Dissertations & Theses in Natural Resources

Amphibian Occupancy and Functional Connectivity of Restored Wetlands in the Missouri River Floodplain

Michelle L. Hellman — Mon, 29 Apr 2013 06:50:56 PDT

Wetland decline may threaten many taxa including shorebirds, amphibians, and fish. As agencies increase restoration of wetland habitat, monitoring is crucial to inform the process. Permeable skin sensitive to water quality and biphasic life histories requiring both terrestrial and aquatic habitat make amphibians good indicators of wetland health. I modeled amphibian occupancy in restored Missouri River bends to determine habitat characteristics associated with the presence of amphibians.

Occupancy modeling acknowledges imperfect detection and allows the inclusion of detection covariates. To assess detection I examined two methods currently used to assess anuran occupancy in wetlands, aural anuran surveys and tadpole dip-netting. I assessed survey and site-specific factors that may influence detection success of anuran species using these two methods and found that water temperature appears to play a role in aural detection of some species during call surveys. Slope impacts detection of tadpoles and may be indicative of a sampling bias.

I incorporated the top detection models into my candidate models testing the effect of habitat characteristics on amphibian occupancy. My results indicate that the slope of a wetland is driving occupancy of many species at the research sites. In most cases slope had a negative impact on occupancy. Landscape characteristics, like connectivity of wetlands, facilitate between-patch dispersal and may be just as important to the local persistence of amphibians. I assessed connectivity for anurans of wetlands within a bend and recommend locations for new restorations that can improve connectivity of the bend. I found that average connectivity of a bend may not be the best indicator of functional connectivity. All of the research bends had clusters of wetlands that were highly connected to one another but relatively unconnected to the rest of the complex.

I suggest that future site selection should focus on shallow, gently sloping wetlands and that a few well-placed restorations could increase functional connectivity of the complex and improve the resilience of amphibian populations to droughts, floods, and localized disturbances like land-use changes.

Advisor: Craig Allen

Assessment of Tillage Practices Using Landsat-TM 5 in Nebraska.

Sonisa Sharma — Mon, 22 Apr 2013 09:31:05 PDT

Tillage management practices are an important component to crop production and to federal and state conservation efforts and crop subsidy programs. Crop residue created by conservation tillage reduces soil erosion and reduce evaporation from exposed soil. Agro-hydrological models require information on tillage practices to estimate their impacts on soil-water-holding capacity, total evapotranspiration, carbon sequestration, water runoff and water and wind erosion for agricultural lands. Classification of tillage practices using remote sensing offers promise for the rapid collection of tillage information on individual fields over large areas. Using satellite imagery proves to be challenging due to the similarity in spectral signatures for soils and crop residues and the typically broad spectral bands used by moderate resolution satellites needed to cover large areas and with frequent revisit time. In this study, Landsat 5 images from Path 29, Row 32 in years 2008 and 2009 acquired over southeastern Nebraska (NE) were used to discriminate tillage practices using a Quadratic Discriminant Analysis (QDA). Ground truth data regarding the presence or absence of no-till practices were collected by the US Department of Agriculture–Natural Resources and Conservation Service (USDA–NRCS) at 31 locations in Adams and Fillmore Counties. Results indicated that Landsat‑TM bands 1, 3, 4, 5 and 7 classified 75-91% correctly for no-till and 20-55% for till in March and May of 2008 and 2009 respectively. Similarly, the Landsat based tillage indices such as simple tillage index, and the normalized difference tillage index and Normalized difference of Bands 1 and 5 discriminated tillage practices in March and May of 2008 and 2009 images with 81-91% for no-till and 60%, 12-26% for till respectively. When prediction was performed using training model May 2009, there was 81% classification accuracy under no-till and 24 % under till for May 2008 image. The QDA approach with Landsat 5 data appears to be efficient and effective in classifying tillage practices over large areas.

Adviser: Ayse Kilic

Building Upon Common-Pool Resource Theory to Explore Success in Transitioning Water Management Institutions

Christina M. Hoffman — Thu, 11 Apr 2013 13:01:20 PDT

Nebraska, like many regions around the world, is faced with the challenge of adapting to a new era in water management. Increasing demands for water resources, mounting concerns over threatened and endangered species, and obligations to abide by interstate water allocation agreements have motivated Nebraska to revisit traditional water management approaches. However, although Nebraska’s water management institutions have undergone much change, little research exists on the influence these changes have had on the ability of water institutions to successfully manage water allocations. This research (1) qualitatively explores the perspectives and experiences of stakeholders in the overappropriated region of the Platte River Basin (PRB), Nebraska, to gain an in-depth understanding of how the current water management system is working, (2) develops and implements a survey instrument to quantitatively measure and assess how well the newly devised management system is working as seen by water users in the PRB, (3) generates a comprehensive assessment into the characteristics that either promote or impede successful water management within the basin, and (4) uses Nebraska’s complex water resource governance system to build upon established principles of successful common-pool resource governance. This research provides information necessary to continue to improve management efforts within the basin and throughout the State, and serves as a fundamental baseline assessment from which to measure improvements moving forward. Improving resource managers’ ability to learn about and better understand the implications of management approaches and policies can lead to more successful water resource institutions.

Advisors: Sandra B. Zellmer and Ann Bleed

Winter Ecology of Sandhill Cranes (Grus canandensis) in Northern Mexico

Ingrid Barcelo — Fri, 11 Jan 2013 12:35:52 PST

Sandhill Cranes (Grus canadensis) are a widespread species in North America and one of the most studied cranes in the world. However, most of the research has focused on the breeding grounds of Canada and Alaska and the staging grounds of Nebraska. Although an important proportion of the Mid-continent Population of Sandhill Cranes winters in northern Mexico, little information exists on distribution, status, and ecology of the species in Mexico. The goal of this dissertation was to provide new information on Sandhill Crane winter ecology from a regional perspective to better understand population trends. I examined the physiological state of Sandhill Cranes in wild conditions by quantifying the effects of environmental factors on stress levels. My data suggests that access to water resources is the main factor affecting corticosterone levels of cranes. I validated a method to measure glucocorticoid metabolites in fecal samples using an affordable and commercially available enzyme immunoassay. I demonstrated that the use of an enzyme immunoassay provides accurate measurements of steroid metabolite concentrations comparable to the traditional radioimmunoassay. I examined winter diet of Sandhill Cranes and investigated if the species exhibits a specialized or generalized diet in Mexico. I also explored the ecological response of the species to low food availability conditions. According to my results, cranes exhibit a specialized diet of corn during winter as patterns of consumption did not vary with corn availability. Cranes responded to low food availability by moving geographically to a location where corn was available instead of shifting diets. Finally, I included a human dimensions perspective to document the attitudes of rural inhabitants towards Sandhill Cranes. I investigated if crop consumption by cranes represented a problem for Mexican farmers in the wintering grounds. The results of my interviews indicate that Mexican farmers are not affected by the arrival of cranes and do not consider the species to be a problem.

Effects of Length Limits on Sexually Size Dimorphic Fishes

Peter J. Spirk — Fri, 07 Dec 2012 08:56:04 PST

Length limits are used by fishery managers as a method to alter size structure of fish populations. Unfortunately, biological differences between fish sexes (i.e., sexual-size dimorphism) may lead to sex-specific rates of recruitment, growth, and mortality. The addition of angler harvest to most aquatic systems likely accentuates differences in sex-specific rates by selectively harvesting the fastest-growing and largest fish from a population. The first objective of this study was to document the extent of sexual-size dimorphism for white bass and walleye at a Nebraska reservoir. Growth rates were similar between male and female white bass although male white bass were consistently shorter than their female counterparts at a given age. Male walleye grew slower and were consistently shorter than their female counterparts at a given age. The second objective was to document the size, sex, and age of white crappie, white bass and walleye harvested in two Nebraska reservoirs. Harvest was female biased for both white crappie and white bass, whereas harvest was similar for both male and female walleye. The third objective was to determine if size-, sex- or age-selective harvest was occurring for white bass and walleye at a Nebraska reservoir. Anglers harvested female white bass at a greater proportion than was sampled during NGPC annual population surveys. Anglers at Sherman Reservoir did selectively harvest walleye based on size, although in contrast to the white bass population, sex-selective harvest was not apparent for walleye. The final objective was to provide a model that predicts possible outcomes from using different length limits for sexually size dimorphic fishes. Although there was a noticeable difference in the number of fish in a population for each length limit, the pressure applied to the population by catch-and-release mortality kept the sex ratio close to a 1:1.

Advisor: Kevin L. Pope

The Use of Tree Rings to Study the Impacts of Stream Flow and Climate Variability on Native and Invasive Woody Species along a Semi-Arid Riparian Ecosystem in the Great Plains, USA.

Kristen M. Skolaut — Tue, 04 Dec 2012 14:21:00 PST

Forested riparian areas of the Northern Great Plains have historically been dominated by the native Populus deltoides L. vegetation type. Changes in climate, stream flow, groundwater, and management practices in the past few decades have promoted the expansion of the upland native woody species Juniperus virginiana L. and the invasion of the non-native Elaeagnus angustifolia L. into these riparian ecosystems. This study aims at using dendrochronology, or the study of tree rings, to assess the impacts of intra- and inter- annual climatic variability and stream flow over the past decades, on the annual tree ring growth, oxygen and carbon isotopic signatures, and performance of native and invasive woody species in a riparian ecosystem along the Republican River in Nebraska.

Tree ring analysis showed that P. deltoides and J. virginiana growth displayed a greater dependency on climatic factors than E. angustifolia. Populus deltoides growth was significantly dependent on previous year summer temperatures, and on annual stream flow, and Juniperus virginiana growth showed a significant dependency on the previous growing-season precipitation and on annual stream flow. On the other hand, E. angustifolia growth was negatively correlated with annual stream flow and the species displayed the least growth response to climate variability.

Oxygen and carbon isotopic ratios (δ¹³O and δ¹⁸C, respectively) of tree rings indicated that water use efficiency (WUE) in J. virginiana was significantly greater and showed the most response (i.e., increased) under stressful environmental conditions compared to the other two species. Water use efficiency in P. deltoides showed little dependency on climate variability and/or water availability. Results show that the three species followed different strategies to co-op with environmental stresses. The significance of these results and their consequence on the ecology of the ecosystem will be discussed.

Advisor: Tala Awada

Population Characteristics, Development of a Predictive Population Viability Model, and Catch Dynamics for Pallid Sturgeon in the Lower Missouri River

Kirk D. Steffensen — Thu, 29 Nov 2012 12:21:25 PST

Population characteristics and long-term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. As recovery efforts continue, understanding and quantifying these characteristics and trends are critical for species recovery and future management decisions. Therefore, the objectives of this study were to determine the pallid sturgeon population characteristics, predict changes to the pallid sturgeon population based on different management and life history scenarios, and examine trot line catch dynamics in the lower Missouri River. Catch rates for pallid sturgeon collected with gill nets did not significantly change while catch rates using trot lines significantly declined for wild pallid sturgeon (P=0.0001) but did not differ among years for hatchery-reared fish (P=0.0610). The proportion of reproductively ready females to non-reproductively ready females was 1:2.0, compared to the male ratio of 1:0.9. The minimum female length-at-maturity was 788 mm and 798 mm for males while the minimum age-at-maturity for known aged hatchery-reared fish was age-9 for females and age-7 for males. The mean relative fecundity was 7%. Our population viability model was most sensitive to ≥age-1 survival rates. Fluctuating female spawning frequency by one year had minimal effect on the overall population growth and age-at-maturity was less sensitive than spawning frequency. Catch per unit effort was 14.6 fish per trot line rigged with hook timers to study the catch dynamics; however, several hook timers were activated but did not capture a fish. Therefore, the corrected CPUE was 17.7 fish per line with over half of the hook timer activations occurring 4-h post-deployment. Detecting shifts in population characteristics is essential for understanding population dynamics as hatchery inputs and natural perturbations continue to change the population structure. Barring any unforeseen natural catastrophes, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be a far from viable nor self-sustaining.

Advisor: Mark A. Pegg

STOPOVER DECISIONS OF MIGRATORY SHOREBIRDS: AN ASSESSMENT OF HABITAT USE, FOOD AVAILABILITY, BEHAVIOR AND PHENOLOGY

Ryan Stutzman — Thu, 29 Nov 2012 06:55:52 PST

Habitat loss and alteration from land use change, species invasion, and more recently, climate change has reduced biodiversity and ecosystem function worldwide. Habitat decisions have important implications to individual fitness as well as population dynamics and community structure. Resource limitation, predation, competition, and unfavorable abiotic conditions all have the potential to influence survival and future reproductive potential. Understanding how changes to ecosystem structure and function impact species and populations of conservation concern is essential for conservation delivery to be effective. Similar to many migratory species, shorebird populations are declining worldwide and declines may be related to the loss of important stopover habitat in the form of mid-continental wetlands.

During 2010-2011, I examined how long-distance migratory shorebirds have responded to extensive, agriculturally-driven, alterations to wetland habitats. I focused on a suite of ecological conditions that are expected to influence migrant fitness including habitat preference, resource availability and behavior. Additionally, because land use change is expected to act in conjunction with climate change to alter wetland habitats, I examined a number of phenologic variables and made predictions on how migrants might be affected in the future.

Migrant shorebirds were more likely to use highly-altered, agricultural wetlands than wetlands embedded in native grasslands and did so in greater numbers. Preference for altered habitat was unexpected because these habitats had lower food availability, but preference may be explained by the role of mud flat as an influential cue, which would increase the attractiveness of agricultural wetlands. Such a scenario can be indicative of an ecological trap, where individuals prefer lower quality habitat. However, behavioral analysis indicates that migrants have adapted to using novel habitats through increased foraging efficiency. Despite their apparent adaptability to changing conditions, migrant shorebirds may be susceptible to further population decline as a result of changes in phenology brought about by climate change. Results show that peak migration is correlated with the availability of food resources. Given that shorebirds already prefer habitat with lower resource availability, any changes to invertebrate or migration phenology that is not congruent in magnitude and direction to the other could affect migrant populations.

Advisor: Joseph J. Fontaine

Assessing Local and Landscape Constraints on Habitat Management for Grassland and Upland Birds

Christopher F. Jorgensen — Wed, 21 Nov 2012 11:46:05 PST

Species-habitat relationships are a central tenant to ecological theory and are critical in species management. Yet, despite a long-standing tradition of utilizing species-habitat relationships in both theoretical and applied ecology, there remains to be no clear predictors of how species relate to habitat. In order to further our understanding of the habitat selection process, we must begin to comprehend what spatial scales species form habitat decisions and what potential behavioral or life-history predictors underlie the scale of habitat decisions. During 2010-2012, I conducted point counts for grassland birds across Nebraska and assessed habitat relationships over multiple spatial scales to construct predictive species distribution models. Results indicated that landscape scale habitat variables drastically constrained or, alternatively, facilitated the positive effects of local land management for Ring-necked Pheasants. Hierarchical theory suggests that ecological processes function concurrently over multiple spatial scales and not all scales may be appropriate in determining species occurrence. I predicted that the spatial scale in which a species forms habitat decisions would correlate with body size, a predictor of life-history expression, if the scale is a function of how the species interacts with its environment. I tested this hypothesis on 10 obligate grassland bird species in Nebraska, USA. For seven species, I found evidence of a characteristic habitat selection scale, but no relationship to body mass. To quantify local habitat quality, a predictor of species occurrence, I assessed the precision of five methods of measuring plant structure using ground-based imagery and processing techniques. I recorded standing herbaceous cover using digital imagery at two locations in a mixed-grass prairie. I compared the precision of the digital imagery vegetation analysis (DIVA) methods and quantified variability within each technique using the coefficient of variation. Vertical herbaceous cover estimates varied among DIVA techniques but the precision of four of the five techniques was consistently high. Overall, DIVA techniques are sufficient for measuring standing herbaceous cover and can adequately reduce measurement error associated with multiple observers.

Advisor: Joseph J. Fontaine

Using Landscape Pattern Metrics to Characterize Ecoregions

Martha Isabel Posada Posada — Mon, 12 Nov 2012 07:00:56 PST

Ecological regions, or ecoregions, are areas that exhibit “relative homogeneity in ecosystems”. The principal objective of this research was to determine if and how landscape structure (quantified by landscape pattern metrics) may be related to ecoregions defined using Omernik’s approach to ecoregionalization. Nine key landscape pattern metrics (number or LULC classes and the proportion of each class, number of patches, mean patch size and area-weighted fractal dimension, perimeter-area fractal dimension, contagion, mean Euclidean nearest neighbor distance and interspersion and juxtaposition index) where used to asses landscape structure in a sample of 26 Omernik Level III ecoregions located in the central United States. The results indicated that the behavior of most of the metrics (such as Number of Patches, Mean Patch Size, Mean Euclidean Nearest Neighbor, and Contagion) could only be explained when they were considered in context with the other metrics. There were significant correlations among several of the metrics used, reasserting the redundancy of information provided by some of these indices.

Adviser: James Merchant

Interactions of Zooplankton and Phytoplankton with Cyanobacteria

Rebecca Alexander — Wed, 17 Oct 2012 14:06:39 PDT

Cyanobacteria are a major concern in Nebraska reservoirs and are capable of producing toxins that can cause skin irritations and gastrointestinal problems, as well as affect the nervous system. It is important to determine the mechanisms that can cause cyanobacteria blooms due to the effect they can have on human health. The interaction of zooplankton and other phytoplankton groups with cyanobacteria is important because there is a biological component in surface waters that should be taken into consideration along with the physical and chemical parameters that have been noted to promote cyanobacteria. For example, zooplankton have the ability to alter the phytoplankton composition through their grazing and previous research has shown that cyanobacteria can have diverse effects on different zooplankton, which could promote and perpetuate cyanobacteria. Weekly samples were collected from six Nebraska reservoirs and analyzed to determine the interactions of zooplankton and phytoplankton with cyanobacteria using two generalized additive models with cyanobacteria relative percentage or cyanobacteria biovolume as explanatory variables. In most cases, cyanobacteria relative percentage and biovolume had similar effects on phytoplankton and zooplankton groups with little difference in the predicted biovolume/biomass or density. Chemical and physical data collected from the reservoirs were analyzed with spearman rank correlations to determine their relationships with cyanobacteria biovolume. Including biological, chemical and physical parameters to ascertain the interactions and relationships with cyanobacteria can help establish grounds for management techniques, such as biomanipulation. Biomanipulation can prove to have positive results in surface waters, but further research is needed to determine its effectiveness in Nebraska reservoirs. This study provides the first steps in helping to establish its possible effectiveness by determining the interactions of zooplankton and phytoplankton with cyanobacteria in reservoirs.

Adviser: Kyle D. Hoagland

IMPACTS OF CLIMATE CHANGE ON THE SURFACE WATER BALANCE OF THE CENTRAL UNITED STATES, 1984-2007

Bo Dong — Thu, 11 Oct 2012 13:30:55 PDT

The climate system and the hydrologic cycle are strongly connected with each other. Understanding the interactions between these two systems is important, since variations in climate can trigger extensive changes in the hydrologic cycle, with significant impacts on agriculture, ecosystems, and society. Observations over the central U.S. in recent decades show numerous changes in climatic variables. This includes decreases in cloud cover and wind speed, increases in air temperature, and seasonal shifts in precipitation rate and rain/snow fraction. To assess the impacts of these variations in climate on the regional water cycle, a terrestrial ecosystem/land surface hydrologic model (Agro-IBIS) is employed in this study, forced by observed climatic inputs for the period 1984-2007. The results generally show an acceleration of the water cycle in the Upper Mississippi, Missouri, Ohio, and Great Lakes basins, but with significant seasonal and spatial complexity. Over the past 24 years, evapotranspiration has increased in most regions and most seasons, particularly during the fall, which is also a time of pronounced solar brightening. Trends in runoff are characterized by distinct spatial and seasonal variations. Since recent warming has led to a greater fraction of winter precipitation falling as rain rather than snow, spring runoff in some snow-dominated regions (such as the northern Great Lakes) has declined significantly since 1984. Other regions, however, such as the northern Missouri basin, show large increases in runoff throughout all seasons, primarily as a result of increased precipitation. Sensitivity experiments show that the water balance is most linearly sensitive to solar radiation and relative humidity, followed by precipitation, air temperature and wind speed. Because of the interdependencies among the climate factors, the hydrological responses of climate change are highly non-linear. Seasonal hydrological responses are notably dependent on regional water and energy availability, and are affected by seasonal conditions of soil moisture and snow cover. Furthermore, precipitation is characterized as the predominant factor that affects the decadal scale hydroclimatic changes in the central U.S..

Adviser: John D. Lenters

CHANNEL CATFISH POPULATION DYNAMICS, ABUNDANCE ESTIMATES, AND SHORT-TERM TRENDS IN THE PLATTE RIVER, NEBRASKA

Aaron J. Blank — Thu, 02 Aug 2012 06:12:35 PDT

Fishing for channel catfish (Ictalurus punctatus) is popular in Nebraska and channel catfish are the most sought after fish species in the Platte River. Anglers on the Platte River are also harvest oriented. Little is known about the effects anglers have on channel catfish population dynamics in the lower Platte River. The goal of this study was to determine if there were effects of angling on channel catfish at two high use fishing areas in the lower Platte River. My first objective was to evaluate differences in relative abundance, size structure, condition, age structure, growth, and mortality between two high use areas (near Fremont and Louisville, NE). I also used a robust design capture-mark-recapture study to estimate density and abundance of channel catfish > 200 mm within a 10-km stretch of the Platte River at each sampling site. The second objective was to assess the 5 year standardized monitoring data for spatial and temporal differences in relative abundance, size structure, condition, age structure, growth, and mortality across two river reaches and three river segments. Channel catfish at Fremont displayed lower size structure, slower growth, and were more abundant compared to channel catfish at Louisville. Population characteristics displayed considerable variation throughout the Platte River in the last five years. However, channel catfish sampled between the Loup River Power Canal and the Elkhorn River confluence were more abundant, grew slower, and had a lower size structure compared to channel catfish above and below that segment. Key factors influencing differences in channel catfish population characteristics may be due to hydrology (e.g., flow modifications caused by the Loup River Power Canal, irrigation withdrawals, and precipitation amounts) and the resulting changes to other abiotic factors (e.g., water temperature extremes, ice flow), angler exploitation, predation, habitat characteristics, and tributary inflows.

Adviser: Mark A. Pegg

Modeling Field-Scale Vulnerability to Pesticide Runoff

Atefeh Hosseini — Mon, 30 Jul 2012 10:31:49 PDT

Identifying areas vulnerable to off-site agrichemical movement and surface and ground water contamination through conventional data collection is labor-intensive, costly and time-consuming. To promote efficient pesticide use and protect water resources, a process-based index model was previously developed to estimate landscape vulnerability to pesticide runoff and leaching at a watershed or regional scale using Soil Survey Geographic (SSURGO) data. Because mitigation of contamination requires implementation of best management practices, the model was adapted to the field scale. The field-scale model was developed based on a Digital Elevation Model (DEM) with 5 ´ 5 m resolution for a research site in Boone County, Missouri. The model uses inputs and functions associated with hydrologic and pesticide dissipation processes. These include saturated hydraulic conductivity of the soil, pH, organic matter, clay content, clay mineralogy, slope, unfilled pore volume above a restrictive layer, and soil moisture content along with pesticide adsorption intensity, relative persistence, and susceptibility to abiotic hydrolysis. Input data were obtained from field measurements, Agricultural Policy/Environmental eXtender (APEX) model soil moisture output, the Soil Survey Geographic (SSURGO) database (flooding frequency class), and pesticide property references. The hydrologic component of the model was converted to a dynamic function using APEX estimates of soil moisture and the model was coded into the ESRI^TM (Environmental Systems Research Institute, Inc., Redlands, CA) ArcGIS (10.0) Model Builder. Sensitivity analyses were performed to assess the weighting of the restrictive layer modifier of the Index Surface Runoff (ISRO) function and to evaluate the hydrolysis time frame. Model estimates of atrazine remaining in the field (assuming no previous runoff or leaching losses) were significantly related to measurements of atrazine in runoff made at the field outlet for odd (corn) years from 1993 to 2001. However, estimates of remaining pesticide exceeded field measurements. The model can be used to identify vulnerable areas within agricultural fields and target sites for implementation of best management practices (BMPs) and regulatory strategies to effectively address water quality issues.

Advisor: Patrick J. Shea

Characterization of the Stream-Aquifer Hydrologic Connection in the Elkhorn River Basin

Zhaowei Wang — Mon, 30 Jul 2012 09:18:30 PDT

In this study, the hydrologic relationship between the Elkhorn River and the surrounding aquifer at eight study sites were studied. The calculated hydraulic gradient showed that the adjacent aquifer recharges the Elkhorn River all year. Reversed gradient was only found at Atkinson site during pumping seasons from 2008 to 2010. Geoprobe log data and in-situ permeameter test data were combined to calculate the equivalent hydraulic conductivity (K) and unit-length streambed conductance (C) at eight sites, where the greatest values were found at Neligh and the lowest values found at Hadar. Accordingly, the result of cross correlation analysis on the lag effect between stream stage and groundwater level was consistent with the indication of K and C.

A geological model of multimillion grids was built based on well log data of test holes and registered wells using IDW interpolation method. The grids were grouped into eight hydrofacies and their corresponding hydraulic conductivity values were assigned based on empirical value from books and former studies in this area. Then the geological model was upscaled to three aquifer units by coarser grid using an averaging technique (Li, 1999) and bound method (Cardwell, 1945).

A groundwater flow model (ULEN) was also built using MODFLOW to calculate the stream depletion ratio at Neligh and Hadar site based on the hydrostratigraphic model. A hypothetical well was created and pumped water at a rate of 1000 GPM under three scenarios in June, July and August: the well is located from the river at 1000 ft, 1 mile and 3 miles. The modeling results are consistent with the data analysis which showed that the stream depletion ratio is more pronounced at Neligh than Hadar.

Advisor: Xun-Hong Chen

Role of the Leguminous Shrub Amorpha canescens (Leadplant) in the Nebraska Sandhills Grasslands: Water Relations and Patterns of Water Uptake

Adam Yarina — Mon, 30 Jul 2012 09:18:28 PDT

This study investigated the ecophysiological role of Amorpha canescens, a leguminous shrub native to the Nebraska Sandhills. Although A. canescens is an important ecological player in the Sandhills, its impacts on the surrounding plant community are poorly understood. To remedy this, two sites were selected for study at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska – one with A. canescens (G-L) and one without A. canescens (G-NL). Both sites contained five representative herbaceous species: two C₃ grasses (Hesperostipa comata and Koeleria macrantha), two C₄ grasses (Andropogon hallii and Calamovilfa longifolia), and one forb (Helianthus pauciflorus). Plant canopy cover and aboveground biomass were characterized on both sites in June and August 2010, along with soil composition, organic matter, carbon, and nitrogen content. Seasonal trends in transpiration (E), water use efficiency (WUE), and predawn (Ψ_pre) and midday (Ψ_mid) water potentials were determined for all species in both plots at 2-week intervals from June through September. Precipitation, groundwater, plant root crown, and soil water samples were collected to determine sources of plant water uptake via stable isotope analysis and the IsoSource mixing model. The results indicate that the presence of A. canescens is favorable to C₃ grasses when water is plentiful. However, under water limited conditions, the additional demands on shallow soil water coupled with increased rainfall interception from shrub canopy and litter were disadvantageous to C₃ grasses. A. canescens also appeared to enhance the amount of water available deeper in the soil profile, resulting in greater overall moisture in the upper 1 m of soil. Water resource partitioning was not observed during the wetter periods in the first half of the study period, with all species predominantly using shallow soil water. However, H. pauciflorus and A. canescens switched to deeper water sources as water became limited, while C₃ and C₄ grasses senesced or reduced stomatal conductance to limit water loss. The ecological implications of these results are discussed.

Advisor: Tala Awada

Interactions Among Evaporation, Ice Cover, and Water Temperature on Lake Superior: Decadal, Interannual, and Seasonal Variability

Katherine Van Cleave — Mon, 30 Jul 2012 08:41:38 PDT

Lake Superior, the largest freshwater lake in the world by surface area, has enormous impacts on the regional weather and climate. The lake also comprises over half of the total water volume in the Great Lakes system and is an important resource for commercial shipping, water supplies, hydropower, recreation, and aquatic ecosystems. Water temperature and evaporation on Lake Superior have been found to be increasing in recent decades, while ice cover has been decreasing at a very rapid pace. A careful analysis of the long-term trends, however, shows that these changes have not been linear through time. Rather, a step-change occurred in 1997/98 that resulted in a drop in ice duration of nearly 40 days, a 3°C increase in summer water temperature, and a near doubling of July-August evaporation rates. Linear regression analysis of data on either side of this step change shows trends which are largely insignificant and even opposite in sign from those of the step change. Using time-lagged correlation and composite analysis, interactions among ice cover, water temperature, and evaporation are explored across seasonal and interannual timescales. Fall evaporation rates are found to be significantly correlated with ice cover in the following winter, presumably as a result of strong latent heat flux leading to rapid ice onset and growth. Similarly, ice cover is found to be a strong determinant of summer water temperature. This, in turn, can lead to changes in late-summer evaporation rates. Quantifying these complex interactions is important for assessing the potential impacts of future climate change on large-lake systems. Key to this understanding is the direct measurement of lake surface processes such as evaporation and sensible heat flux. As such, this study includes an analysis of the first direct observations of nearshore evaporation rates on the Great Lakes, using eddy covariance data collected from a monitoring station on Granite Island (near Marquette, Michigan). The data are analyzed for the period October 2010 to April 2012 to explore the seasonal and interannual variations in latent and sensible heat fluxes over Lake Superior, as well as some of the primary climatic factors driving this variability.

Adviser: John D. Lenters

A Climatological Analysis of the Warm-Season Wind Regimes of the Beaufort/Chukchi Seas Coasts

William J. Baule — Fri, 27 Jul 2012 08:10:18 PDT

Climate records for wind speed, wind direction, and temperature are analyzed for the period from 1979-2009 for the Beaufort/Chukchi Seas region of the Arctic. Wind records have historically been subject to far fewer analyses than other meteorological variables, such as temperature or precipitation. This is particularly true for data sparse regions. Data were collected for a large area in the Beaufort/Chukchi Seas region, which includes portions of Russia, the United States, and Canada. Data from 250 stations were collected from a variety of networks throughout the region and uniformly quality controlled. Eight long-term stations were identified for data completeness and length of record. Climatologies were developed for these eight stations for wind speed, wind direction, and temperature for the period from 1979-2009. Trends in monthly and annual wind speed and temperature were examined. Results from the climatologies and trend tests were then compared to gridded output from the North American Regional Reanalysis (NARR). Using a combination of data sets, a case study focusing on warm-season seas breezes in a smaller study area was performed for 2009. Climatologies show an Arctic climate with clear distinctions between coastal and interior locations for the variables analyzed and strong seasonal characteristics. Strong warming was evident at all locations, particularly in the late warm-season/early cold-season. Negative wind speed trends were observed at several locations, though seasonality was less evident. Biases in NARR were noted for variables analyzed. Trends in NARR temperature compared well with observations in sign and magnitude. Wind speed trends were not well represented. Further investigations into physical mechanism behind wind speed trends and differences in reanalysis are required. Sea breezes were found to occur around Deadhorse, Alaska in the summer of 2009. Frequency was highest in June (43% of days) decreasing through the warm season (26% of days). Direction and inland penetration of sea breezes appears to be related to the strength of the temperature gradient over the region.

Advisor: Martha D. Shulski

Agricultural Landuse Change Impacts on Bioenergy Production, Avifauna, and Water Use in Nebraska's Rainwater Basin

Daniel R. Uden — Tue, 24 Jul 2012 07:35:37 PDT

Agriculture is an economically important form of landuse in the North American Great Plains. Since 19^th Century European settlement, conversion of grasslands to rowcrops has increased food and bioenergy production, but has decreased wildlife habitat. Future agricultural landuse changes may be driven by alternative energy demands and regional climatic changes. Landuse change and its drivers could affect bioenergy production, wildlife populations and natural resources, and considering the potential impacts of impending changes in advance could assist with preparations for an uncertain future.

This study addressed how the conversion of marginally productive agricultural lands in the Rainwater Basin region of south–central Nebraska, U.S.A. to bioenergy switchgrass (Panicum virgatum) might impact ethanol production, grassland bird populations and agricultural groundwater withdrawals. This study also used multi–model inference to develop predictive models explaining annual variation in springtime wetland occurrence and flooded area in the Rainwater Basin.

Results suggest that producing adequate biomass for year round cellulosic ethanol production from switchgrass and residual maize (Zea mays) stover within existing starch–based ethanol plant service areas is feasible at current feedstock yields, removal rates and bioconversion efficiencies. Throughout the Rainwater Basin, the replacement of marginally productive rowcrop fields with switchgrass could increase ethanol production, conserve groundwater and benefit grassland birds under novel future climatic conditions. However, converting Conservation Reserve Program (CRP) grassland to switchgrass could be detrimental to grassland bird populations. Predictive wetland inundation models suggest that springtime wetland inundation in the Rainwater Basin is a complex process driven by individual wetland characteristics, surrounding landuse and local weather events. The impacts of future climatic and landuse changes in the Rainwater Basin and surrounding Great Plains is ultimately likely to depend on which forms of alternative landuse are adopted and on how intensely change occurs.

Advisor: Craig R. Allen

RIVER OTTER (LONTRA CANADENSIS) HOME RANGE, HABITAT USE, OVERNIGHT MOVEMENT, AND SURVIVAL IN THE PLATTE RIVER OF NEBRASKA

Samuel P. Wilson — Mon, 23 Jul 2012 06:31:48 PDT

River otters (Lontra canadensis) are native to Nebraska but were extirpated by the early 1900s. The Nebraska Game and Parks Commission (NGPC) reintroduced river otters during 1986–1991 to restore the species in the state but little is known regarding the habitat needs and status of this high profile threatened species. To provide information for management I conducted research to determine home range, habitat use, overnight movement distance, and annual survival of river otters in the central Platte River of Nebraska.

I trapped, implanted telemetry transmitters, and tracked 18 river otters during 2006–2009. I obtained 996 locations and constructed 13 annual home ranges. Mean home range size using the 95% fixed kernel (FK) method was 3,711.6 ha (SD = 2,995.4) and 1,361.0 ha (SD = 1,075.2) using the 95% minimum convex polygon method (MCP). Male home ranges were larger than females for both FK (P = 0.02) and MCP methods (P = 0.02). Habitat use was determined by comparing used versus available habitats using compositional analysis. Open water was used more than any other habitat type in all three comparisons tested.

I recorded 19 overnight movements (465 total telemetry locations) for four river otters during 2007–2008. Mean distance moved overnight was 3.5 km (SD = 3.0). Movements during Jan–Feb when NGPC conducts bridge surveys were lower than during the rest of the year (P = 0.03). Annual survival was 100% as no river otter mortalities were detected during the study (Oct 2006–Dec 2009). The mean number of days that a marked river otter was known to be alive was 470.5 (SD = 168.8).

River otters in the central Platte River select open water over other habitat types, exhibit reduced movements during winter months, and have high annual survival. This information will be used by the Nebraska Game and Parks Commission to assess the status of river otters in Nebraska and direct management efforts for the species.

Advisor: Craig Allen