Physical Sciences and Mathematics Commons^™

Analyzing Ecohydrology Of Subirrigated Meadow, Dry Valley And Upland Dune Ecosystems Using Remote Sensing And In-Situ Estimations In The Semiarid Sand Hills Region Of Nebraska, Usa, Nathan C. Healey

School of Natural Resources: Dissertations, Theses, and Student Research

Nebraska’s dependence upon the High Plains (Ogallala) Aquifer for agricultural production is vital to the state’s economy, ecology and hydrology. The Sand Hills region (58,000 km²) of Nebraska is a unique system of lakes, (~5%) wetlands, (~10%) subirrigated meadows, (~20%) dry valleys and (~65%) upland sand dune ecosystems. Understanding how each of these land cover types reacts to climate conditions of different water limitations is vital to regional water resource management. This research explores the ecohydrological behavior of different land cover types at the Gudmundsen Sand Hills Research Laboratory (GSRL) near Whitman, Nebraska in the heart of the …

Ecophysiological Responses Of Herbaceous Plants To The Presence Or Absence Of Amorpha Canescens In A Nebraska Sandhills Grassland, Jessica L. Milby

School of Natural Resources: Dissertations, Theses, and Student Research

Deeply-rooted shrubs are a common component of grasslands. This study investigated the ecophysiological role of Amorpha canescens, a common leguminous shrub, in Sandhills grassland, and response of herbaceous plants to the presence or absence of A. canescens. Two sites were selected for the study at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska – one with A. canescens (G-L) and one without (G-NL) A. canescens. Plant canopy cover and aboveground biomass were characterized on both sites in June and August 2010. Seasonal trends in net photosynthesis (A), stomatal conductance (gs), transpiration (E), water use efficiency (WUE), and predawn …

Climatic Controls On The Summertime Energy Balance Of A Thermokarst Lake In Northern Alaska: Short-Term, Seasonal, And Interannual Variability, Brittany L. Potter

School of Natural Resources: Dissertations, Theses, and Student Research

Shallow, thermokarst lakes that develop atop permafrost are a prominent landscape feature on the Arctic Coastal Plain (ACP) of northern Alaska. The ACP is vulnerable to ongoing climate change and landscape modification, as thousands of thaw lakes and ponds are impacted by changes in temperature, precipitation, thawing permafrost, and human activity. Although summer in the Arctic is short, incoming solar radiation and lake evaporation are relatively high, and both factors play a significant role in the landscape water balance. Furthermore, lake evaporation is anticipated to increase as the ice-free season lengthens and water temperatures become warmer. To improve our understanding …

Abiotic Stress Responses In Photosynthetic Organisms, Joseph Msanne

School of Natural Resources: Dissertations, Theses, and Student Research

Cellular and molecular aspects of abiotic stress responses in Arabidopsis thaliana subjected to cold, drought, and high salinity and in two photosynthetic green alga, Chlamydomonas reinhardtii and Coccomyxa sp. C-169, subjected to nitrogen deprivation were investigated. Cold, drought, and high salinity can negatively affect plant growth and crop production. The first research aimed at determining the physiological functions of the stress-responsive Arabidopsis thaliana RD29A and RD29B genes. Cold, drought, and salt induced both genes; the promoter of RD29Awas found to be more responsive to drought and cold stresses, whereas the promoter of RD29B was highly responsive to salt stress. …

Habitat Use And Abundance Patterns Of Sandhill Cranes In The Central Platte River Valley, Nebraska, 2003–2010, Todd Joseph Buckley

School of Natural Resources: Dissertations, Theses, and Student Research

The Central Platte River Valley (CPRV) in Nebraska is an important spring stopover area for the midcontinent population of sandhill cranes. Alterations to crop rotation and loss habitat in the CPRV pose a risk to the population. Personnel drove designated routes in the CPRV from 2003–2010 to record the presence of cranes in agricultural fields and estimate abundance. I developed and evaluated models to predict habitat use and flock sizes. Alfalfa was predicted to receive the highest use followed by corn, soybeans, winter wheat, grassland, and shrubland. Use of all habitats and flock size increased as field area increased. Flock …

Avian Influenza In Migratory Birds In The United States, 2007–2009, And Effects Of September Hunting Seasons On Survival, Harvest, And Recovery Rates Of Canada Geese Banded In Southeast Nebraska, Scott R. Groepper

School of Natural Resources: Dissertations, Theses, and Student Research

Highly-pathogenic avian influenza virus (HPAIV H5N1) poses risks to wild birds, poultry, and humans. Personnel with the United States Department of Agriculture-Animal Plant Health Inspection Service-Wildlife Services, state, and tribal wildlife agencies collected 168,940 samples from migratory birds from 2007 to 2009 to test for presence of HPAIV H5N1. No HPAIV was found, but other subtypes were discovered, including H5 and H7. I estimated prevalence of avian influenza virus by flyway and found prevalence was lowest each year in the Atlantic Flyway (6.7%–8.3%), highest in the Pacific Flyway in 2007 (13.3%) and 2008 (13.4%), and highest in the Mississippi Flyway …

Breeding Fidelity And Landscape Effects On Distribution Of Mallards And Duck Broods In The Nebraska Sandhills, Zachary J. Cunningham

School of Natural Resources: Dissertations, Theses, and Student Research

I investigated aspects of mallard (Anas platyrhnchos) breeding ecology in the Nebraska Sandhills during 2007-2008. Previous work in this region suggests that nest success is low for a large area of intact grassland such as the Sandhills. My goal was to conduct a local-scale examination of age distribution and return rates of mallards, and a large-scale examination of brood distribution in the Sandhills region as a whole. This information will help explain factors contributing to the low nest success previously observed, determine relationships between landscape composition and spatial distribution of waterfowl in the Sandhills, and predict productivity and …

Using Slow-Release Permanganate To Remove Tce From A Low Permeable Aquifer At A Former Landfill, Mark D. Christenson

School of Natural Resources: Dissertations, Theses, and Student Research

Past disposal of industrial solvents into unregulated landfills is a significant source of groundwater contamination. In 2009, we began investigating a former unregulated landfill with known trichloroethene (TCE) contamination. Our objective was to pinpoint the location of the plume and treat the TCE using in situ chemical oxidation (ISCO). We accomplished this by using electrical resistivity imaging (ERI) to survey the landfill and map the subsurface lithology. We then used the ERI maps to guide direct push groundwater sampling. A TCE plume (100-600 µg L^-1) was identified in a low permeable silty-clay aquifer (K_h = 0.5 m …

Impact Of Alternative Range Management Systems On Grasslands In The Central Platte River Valley, Nebraska, Luis E. Ramirez

School of Natural Resources: Dissertations, Theses, and Student Research

Land management strategies can directly and indirectly affect plant assemblages and their behavior. Little research has been performed in south central Nebraska to quantify the effect of fire and grazing interactions on species composition, vegetation structure, forage quality, and potential cost associated with land management.

I evaluate the effect of season-long continuous, patch-burning, and rotational grazing approaches on vegetation and ranching costs to determine their value as conservation tools. This study includes data collected between 2007 and 2009 from grasslands in south central Nebraska. I found that land management influence plant assemblages by shifting communities when grazing and/or fire are …

Discontinuities: Predicting Invasions And Extinctions, Aaron Lotz

School of Natural Resources: Dissertations, Theses, and Student Research

In this dissertation, I explore multiple tenets of the textural discontinuity hypothesis, which states that hierarchical landscape structures with scale-specific pattern entrain attributes of animals inhabiting the landscape. Landscapes form hierarchies that are structured by vegetative, geomorphological and contagious disturbance processes. The spatial and temporal patterns inherent in landscapes reflect numerous processes, interacting on distinct scales, which shape the assembly of animal communities. Analysis of body mass patterns and functional group distributions has been suggested as methods to provide insight about these underlying hierarchical processes. Scientists have posited that species at the edges of body mass aggregations may be exposed …

Spatial Accuracy Of Climate Networks In Nebraska, Andrea J. Coop

School of Natural Resources: Dissertations, Theses, and Student Research

Climate data has become increasingly scrutinized for its accuracy because of the need for reliable predictions about climate change. The U.S. has taken great strides to keep up with the demand for accurate climate data. Over the last thirty years, vast improvements to instrumentation, data collection, and station siting have created more accurate data records. This study is to explore the accuracy of existing networks. This study analyzes three climate networks used in Nebraska: the U.S. Historical Climatology Network (HCN), the Automated Weather Data Network (AWDN), and the newest network, the U.S. Climate Reference Network (CRN). Each of these networks …

Late Holocene History Of Dune Activity Along The Elkhorn River In Northeastern Nebraska, Rebecca A. Young

School of Natural Resources: Dissertations, Theses, and Student Research

The Nebraska Sand Hills have been an important study area for dune activation and the nature of prehistoric drought events in the Great Plains. However, little has been done to understand the impact of these droughts to smaller dune fields along the eastern margin of the Great Plains. This study focuses on the Stanton dune field which is found about 145 km east of the Sand Hills along the southern edge of the Elkhorn River valley in northeastern Nebraska. With a wetter and slightly cooler climate regime than that of the Nebraska Sand Hills and most other central Great Plains …

Benthic Macroinvertebrate Response To The Restoration Of A Hypereutrophic Midwestern Reservoir, Jennifer L. Swanson

School of Natural Resources: Dissertations, Theses, and Student Research

Eutrophication has been the most challenging global threat to the quality of our freshwater resources (Likens, 2010). Reversing the effects of eutrophication can be difficult and takes a great deal of time and money. A hypereutrophic Midwestern reservoir underwent a restoration from 2000-2002, which added a sediment basin at the inlet, three islands, five rock jetties, and the removal of rough fish. The primary objective of this study was to determine changes in the benthic macroinvertebrate community in response to the restoration. Water quality and benthic macroinvertebrate samples were collected once per month in June, July, August, and September in …

Natural Selection And Age-Related Variation In Morphology Of A Colonial Bird, Mary Bomberger Brown

School of Natural Resources: Dissertations, Theses, and Student Research

In May 1996, inclement weather led to the deaths of thousands of Cliff Swallows (Petrochelidon pyrrhonota) in Nebraska. Survivors had larger skeletons, shorter wings and tails, and less wing asymmetry than non-survivors. This population was followed for 10 years to study 1) whether natural selection events result in permanent microevolutionary changes, 2) if variation in climate affects the development of morphological traits, and 3) if morphological traits vary systematically with age.

Patterns in morphology exhibited by swallows following the selection event were studied by measuring yearling birds. Wing and middle tail lengths decreased, beak length and width increased, …

Quantifying Evapotranspiration And Water Table Interactions In Regions Of Shallow Groundwater: Sensitivity To Soil Properties, Vegetation, And Climate Variability, Mehmet E. Soylu

School of Natural Resources: Dissertations, Theses, and Student Research

Evapotranspiration (ET) is an important component of the water and energy balance, yet it is also one of the most challenging components to estimate. There has been great effort to understand the nature of controlling mechanisms and interactions between ET and other earth system processes. The controlling factors of ET can be grouped into two broad categories – namely moisture availability and energy availability (e.g., solar radiation). Soil moisture is a key factor that most of the land surface hydrologic processes are dependent on. While plant water use is mainly controlled by radiation, temperature is another key factor for ET …

Morphological Variation Between Juvenile White Bass And Juvenile Hybrid Striped Bass, Ryan W. Lueckenhoff

School of Natural Resources: Dissertations, Theses, and Student Research

While identifying recruitment bottlenecks for white bass Morone chrysops, we encountered difficulty distinguishing between age-0 white bass and age-0 hybrid striped bass M. saxatilis x chrysops. Accurate identification of juvenile white bass and hybrid striped bass will improve the quality of data gathered for research and monitoring efforts. The first objective of this study was to estimate biologists’ accuracy identifying juvenile white bass and juvenile hybrid striped bass, and to determine which characteristics biologists were using during identification. Overall, identification accuracy was 71%. Biologists who placed less emphasis using the characteristic "broken horizontal lines" or who examined >99 …

Applications And Challenges For Adaptive Management, Jamie E. Mcfadden

School of Natural Resources: Dissertations, Theses, and Student Research

Adaptive management is becoming an increasingly popular management-decision tool within the scientific community. The application of adaptive management is appropriate for complicated natural-resources management problems high in uncertainty. Two primary schools of thought have developed that may yield varying levels of success as they primarily differ in stakeholder involvement and model complexity. I evaluated peer-reviewed literature that incorporated adaptive management to identify components of successful adaptive management plans and to make comparisons between the two schools of thought. Identifying the elements of successful adaptive management is advantageous to natural-resources managers, such as those managing the Platte River, Nebraska. The Platte …

Formation, Adsorption, And Degradation Of N-Nitrosoatrazine In Water And Soil, Hsin-Ro Wei

School of Natural Resources: Dissertations, Theses, and Student Research

The products of xenobiotic reactions in environmental mammalian systems may pose risks equal to or greater than parent compounds. Products of concern include nitrosamines, which can be carcinogenic, mutagenic, and teratogenic. Nitrosamines may form in soil, lake water, and sewage; they also can form in agricultural soils treated with agrichemicals containing amine moieties and nitrogen fertilizer. The nitrosamine-forming reaction of amines with nitrite is promoted at acidic pH. The widely used herbicide atrazine has secondary amine groups that can react with nitrite to form N-nitrosoatrazine (NNAT). The primary objective of this research was to characterize the formation, stability, and …

Ecology And Management Of Channel Catfish Ictalurus Punctatus And Flathead Catfish Pylodictis Olivaris Populations In The Missouri River, Ne, Cameron Wesley Goble

School of Natural Resources: Dissertations, Theses, and Student Research

Channel catfish Ictalurus punctatus and flathead catfish Pylodictis olivaris are two of the most important freshwater recreational or commercial species in the United States. Catfish populations in the Missouri River are important resources to the people of Nebraska and surrounding states. The objective of my study was to determine the present status of catfish populations in the Missouri River, Nebraska. Specifically I evaluated population characteristics such as relative abundance, population size and density, size structure, condition, age structure, growth, and mortality. I used a stratified random sampling design and generalized linear mixed modeling approach to assess differences in population characteristics …

River Otter (Lontra Canadensis) Use Of Phragmites Australis And Density Estimation Using Genetic Techniques, Amy R. Williams

School of Natural Resources: Dissertations, Theses, and Student Research

River otters were extirpated in Nebraska in the early 1900’s. In 1986 Nebraska Game and Parks Commission began reintroducing otters. In support of developing an otter management plan, I conducted research on two aspects of otter ecology in Nebraska. First, I examined otter use of habitats dominated by the non–native aquatic plant, Phragmites australis, in the Big Bend reach of the Platte River. Sixteen otters were trapped, radio–tagged, and tracked between 2006 and 2009. I identified 517 den/resting locations, 127 of which were unique locations. I compared den/resting site habitat use to availability to determine if otters were using …