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Evaluating Vegetation Response to Water Stress using Close-range and Satellite Remote Sensing - Sharmistha Swain
- Dissertation Defense
- 5/17/2012
During the last century, almost all parts of the contiguous U.S. had experienced several prolonged drought events with considerable impacts on the agricultural economy and environment. With changing climates, the drought events are expected to be more severe, longer, and widespread in many parts of the world. Understanding vegetation response to water stress using remote sensing technologies will enhance our ability to detect and monitor drought. This dissertation research evaluates the response of vegetation to drought-related water stress at the leaf, canopy, and regional scales using close-range and satellite based reflectance and/or thermal data. At the leaf level, a crop water stress index-based model was developed using high spatial resolution thermal imageries to estimate water content in soybean leaves. The model showed a higher accuracy in leaf water content estimation as compared to water content estimated using the raw leaf temperature. At the canopy level, multi-year close-range reflectance based vegetation indices (VIs) data were correlated with soil moisture measured at four depths of corn and soybean root zone. Results indicated that corn VIs were significantly related to soil moisture at deeper depths and kept the soil moisture memory for a relatively longer period of time compared to those of soybeans. At the regional scale, Terra-MODIS Land Surface Temperature (LST) and NDVI products were used to detect drought-induced stress on cropland and grassland cover types across the state of Nebraska. Results showed that the majority of the land cover sites experienced statistically significant increase in daytime and nighttime LST and statistically significant decrease in NDVI during the drought-year growing season as compared to the non-drought year. The findings of this dissertation research will contribute toward the development of more robust tools for monitoring drought stress on vegetation.
Chlorophyll-based Models for Remote Estimation of Crop Gross Primary Production: From in situ Measurements to Satellite Observations - Yi Peng
- Dissertation Defense
- 5/15/2012
Crop gross primary production (GPP) is the rate at which a cropland captures and stores carbon as biomass. The synoptic and accurate quantification of crop GPP is essential for studying carbon budgets in croplands and monitoring crop status. Remote sensing can be used as a powerful and expedient tool for assessing regional and global crop GPP. The objective of this study is to develop a quantitative technique to remotely estimate crop GPP with in situ measurements and satellite observations. A recently developed model, which relates crop GPP to a product of total crop chlorophyll content and photosynthetically active radiation (PAR), was justified and applied for estimating GPP in maize-soybean croplands. The model was tested at close range with vegetation indices retrieved from in situ measured spectral reflectance and ground-observed incoming PAR, and it was able to provide accurate GPP estimates in maize and soybean under different irrigation practices, crop managements, field histories and climatic conditions. The model was also applied to satellite observations to estimate crop GPP, with vegetation indices retrieved from Landsat and MODIS 250 m data and calculated potential PAR values, which is incoming PAR under a condition of minimal atmospheric aerosol loading. The model using vegetation indices and potential PAR can accurately estimate crop GPP based entirely on remotely sensed data.
Exploration of near Infrared-Red Models for the Remote Estimation of Chlorophyll-a Concentration in Optically Complex Turbid Productive Waters: From In Situ Measurements to Aerial Imagery - Daniela Gurlin
- Dissertation Defense
- 5/3/2012
Today the water quality of many inland and coastal waters is compromised by cultural eutrophication in consequence of increased human agricultural and industrial activities. This is reflected in an increase in productivity and changes in the phytoplankton species composition with possible harmful algae blooms. The optical complexity of inland and coastal waters makes the application of remote sensing techniques to monitor the productivity of these waters a difficult task. This study presents a technique for the estimation of chlorophyll-a concentrations, a measure of the productivity of waters and one of the standard water quality parameters for the evaluation of the trophic state of inland and coastal waters, for in situ and aircraft data. The developed algorithms make it possible to estimate chlorophyll-a concentrations without the need for analytical measurements and provide important information for the estimation of the productivity in coastal waters for studies of the carbon budget when they are applied to satellite data.
Predictors of Insect Diversity and Abundance in a Fragmented Tallgrass Prairie Ecosystem - Kody Unstad
- Thesis Defense
- 4/26/2012
Despite providing many services, the tallgrass prairie and its ecological community is one of the most endangered ecosystems in North America. Remaining habitat exists as remnants in a highly-fragmented landscape. To make informed conservation decisions we need to better understand the effects of this fragmentation. Using the ecologically important insect groups, ants and ground beetles, this study provides baseline data on the biological diversity of southeast Nebraska prairies and investigates what management, landscape, and habitat characteristics affect them. Pitfall trap sampling was conducted in 23 tallgrass remnants scattered throughout the Southeast Prairies Biologically Unique Landscape in 2010 and 2011. Multi-model inference was used for analysis of the data.
Twenty-eight species of ants were collected with the majority being grassland-obligates. With a positive correlation, model selection results indicate that Shannon diversity of grassland ants is best predicted by the average number of grass species per m2 while their abundance is positively associated with the amount of nearby haymeadow.
Most ants belonged to the Opportunist and Cold Climate Specialist functional groups. A comparison with prior studies indicates this functional group composition to be most similar to cool-temperate forests. Though different habitats, their cooler climates likely produce this similar composition.
Nineteen species of ground beetles were collected, with two species comprising nearly 95% of the collection. These two species are incapable of flight, a physiological factor that may contribute to their high abundances by leaving them hidden from predators. As with grassland ants, the strongest predictor of Shannon diversity for ground beetles was the average number of grass species per m2.
Results suggest that ants and ground beetles are non-randomly distributed in relation to landscape, habitat, and management factors. High abundances of grassland-obligate ants are associated with high amounts of haymeadow suggesting these areas may be a priority for ant conservation. Results also suggest that sites with more grass species sustain more diverse communities of ants and ground beetles, information that can be incorporated into relevant conservation decisions.
Swift Fox Survey Assessment and Estimation of Detection Probability in Sioux County, Nebraska - Lucia Corral Hurtado
- Thesis Defense
- 4/17/2012
Greater Prairie-Chicken Nest and Brood Site Selection and Survival in the Eastern Sandhills of Nebraska - Lars Anderson
- Thesis Defense
- 4/16/2012
Crop Imporvement through Biotechnology: Targeting Drought and Photosynthesis - Saadia Bihmidine
- Dissertation Defense
- 4/13/2012
The world population is projected to grow from the current 7 to about 9 billion by 2050. One of the major challenges that will face agriculture in the next few decades is sustainable food production under climate uncertainties and dwindling natural resources to meet the increased global needs for food. Plant biotechnology plays a vital role in meeting this global challenge. The goal of this research was to investigate the use of biotechnology to improve plant photosynthesis, water use efficiency and drought resistance, to either increase yield and/or alleviate the impacts of water stress on biomass and yield. In the first essay, the use of two Arabidopsis thaliana promoters RD29A and RD29B in soybean (Glycine max (L.) Merr.), was investigated and results suggest that they may be useful in controlling transgenes targeted to enhance drought resistance in soybean as long as there are no agronomic penalties associated with low-level expression in the absence of stress. In the second essay, the expression of AQPV1, an aquaporin gene from Chlorella virus MT325, and its effect in mitigating drought stress in tobacco (Nicotiana tabacum) was investigated. Results showed that the transformed AQPV1 plants maintained higher photosynthetic rates, less negative water and osmotic potentials, and accumulated greater biomass compared to control plants. In the third essay, the potential use of C4 enzymes from Cyanobacteria to improve C3 photosynthesis was investigated. The cyanobacterial ictB (inorganic carbon transporter B) and FBP/SBPase (fructose-1,6-/sedoheptulose-1,7-biphosphatase) genes were placed under control of constitutive promoters and introduced into soybean chloroplasts via Agrobacterium-mediated transformation. The former gene is involved in HCO3- accumulation and the latter catalyzes the hydrolysis of both fructose-1,6-bisphosphate and sedoheptulose-1,7-bisphosphate in the Calvin cycle. Leaf physiological data collected in both the greenhouse and the field revealed that transgenic soybeans displayed higher leaf photosynthetic rates compared to control plants. In addition, some of the tested transgenic events performed better than control plants when exposed to soil dry-down experiments. Results from these essays contribute to the ongoing research aiming at using plant genetic manipulations to increase crop productivity and alleviate environmental stresses.
Hydrological Information System: An Integrated System for Modeling, Simulation, Analysis, and Distribution of Climate and Hydrology Data - Baburao Kamble
- Dissertation Defense
- 4/10/2012
This principal thrust of this research was to develop an integrated Hydrologic Information System (HIS) with advanced data acquisition, modeling, and processing techniques to simulate hydrological processes, in particularly evapotranspiration (ET), at varying spatial scales using easily and freely available remotely sensing data. A second important component was to develop a web-portal to disseminate hydrological data online for the purpose of improved water management decisions in Nebraska. The five main chapters of this dissertation represent the foundation on which the specific findings within this research are grounded.
A suite of procedures, tools and products related to water consumption in Nebraska, the High Plains, and the nation are investigated and developed, including methods for efficient delivery to end-users and facilitation of effective spatial data handling. The methods and accomplishments described are considered to be a 'first cut' in establishing a responsive information production and delivery system to support near-real time resources management, in particular the management of water resources over the High Plains. The products, procedures and architectures are described or developed during this dissertation.
Groundwater Pollution Risk Assessment under Scenarios of Climate and Land Use Change in the Northern Great Plains - Ruopu Li
- Dissertation Defense
- 2/9/2012
Modeling groundwater vulnerability to pollution is critical for implementing programs to protect groundwater quality. Groundwater vulnerability is strongly dependent on factors such as depth-to-water, recharge and land use conditions that may change in response to future changes in climate and/or socio-economic conditions. For example, global warming may lead to northward shifts in cropping patterns and changes in crop mixes (and use of farm chemicals) in the Northern Great Plains. Meanwhile, growing demands for biofuels are resulting in expanding corn acreage, and may lead to pressures to remove land from the Conservation Reserve Program (CRP) or otherwise open lands that are currently not cropped to cultivation. Such changes may have significant implications for groundwater quality. In this research, a new modeling framework which employs four sub-models linked within a GIS environment is proposed and evaluated. The research focuses on North Dakota. The results of modeling under several different scenarios suggest that over the next 50 years areas having high vulnerability to pollution will expand northward and/or northwestward in eastern North Dakota. GIS-based models that account for future changes in climate and land use can help decision makers identify potential future threats to groundwater quality, and take early steps to protect this critical resource.
Understanding of the Hydrologic Connections Between Wide-channel and Adjacent Aquifers Using Numerical and Field Techniques - Cheng Cheng
- Dissertation Defense
- 1/24/2012
Streambed sedimentary structure plays a vital role in controlling the interactions between the surface water and groundwater. Previous researches usually used a lumped parameter, streambed conductance, to analyze stream-aquifer interactions and assumed that a low-permeability clogging layer occurs at the channel surface. However, a number of recent studies noted that hyporheic processes can affect streambed permeability and declogging processes may exist. Accordingly, the assumption of a low-permeability clogging layer at the channel surface can lead to the underestimations of the real-world stream-aquifer interactions. Streambed vertical hydraulic conductivity (Kv) and thickness (M) are two most important parameters of streambed conductance, and thus a detailed characterization of streambed Kv and M is crucial to understand and quantify the exchange between the near-channel and in-channel water.
In this dissertation, the variations of streambed Kv values relative to the depth are investigated for three rivers (the Big Blue River, the Little Blue River, and the Platte River) in Nebraska. The Kv values in the top 2-m of the streambed sediments are generally larger than 1 m/d. In addition, streambed Kv values have a decreasing below the channel surface, which may be a result of hyporheic process and indicate that stream-aquifer interactions are more intense near the channel surface. Consequently, this study confirms the absence of a low-permeability clogging layer at the channel surface. Furthermore, the estimated values of M may vary largely in space. From these results, the constant head boundary is proposed to be an alternative solution in the simulation of stream-aquifer interactions. This approach is applied in a regional groundwater flow model to evaluate the impact of groundwater irrigation on the streamflow in the lower reach of the Platte River. Additionally, the model provides an accurate estimation of the streambed leakance of the Platte River using numerical and field techniques, which is beneficial in assessing stream-aquifer interactions when an analytical solution is employed. Furthermore, the statistical distribution of streambed Kv values along a 300-km segment of the Platte River is also examined. We found they are normally distributed at nearly each of the 18 test sites in the Platte River.
An evaluation of stocking and habitat influences on channel catfish populations in lentic ecosystems of the Great Plains - Lindsey Chizinski (Richters)
- Thesis Defense
- 1/18/2012
Abstract: Channel catfish are highly sought after by Nebraska anglers, and the Nebraska Game and Parks Commission invests considerable resources in statewide stocking programs to establish and maintain the species in Nebraska’s public waters. Assessments of stocking programs are lacking, in large part because channel catfish are ineffectively sampled with current methods. The objective of this study was to utilize a recently developed sampling method, tandem-set hoop nets, to collect channel catfish in sufficient quantities to describe the effects of stocking and habitat variability on populations in lentic ecosystems. Three lentic ecosystems common to the Great Plains were considered: sand pits, flood control reservoirs, and irrigation/power generation reservoirs. The influence of stocking on abundance and condition of channel catfish varied with ecosystem type. In sand pits, stocking negatively influenced fish condition, and only frequent stocking positively influenced abundance. In flood control reservoirs, stocking did not influence fish condition, but was associated with greater abundance. Stocking did not influence fish condition or abundance in irrigation/power generation reservoirs. Additionally, there was evidence that mortality and growth rates varied with ecosystem type. In general, populations from irrigation/power generation reservoirs were predicted to experience slower growth and lower mortality, where as sand pit populations were predicted to experience the fastest growth and highest mortality. This knowledge can inform decisions regarding future stocking protocol for channel catfish and provide fisheries biologists with useful tools for population assessments.
Atrazine Runoff in the Blue River Basin: Geomorphology, Rainfall, and Agronomic Practices - Kundan Dhakal
- Thesis Defense
- 12/1/2011
Atrazine concentrations in the Big Blue River Basin in Nebraska and Kansas periodically exceed the EPA Total Maximum Daily Load (TMDL) of 3 mg L-1. The present study is focused on watershed variables influencing surface runoff of atrazine. The assessment includes the impact of corn and sorghum progress (indicating atrazine application), rainfall, antecedent soil water content, and soil restrictive layer on stream-measured weekly atrazine load in independent subwatersheds for 1997 - 2004. Maximum atrazine loading occurred after most of the corn had been planted but during sorghum planting from mid-May to early June, immediately following multiple rainfall events that saturated the soil profile and caused runoff from fields. Analysis of covariance was conducted from day 110 when about 10% of the corn was planted to day 170 when 90% of the sorghum was planted. Results from independent subwatersheds imply that atrazine load weighted by area is related to cumulative weekly rainfall across all years. Statistical analysis showed rainfall was the most significant factor associated with atrazine loading, but soil moisture, corn and sorghum planting progress, and the presence of a soil restrictive layer were also important. Results provide decision support to farmers, agencies, extension workers, and scientists for targeting of best management practices.
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 Healey
- Dissertation Defense
- 11/30/2011
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 Sand Hills region of Nebraska by using remote sensing and in-situ estimations of energy partitioning. By employing satellite technology and micrometeorological instrumentation this research establishes a better understanding how energy partitioning, and resulting evapotranspiration (ET), differs between different vegetative communities. We present findings of diurnal and seasonal estimates of energy partitioning as well as daily estimations of ET from both satellite image processing and in-situ observations by Bowen ratio energy balance systems (BREBS). This research also employed different techniques to estimate energy partitioning via remote sensing by adjusting radiation, wind speed, and stability parameters to better represent areas with high topographic relief. The last focal point of this research was to analyze how energy partitioning and ET varied both spatially and temporally under different climate conditions between 2004 (normal year), 2006 (dry year), and 2009 (wet year).
Ecophysiological Responses of Herbaceous Plants to the Presence or Absence of Leadplant (Amorpha Canescens) in a Nebraska Sandhills Grassland - Jessica Milby
- Thesis Defense
- 11/28/2011
Deeply-rooted shrubs are common component of grasslands. This study investigated the ecophysiological role of leadplant (Amorpha canescens), a common leguminous shrub, in Sandhills grassland, and response of herbaceous plants to the presence or absence of leadplant. Two sites were selected for the study at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska—one with leadplant (G-L) and one without (G-NL) leadplant. Species diversity, 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 €, water use efficiency (WUE), and predawn (ψpre) and midday (ψmid) water potentials of leadplant and five representative herbaceous species were determined twice a month, and carbon isotope ratio (ä15C) and specific leaf area (SLA) were determined once a month between June and September. The herbaceous species included two C3 grasses [needleandthread (Hesperostipa comata) and prairie junegrass (Koeleria macrantha)], two C4 grasses [sand bluestem (Andropogon hallii) and prairie sandreed (Calomovilfa longifolia)], and one forb [stiff sunflower (Helianthus pauciflorus)]. Differences in rates of A, gs, and WUE were species dependent and were not impacted by the presence of leadplant. Net photosynthesis exhibited seasonal variability, increasing early in the growing season and peaking by midsummer. The C3 stiff sunflower had the highest rates of A, E, and gs; and the C4 grasses had the greatest WUE. Site significant impact (G-L vs. G-NL) was only observed in E, which was likely related to higher soil water content in the G-L site. ψpre and ψmid differed significantly among sampling dates and species, but not between sites. The C3 grasses exhibited the lowest (most negative) ψpre and ψmid. Leadplant improved soil nitrogen content on the G-L site, resulting in higher leaf N content, and lower photosynthetic nitrogen use efficiency (PNUE) in plants on the G-L compared to the G-NL site. Leadplant presence had positive impacts on soil and associated plants’ leaf nitrogen content and soil water content. Ecological significance of the results is discussed.
ABIOTIC STRESS RESPONSES IN PHOTOSYNTHETIC ORGANISMS - Joseph Msanne
- Dissertation Defense
- 11/22/2011
Cellular and molecular aspects of abiotic stress responses in Arabidopsis thalianasubjected 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 RD29Bwas highly responsive to salt stress. Therefore, RD29A and RD29B gene sequences have the potential to confer abiotic stress resistance in crop species grown in arid and semi-arid regions. RD29A and RD29B proteins were also found to unlikely serve directly as protective molecules. The second study aimed at investigating the impacts nitrogen deprivation in Chlamydomonas reinhardtii and Coccomyxa sp. C-169, results showed that these microalgae altered their lipid metabolism by synthesizing and accumulating the neutral lipid triacylglycerol (TAG). Since microalgae have emerged as suitable feedstocks for renewable biofuel production, the purpose of this analysis was to understand the genetic and biochemical mechanisms associated with the induction of TAG synthesis in Chlamydomonas and Coccomyxa subjected to nitrogen deprivation under photoautotrophic conditions. In addition to TAG accumulation, nitrogen depletion triggered an early synthesis of starch and up-regulation of several genes in Chlamydomonas, including some diacylglycerol:acyl-CoA acyltransferases, catalyzing the acylation of diacylglycerol to TAG. Protein degradation in nitrogen-deprived cells might provide carbon skeletons for TAG biosynthesis. In a related study, the effects of the autophagy-inducer rapamycin and the autophagy-inhibitor 3-methyladenine (3-MA) on the accumulation of TAG in Chlamydomonas cells subjected to nitrogen deprivation were investigated. 3-MA induced TAG accumulation in cells growing in both nitrogen-deprived and control media. The increase in TAG content in cells subjected to nitrogen deprivation might not be a direct response to an autophagic activity induced by nutrient depletion.
Climatic controls on the summertime energy balance of a thermokarst lake in northern Alaska: Short-term, seasonal, and interannual variability - Brittany Potter
- Thesis Defense
- 11/21/2011
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 of these processes, we performed a multi-year energy balance analysis of a shallow, thermokarst lake near Barrow, Alaska. Timeseries of net radiation, Bowen ratio, and rates of heat storage in the water and sediments were used to calculate sensible and latent heat fluxes during the 2008-2010 ice-free periods. Results of the energy balance analysis show rapid lake warming immediately following ice-off (due to high insolation), followed by similar increases in sensible and latent heat flux. Lake evaporation averaged around 1.3 mm/day during the ice-free period, which is nearly twice the mean summertime precipitation rate of 0.7 mm/day for Barrow, Alaska. Daily evaporation rates ranged from zero to greater than 4 mm/day, while short-term and seasonal patterns varied significantly from one year to the next. Much of this variability was associated with changes in cloud cover, water temperature, relative humidity, and wind speed.
Habitat Use and Abundance Patterns of Sandhill Cranes in the Central Platte River Valley, Nebraska, 2003-2010. - Todd Buckley
- Thesis Defense
- 11/2/2011
The Central Platte River Valley (CPRV) in Nebraska is an important spring stopover area for the midcontinent population of sandhill cranes (Grus canadensis). Alterations to crop rotation and loss of native habitat in the CPRV pose a risk to the future population. Personnel made observations of agricultural fields along designated routes in the CPRV from 2003-2010 to record the presence of cranes and estimate abundance. I developed and evaluated models to predict habitat use and flock sizes of cranes. My results suggest diverse crop rotations in large fields far from development but near roosting habitat are the most beneficial stopover habitat conditions for cranes in the CPRV. However, seasonal variation in the distance travelled to fields suggests roosting habitat might be limiting the distribution of cranes. Understanding the use of the Platte River by cranes is critical for future management of roosting habitat. Personnel made observations of the Platte River during aerial surveys from 2004-2010 to determine the presence of cranes and estimate roost sizes. I developed and evaluated models to predict roosting habitat use and roost sizes. Segments of the Platte River not adjacent to disturbance, wider than 150 meters, and free of tall woody vegetation received the highest use and contained the largest roosts. The results of my entire study suggest management in the CPRV for cranes should be focused west of Kearney, Nebraska, due to the potential for roosting habitat expansion and the characteristics of surrounding agricultural fields.
Impact of copper mine tailings (stamp sand) on survival and development of aquatic organisms near Gay, Michigan. - Danielle Haak
- Thesis Defense
- 8/1/2011
Using slow-release permanganate to remove TCE from a low permeable aquifer at a former landfill - Mark Christenson
- Thesis Defense
- 7/18/2011
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 by 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 groundwater sampling via direct push. A TCE plume (100-600 µg L-1) was identified in a low permeable silty-clay aquifer (Kh = 0.5 m d-1) that was within 6 m of ground surface and underlain by an even lower permeable zone (Kh = 0.04 m d-1). Because injecting a liquid oxidant into the low permeable aquifer would have been difficult, we manufactured slow-release potassium permanganate candles (SRPCs) to treat the TCE. SRPCs were prepared by heating and mixing KMnO4 and paraffin wax at a 4.6 to 1 ratio (w/w), and then pouring the heated mixture into circular cardboard molds (91.4 cm long) that were either 5.1 cm (2 in) or 7.6 cm (3 in) in diameter. For comparison, we inserted equal masses of SRPCs (7.6-cm vs 5.1-cm diam) into a low permeable aquifer (4.6 m vertical thickness) in staggered rows that intersected the TCE plume. The 5.1-cm diam candles were inserted directly into the formation using direct push hollow rods at 21 locations. The 7.6-cm SRPCs were encased in slotted containers and placed in 10 permanent wells. Pneumatic recirculators that emitted small air bubbles were placed at the bottom of the 7.6-cm SRPCs in the second year to facilitate permanganate distribution. Results obtained prior to inserting recirculators showed a 64 to 82% reduction of TCE in the 7.6-cm candle treatment zone after 342 d and between 64 to 100% decrease in associated ethene degradates. These results support using slow-release permanganate candles as a means of treating chlorinated solvents in low permeable aquifers.
Breeding fidelity and landscapes effects on distribution of mallards and duck broods in the Nebraska Sandhills - Zach Cunningham
- Thesis Defense
- 7/15/2011
n/a
Avian Influenza Surveillance in Wild 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 Groepper
- Thesis Defense
- 7/12/2011
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 2007-2009 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 in 2009 (15.9%). I plotted prevalence monthly and found July-October was optimal time for sampling due to highest prevalence in all flyways. Dabbling ducks had significantly higher prevalence of AIV ( = 14.1%, range = 9.3%-19.4%) than other functional groups across all flyways and study years. My results suggest future surveillance should focus on species from the dabbling duck functional group.
Restoration efforts in Nebraska have contributed to increased populations of resident Canada geese (Branta canadensis) that now are considered a nuisance. In 2004, an early September hunting season was initiated to reduce populations. I analyzed band returns from geese banded in Nebraska to determine if early September hunting seasons affected survival, harvest, and recovery rates. The top model in my survival analysis revealed early September hunting seasons did not reduce survival of geese (S = 0.696). In addition, models indicated survival was not different between geese inside and outside the early hunting zone (southeast vs. northeast, S = 0.711) and survival did not differ by sex (S = 0.708). Survival differed between the metropolitan areas of Omaha and Lincoln, Nebraska (S = 0.742 and 0.678, respectively). A combination of urbanization and non-migratory behavior may be leading to higher survival of geese in Nebraska.
Late Holocene History of Dune Activity Along the Elkhorn River in Northeastern Nebraska - Rebecca Puta
- Thesis Defense
- 7/7/2011
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 dunes, the Stanton dunes could provide valuable insight into the extent of large-scale dune activation and the nature of regional drought events. Twenty-four optically stimulated luminescence (OSL) ages from the Stanton dunes reveal several activation periods that cluster into several distinct groups: less than 120 years ago (n=2), around 410-630 years ago (n = 7), around 1000 years ago (n = 2), and around 3,800 to 5,800 years ago (n = 6). The two younger clusters do not correspond to major dune activation events in the Nebraska Sand Hills, while both of the older periods chronologically overlap with the activation of dunes in the Nebraska Sand Hills and other major central Great Plains dune fields. Optical ages in the Stanton dune field suggest that megadroughts reach far beyond the eastern edge of the Nebraska Sand Hills. Geochemical evidence indicates that the Stanton dunes and the underlying alluvium are similar to the sand found in the Nebraska Sand Hills. The two older dune formation events from the Stanton dunes may be related to drought-induced changes in sediment supply in the Elkhorn River which drains a portion of the Nebraska Sand Hills. Thus, the activation events of the Stanton dunes may have been driven by a combination of drought and changes in sediment supply.
Spatial Accuracy of Climate Networks in Nebraska - Andrea Coop
- Thesis Defense
- 7/6/2011
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 has its own instrumentation, collection methods and station sites. Maximum and minimum surface temperature from the three networks and the spatial structure of temperature variations at the surface are compared. Two different timeframes, 2005-2009 and 1985-2005, were used to include the newest network, CRN, in the analysis. Daily data was collected from each of these networks within the specified timeframe. Root mean square error (RMSE) between each candidate station and the surrounding stations within 500 kilometers were calculated and evaluated to determine spatial accuracy of the network. This study found that in the 5 year analysis, CRN versus AWDN, the two networks were not significantly different enough to denote the network with high spatial accuracy. For the 21 year analysis, HCN versus AWDN, AWDN stations showed higher spatial accuracy (smaller error) than HCN stations for the variable of maximum temperature. The error for the two networks were not significantly different enough to decipher the network with the higher spatial accuracy.
Discontinuities: Predicting the Architecture of Invasions and Extinctions - Aaron Lotz
- Dissertation Defense
- 7/1/2011
One of the major unresolved problems, at the forefront of worldwide environmental concerns, is the increase in non-indigenous species (NIS) and endangered species. Invasions and extinctions fundamentally change community structure, which potentially affects ecosystem processes. This potential loss of ecological processes inherently affects landscape structure and dynamics, including predator-prey interactions, dispersal, foraging behavior and functional group composition.
I explored multiple tenets of the textural discontinuity hypothesis. This hypothesis 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 to highly variable resources. Literature indicates NIS and endangered bird and mammal species occur at the edges of body mass aggregations more frequently than expected. This work focuses on the distribution of biological diversity in space and time and socio-ecological factors that are contributing to the worldwide increase in NIS and endangered species.
I analyzed invasions and extinctions of birds and mammals across five Mediterranean-climate ecosystems and in 100 countries using Bayesian CART analysis and an information-theoretic approach. All body mass distribution data analyzed were discontinuous. This work provided further support for Holling's textural discontinuity hypothesis. Alpha and beta diversity of function decreased in most datasets when NIS were introduced into the community. After the introduction of NIS, I observed a decrease in cross-scale redundancy of functional groups in mammals and when both taxonomic groups were combined. In Eocene Epoch mammal data, speciation events were not detected near body mass aggregation edges. However, this was most likely due to the low power of the statistical tests, high species turnover, and small sample size. Only 64% of the biomes in mammals had ecoregions with similar structure and only 50% of the biomes in birds had ecoregions with similar structure, which may be a result of coarse landscape classification schemes. GDP per capita was positively correlated with the proportion of NIS bird and mammal species within a country. Resilience of a country was correlated to life expectancy. As life expectancy increased, resilience of a country decreased. Results may help us make proper management decisions in monitoring particular non-indigenous species and focus conservation efforts on those native species.
Quantifying Evapotranspiration and Water Table Interactions in Regions of Shallow Groundwater: Sensitivity to Soil Properties, Vegetation, and Climate Variability - Evren Soylu
- Dissertation Defense
- 5/27/2011
A growing world population requires increased agricultural production, which relies heavily on irrigation. Up to 90% of fresh water is used for producing food, and sustainable management of water resources requires understanding various components of the hydrologic cycle, including the impacts of human activities and climate on evapotranspiration (ET) and groundwater recharge. Many watersheds around the globe are suffering from declines in streamflow, including the Republican River basin in the central Great Plains. Decreased streamflow can be attributed to human activities – such as land cover change and groundwater consumption – as well as climate variability. In this study, we investigated the interactions between groundwater and ET in shallow water table environments of the central Great Plains region. ET is a major component of the water cycle, plays an important role in the land surface energy and water balance, and interacts strongly with groundwater in riparian zones. We examined the modeled sensitivity of ET to soil parameters and changes in groundwater depth (for a specific field site in the Republican River basin) by means of a hierarchy of land surface models with varying degrees of complexity. The impacts of interannual climate variability and land cover on ET were also investigated for the central Great Plains using a land surface hydrologic / ecosystem model known as Agro-IBIS (the "Integrated Biosphere Simulator"). Finally, a new and improved field method was developed to estimate ET from diurnal fluctuations in shallow groundwater. This technique is similar to the White method, but it uses a multi-day, moving Fourier window to provide more accurate estimates of ET, and it also includes a new formulation for specific yield that facilitates application of the methodology to variably saturated environments (e.g., wetlands with standing water).
Natural Selection and Age-related Variation in Morphology of a Colonial Bird - Mary Brown
- Dissertation Defense
- 4/18/2011
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, tarsus length was unchanged, and the amount of wing asymmetry increased. The cumulative directional change in wing, tail, and beak length was greater after the selection event than during the event. This variation was not explained by phenotypic plasticity resulting from better environmental conditions, because conditions were not significantly different before and after the event. There was no evidence opposing selection restored skeletal size or wing or tail length to that before the selection event. This continued change in morphology may represent the population shifting to a different fitness peak in the adaptive landscape.
The way variation in climatic conditions (and food resources) affects the morphological development of juvenile swallows was studied. In cooler years birds allocated less growth to wings and tails than they did in warmer years, while maintaining normal levels of skeletal growth and body mass. Changes in juvenile feather growth in response to rearing conditions persisted into the first breeding season.
The extent morphological traits vary with age across a bird's lifetime was examined. Juveniles had shorter wings and tails, lower body mass, smaller skeletal size and lower levels of fluctuating asymmetry than adults. Among adult age classes, wing and tail length increased with age and wing and tail fluctuating asymmetry decreased with age. There was no evidence for degenerative senescence in swallows, as the decline in fluctuating asymmetry suggests the oldest birds maintain high levels of phenotypic performance. This age-related variation in morphology suggests that age should be considered in future analyses of morphological variation in passerines.
Life and Death Carved in Stone: Necrogeography and Landscape Archaeology of the Brownville, Nebraska Cemetery - Ashley Barnett
- Dissertation Defense
- 2/25/2011
Unlike cemeteries and gravestones in the eastern United States, there has been relatively little published about cemeteries and gravestones in the central Plains. This dissertation will explore the gravestones of Brownville, an early Nebraska river town, to determine changes in culture, relating to gender roles, race, and concepts of death and dying. Following in the footsteps of James Deetz, this project aims to decode the ideologies conveyed by words and images carved into the Brownville gravestones. The study will explore the effects of time, distance, and carver(s) on the material culture of the cemetery and will suggest methodological processes for studying other pioneer cemeteries in the central Plains.
Propagating and Non-propagating Interseasonal Oscillations in the Tropical Atmosphere: Their Vertical and Horizontal Structures and Developing Mechanisms - Zhaoning Liang
- Dissertation Defense
- 11/30/2010
A fixed beamformer is proposed and designed to identify source regions of Intra-Seasonal Oscillations (ISO) in the tropical atmosphere. After tested by simulations of single and complex sources of waves, the fixed beamformer is applied to the ECMWF interpolated data grids to detect and identify source regions of the ISO in the tropical Indian and Pacific Ocean region. Results show that the fixed beamforming technique can uniquely identify the source region of the ISO, and the source regions of all major ISO in the tropical Indian and western equatorial Pacific region during the 29 yr from 1974 to 2002 have been identified.
Examinations of ISO development in the source regions indicate that besides the eastward propagating ISO, there were non-propagating ISO during this 29-year period. To understand why some ISO propagate while others are stationary, statistical analyses are used to examine the vertical and horizontal structures of these two types of ISO. Results show very different structures during the development and evolution of these two different types of ISO. For the propagating ISO, both moisture and temperature processes/disturbances are very important for the development of the ISO. This type of ISO is developed in a relatively warm and wet large-scale environment, and wind enhanced surface evaporation is a major mechanism. For the non-propagating ISO, temperature process is not as important as the moisture process in the development of ISO. Temperature anomalies remained weak before the onset of major convection in the ISO and reached peak intensity afterward peak convection. Both temperature and moisture anomalies developed but confined within the source region. The non-propagating ISO develop in a relatively cool and dry environment. Although weak low-level easterly anomalies and surface evaporation existed before the onset of major convection in these ISO, radiation-convection interaction mechanism seems playing an important role in triggering the non-propagating ISO. A key support for this notion is that relatively cold temperature anomalies persisted in the middle troposphere during the development of the ISO. This radiative cooling destabilized the troposphere profile and favored convection development.
Challenges for the Implementation of Adaptive Management and two Quantitative Applications - Jamie McFadden
- Thesis Defense
- 11/8/2010
Adaptive management is becoming an increasingly popular management-decision tool within the scientific community. The application of adaptive management is appropriate for complex 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. We 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 considering adaptive management as a decision tool, such as those managing the Platte River, Nebraska. The Platte River is a complex ecosystem where resource management decisions affect endangered and threatened species such as the Interior Least Tern (Sternula antillarum athalassos) and Piping Plover (Charadius melodus). Because high uncertainty is associated with the responses of these species to habitat restoration and other resource uses and management efforts differ between the lower Platte River (LPR) and the central Platte River (CPR), we developed quantitative applications for each section. For terns and plovers on the LPR, we developed a population model that estimates population characteristics for on-channel and off-channel breeding and nesting habitat. The population model is a valuable tool in measuring and managing adaptively the annual status of the two avian species on the LPR. The ability of this quantitative model to adapt to new information makes it ideal for projecting management implications within an adaptive management context. As the CPR is further along in the adaptive management process, we developed a multi-model analysis based on simulated data to simplify hypotheses and prioritizing research and management needs. By utilizing statistical models for evaluating management consequences, iterative decision-making will for continuous updating as more monitoring data becomes available, influencing future management decisions. The process of evaluating effects of ecological features is helpful in setting and prioritizing objectives and implementing actions for adaptively managing complex ecosystems.
Detection and Measurement of Water Stress in Vegetation Using Visible Spectrum Reflectance - Art Zygielbaum
- Dissertation Defense
- 12/2/2009
At any scale, from a single microbe to the planet that nurtures us, water defines our place in the universe. It provides the hydraulic forces needed to give plants structure, and the medium enabling photosynthesis, the basis for most life on earth, to occur. Knowledge about the water status of plants is vital to understanding the state or condition of vegetation, which is important to scientists in disciplines as diverse as agriculture, geography, and climatology. Non-destructive and remote sensing of plant water status allows the gathering of such information across wide geographic extents and over long periods of time. During this seminar, the results of extensive greenhouse research on corn and soy plants undergoing water deficit will be presented. The effort resulted in the identification of a previously unknown systematic increase in visible light reflectance as plants become increasingly water stressed. The effect is more pronounced in corn than in soy. Because water molecules do not absorb light in the visible spectral range, this finding offers new insights into the physical and chemical processes which protect plants from damage due to water stress. The finding also suggests a potential for using only visible light to detect and measure plant water status non-destructively, and perhaps even by means of sensors on remote platforms.
The Textural Discontinuity Hypothesis and its relation to nomadism, migration, decline and competition - Aaron Alai
- Thesis Defense
- 11/30/2009
The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecological sciences. Literature suggests nomadism may arise in species that specialize in granivory, nectivory, or the utilization of rodent outbreaks. Literature suggests species become migratory because they exploit certain scarce or variable food types. Species decline is hypothesized to be the result of many different factors as well; large species, island species and specialists may be more prone to decline.
A fresh perspective regarding the causes for species nomadism, migration, and decline is being investigated with the Textural Discontinuity Hypothesis. The Textural Discontinuity Hypothesis stems from complex systems analysis and posits that body mass distributions form clusters within ecological systems, and that those body mass clusters reflect discontinuous distributions of resources. Additionally scientists have posited that species at the edges of body mass clusters may be exposed to highly variable resources. Nomadic and declining bird species populations occur at the edges of body mass clusters more frequently than expected. Migratory bird species also may be located at the edges of body mass clusters more frequently than expected. The morphological spacing of species within clusters may yield clues regarding species interactions. The distribution of species within a body mass cluster would have low variance if species within a cluster interact with each other strongly – morphological overdispersion has been documented in many animal communities and reflects strong competitive interactions among species.
I analyzed nomadism, migration, and decline in South African birds using an information-theoretic approach. I assembled a series of plausible models based upon suggested or theoretically predictive characteristics. Additionally, I used a series of Monte Carlo simulations to investigate the distribution of species within clusters, in terms of body mass.
Results suggest that a combination of species characteristics, including the distance to the edge of a body mass cluster, explain the complex phenomena of nomadism, migration and decline. Generally there was no single model supported, and often many models were in the confidence set, providing only weak inference. Within body mass clusters, there is more variance among species than null expectations, thus with my dataset morphological overdispersion is not present within body mass clusters. Nomadism, migration, and decline are complex phenomena which incorporate different species characteristics, perhaps explaining why such debate still exists over the causes of such phenomena
The Effect of Regulation on Household Solid Waste Management in Lincoln and Augsburg: A Comparative Study - Amir Vafa
- Thesis Defense
- 11/24/2009
Nest and brood survival and habitat selection of ring-necked pheasants and greater prairie-chickens in Nebraska - Ty Matthews
- Dissertation Defense
- 11/13/2009
n/a
Satellite-based Esitmation of Chlorophyll-a Concentration in Turbid Productive Waters - Wesley Moses
- Dissertation Defense
- 10/8/2009
Inland, coastal, and estuarine waters, which are often turbid and productive, play a crucial role in maintaining global bio-diversity and are of immense value to aquatic life as well as human-beings. Concentration of chlorophyll-a is a key indicator of the trophic status of these waters, which should be regularly monitored to ensure that their ecological balance is not disturbed. Remote Sensing is a powerful tool for this.
Reflectance models that are based on the red and near-infrared spectral channels of MODIS and MERIS satellites have been developed for estimating chlorophyll-a concentration. The results obtained from data collected by field spectrometers, airborne sensors, and space-borne sensors over inland, estuarine, and coastal waters from various geographic regions, with widely varying biophysical characteristics, show that the developed models have a very close and stable relationship with chlorophyll-a concentration, thereby precluding the need for re-parameterization of the models for each water body. Chlorophyll-a algorithms have been developed and calibrated, which have the potential for universal application to estimate chlorophyll-a concentration from satellite data routinely acquired over turbid and productive waters from around the globe.
Evaluation and Application of Predictive Habitat Modeling in Ecology - Justin Hoffman
- Dissertation Defense
- 4/21/2008
My dissertation research is an important contribution to the growing field of predictive habitat modeling in ecology. I investigate innovative approaches for evaluating the performance of different predictive habitat models and applying these methods to large scale ecological phenomena. Several predictive habitat models currently exist. It has been the focus of much research to determine which is the best model(s). However, much of this research is undermined by biased data sets. To resolve this issue, I tested model performance with simulated data that is not prone to the usual biases of real data sets. In general, my results support the findings of previous studies in that models that accurately predicted species distributions with real occurrence data also showed superior performance using simulated occurrence data. Using the conclusions from the model evaluation analysis as a basis, I applied these methods to two independent research questions. I first identified certain variables that best predicted the occurrence of chronic wasting disease (CWD) in Nebraska. Chronic wasting disease is a newly emerging infectious disease found only in members of the deer family (Family Cervidae). Analysis of several different combinations of spatial, temporal, and environmental variables showed that the chance of recording a positive CWD case was greater the more time spent sampling and when that sampling was conducted in western Nebraska. For the second question, I predicted range expansion among six North American mammals and ascertaining what role environmental variables have in predicting those expansions. I used two predictive habitat models combined with climate, land cover, and elevation variables to predict distributions. I predicted range expansions accurately for two of the six species, suggesting that other factors influenced the distributions of the remaining species. My results demonstrate the applicability of predictive habitat modeling in ecology and provide insights into novel methods of evaluating model performance.