was little difference in utility gained among other sociodemographic factors. Further, there was indication that foraging by Nebraskans was already at satiation, whereas other activities like the arts and culture were still not at satiation. By understanding the behaviors and motivations of foragers and how foraging fits into the recreation landscape, we gained further insight into the importance of foraging and the behaviors of those participating, which has important implications in the formulation of appropriate policies and management of recreational opportunities.

Soils Morphology and Carbon Stocks of Playa Wetlands in Eastern Nebraska, USA - Aubrey Kemper

  • Thesis Defense
  • 07/12/2021

Wetlands contribute important ecosystem services such as water filtration and storage, wildlife habitat, and carbon sequestration. The objective of this study was to compare both the morphology and the carbon and nitrogen stocks between the upland, basin edge, and basin floor in playa wetlands of eastern Nebraska. This work was conducted in three playa wetlands in the Todd Valley. Morphological descriptions were evaluated to two meters’ depth using cores collected along three transects from the upland to the playa floor in three playas, carbon and nitrogen stocks were evaluated in two of those playas. Results show evidence of erosion, deposition, and both leaching and accumulation of clay in all three playas, and presence of calcium carbonate in one playa. In one playa, both carbon and nitrogen stocks were lower at the basin edge compared to the surrounding uplands and in the other, there was no significant difference in carbon and nitrogen stocks between the upland, basin edge, and playa floor. Morphological features of the soils show colluvium deposition and clay accumulation in two basins and calcium carbonate accumulation in one basin. Profile distributions of carbon suggest that the limited carbon storage in these playa wetlands is, at least in part, due to leaching losses of dissolved organic carbon. The playas of eastern Nebraska show evidence of colluvium deposition caused by human-accelerated erosion and, compared to other depressional wetlands in the region, a limited capacity to accumulate organic matter and store carbon.

Health is more than humans: a qualitative study exploring rural Tanzanian students’ perceptions of health at the human-animal-ecosystem interface. - Brianne Wolf

  • Thesis Defense
  • 06/28/2021
One Health, or the holistic approach of viewing human, animal and ecosystem health as interconnected, can play an important role in developing solutions to address diverse health challenges. For young people to grasp contemporary societal and planetary challenges, this understanding is critical. Using data collected through a classroom activity and an iterative coding approach, I analyzed art and written elements developed by primary school students in a biodiverse, rural region of Tanzania to explore their understanding of links among the health of people, animals, and local environments. The students perceived human health in an expansive way, tying it to the health of domestic animals and wildlife, water sources, forests, and ecosystems. They drew varied connections, identifying both direct and indirect impacts on their own health, as well as the broader health of their communities. The students made connections at microscopic and landscape levels, including issues of polluted water and disease and impacts of forests on rainfall and drought. Learning how students understand these connections can aid the efforts of teachers and environmental and health educators in the region, as well as inform curriculum development for students in Tanzania, East Africa, and beyond.

Developing a Method for Timely Estimates of Annual Forage Production to Inform Drought Decision Making - Marketa Podebradska

  • Dissertation Defense
  • 06/22/2021
High interannual variability of forage production in semi-arid grasslands leads to uncertainty when livestock producers make decisions. To inform proactive drought decision making at the ranch level, I developed a largescale model that estimates the amount of annual forage production using environmental and weather variables and the remote sensing-based Normalized Difference Vegetation Index as a proxy for grassland productivity. This model can be used with up-to-date spring climate data and summer climate scenarios (e.g., warm and dry, cool and wet) to create a range of possible end-of-season forage scenarios in a specific year. When provided on an operational basis, these scenarios can serve as a decision support tool for livestock producers, rangeland managers, and other decision makers.

Describing How Students Make Decisions About Complex Issues - Citlally Jimenez

  • Dissertation Defense
  • 04/13/2021

Through a mixed methods approach, my work explored students’ decision-making practices as they worked through a structured decision-making tool to reason about socioscientific issues (e.g., how do we manage water?). The resulting tools can help researchers explore how students:

  • Provide reasoning using interdisciplinary evidence
  • Engage with tradeoffs in their decision-making process

Impacts of Irrigated Agriculture on the Near Surface and Planetary Boundary Layer Atmosphere: Results from the Great Plains Irrigation Experiment (GRAINEX) - Emilee Lachenmeier

  • Thesis Defense
  • 11/23/2020

Modification of natural prairie grasslands into irrigated and rainfed agriculture in the Great Plains produced significant impacts on regional weather and climate including temperatures, precipitation, energy fluxes, and the planetary boundary layer (PBL) atmosphere. The Great Plains Irrigation Experiment (GRAINEX) during the 2018 growing season collected data over irrigated and non-irrigated crop fields to further understand these impacts. The data were collected during two intensive observation periods (IOPs) in early June (IOP 1: 30 May – 13 June of 2018) and late July (IOP 2: 16 July – 30 July of 2018). The data analyzed include latent (LE) and sensible (H) heat fluxes, air temperature, dew point temperature, specific humidity, and equivalent temperature (moist enthalpy). PBL and lower tropospheric development was assessed using radiosonde data. In addition, near surface soil moisture data collected during IOP 1 and 2 were used to model and subsequent analysis of root zone soil moisture utilizing Wang et al. (2017) Exponential Filter Model. The results from this extensive analysis of the GRAINEX data set will be presented for the consideration of the degree of Master of Science. Committee members include Rezaul Mahmood, Trenton Franz and Michael Hayes.

An Analysis of Food Systems Resilience in Nigeria - Azariah Lawal

  • Thesis Defense
  • 11/13/2020

Disturbances are inherent in every socio-ecological system (SES). However, the spate and scope of upheavals in contemporary SES has increased dramatically in recent years. These events, which have a global reach, include earthquakes in Mexico, hurricanes in the Caribbean and severe floods in India. Agricultural systems are perhaps the most impacted when disasters occur because different aspects of agricultural production are directly affected. The burgeoning farmers-Fulani herdsmen conflict in West Africa is a manifestation of these challenges. The industrial revolution, the 1930s Dust Bowl, and the current COVID-19 pandemic are examples of events that transformed, or are transforming, agricultural systems. When faced with events like these, contemporary food systems are faced with two options: collapse or transform. It is essential to have resilient agricultural systems because these systems lie at the nexus of resolving emerging global issues.

Nigeria is an important country in western Africa; it is the most populous African country. Agriculture play an indispensable role in the country employing two-thirds of the labor force. However the sector is bedeviled by a plethora of challenges like outdated land tenure system that constrains access to land, very low adoption of irrigation, limited adoption of research findings and technologies, high cost of farm inputs, poor access to credit, inefficient fertilizer procurement and distribution, inadequate storage facilities and poor access to markets. Despite these challenges, it is the world’s largest producer of Cassava with about 50 million metric tons produced annually. The average yield of 13.63 metric tons (MT) per ha, against potential yield of up to 40 MT per ha (FAO, 2020), this huge difference between current yield and potential yield underscores the importance of resilience. In Agricultural systems resilience analysis research, the work of Meuwissen et al. (2018) stands out. They developed a five-step framework (“Resilience of what?”, “Resilience to what?”, “Resilience for what”, “Resilience Capacities”, “Resilience enhancing attributes”), which was used in this work to analyze the resilience of food systems in Nigeria. This is an important research because after decades of reliance on crude oil, the government is now going back to an agriculture driven economy. We conclude that food systems in Nigeria have been at the reorientation phase of the adaptive cycle and that there is need for increased stakeholder involvement, particularly at the government level, to help farmers harness the benefits of resilience in the system.

Population Demographics, Distribution, and Environmental History of Asian Carp in a Great Plains River - Jake Werner

  • Thesis Defense
  • 11/12/2020

Silver Carp Hypophthalmichthys molitrix, Bighead Carp H. nobilis, and Black Carp Mylopharyngodon piceus, collectively known as Asian carp, are a group of invasive fishes in the U.S. that have garnered much attention over the last couple decades. Most research devoted to this group of fishes has been focused in the Mississippi River basin with little investigation in the Missouri River drainage, particularly in tributary systems. The Kansas River is a major tributary to the Missouri River that has multiple anthropogenic barriers creating varying levels of connectivity within the Kansas River itself, and with the Missouri River. Information on various life history traits of Asian carp are needed before a management plan can be formed. Here, we investigated 1) population demographics, 2) distribution with environmental DNA (eDNA), and 3) environmental history using otolith microchemistry of Asian carp in the lower Kansas River. Silver Carp exhibited spatiotemporal differences in population demographics. Individuals captured above the lowermost barrier had longer lengths-at-age, longer total lengths, and occurred at lower relative abundance than individuals captured below the barrier. Neither Silver Carp nor Bighead Carp were detected above the second barrier on the river with mechanical sampling or with the eDNA assay. However, Black Carp were detected near the confluence with the Missouri River with the eDNA analysis. Otolith microchemistry results indicated the population of Silver Carp in the Kansas River is comprised of predominantly residential individuals. Few carp exhibited natal origin signatures of the Missouri River. Transient individuals within the population exhibited short durations of signatures indicative of the Missouri River, suggesting that movements into the Missouri River are brief. These results highlight the importance of tributary habitat for Asian carp in the Missouri River drainage. Management efforts within the Kansas River could be effective means of population control and mitigating secondary introductions. Additionally, management efforts focused in particular reaches of the Kansas River could affect the greater Missouri River population.

Population Characteristics and Movement of Blue Catfish in the Kansas River - Quintin Dean

  • Thesis Defense
  • 11/09/2020
Blue catfish Ictalurus furcatus are a mobile, large-river species native to the Missouri River and its tributaries, including the Kansas River. Historical data regarding the Kansas River population is negligible, limiting managers’ ability to appropriately manage this population. Multiple anthropogenic barriers along the Kansas River create a gradient of connectivity within the Kansas River, and with the Missouri River, possibly limiting Blue Catfish movement. Additionally, the contribution of tributary reservoir populations to the Kansas River remains unknown. My objectives were to: 1) describe the population characteristics and 2) quantify stock contributions from the Missouri River and Kansas River tributary reservoirs to the lower Kansas River population. Relative abundance and condition were variable among years with little variation across the gradient of connectivity. Somatic growth of disconnected reaches were greater than connected reaches; however, the mean length of adult age classes were consistent across the study area. River segments connected with the Missouri River had lower annual mortality and higher proportions of large fish compared to disconnected reaches. Upstream passage was not documented at the second barrier on the Kansas River, suggesting the population upstream of the barrier is isolated from the Missouri River. Adult fish collected within river reaches connected to the Missouri River displayed relatively equal natal contributions from the Kansas River and Missouri River. Half of adult and juvenile fish sampled in reaches disconnected from the Missouri River originated from Kansas River tributary reservoirs. Our data suggests adopting two spatial scales for investigating and managing Blue Catfish in the Kansas River, with the second barrier as a point of division. Current state-wide regulations are adequate for maintaining high trophy-potential in downstream river reaches. The large number of fish using the Missouri River indicates appropriate management requires a broad spatial scale that incorporates a dendritic river network framework. Future monitoring efforts, particularly for the disconnected reaches, is imperative as large reservoir stock contributions may elicit change in population characteristics.

Prairie Grouse Population Trends and their Historical Drivers in the Nebraska Sandhills - Dani Berger

  • Thesis Defense
  • 07/24/2020
The Nebraska Game and Parks Commission (NGPC) has monitored greater prairie-chicken (Tympanuchus cupido pinnatus) and plains sharp-tailed grouse populations (Tympanuchus phasianellus jamesi), collectively known as prairie grouse, since the 1950s using spring breeding ground counts and wing-ratio data collected from harvested birds in the fall. These indices have been used to evaluate population trends, but may be able to provide insight into the processes that drive patterns in the counts if related in space and time to environmental factors. An understanding of the processes shaping populations is of particular importance to prairie grouse because both greater prairie-chickens and sharp-tailed grouse are of conservation concern in portions of their respective ranges. My research modeled long-term, species-specific spatial and temporal trends of prairie grouse abundance and production and their drivers in the Nebraska Sandhills using NGPC’s historical prairie grouse monitoring data. Prairie-chicken populations have increased since the 1950s while sharp-tailed grouse populations have remained stable or slightly declined. Production of both species has decreased over time. These population trends arise in the context of a dynamic landscape. I created indices representing raptor predation and hunting pressure, cropland, hay and CRP acreage, cattle stocking rate, drought and winter severity, landscape-level factors known to influence prairie grouse populations via mechanisms supported in the literature. I used a Ricker population process model in a Bayesian state-space framework to explore the relationship between species-specific breeding ground count data and environmental covariates with a one-year time lag. I incorporated indicator variable selection into the model to determine which covariates most strongly influence population trends. The most competitive greater prairie-chicken model included negative density dependence (β = -0.003, SD = 0.000, BCI = -0.004- -0.003) and a positive effect of increased precipitation (β = 0.046, SD = 0.021, BCI = 0.005-0.089) on population growth rates, while the sharp-tailed grouse model that received the most support included negative density dependence (β = -0.005, SD = 0.001, BCI = -0.007- -0.003) and a negative effect of increasing cropland acres (β = -0.084, SD = 0,041, BCI = -0.168- -0.005). The effect of grazing was also strongly supported for both species, although the effect was positive for prairie chickens and negative for sharp-tailed grouse. Although prairie-chickens and sharp-tailed grouse have traditionally been managed as a single species because of their similar resource needs, my findings suggest that prairie grouse conservation measures may be more successful if they are species-specific. My study provides a framework for wildlife managers to use existing count-based monitoring records and free, publicly-available environmental data to explore population drivers in addition to abundance trends.

Space use and resource selection of bighorn sheep (ovis canadensis) ewes in a prairie badlands population - Erin Wood

  • Thesis Defense
  • 07/23/2020
The basic spatial ecology and habitat relationships of female bighorn sheep in Nebraska are poorly understood. Establishing seasonal patterns of space use and resource selection for this population at the margin of their historical and current range addresses a key knowledge gap and provides important baseline information for ongoing conservation efforts in Nebraska. We investigated behavioral attributes of bighorn sheep in western Nebraska with a focus on understanding how this reintroduced population uses the landscape at the eastern periphery of the range of the species. To investigate spatial ecology, we quantified movements of ewes and the factors that influence home range size, seasonal use, and spatial stability across seasons. We also quantified resource selection patterns of female bighorn sheep within their home ranges and inferred factors that influence resource selection with a focus on predation risk, forage efficiency, and human disturbance. Our work elucidated behavioral patterns of female bighorn sheep in Nebraska that may influence their survival and reproductive success. Our results should contribute to our understanding of the factors limiting population growth for this declining population of conservation concern.

Using Return Intervals and Nutrient Spiraling to Examine the 2019 Nebraska, USA Flood - Alexa Davis

  • Thesis Defense
  • 07/16/2020

In March of 2019, many of Nebraska’s streams and rivers had the worst flooding in decades, and in some locations, the worst flooding on record occurred. The historic floods in Nebraska presented an optimal case study to examine how current technological resources can be used to enhance our understanding of floods and how these floods impact in situ stream ecosystem processes like nitrogen and phosphorus cycling. Currently, there are only a few resources available to quantify the extent of floods. However, by analyzing the discharge records of 94 streams across the state, flood stage records and calculated flood return intervals. While the flood stage was reached primarily along streams in the Niobrara, Platte, and Elkhorn River watersheds, seventeen streams across the state had a flood return interval of over 100 years. The average return interval was 48 years ± 73. We also compared nutrient spiraling metrics in ten streams across the state in the summer before and after the flood to compare the flood impacts on stream ecosystem processes. There were no differences (p> 0.05) of NH4 or PO4 in uptake length (Sw), vertical velocity (Vf) ,or aerial uptake rate (U) between years. These data suggest Nebraska streams were resilient to the flood. Yet, given the high uptake lengths and low uptake velocity and areal uptake values, these data also suggest that small streams are enriched with N and P well beyond their biological demand for these nutrients. Furthering our knowledge of the quantification of floods and their impacts on stream ecosystem processes can help mitigate the deleterious consequences of floods.

Nitrate Dynamics and Source within Nested Watersheds of an Agricultural Stream, Nebraska, USA - Galen Richards

  • Thesis Defense
  • 07/14/2020

Bazile Creek lies within the Bazile Groundwater Management Area, characterized by high (>10 mg/L) groundwater nitrate concentrations originating from nonpoint sources. The purpose of the research was to determine how nitrate concentrations and source in Bazile Creek vary throughout the watershed and over time. Surface water nitrate samples were collected monthly from July 2018 through September 2019, and δ15N/δ18O nitrate isotope samples were collected seasonally and after three summer rain events. Surface water nitrate concentrations varied seasonally in the main channel and most tributaries, with nitrate concentrations being highest in the winter. Analysis of soils and land use indicated that nitrate was leaching from fields into the underlying aquifer, eventually entering streams as groundwater discharge. Seasonal and rain event nitrate isotope sampling showed that the primary nitrate source was ammonium from fertilizer, and evidence of seasonal microbial denitrification was also detected. The results of this research showed that surface water nitrate concentrations in an agricultural watershed can vary substantially over small distances, and that sub-watershed scale factors such as land use play a role in dictating surface water nitrate concentrations. The collection of nitrate isotope samples was shown to be beneficial, providing insight on source and seasonal denitrification. This research will provide data for future projects in the area, and ultimately aid in the development of targeted best management practices tasked with reducing overall nitrate loading to Bazile Creek.

Vegetation and Large Carnivore Responses in an Encroached Landscape - Hugh Ellerman

  • Thesis Defense
  • 06/19/2020

The Great Plains biome supports biodiverse plant and animal communities, provides a wide array of ecosystem services, and is depended upon by agricultural economies. Despite these advantages, however, Great Plains grasslands are becoming increasingly degraded by land cover changes due to agriculture and urbanization, fragmentation, loss of biodiversity and invasion by woody species. Woody encroachment is a biome-wide threat to Great Plains plant and wildlife communities and is therefore managed, though with variable success. I investigated the efficacy of invasive tree management projects in restoring tallgrass prairies in southeast Nebraska and regenerating oak gallery forests along the Niobrara River. I measured plant community species composition and frequency at 9 sites in southeast Nebraska to quantify woody reinvasion of restored grasslands. Along the Niobrara River, I surveyed oak-planted plots and quantified oak survival and plant community abundance at 7 sites to determine success of restorations. In each case, restorations had mixed, but mostly negative results. Management decisions following initial treatment of invasive trees compromised the long term success of restorations. Management is therefore a process, not an action, and must extend beyond initial treatment if restorations are to sustain native plant communities. I also studied habitat use of the newly establishing cougar (Puma concolor) as they recolonize Nebraska. I used radio-collar locations of 2 cougars to evaluate habitat preferences in a use-availability design. Cougars selected riparian woodlands, but crops and tree plantings may play a role as habitat corridors.

Comprehensive and Agricultural Greenhouse Gas Emissions Inventories for Nebraska and the Midwest as Baselines for Climate Change Mitigation - Eric Holley

  • Dissertation Defense
  • 04/23/2020

Climate change is the paramount challenge of today for a sustainable future and mitigation of greenhouse gas (GHG) emissions is necessary to reduce the associated risks and impacts on society. Inventories of GHG emissions are a method to provide a basis to develop effective and sustainable mitigation plans. Using the EPA’s state inventory tool and literature review, comprehensive GHG-emissions inventories were developed for the state of Nebraska over 25 years (1990-2015) and agricultural GHG emissions inventories were developed for the Midwest U.S for one year (2016). Nebraska’s net emissions increased from 56.2 million metric tons of carbon dioxide equivalents (MMtCO2e) in 1990 to 87.4 MMtCO2e in 2016. Agriculture was found to be the sector with the most emissions (36 MMtCO2e ), primarily from beef cattle, followed by electricity generation (21 MMtCO2e ), primarily from coal. Emissions in Nebraska were found to be 47.4 MMtCO2e per capita in 2015, compared to 20.6 in the U.S. due to concentrated agricultural emissions and low population. Total agricultural GHG emissions per state in the Midwest in 2016 were found to range from 10.3 MMtCO2e (Michigan) to 41.0 MMtCO2e (Iowa), with an average of 23.3 MMtCO2e. In 2016, Wisconsin was the least efficient state (0.86 MtCO2e /kg product) and Illinois was the most efficient (0.34 MtCO2e /kg product) in terms of emissions per product, which aligned with these states having the highest (71.5%) and lowest (21%) percentage of livestock, respectively. Agricultural emissions per capita ranged from 1.0 MtCO2e (MI) to 26.2 MtCO2e (SD), driven by cattle population and, largely, state population.

A review of literature was also conducted to explore the interactions between climate change and the insurance industry. Climatic events accounted for 91% of $1.05 trillion in insured costs for global catastrophic events from 1980 to 2016. Costs are driven by socio-economic development and increased frequency and severity of climatic disasters exacerbated by climate change. Insurance feedbacks in response to disaster events caused by climate change include changes in 1) premiums and insurance policies, 2) non-coverage, and 3) policy making and litigation. Alongside government policies, insurance feedbacks could be used to facilitate and manage climate change adaptation and mitigation.

The Effects of Temperature on Evacuation Rates and Absorption Efficiency of Flathead Catfish - Zach Horstman

  • Thesis Defense
  • 03/31/2020
Knowledge of fish gastric evacuation rates (GER) is a necessary component for both field and laboratory studies when trying to understand feeding rates, modeling energy budgets, and understanding trophic dynamics of aquatic ecosystems. Many freshwater fish encounter a broad range of environmental temperatures across life history stages, but the mechanistic link between temperature and physiological processes often remains poorly understood. We designed three recirculating aquatic systems capable of rearing Flathead Catfish Plyodictis olivaris in order to quantify GER and gross energy absorption at three temperatures (17oC, 22oC and 25oC). We examined the relationship between temperature and its influences on consumption, GER, and meal passage through the intestines of juvenile Flathead Catfish fed a single ration of food. We then used bomb calorimetry to examine the absorption efficiencies of juvenile Flathead Catfish by quantifying the proportion of calories remaining in dissected stomach and intestinal contents through time and by treatment. Treatment (temperature) was found to significantly affect consumption, GER, and the potential for gross calorie absC>rption within the intestines of juvenile Flathead Catfish. Insight into the GER of juvenile Flathead Catfish provides managers with a better understanding of consumption demands of these important top predators, and our results begin to shed light on the bioenergetics of this species.

In Hot Water: Influence of Multiple Stressors on Thermal Tolerance of Fathead Minnows Pimephales promelas - Alex Engel

  • Thesis Defense
  • 03/24/2020
Freshwater aquatic systems around the globe are often subjected to physical, biological, and chemical alterations to support societal needs. The Great Plains contains one of the largest agricultural industries in North America, but its productivity has ecological repercussions for adjacent freshwater ecosystems. Specifically, the dependency on surface water irrigation and application of chemical treatments has altered the thermal and chemical composition of freshwater ecosystems throughout the region. Stressors such as elevated temperatures, altered flow regimes, increased contaminant loads affect the physiology and behavior of fishes and can lead to long-term population effects. We examined thermal tolerance of Fathead minnows Pimephales pro me las in two experiments, 1) after exposure to atrazine and 2) after an acute thermal stressor. Understanding the thermal dynamics of Fathead minnows and the influence of multiple stressors on thermal tolerance will provide insights into how changing environmental conditions will affect native fish populations. Furthermore, we hope this knowledge will allow managers to more effectively concentrate conservation efforts.

Charismatic Predators in Modern Africa: Spotted hyenas (Crocuta crocuta) and Human Coexistence in the Northern Tuli Game Reserve, Botswana - Jasmin Castillo

  • Thesis Defense
  • 03/12/2020
Despite having the lowest population living in urban areas, the African continent currently has the greatest growing population rate at 2.53% with a population of 1.2 billion people. Spotted hyenas hold a unique place in African ecosystems due to being a very successful predator with an adaptable diet while many of the other predators are rapidly decreasing in abundance. The Northern Tuli Game Reserve (NTGR) was established in the mid-1960s with initially low predator populations. Predator calling stations were conducted in 2008, 2009, 2015, and 2016 to determine changes in abundance and distribution of spotted hyenas within NTGR. In 2014, a leopard occupancy study provided by-catch data to analyze brown hyena (Hyaena brunnea) and spotted hyena occupancy in NTGR. We anticipate this project to being a building block in better management ofNTGR for future research. Understanding the ecological dynamics of spotted hyenas and the impact of various types of human settlements throughout the reserve will aid in a better understanding of large predator coexistence as human populations continue to increase.

Exploring New Opportunities for Drought Risk Assessment and Awareness to Enhance Drought Risk Management at the Local Levels - Elliot Wickham

  • Dissertation Defense
  • 11/07/2019

Drought risk management in the United States has traditionally taken the form of drought plans at the state-level. Although drought planning efforts have been increasing over time, drought is still a poorly understood hazard and drought planning efforts at the local levels, particularly in urban areas, generally focus on short-term crisis management practices to protect water supplies rather than long-term risk management practices that aim protect water supplies before a drought event. Successful drought risk management is built upon three pillars: (1) monitoring and early warning; (2) impact and vulnerability assessment; and (3) mitigation, preparedness, and response. This research focuses on the second and third pillars of drought risk management to provide the local levels new opportunities and approaches to reduce drought risk.

The first article in this dissertation is a national risk assessment of urban counties in the United States, where risk is a product of both physical drought characteristics and societal factors that enhance the impacts on water supplies. The second article evaluates survey data of land use planners across the United States, since land use planning has strong potential for drought risk management applications, but generally does not incorporate drought risk reduction strategies. The final article uses the findings of a drought-specific THIRA workshop (FEMA risk assessment process, focused solely on drought) in the Platte River Basin, NE to evaluate the current drought planning efforts in the study area. The three research topics of this work provide local jurisdictions, particularly urban areas, new opportunities and methodologies to switch from crisis management to risk management techniques that will help protect future water supplies from the combination of drought periods and increasing water demands.

Ecology of Cincindela Heamorrhagica in the Extreme Environments of thermal pools in Yellowstone National Park - Kelly Willemssens

  • Dissertation Defense
  • 10/30/2019

In 2006, Leon G. Higley noted a tiger beetle species, Cicindela haemorrhagica, walking and feeding in thermal pools of Yellowstone National Park (YNP). Although this species was first recorded in the park more than 100 years ago (Hubbard, 1891), its distribution, ecology, and association with thermal features are not known. In this study, we examined its distribution, abundance, and habitat characteristics to determine if they are exclusively associated with thermal springs and to determine the physical and chemical extremes in which these beetles can live. We transcribed their behavior to determine if they use thermoregulatory behavior to cope with the high temperatures associated with thermal springs. Lastly, we studied their lethal thermal maxima to determine if they have an increased thermal tolerance, which indicates a structural or physiological adaptation. Our results show that C. haemorrhagica are seemingly exclusively associated with thermal springs and are habitat (thermal spring) generalists. Springs range between pH 2.73 and 9.0, temperatures of 29.1 oand 70 o, and varying metal concentrations. However, all thermal springs were surrounded by barren soil with a gradual edge (gentle slope) towards the thermal water. We propose census and observations as the best methods to estimate the abundance for highly mobile species near thermal springs. Conservative population sizes of C. haemorrhagica ranged between 500-1500 individuals for thermal springs within YNP.

Cicindela haemorrhagica populations not associated with thermal springs have a strong positive correlation between thennoregulatory behavior and temperature (Pearson Correlation Coefficient = 0.276, p= 0.0127). In contrast, C. h. haemorrhagica populations inside YNP have a strong negative correlation between thermoregulatory behavior and temperature (Pearson Correlation Coefficient= -0.224, p= 0.0001). Interestingly, the YNP populations thermoregulate to heat up at cold temperatures, but do not use this strategy to cool off at high temperatures. To our knowledge, there is no other example of dramatically different behaviors between two populations of insects in the same species. This may indicate a thermophilic adaptation of these beetles to the thermal springs of YNP. However, the lethal thermal maxima of YNP C. h. haemorrhagica (50.41 oC +/- 0.26) is only 1.08 oC higher than non-thermal spring C. h. haemorrhagica ( 49.33 oC +/- 0.20) (Mixed model, p= 0.0023). Although these lethal thermal maxima are a new record for reproductive metazoans, it is not high enough to explain its occurrence at thermal springs as much as 70 oC.

These results indicate that C. haemorrhagica filled a new niche inside Yellowstone National Park where the benefits (i.e. carrion drifting ashore, high temperatures during the winter, reduced competition, among others) outweighed the costs (i.e. high temperatures, pH, and heavy metals). These beetles were able to adapt to the extreme conditions of the thermal springs in YNP causing them to behave differently than other tiger beetles, including C. haemorrhagica outside YNP. We can conclude that the mechanism used by these beetles are not behavioral nor physiological, but are more likely to be structural.

Using Post-Event Surveys of Rangeland Managers to Assess Adaptive Capacity - Tonya Haigh

  • Dissertation Defense
  • 10/25/2019

Rangeland managers face challenges to adapt to climate extremes. Post-event assessments might be useful for understanding managers' adaptive capacity to hazards such as drought. This study evaluates adaptive capacity using an integrated vulnerability and resilience conceptual model and protective action decision-making models. Overarching research questions include: 1) For rangeland managers experiencing drought, how should we describe the relationship between protective action and impacts? 2) For rangeland managers experiencing drought, what are the best predictors of taking protective action?

The study addresses these questions using quantitative data collected from two post-drought (2012-2013 and 2016) surveys of rangeland-based livestock managers in the Northern Great Plains of the U.S. Statistical analysis showed that drought management actions only lessened impacts if taken at appropriate times during the drought. The timing of protective actions was predicted by characteristics of the operation that provided management flexibility during drought, and was associated with managers' on-farm monitoring of conditions and perception of drought management knowledge as a barrier to their success. Neither the use of drought early warning information, nor having a drought plan, was associated with the timing of most actions.

Assessing adaptive capacity requires identifying the actions (and the timing of the actions) that lessen impact, as well as the characteristics of the system that enable or support those actions. The post-drought survey appears to be an effective means of assessing these relationships and informing decisions about investments in adaptive capacity for agricultural management.

Modeling Waterfowl Hunter and Duck Unlimited Member Behavior using Mark-Recapture Methods - Katherine Graham

  • Thesis Defense
  • 10/23/2019

The number of individuals participating in waterfowl hunting has substantially declined since the 1980s, despite relatively abundant waterfowl populations and hunting opportunities. To avoid further losses in political support for wildlife management, losses in habitat conservation revenue, and to broaden the base of waterfowl and wetland conservation support, there has been an increased focus on growing the number of waterfowl hunters, and waterfowl and wetland conservation supporters. The purpose of this study was to aid this goal by estimating resident waterfowl hunter and Ducks Unlimited (DU) member recruitment rates, retention probabilities, and license/membership purchase probabilities; to provide a better understanding of the factors influencing these populations, and to provide a foundation for measuring the success of R3 programs aimed at these populations.

To estimate both waterfowl hunter and DU member recruitment rates, retention probabilities, and license/membership purchase probabilities, we analyzed five state electronic license systems and DU membership databases (Nebraska, Kansas, Missouri, Montana, South Dakota) using a Pradel model in a mark-recapture framework. We included five covariates (gender, generation, hunting opportunity, rurality, and DU membership class) to improve parameter estimates. For waterfowl hunters, the top models indicated that recruitment and retention rates decreased over time for all groups, and that while males had higher retention rates than females, females had higher recruitment rates. In addition, as DU membership class increased so did retention and license purchase probabilities. For DU members we found similar trends with males having higher retention rates and membership purchase probabilities than females, but females having higher recruitment rates. Additionally, we found in most states, that Baby Boomers had the highest retention and membership purchase probabilities compared to other generations. These results confirmed some assumptions that we have about both waterfowl hunters and DU members. Additionally, they suggest that social habitat for hunters and developing a conservationist's identity for DU members is important for recruitment and retention. These results can be used to both inform and evaluate future R3 programs focused on waterfowl hunters and DU members.

Traffic Noise and Sexual Selection: Studies of Anthropogenic Impact on Bird Songs and Undergraduate Student Reasoning of Evolutionary Mechanisms - Sarah Spier

  • Thesis Defense
  • 07/01/2019

Humans have transformed much of the natural landscape, consequently changing wildlife behavior. The expansion of roads has contributed to our impact on wildlife by fragmenting habitat and introducing loud traffic noise into the environment. Birds are especially susceptible to traffic noise because they rely on singing for communication, establishing territory, and mating. Different bird species may respond differently to traffic noise. Through the first study, I show how traffic noise affects the detection of birds, specifically three different species with different songs. Conducting more experiments on individual species detection will help ecologists better understand how consequences of human behavior, like traffic noise, may influence the behavior of wildlife residing near roads.

The effect of human activity on the environment should be better understood by more than just ecologists, yet the general public lacks scientific understanding. For example, humans can impact evolutionary change, yet evolutionary concepts are challenging for people to understand and learn. When describing evolutionary change, many undergraduate biology students emphasize the importance of survival and natural selection in evolution and many leave out other important evolutionary ideas, such as reproductive potential and sexual selection. My second study shows how scenarios with different sexual selection contexts affected which ideas students included in their evolutionary reasoning.

Drought impacts assessment in Brazil - a remote sensing approach - Denis Mariano

  • Dissertation Defense
  • 06/28/2019
Climate extremes are expected to increase in frequency and intensity globally, according to the scientific community. In Brazil, one of the main concerns is the increased incidence of drought, bringing unprecedented scenarios, which requires understanding, adaptation, and mitigation. Remote sensing data, once scientifically interpreted, is capable of providing information for the policymakers to better deal with the apparent lack of preparedness to deal with drought impacts. Drought has many facets depending on where, how, when, and for how long it happens. A series of studies were conducted to assess the impacts of drought on different regions in Brazil in the 2000s, thus providing a better understanding of the phenomenon and, in some cases, proposing solutions to deal with them. One study covers agriculture in southern Brazil, designing a methodology to anticipate drought impacts on crop yield. The second research aimed at assessing the effects of an extended drought period in the drylands of the northeastern region of Brazil, which possibly caused land degradation. The last study is based on the southern Amazon, which includes the Indigenous Park of Xingu -- in this research, we assessed the complex degradation cycle encompassing land use changes, fire occurrences, forest resilience loss, crop productivity and, alterations in the carbon balance. The results bring new insights on the impacts assessment of the 2000s droughts and, therefore, set the stage for the development of a framework adapted to the new scenario, at where climate extremes will be a common threat to human wellbeing.

Data to Decisions: Utilizing Climate Data to Inform Municipal Planning in the Lower Missouri River Basin - Natalie Umphlett

  • Dissertation Defense
  • 06/14/2019

Communities all across the U.S. face a number of challenges due to a variable and changing climate, and recent events, both climatologically and politically, have shifted climate mitigation and adaptation efforts to the local level. Although many states and cities have begun implementing plans addressing the impacts of climate change, most are focused on coastal or high population areas.

In an attempt to better understand the current use of climate data and information at the municipal level in the Central U.S., a survey and focus group sessions were conducted with communities in the four states of the lower Missouri River Basin (Iowa, Kansas, Missouri, and Nebraska). Results indicate that the use of climate data and information is generally low for planning efforts; however, communities could be encouraged to increase this use through the development of municipal-specific resources. A direct outcome of these results was the creation of 1) eleven customized city-specific climate reports for communities in the lower Missouri River Basin and 2) a suite of web-based tools that allows communities to explore their historic climate trends and future projections, as well as example plans that address climate-related topics from cities across the U.S. Although new, some of the resources developed through this project have already been used to support planning efforts and to better communicate the issues surrounding climate change.

Developing a Framework to Link Multi-sector Drought Impacts to Drought Severity at the State Level - Mary Noel

  • Thesis Defense
  • 06/10/2019
The United States Drought Monitor (USDM), a weekly-updated map depicting severity and spatial extent of drought, is a key indicator for federal and state policy decisions including the distribution of hundreds of millions of dollars for agricultural financial relief in the United States annually. However, the current table describing potential drought impacts for the map's severity levels fails to adequately represent a state's unique environmental, economic, and social values affected by drought. One approach to improve this broad, national-scale assessment is to transition from the former platform to a more detailed characterization of drought impacts at the state level. To accomplish this, state and regionally specific drought impact classification tables were developed by linking multi-sector, qualitative impacts chronicled in the Drought Impact Reporter (DIR) to historic USDM severity levels across the United States and Puerto Rico. After creating state-level tables, a nationwide survey was administered to local experts and decision makers (n=89), including the USDM authors, in an effort to capture greater resolution of drought impacts at a local level. As a result, 76% of responses indicated the state table as acceptable or good when classifying drought impacts in their respective state. This updated classification scheme builds a narrative supported by a reproducible methodology that can be simulated in future research for a multiplicity of drought events to better understand the complex relationship between drought severity and corresponding impacts. This thesis includes one article (Chapter Two) currently in preparation for publication in the Bulletin of the American Meteorological Society. It highlights the methodology, products, and next steps surrounding the drought impact classification table scheme, building upon the importance of enhancing qualitative impact reporting and drought characterization to improve drought preparedness, planning, and mitigation.

Assessing the Ecological Condition of Nebraska's Wetland Resources and Amphibian Communities - Nick Smeenk

  • Dissertation Defense
  • 04/26/2019
Wetlands provide valuable ecosystem services including flood control, nutrient retention, recreational opportunities, and wildlife habitat. Despite their importance, wetlands were historically displaced across the landscape in favor of alternative land uses. While general trends in wetland area have been tracked, the ecological condition of wetlands remains largely unknown. From 2011 - 2013, I conducted ecological assessments at 109 wetland sites in 11 wetland complexes across Nebraska. Using a novel standardized Floristic Quality Assessment Index score and additional vegetative metrics I determined the ecological condition of wetland sites. I subsequently tested the efficacy of multiple landscape methods and metrics as additional measures of ecological condition. Additionally, I assessed the detection and occupancy of amphibian communities in the Rainwater Basins using both landscape and local factors. Responses of plant and amphibian communities to landscape and local factors were varied and complex. Results of this research provide baseline data for Nebraska's wetlands and wetland reliant amphibian communities. Further, they illustrate the need to consider multiple spatial scales and the importance of spatial context for ecosystem conservation planning and management. While plant communities thrive with minimal 100 m vegetative buffers, other taxa such as anurans and birds may respond to factors at much larger spatial scales and require broader planning and consideration of landscape context, particularly in highly modified agricultural landscapes.

Evaluation of METRIC model for mapping the energy balance components and actual evapotranspiration of a super-intensive drip-irrigated olive orchard - Sam Ortega-Salazar

  • Thesis Defense
  • 04/17/2019
A field experiment was carried out to evaluate the METRIC (Mapping EvapoTranspiration at high Resolution Internalized with Calibration) model for mapping net radiation (Rn), soil heat flux (G), sensible heat flux (H), latent heat flux (LE), actual evapotranspiration (ETa) and crop coefficient (Kc) of a superintensive drip-irrigated olive (Olea europeae L. cv Arbequina) orchard located in Pencahue Valley, Region del Maule, Chile (35 23' LS; 71 44' LW; 96 m above sea level). The study was conducted in an experimental plot of 21.1 hectares using 9 satellite images (Landsat 7 ETM+) acquired on clear sky days during 2011/2012 and 2012/2013 growing seasons. Specific functions to estimate Gi, leaf area index (LAI) and aerodynamic roughness length for momentum transfer (Zom) for olive orchards were incorporated in the standard METRIC model. The performance of the METRIC model was evaluated at the time of satellite overpasses using measurements of LE and H obtained from an eddy correlation system. Performance of the METRIC model was quite good and indicates that Landsat thermal satellite technology is capable of being employed operationally to estimate and manage water consumption of intensive olive production in water-scarce areas of Chile and elsewhere

The Role of Resource Availability and Habitat Quality in Structuring Prairie Bee Communities - Bethany Teeters

  • Dissertation Defense
  • 03/29/2019
Wild bees are a rich natural resource. In grasslands, they play a critical role in maintaining ecological functioning through the pollination services they provide. Grasslands, however, are among the most endangered of terrestrial ecosystems and diversity of both partners in plant-pollinator networks declines as prairie landscapes are converted to cropland. In the fragments that remain, the availability and quality of nesting and forage resources for wild bees becomes increasingly important for grassland resilience. This dissertation explores the functional composition of wild bee communities in fragmented prairies and how these communities are structured by floral resource availability, habitat quality, and the composition of the broader landscape. Overall, results indicate that the although well connected grasslands may currently serve as reservoirs of wild bees, including vulnerable species known to be declining throughout most of their former range, the pollination services that diverse suites of species provide may be restricted to this landscape. Therefore, thresholds of land cover in cropland and available forage were determined. These provide a valuable tool which can be used to inform land management and restoration decisions on a landscape scale, and to identify areas where conservation measures would be most effective for maintaining ecological function. After all, the persistence of grasslands and their biodiversity is largely dependent on maintaining and restoring ecological connections between species.

Population Dynamics of the Freshwater Mussel Lampsilis Cardium Reintroduced in Nebraska - Lindsay Ohlman

  • Thesis Defense
  • 03/25/2019

The global decline of native freshwater mussels has accelerated conservation projects that preserve and restore populations, but the complex life histories among species challenges biologists in determining the most effective management strategies. This study details the conservation of plain pocketbook, a Tier I threatened mussel species in Nebraska that was artificially propagated and reintroduced into 13 sites from autumn 2016 to summer 2017. The objectives of this study were: 1) determine how handling influences mussels, and 2) evaluate mussel population dynamics following introductions.

We conducted a 12-week laboratory experiment to assess the effects of handling on plain pocketbook growth and survival. We found this species is tolerant of short-term repeated handling and used results to develop a mark-recapture sampling design to assess population dynamics of introduced mussels. We then sampled mussels and habitats seasonally 2017 - 2018 to relate mussel growth and survival to habitat, timing of introduction, and shell size. We found mussels were at heightened risk for mortality during introduction and spring and correlated these time periods to environmental stressors. We used this information to develop a rigorous process for identifying suitable habitats as well as choosing optimal introduction times.

Handling is an anthropogenic stressor for mussels that can be moderated through proper research and techniques. Short-term monitoring studies can provide valuable insight on introduced mussel populations. Implementing best management practices for future introduction projects will enhance the conservation of this imperiled taxon.

Managing for ecosystem resilience in a non-stationary world - Caleb Roberts

  • Dissertation Defense
  • 03/13/2019
Globally, environmental change is on the rise, and ecological resilience of many ecosystems is eroding. This is leading to increases in regime shifts, where fundamental structures and functions of ecosystems change. Loss of resilience and regime shifts can strongly affect human well-being via alteration or loss of ecosystem services such as food production and biodiversity. The ability to quantify ecosystem resilience and detect early warnings of regime shifts would allow land managers, land owners, and policymakers to make informed decisions, appropriate conservation efforts, and take adaptive measures in the midst of ecological change and uncertainty. In this dissertation, I investigate methods for quantifying ecosystem resilience, novel tools for detecting early warnings of regime shifts, and review current natural resource management policies to determine their ability to foster and maintain ecosystem resilience. Overall results include development of a method for detecting spatiotemporal early warnings of regime shifts decades ahead of time, interpretable metrics for quantifying and comparing ecological resilience over time, and frameworks for prioritizing conservation efforts and land management in this era of non-stationarity. With the current global level of anthropogenic disturbance, these findings demonstrate that assuming constant, linear behavior in ecological systems and not taking preemptive, preventative, and adaptive measures in the face of change will lead to conservation failures and loss of ecosystem services. Instead, this dissertation provides support for a land management paradigm that embraces ecological complexity, takes action at meaningful scales, and is proactive.

The Niobrara National Scenic River: Exploring Co-management through A Case Study of the Niobrara Council - Melissa Mosier

  • Thesis Defense
  • 03/07/2019

In recent decades, government staff and local citizens have increasingly employed cooperative schemes of natural resource management (co-management), in lieu of more conventional, top-down approaches of addressing user conflicts as they relate to water resources. The focus of this project was on the Niobrara Council, a partnership of local, state, and federal representatives charged with cooperatively managing the reach of the Niobrara River that was federally designated under the Wild and Scenic Rivers Act in 1991. The project's purpose was to explore the co-management framework of the Council, using the methodology outlined by Carlsson and Berkes (2005). This methodology involved investigating the functional tasks of the Council and analyzing the linkages between those tasks and the individuals who perform them in order to develop a descriptive picture of how the Council functions. Qualitative data for this project was gathered through interviews with the Council members, Council meeting minutes, and enabling documents and laws related to the Niobrara National Scenic River (NNSR) and the Council. This data was used to inform a qualitative thematic analysis of the Council and clarify how relationships between participants and management activities in a co-management framework are organized, and how they might be enhanced to promote institutional capacity-building and long-term problem solving.

The findings from this project provided a clearer picture of how the various partners involved in the co-management framework of the Council manage the NNSR. A better understanding of the roles of various partners and the specific management tasks that they were responsible for was uncovered; illustrating where various actors play key roles, how responsibility for some tasks is shared, where collaboration is most prevalent and where it is intermittent, and at which junctures entities outside of the Council play a significant part. Additionally, data was analyzed in order to define what aspects of the co-management framework could be enhanced for capacity building, the most prevalent needs being increased access to resources, enhancing institutional arrangements, supporting appropriate government policies and planning, and enhancing stakeholder participation. These and other themes that emerged from the findings of this analysis provide a starting point for the Council to use when reflecting upon potential enhancements to their management framework and planning for future endeavors.

Assessment of Motivations, Constraints, and Future Waterfowl Hunting Opportunities of Hunters and Anglers Across the Central United States - Matthew Hinrichs

  • Thesis Defense
  • 02/27/2019

Since the mid-1980s, there has been a decrease in individuals participating in waterfowl hunting in the United States. The decline in participation has over-arching consequences for state and federal wildlife agencies in their ability to fund and ability manage habitat and waterfowl populations. There is a fundamental need to understand why individuals participate in waterfowl hunting and what barriers there are to participating in waterfowl hunting.

An online survey was conducted in the summer and fall of 2018 asking waterfowl hunters, anglers, big game hunters, combination users (i.e., hunters that have multiple hunting and fishing permits), and small game hunters about their motivations, barriers toward waterfowl hunting, stated preferences, mentorship, and demographics. Results suggested that all respondents, regardless of the activity they preferred, were strongly motivated by being outside and connecting with nature. In addition, big game hunters were strongly motivated by consumptive motivations, such as eating meat and knowing where their food came from. The most limiting barrier toward waterfowl hunting was land access (i.e., lack of public land and private land access), crowding at hunting locations, and encounters with other hunters. All individuals were likely to increase participation in waterfowl given the scenarios provided but highest ranked scenarios were to hunt an area with a quality hunt or someone to take them hunting. Further, respondents who had never participated in waterfowl hunting were more likely to hunt waterfowl with a mentor who is someone they know (i.e., family, friend, co-worker).

The study results provides information on factors associated with hunting participation and future. By understanding multiple attributes of hunters and anglers within the central United States, we gain further insight into participation trends and recreationists needs and expectations, with important implications to the recruitment, retention, and reactivation of hunters and anglers.

Implications of Channel Catfish Movement in An Internationally Managed System - Henry Hansen

  • Thesis Defense
  • 01/29/2019

The largescale movements and spatial behavior of channel catfish in the Red River of the North, have direct interactions with geopolitics, anthropogenic structures, and ecosystems. Investigating the spatial dynamics and exploitation of this mobile and internationally managed fish species provides opportunities for resource managers to design evidence-based policy for the diverse interest groups that utilize the fishery. My thesis comprised two parts: 1) characterize system-wide movement and survival patterns using mark-recapture methods and acoustic telemetry and 2) project the interaction of hypothetical exploitation scenarios and alternative movement methodologies to assess the fishery from an ecosystem service flow perspective. Channel catfish were tagged with T-bar tags and acoustic transmitters to track movement patterns and quantify harvest. Approximately 40% of individuals tagged with acoustic transmitters moved into Lake Winnipeg at least once during the study. Conversely, about 30% of T-bar tag recaptures in the U.S.A. had been initially marked in Canada. A large proportion (0.89- 0.97) of the individuals remained within the initial study reach where they were tagged. Fishing mortality was estimated to be less than 0.001, and natural mortality was estimated to be 0.16 across the entire system. Projection models demonstrated that trophy stages of channel catfish were highly sensitive to exploitation and were typically depleted at or below a 0.30 exploitation rate. Depletion of populations and changes in stock structure affected subregions within the Red River system differently which resulted in competing strategies among countries and fishers from the perspective of economic valuation of harvests. We found that recruitment from areas with greatest population size appeared to buffer aspects of harvest within regions and to some extent immediately adjacent regions. Movement, regardless of methodology, was critical in supporting exploitation for regions with low recruitment. The sustainability of exploiting highly mobile fish species from an ecosystem service flow perspective hinges on the ability of fisheries management organizations to incorporate spatial variability and understand the economic consequences of exploitation for competing interests.

Urban Forests in a Changing Environment: Midwestern Motivations for Tree Planting and Perspectives of Climate Change Impacts on Urban Forest Systems - Toby Burnham

  • Thesis Defense
  • 01/22/2019

Urban trees perform several ecosystem services important to humans. Climate variability and poor management threatens urban forests with ecological and socio-economic consequences. Therefore, it is critical urban trees are sustainably managed. For an urban tree management plan to succeed, social inputs at the residential scale must be taken into consideration.

The aim of this research is to help inform urban forest managers of social variables that may play an integral role in successful implementation of urban forest management plans. Social factors behind home-owner decision-making to plant or remove trees in the Lincoln and Omaha metro areas show that 75% of respondents consider aesthetics as extremely important in motivating tree planting, 74% cited space availability as very or extremely important for choosing the tree species planted, and 83% responded that tree health was the most important factor for removing trees. Most common types of trees planted were maples, and the most common types of trees removed were pines. Additionally, respondents primarily received information about trees from the internet (38.1%), and acquiring trees from nurseries (55.7%). Additionally, 59% of respondents agreed that changes in climate were already occurring, 46% agreed that climate change is mainly caused by humans, and 47% thought climate change will have negative consequences. Respondents generally perceive themselves as moderately knowledgeable about climate change. The majority of respondents (72.3%) are concerned about climate changes impacts on trees and most (63%) believe planting trees to reduce climate change is important. Overall, 59.8% are extremely likely to support more tree-planting in parks, streets, and other public places. Results from these studies are important for the development of sustainable management plans, and educational outreach programs related to urban tree management.

Examining Patterns in Nest Predation Using Artifical Nets - Vicki Simonsen

  • Thesis Defense
  • 11/16/2018
The use of artificial nests to study predation rates of avian nests has faced disregard by ecologists due to inconsistencies found between the survival rates of real and artificial nests across studies and reviews. The negative perception of artificial nests providing an inconsistent assessment of survival has thus fostered the perception that artificial nests are a secondary option to be used to overcome logistical hurdles associated with achieving sufficient sample sizes in systems where study species are rare or elusive, or as merely a preliminary method to study predation across gradients. We argue that the greatest mistake ecologists have made with artificial nests is not the flaws within poorly designed studies, but rather the rash decision to write-off the utility of artificial nests and failure to look for patterns in inconsistencies between properly designed studies. Therefore, we conducted a case study to demonstrated the utility of artificial nests as a tool to consistently measure inherent nest predation risk across a set of manipulated experimental treatments. We also conducted a meta-analysis to examine the patterns of real and artificial nest survival across several gradients theorized to influence nest survival (e.g., absolute latitude). We used only data from peer-reviewed journal articles where researchers recorded the survival of both real and artificial nests, to demonstrate that when extraneous variation is reduced inconsistencies give way to prominent patterns in survival.

Managing for Vegetation Heterogeneity on Rangelands: An Exploration of Ranchers' Attitudes - Stephanie Kennedy

  • Dissertation Defense
  • 11/16/2018

Grasslands provide food, fiber, and numerous ecosystem services to human populations as well as habitat for wildlife. They are also some of the most endangered ecosystems in the world because of accelerating conversion of grassland to cropland and encroaching trees and shrubs. The quality of remaining grasslands will be critical to protecting the biodiversity and vital ecosystem services they provide. Heterogeneity is a term specific to rangeland science that is illustrative of grassland health. Grassland species require very specific and differing habitats and without the variation in vegetation (heterogeneity) the number of species that can thrive on the land is minimized, as are the interconnected ecosystem services. Increasing heterogeneity on working rangelands may be a partial solution to preserving the vital ecosystem services provided by grasslands, balancing the needs of conservation with that of cattle production. This dissertation followed a three article format.

The first article explored what factors impact the grassland management decisions of progressive Nebraska ranchers, using an interpretative phenomenological approach. We found four major themes: 1) livelihoods are connected to the quality of the land; 2) variability is the very nature of ranching; 3) ranching is an enjoyable way of life; and 4) stewardship is a calling. Subthemes were also included to better articulate findings and provide further clarification of the superordinate themes.

In the second study, a multiple case study analysis was used to explicate four ranches within the Great Plains region that manage specifically for habitat heterogeneity. Three overlapping themes emerged: 1) Managing a tallgrass prairie, not running a pasture; 2) Good management is good for everyone; 3) We don't have all the answers. While these ranchers are unique in some of their perspectives and management techniques, they don't think of themselves as different or unique. Despite not believing they manage at the landscape scale, they clearly see their property, and their actions on it, fitting into the larger mosaic of managed properties in the Great Plains.

In the third study, we tested a predictive model of factors influencing attitudes toward heterogeneous landscape-scale ranch management. An online survey was sent to ranchers within prescribed-burn and grazing groups in the Great Plains. Significant predictors of attitudes toward heterogeneous grassland management were: social injunctive norms; consideration of future consequence; and the social responsibility facet of property rights orientation. Significant predictors of landscape-scale management were: descriptive norms, consideration for future consequence, and participation in grassland activities. Furthermore, the ranchers are not interested in converting their grasslands to croplands and do not feel financially pressured to do so. They prefer native forage species and control for invasives; however, only about half use prescribed burning, although 77.6% viewed it as beneficial for their rangelands.

Even though the survey targeted ranchers that were predicted to have favorable attitudes toward heterogeneous grassland management, there are still a vast majority who follow the "manage to the middle" paradigm. This supports other studies that found the paradigm shift of rangeland ecology professionals to heterogeneity has not made its way to producers.

Heterogeneity of Preferences and Values of Consumptive Outdoor-Recreation Participants - Nick Cole

  • Dissertation Defense
  • 11/14/2018
Consumptive outdoor-recreational activities, represented by various forms of recreational hunting and fishing, are heterogenous systems of leisure that millions of people participate in around the world. Further, animal conservation is fundamentally intertwined with consumptive outdoor recreation through funding generation, population control, and human diet supplementation. Monetizing the protection and use of natural resources within the ecosystem-services framework has been suggested as a functional approach for assessing tradeoffs in policy decisions that are imperative to maintaining stable social-ecological interactions within consumptive outdoor recreation. Though this approach allows for increased comparability and recognition of tradeoffs between policy decisions that emphasize specific ecosystem service benefits over others, the inherent heterogeneity of consumptive outdoor recreation participants introduces uncertainty. Describing the heterogeneity of consumptive outdoor recreational participants may ameliorate such uncertainty by identifying commonalities among segments of participants that better represent expected outcomes under different policy regimes.

Spatial and Temporal Structure of a Canid Community in Nebraska - Lucia Corral Hurtado

  • Dissertation Defense
  • 11/05/2018
Understanding patterns of space-use by individuals, their distribution, and how they coexist with ecologically similar species is crucial in ecology, wildlife management and conservation. However, the study of such patterns is challenging because the relationship among species and their environment is shaped by multiple ecological processes, acting at different scales and in a hierarchical manner. In canid systems, for example, there is evidence that intraguild interactions affect species distribution and habitat use, particularly for smaller canid species. We aimed to understand the ecological mechanisms shaping the distribution of a canid community; to investigate if temporal segregation among species may be the mechanism allowing their coexistence; and to assess the genetic structure and diversity of swift fox population in Nebraska and explored whether or not genetic structure could be influenced by landscape feature and habitat constraints.

Relationships among Biodiversity Dimensions of Bird in Nebraska - Nadejda (Nadya) Mirochnitchenko

  • Thesis Defense
  • 10/31/2018
Biodiversity is important for environmental stability and human well-being. The way we think about and measure biodiversity often simplifies the many kinds of biological variation among species into one type of diversity: taxonomic diversity. Other ways to examine biodiversity more directly link important features of biological diversity to ecological questions and conservation values. We examine under what conditions different kinds of diversity (i.e., species richness, phylogenetic diversity, functional diversity) vary across a landscape. Using bird biodiversity across Nebraska, we also examine what the differences among diversity types mean for ecology and conservation.

Examination of Motivations, Constraints, and Identities of Nebraska Hunters - Alisha Grams

  • Thesis Defense
  • 10/25/2018

Hunting participation has been decreasing in the United States for several decades. This decline is concerning because of the role that hunting plays in funding wildlife and conservation programs. Without an alternative funding source, management agencies will have difficulty managing and restoring wild bird and mammal communities as well as acquiring, developing and managing their habitats. Thus, there has been a concerted effort to slow the decline by understanding hunter recruitment, retention, and reactivation (R3). As part of this understanding process, there is a critical need to know why hunters participate in hunting activities and what things may hinder participation. The objective of our research was to examine the hunter identities, preferences, motivations, and constraints among Nebraska resident big game (deer and turkey) and small game hunters

We conducted a statewide, web-based survey to collect data on motivations, specializations, constraints, and identities of Nebraska hunters. We assessed whether there were any differences or barriers between groups identified as big game hunters and small game hunters. The two groups responded similarly to the motivation questions with very small differences between the groups. The primary reason most hunters were hunting were to spend time outdoors and spending time with family and friends. Similarly, there were few differences between the hunter groups in their perception of barriers to hunting. Access (e.g., location and amount of public land) and game population related (e.g., abundance of game) barriers were considered the greatest barriers to hunting in Nebraska. Using cluster analysis, we found two groups of hunters based on species preferences: upland game hunters (preferred pheasant and quail) and deer hunters (preferred deer, turkey and pheasant). We assessed the role that species preference groups and hunter identity had on recreational specialization. The deer preference hunters rated centrality to life greater than the upland game preference group, whereas skill development and self-expression were similar between the two groups. Further, we observed a continuum among both species preference groups that as you moved from those that did not identify as a hunter to those that currently identify as a hunter that there was an increased prominence that hunting has in their lives.

One potential tool in engaging hunters may be the use of hunting tournaments. However, the information on hunting tournaments in the scientific literature is sparse. We conducted in-person survey of participants at the Sharptail Shootout in Mullen, NE to better understand the reasons why hunters may participate in a grouse tournament. We interviewed 62% (n = 69) of the participants over two days of the tournament. Surprisingly, we found that tournament participants were primarily from out of state and motivated to attend the Sharptail Shootout to spend time with friends, instead of competition related reasons.

Examining of motivations, constraints, and identities of Nebraska hunters offers a useful tool in differentiating recreationists and understanding participation patterns, which may provide greater insight into more effective R3 practices.

The freshwater gastropods of Nebraska and South Dakota: A review of historical records, current geographic distribution, and conservation status. - Bruce Stephen

  • Dissertation Defense
  • 10/11/2018
This is an investigation of the historical and current distribution of freshwater snails of Nebraska and South Dakota. This study ranges from historical surveys conducted in the late 1800's to the early 1900's, to recent survey results from over 260 water bodies throughout eight EPA Level III ecoregions. Species composition is compared among regions. Some species were observed in many water bodies across both states while other were comparatively rare: Common species include the left-handed pondsnail, Physa gyrina, and the large planorbid Helisoma trivolvis, while rare species include the freshwater limpet, Ferrissia rivularis, and the Prairie Lymneid, Lymnaea bulimoides. Reasons for their distribution is explored and I assign a conservation status to each species based on incidence, historical presence, and geographic distribution. Three species are imperiled, one species is critically imperiled, and at least seven species, observed only in historic studies, may be extirpated.

Assessing the Relationship between Groundwater Nitrate Concentrations and Environmental Variables through Repeat Sampling and Statistical Machine Learning:Dutch Flats, Nebraska - Martin Wells

  • Thesis Defense
  • 09/18/2018

Nitrate-contaminated aquifers are common in landscapes dominated by agricultural land use. Health concerns related to consuming nitrate-contaminated groundwater are well documented and continued research aimed at decreasing concentrations is critical. A 1990s U.S. Geological Survey (USGS) study focused on groundwater characteristics in the Dutch Flats area of western Nebraska. Agricultural-related practices were determined to largely influence groundwater recharge and nitrate concentrations ([NO3-]). Since the conclusion of the USGS study, a transition to more efficient irrigation technology has been observed in this region. The emphasis of this 2016 study was to resample several well nests examined in 1998 to determine whether shifts in water resources management have (1) reduced groundwater recharge rates, (2) increased biogeochemical processes, and (3) reduced groundwater ([NO3-]). Though 2016 3H/3He age-dating indicated an increase in groundwater age and decreased recharge rate (19.3 years; 0.35 m/year; n = 8), the mean values were not statistically different from 1998 (15.6 years; R = 0.5 m/year). Samples of d15N-NO3- and dissolved oxygen (n=14) did not indicate major changes in biogeochemical processes, including denitrification. Long-term ([NO3-]) data from the North Platte Natural Resources District (NPNRD) showed 60% of wells sampled in both 1998 and/or 1999 and 2016 (n = 87) had decreased in ([NO3-]), though median concentrations were not statistically different. Given the extensive long-term NPNRD nitrate dataset (n=1,049), we also applied statistical machine learning to (1) evaluate the method as a means to estimate groundwater lag time, (2) assess the influence of 15 predictor variables on Dutch Flats groundwater ([NO3-]), and (3) evaluate the validity of the model through comparisons with field investigations. Overall, Random Forest displayed promising results for evaluating Dutch Flats groundwater[NO3-], though limitations were discovered when modeling temporal data.

Distribution and Habitat Association of the Northern Long-eared Bat - Zac Warren

  • Thesis Defense
  • 08/16/2018

Because of white-nose syndrome, the northern long-eared bat (Myotis septentrionalis) is experiencing rapid population declines across the majority of its range. This decline has prompted increased regulatory protection and thus an increased need for effective habitat management strategies. Insight into the species habitat associations, however, is a prior necessity to ensure management practices are biologically relevant. Understanding these relationships requires a holistic approach that addresses the multiple ways in which the species is interacting with its environment. The objective of my thesis was to address these relationships following a multi-scale approach that assessed the factors associated with roost tree selection, distribution, and habitat use.

I conducted a quantitative meta-analysis of all northern long-eared bat roost-selection studies, thus enabling inference across the range of the species. Secondly, I sought to understand the factors associated with the northern long-eared distribution in Nebraska by conducting a multi-scale occupancy study with four acoustic survey stations nested within 101 10 km x 10 km grids distributed across Nebraska. Lastly, to assess factors associated with multi-scale occupancy at finer spatial scales, I combined presence/absence results from 5 intensively sampled study sites in Nebraska with on-the-ground habitat measurements.

Results from the meta-analysis indicate selected roost trees had a greater amount of bark remaining on the bole, a larger diameter at breast height, a lower decay class, and were taller. Results from the statewide occupancy study provide evidence for relationships between large-scale occupancy and forest clumpiness, proximity to potential hibernacula, and summer temperature. Within occupied grids, evidence supported a positive relationship between small-scale occupancy and forest area within 125 m. Results failed to provide evidence of habitat factors associated with large-scale occupancy at the 5 study sites likely due to high naive occupancy rates. Evidence, however, did support a positive relationship between canopy closure and small-scale occupancy. Reported occupancy estimates between the two studies results serve as a pre-white-nose syndrome baseline, as I collected all data prior to the detection of white-nose syndrome in Nebraska.

A Comparison of VNIR and MIR Spectroscopy for Predicting Various Soil Properties - Josh Gates

  • Thesis Defense
  • 07/19/2018
Soil plays an important role in our daily lives, namely producing food, cleaning water and storing carbon. The ability to rapidly and cost-effectively quantify the various components in soils can help us understand and better manage this important resource. This study aims to compare the ability of visible near-infrared (VNIR) spectroscopy and mid-infrared (MIR) spectroscopy to quickly and accurately predict various important soil properties (electrical conductivity, soil pH, cation exchange capacity, exchangeable cations, phosphorus, carbon, beta-glucosidase enzyme activity and nitrogen). Prediction models were developed using partial least squares regression (PLSR) techniques. Three different calibration sampling methods were tested along with various spectral preprocessing techniques to find the best predictive ability of VNIR and MIR. Soil components related to carbon, nitrogen and cation exchange capacity had good predictive ability (R2 > 0.8) by both VNIR and MIR, but MIR was more accurate. Electrical conductivity, sodium cations and phosphorus were poorly predicted by both (<0.71). VNIR models were not as robust as MIR models but could be potentially useful for qualitative analyses when rapid analyses are preferred over accuracy. MIR predictions overall were more accurate predictions than VNIR and could potentially be used as a surrogate method for timely laboratory techniques for spectrally active soil components.

Analysis of Grace Percentiles as Groundwater and Drought Monitoring Tools - Anthony Mucia

  • Thesis Defense
  • 07/10/2018
Drought monitoring, specifically groundwater and soil moisture monitoring, is of critical importance to agriculture. NASA's Gravity Recovery and Climate Experiment (GRACE) based groundwater storage and soil moisture percentile products give a high resolution, nationwide view of these responses to drought. But how accurate are these products? And how well do they monitor different types of droughts in different regions and seasons? Measurement comparisons show GRACE groundwater storage percentile does not accurately monitor actual groundwater levels. However when compared to other well-known drought indicators and stakeholder observations, both GRACE groundwater storage and soil moisture products show skill in drought monitoring and early warning.

Boundary spanners and trust development between stakeholders in integrated water resource management: a mixed methods study - Jodi Delozier

  • Thesis Defense
  • 07/06/2018

Natural resource issues are inherently complex, even more so are those that involve the management of water. Because watersheds tend to cross multiple jurisdictional and geographical boundaries, a diverse set of stakeholders are needed to develop appropriate and sustainable management policy. This research sheds light on the importance of boundary spanners assisting in the development of trust between stakeholders in integrated water resource management (IWRM). Previous literature has explored the advantages to boundary spanning leadership in business practice, emergency management, university and community management as well as fish and wildlife management, but has failed to address the area of integrated water management. Boundary spanners are key to establishing stakeholder relationships, providing safe spaces for open and honest communication, and aiding in trust development.

Through a mixed-methods approach, we posed the following quantitative and qualitative questions: 1) Do boundary spanners cultivate trust between stakeholders within the IWRM process? 2) How do boundary spanners cultivate trust between stakeholders within the IWRM process? The quantitative phase surveyed individuals who had previous experience with IWRM in Nebraska. Demographic factors (age, education, and gender) and boundary spanning were used as predictors in a regression analysis of trust building between stakeholders. Power imbalance, scale of governance, conflict, and cooperation were used as moderators of the relationship between boundary spanning and trust building. Autonomy, authentic leadership, and trustworthiness were used as predictors of boundary spanning behavior. Boundary spanning predicted a large percentage of the variance on trust building between stakeholders. Power imbalance, scale of governance and cooperation did not moderate the relationship between boundary spanning and trust building; however, conflict was a weak, negative moderator. A follow-up regression analysis found power imbalance and scale of governance to be direct, but weak negative predictors of trust building and cooperation to be a direct, but weak positive predictor of trust building. Autonomy, authentic leadership, and trustworthiness all predicted an increase in boundary spanning behavior.

In subsequent model testing using hierarchical regression, boundary spanning, cooperation, power imbalance, and scale of governance were found to be predictors of trust building with boundary spanning having the greatest influence on trust building between stakeholders. Authentic leadership, autonomy, trustworthiness, older participants, and females all positively influenced boundary spanners' ability to influence trust building, with trustworthiness being the strongest predictor of boundary spanning.

The qualitative phase involved interviewing 13 individuals who participated in the online survey and scored more than one standard deviation above the mean on boundary spanning behaviors. Seven themes emerged from analysis of the interviews and increase our understanding of the role of boundary spanners in building trust between stakeholders. Boundary spanning behavior sets the stage for improved stakeholder relationships and enhances trust and the likelihood of a more successful IWRM outcome.

The Impact of Land Use on Nitrate Movement and Storage in the Vadose Zone of the Hastings' Well Head Protection Area - Craig Adams

  • Thesis Defense
  • 04/04/2018

Measurement of accumulated nitrate in the vadose is critical for predicting whether changing surface activities are impacting nitrate leaching to groundwater beneath agricultural fields. This research investigated the occurrence and movement of nitrate over time using deep vadose zone soil cores collected from the Hastings, NE Well Head Protection Area (WHPA). Profiles were generated from cores collected from urban and irrigated farmland and compared to a previous study done at the same locations. Sampling previously collected sites allow for direct comparisons of current and historical nitrate-N profiles, potential movement, and can provide a method for evaluating effects of changing land use at the surface. Cumulative nitrate in the top 65 ft for urban irrigated lawns, pivot irrigated farmland, and gravity irrigated farmland had an average of 320, 540, and 700 total lbs-N/acre respectively. In farmland where irrigation changed from gravity to pivot application there was an average reduction of 170 lbs-N/acre in the top 55 ft of the profile over a five-year time span. This observation supports the use of sprinkler irrigation for more uniform water application, reducing potential leaching at the head and tail rows of gravity irrigated fields. While future studies are still needed, the importance of vadose zone monitoring in evaluating and protecting groundwater is beneficial in determining connections between surface activities and the underlying groundwater.

Investigaing Mechansims of Hydraulic Conductivity Transience in Sandy Streambeds - Wilhelm Fraundorfer

  • Thesis Defense
  • 03/30/2018

This research utilized a time series of hydraulic, geophysical, and sedimentological data to differendate between streambed processes that give rise to hydraulic conductivity (K) heterogeneity in streambed sediments. Most research on streambed K has focused on characterizing spatial heterogeneity, this study is unique in its focus on temporal variability and for integrating methods from multiple disciplines. This work has potential implications for hyporheic processes, as well as more traditional applications in hydrology and geomorphology. Permeameters and slug tests were used to densely sample K in a grid on the Loup River in East-central Nebraska between June and August of 2017. K did not change significantly between June and July, but did between July and August in response to an anthropogenic high flow event. This study's results suggest that depositional and erosional processes may play a less significant role in shaping streambed K heterogeneity than has been suggested by some researchers.

Quantifying the roles of land-cover change and remote forcing in the 1930s Dust Bowl drought - Abraham Torres Alavez

  • Dissertation Defense
  • 12/20/2017
This study reveals physical processes resulting from land-cover change and their effects on the 1930s Dust Bowl drought in the U.S. Great Plains. The Weather Research and Forecasting (WRF3.6) regional model, coupled with the Community Land Model (CLM4.0), was used to describe those processes under various land-cover conditions, initial soil conditions and large-scale circulations. Key results from these simulations show that the drastic change in land-cover by the 1930s changed the energy budget and weakened the zonal pressure gradient force in the region enough to collapse the southerly low-level jet. Weakening of this jet reduced moisture transport to the U.S. Great Plains from the Gulf of Mexico. Without a sufficient moisture supply, the drought intensified and lengthened. It was sustained over multiple years by the land-cover condition of the region. These results show that large-scale land-cover change in sensitive regions can change regional atmospheric circulation and result in long-lived severe droughts.

Complex adaptive systems: Cross-scale structure and resilience - Shana Sundstrom

  • Dissertation Defense
  • 12/14/2017

This dissertation moves among several connected ideas that form the backbone of ecological resilience—the discontinuity hypothesis, cross-scale resilience model, regime shift theory, and panarchy. It both expands conceptual arguments and tests some of the hypotheses generated.

Analyses discussed include applying the discontinuity hypothesis to the global economic system, testing candidate socio-political processes to see if they were correlated to the identified scale domains, comparing the cross-scale resilience of coral reef fish communities from the Hawaiian archipelago, and testing a novel information-theory method to detect spatial regimes in zooplankton and avian communities across large spatial scales.

Conceptual arguments include detailing why the discontinuity hypothesis can and should be used to objectively detect scale domains of pattern and process in non-ecological complex systems, why the cross-scale resilience model would benefit from the consideration of abundance, and why adaptive cycles are more than just a metaphor for dynamics of change over time, but are driven by endogenous features inherent to complex adaptive systems.

Improving the Accuracy of Cosmic-Ray Neutron Probe Estimate of Soil Water Content Using Multiple Detectors and Remote Sensing Estimates of Vegetation - Xiaochen Dong

  • Thesis Defense
  • 11/28/2017
The recently developed Cosmic-ray Neutron Probe (CRNP) for estimating soil water content (SWC) fills a critical measurement gap between point scale methods and large scale measurements collected from remote sensing. CRNP works by measuring the change in low-energy neutron intensity over time. However, the accuracy of CRNP to measure SWC is well known to be affected by other hydrogen sources (e.g. soil organic content, atmospheric water vapor, vegetation and surface water). This study focuses on the influence of rapidly growing vegetation in agricultural fields on the accuracy of the CRNP method. Our results indicate that biomass data determined from remote sensing (GrWDRVI) closely follows in-situ sampling of biomass (R2=0.677 for Maize and R2=0.567 for Soybean). We found that local correction factors using bare to moderated ratio removing the influence of vegetation changes can be derived, thus removing bias in the CRNP SWC observations. The improved algorithm for estimating SWC from CRNP will be beneficial for long-term monitoring as well as validating remote sensing SWC products.

Utilizing a Consumer-Grade Camera System to Quantify Surface Reflectance - Joe Lehnert

  • Thesis Defense
  • 07/28/2017
Consumer-grade camera systems are often employed in aerial remote sensing to provide insight into patterns and processes of interest to science and industry, a trend that has largely been encouraged by the rapid growth of the small unmanned aircraft system (sUAS) industry. However, little research exists on the ability of these systems to accurately measure surface reflectance in specific wavebands; a crucial consideration for many remote sensing applications. This research was conducted on the premise that, with proper equipment and calibration techniques, consumer-grade cameras would be capable of accurately measuring surface reflectance in user-defined wavebands of interest. A stereo-pair, Fujifilm IS Pro camera system was constructed and fitted with specialized filters to isolate wavebands related to vegetative features of interest. Multi-colored foam swatches and turf grass nitrogen calibration plots were imaged in a number of environments. Images were subsequently processed using linear calculation, vignette correction, and reflectance adjustment. Image reflectance values were then compared to Ocean Optics 2000+ reflectance captured at the same location and the coefficient of determination (r2) was used to determine the degree of similarity between the two systems. Turf plot reflectance was used to calculate the red edge Chlorophyll Index (CIred edge) from both instruments and these values were also compared using r2. Foam swatch comparisons resulted in r2 = 0.97 or better for all lens/filter combinations, suggesting consumer-grade cameras are capable of accurate measures of reflectance. CIred edge comparisons yielded daily averaged r2 values of 0.86 and 0.70, depending on the lens/filter combination used, suggesting these systems could potentially be utilized in a number of advanced remote sensing roles.

Modeling gross primary production of midwest maize and soybean croplands with satellite and gridded weather data - Gunnar Malek-Madani

  • Thesis Defense
  • 04/17/2017
The gross primary production (GPP) metric is useful in determining trends in the terrestrial carbon cycle. Models that determine GPP utilizing the light use efficiency (LUE) approach in conjunction with biophysical parameters that account for local weather conditions and crop specific factors are beneficial in that they combine the accuracy of the biophysical model with the versatility of the LUE model. One such model developed using in situ data was adapted to operate with remote sensing derived leaf area index (LAI) data and gridded weather datasets. The model, known as the EGM model, uses a four scalar approach to account for biophysical parameters including temperature, water stress, light quality, and phenology. This study drives the EGM model using remotely sensed LAI data and gridded weather data for seven locations in the northern Midwest. Results show an increase in error (RMSE = 3.5 g C m-2 d-1) over the previous iteration in which in situ data were used (2.6 g C m-2 d-1). Poor gridded weather atmospheric pressure and incoming solar radiation inputs, increased climatic variation in the study sites, and the application of LAI algorithms calibrated using solely Nebraska sites to sites in Iowa, Minnesota, and Illinois lead to this increased error. Despite this, the study showed there is good correlation between measured and modeled GPP using this model for the field years under study. As the ultimate objective of research is to develop regional estimates of GPP, the decrease in model accuracy is somewhat offset by the model's ability to function with gridded weather datasets and remotely sensed biophysical data. The level to which the error is found to be acceptable is dependent upon the scope and objectives of the research at hand.

Assessing landslide susceptibility with a GIS using qualitative and quantitative methods in Knox county, Nebraska - Christian Cruz

  • Thesis Defense
  • 04/14/2017
A landslide susceptibility map was developed for Knox County, Nebraska, located along the Missouri River valley. The Missouri River valley has significant changes in relief, gradually receding into rolling loess hills further to the south and southeast of the county. This thesis is designed to assess landslide susceptibility using a DEM derived from LiDAR, land cover, and soil series. Data were assessed using a quantitative approach using logistic regression within Rstudio and a geographic information system (GIS). Based on the quantitative results, factors were qualitatively assigned landslide potential values. The six factors used in determining the area's susceptibility to landslides, were parent material, soil series, land cover, slope degree, slope curvature, and slope aspect. Previous investigations in the region indicate the Cretaceous shale parent material is a major contributing factor in landslide development. Physical map units were acquired to differentiate the soil type and parent material. DEMs derived from LiDAR were analyzed in GIS to provide slope degree, curvature, and aspect information. Logistic regression data was extracted from randomly selected points along landslide scarps. All six factors were reclassified by their odds ratios and the combination of factors was applied to produce a resultant map to show landslide susceptibility. The resultant map of Knox County locates and distinguishes areas that are more likely to incur landslide activity or areas that have already experienced a significant amount of landslides.

Causes of variation in fine-scale pheasant hunter habitat use - Lyndsie Wszola

  • Thesis Defense
  • 04/14/2017

Variation in hunter behavior within regulatory parameters has the potential to influence prey populations in evolutionary time by imposing selection and in ecological time by inducing changes in prey habitat use. When prey leave managed lands in response to hunting, the change in prey distribution may be suboptimal to both hunters and prey. To understand how hunting activity influences prey spatial decisions, we must first understand how hunting pressure becomes distributed in time and space. We assessed how transportation infrastructure, physical stress, variation in vegetation structure, land use on adjacent fields, and fine-scale pheasant distribution influenced hunter movement through public access hunting fields in southwest Nebraska. We found that hunter space use increased with increasing pheasant density and decreased with increasing distance from roads and public access hunting signs. Our results corroborate at a finer scale landscape studies of hunter movement suggesting that hunters are influenced by the distribution of infrastructure and prey. Our results further imply that conservation practitioners may be able to subtly manage fine-scale hunter behavior through the strategic placement of access infrastructure.

Errors in gridded weather data sets and their impacts on estimating reference evapotranspiration - Philip Blankenau

  • Thesis Defense
  • 04/14/2017
Gridded weather data sets are useful for modeling in agriculture, hydrology and ecology. This research explored the error in several gridded weather variables and in reference evapotranspiration computed from those variables. Results show that all gridded data have a tendency to overestimate reference evapotranspiration.

Recreational Angler Behavior and Site Choice within Midwestern Reservoirs - Brian Harmon

  • Thesis Defense
  • 04/12/2017

Recreational anglers are influential predators in inland fisheries that act across multiple scales to complete a fishing trip. Although between-trip and across-waterbody angler behavior and site choice are well documented, within-trip behavior is poorly understood. Recreational fisheries are complex systems, in which interactions occur across scales.

I tested the connections between angler behavior, trip outcome, and angler perceptions to elucidate within-trip angler behavior. I recorded angler site choice across the open-water season at four Salt Valley reservoirs and compared angler location to a suite of habitat variables. I used a competing-models approach to determine what model of physical features best determined angler choice. I compared realized choice results (where I recorded anglers) with stated preferences (what anglers said was most important for site choice). Results are intended to increase understanding of angler behavior for effective fisheries management.

Influences of catch-and-release angling on fish behavior - Alexis Fedele

  • Thesis Defense
  • 04/06/2017

Complex interactions exist between ecological and sociological systems but can be difficult to assess. Newly opened recreational fisheries provide the opportunity to explore direct social effects on naive (i.e., previously unexploited by anglers) population of fish. We examine the influence of angling on wild fish populations, and aim to identify the behavioral outcomes in fish resulting from angling through laboratory experiments. We assessed the short-term (30-d) response of fish populations to recreational angling at two newly opened reservoirs in Nebraska. At one reservoir, we noted declining catch rates in catch-and-release-regulated fish but not in harvest-regulated fish. We hypothesized that caught-and-released fish were given the opportunity to alter behavior, whereas harvested fish were presumably removed from the waterbody after capture with no opportunity to alter behavior. However, this was not observed in both reservoirs, thus further investigation was warranted into the ability of fish to alter behavior to avoid recapture in a controlled environment. In the laboratory, we evaluated whether behavioral types (i.e., bold and shy) in fish affect the ability to learn to avoid subsequent recapture. We observed that both shy and bold individuals had a decreased probability of capture over the seven-day experiment. Bolder individuals exhibited a greater probability of capture across gear types (control, hook, lure) compared to shyer individuals. Ration level appeared to have little influence on the probability of capture. Fish exposed to lures exhibited lower probability of capture than the hook and sham hook treatments across behavioral types. The learned avoidance of capture has strong implications for fishing-induced evolution, efficacy of management regulations, and satisfaction of anglers.

Problematizing socio-scientific issues: An approach to understanding student decision-making using construal level theory - McKinzie Peterson

  • Thesis Defense
  • 03/28/2017

Science literacy refers to the ability to understand and utilize scientific information for personal and societal level decisions. A common recommendation by scientists is to use socio-scientific issues (SSIs) to develop and improve science literacy. Students need structured frameworks to help them learn to navigate and address SSIs. An important step in these frameworks is the problem definition, which can significantly influence solutions proposed by students and their ultimate decisions. Construal Level Theory (CLT), which is a theory that describes the relationship between psychological distance and the extent of abstract and concrete thinking, is one way in which problem definitions can differ. Several studies in CLT suggest differences in how abstract or concrete situations are portrayed to students can significantly change their decisions, perceptions, and use of personal values.

This study explores how CLT is related to decisions and perceptions of 6thgraders (n = 116) on a wind energy SSI and the use of values in decision-making on an undergraduate (n = 73) prairie dog SSI. Mixed/neutral perceptions of wind turbines in the 6thgrade population had higher abstraction scores than those with negative perceptions. In the undergraduate prairie dog study, abstraction is related to values students utilized in their problem statements and criteria during the decision-making process. Teaching implications for this research are discussed.

Heterogeneity of avian breeding habitat on private lands of the Northern Great Plains - Maggi Sliwinski

  • Dissertation Defense
  • 02/17/2017

Most intact rangelands in North America are privately owned and used for beef production. Vegetation heterogeneity is an important habitat component for maintaining biodiversity, but private land may be more homogenous than desired. My research had two major components: 1) to examine whether a variety of grazing strategies created vegetation heterogeneity in a large, intact rangeland, and 2) to understand beef producers' attitudes about vegetation heterogeneity.

First, I sampled vegetation structure, composition, and bird abundance in Cherry County, Nebraska. I examined the relationship of vegetation heterogeneity and bird abundance and communities to management variables. Grazing strategy had few relationships to vegetation structure or bird abundance and communities, but pasture-level management variables were relatively important. Multiple grazing strategies on a landscape did not contribute to vegetation heterogeneity, and vegetation structure and bird communities were more homogenous than expected. Federal land could be used to ensure that heterogeneity exists on the landscape for species that cannot find suitable habitat on private land.

Second, I interviewed 12 beef producers to explore their opinions of heterogeneity, and conducted a mail survey of producers in Nebraska, South Dakota, and North Dakota. Both indicated that beef producers' main concern is sustainable beef production, and this likely contributes to homogenizing the rangeland landscape. My data confirm that producers appreciated wildlife and have positive views toward landscape management. Although fire and prairie dogs might enhance heterogeneity of vegetation, these were negatively viewed because they increased risk to the producer. Producers' responses provided insights on how conservationists should engage them to manage for biodiversity. I recommend engaging producers through Extension educators and hands-on activities.

Causes and Consequences of Landcover Change in Landscapes of Nebraska, USA - Dan Uden

  • Dissertation Defense
  • 01/27/2017

Landcover change is an important global change process with diverse direct and indirect causes and consequences within social-ecological systems. Although substantial uncertainties exist regarding the future of landcover change and its affects, the consideration of past, present, and potential future changes could be useful for learning, assessing, adjusting, and preparing.

I consider case studies of past, present, and future landcover and landcover change in selected landscapes of Nebraska, U.S.A. Specifically, I present species distribution model ensembles for 16 tree species in the Missouri River bluffs of extreme southeast Nebraska, assess functional connectivity of wetland habitats in three central Nebraska landscapes that have experienced varying degrees of human-driven landcover change over the past several centuries, and develop scenario storylines and simulations of future landcover change for the Pine Ridge of extreme northwest Nebraska. Results are useful for increasing understanding about regional landcover changes and for informing ongoing conservation activities.

Integration of Hydrogeophysical Datasets for Improved Water Resource Management in Irrigated Systems - Catie Finkenbiner

  • Thesis Defense
  • 01/07/2017

Water scarcity is predicted to be the major limitation to increasing agronomic outputs to meet future food and fiber demands. With the agricultural sector accounting for 80-90% of all consumptive water use and an average water use efficiency (WUE) of less than 45%, major advances must be made in irrigation water management. Precision agriculture offers the technologies to address and manage for infield variability and incorporate that variability into management decisions. The major limitation to implementing this technology often lies in the management of spatial datasets and the writing of irrigation prescription maps that address variables impacting crop yield and soil moisture. While certain datasets and mapping technologies exist in practice, here I explored the utility of the recently developed cosmic-ray neutron probe (CRNP) which measures soil water content (SWC). The key advantages of CRNPs are the sensor is passive, non-invasive, mobile and soil temperature invariant making data collection more compatible with existing farm operations and extending the mapping period. The objectives of this study were to investigate strategies to: 1) improve the delineation of management zones within a field and 2) estimate spatial soil hydraulic properties (field capacity and wilting point) to make effective irrigation prescriptions. To accomplish this, a series of CRNP SWC surveys were collected in a 53-ha field near Sutherland, Nebraska. The SWC surveys were analyzed using Empirical Orthogonal Functions (EOF) to isolate the underlying spatial structure. I found that measured SWC at field capacity and wilting point were better correlated to CRNP SWC EOF as compared to other commonly used datasets. Based on this work I proposed a sampling strategy for better qualifying soil hydraulic properties. While the proposed strategy will increase overall effort as compared to traditional techniques, rising scrutiny for agricultural water-use may make this technology cost effective.