Browsing by Subject "Nitrogen"
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Item Amending constructed roadside and urban soils with large volume-based compost applications: effects on water quality(Texas A&M University, 2007-04-25) Hansen, Nels EdwardMineral nutrients imported in composted dairy manure (CDM) and municipal biosolid (CMB) amendments for highway-rights-of-way and urban landscapes can pose a threat to surface water quality. Treatments were developed to evaluate recommendations for amending roadside and urban soils with compost at large volumebased rates. Texas Department of Transportation (TxDOT) recommendations were evaluated in 2002 and 2003. Municipal recommendations were evaluated in 2004. Treatments were imposed on 4 by 1.5-m field plots on a constructed soil with an 8.5% slope. Three TxDOT compost application methods were tested; incorporation at 25% by volume (CMT), topdressing over vegetation (GUC), and topdressing a 5-cm compost woodchip mix over bare soil (ECC). In 2003, a 12.5% CMT treatment was substituted for the GUC, and two contrasting composts were compared. In 2002, soil test phosphorus (STP) concentrations (mg kg-1) were 291, 360, 410, and 1921 mg kg-1 in the 0 to 5-cm layer of a course textured CMT, fine textured CMT, GUC, and ECC treatments, respectively using CDM. In 2003, STP concentrations were 264, 439, 496,623, 1115, and 2203 mg kg-1, in the 0 to 5-cm layer after incorporation of CDM and CMB at the 12.5 and 25% volume-based rates, and topdressing the 5-cm CDM- or CMB-woodchip mix over bare soil, respectively. In 2004, contrasting CMB products, relatively low or high in total phosphorus (TP) were incorporated into the soil at 12.5 and 25% by volume, or imported in transplanted sod at the 25% by volume rate. The STP concentrations were 87, 147, 180, 301, 322, and 544 mg kg-1, respective to the previously defined treatments. Runoff water from 14, 10, and 8 natural rain events was used to characterize nutrient and sediment transport in 2002, 2003, and 2004, respectively. Concentration of TDP in runoff water was highly variable for roadside treatments across rain events. Mass losses of TDP were similar after CDM or CMB were incorporated into the soil at 12.5 and 25% by volume. Compost incorporation was the most effective method for limiting TP loss in runoff. Roadway and urban soils are expected to contribute greater TP losses as P concentration increases in soils.Item Ammonia: a review of mechanistic models of ammonia volatilization and theoretical studies of the catalytic reduction of dinitrogen to ammonia by a boron cation, a boron dihydride cation, and beryllium dihydride(2006-05) Bell, Cary JaneAnne; Gellene, Greg; Cobb, George P.; Ridley, Moira K.In order to maintain the food production necessary for sustaining the world's ever increasing population, millions of tons of ammonia fertilizer are produced each year. Studies have been performed to investigate how ammonia fertilizers can be used efficiently and how they can be made more efficiently. A significant amount of nitrogen fertilizer applied to crops is lost through ammonia volatilization. Many investigations have been implemented to study the factors and processes controlling ammonia volatilization including the models that are reviewed. At the core of these models is the calculation of the rate of ammonia volatilization, which is a function of a mass transfer coefficient and the difference between the concentration of gaseous ammonia at the slurry/soil surface and that of the free air, which is input. In general, the mass transfer coefficient equation is a function of friction wind velocity, aerodynamic roughness length, the distance the ammonia is estimated to travel, and in the case of the advection model method, the length of the field. The concentration of gaseous ammonia at the slurry/soil surface is a function of the equilibrium constant, Henry's Law constant, pH, concentration of total ammoniacal nitrogen (ammonia and ammonium), time, depth of ammonia infiltration into the soil, soil water content, porosity, and bulk density, and is dependent on physical and chemical processes such as adsorption, convection, and diffusion. In industrial ammonia synthesis, high temperatures and pressures are required to cleave the bond between the nitrogen atoms of dinitrogen prior to hydrogenation. This study theoretically investigates catalytic reductions of dinitrogen to ammonia by B+, BH2+, Be, and BeH2, in which dinitrogen cleavage is avoided through sequential hydrogenation of dinitrogen. The stationary points and transition states of these catalytic systems are located and characterized at the MP2 and CCSD(T) levels of theory with 6-31g* and double and triple zeta basis sets. Each catalyzed reduction of a nitrogen species (dinitrogen, substituted diimide and hydrazine) occurs by hydrogenating one nitrogen atom and then the other. When dihydrogen is restricted, B+ is the most effective in activating dinitrogen. However, BeH2 is calculated to be the most efficient catalyst.Item Coastal and Marine Nitrogen Sources Shift Isotopic Baselines in Pelagic Food Webs of the Gulf of Mexico(2012-07-16) Dorado, SamuelUpwelling, atmospheric nitrogen (N2) fixation by cyanobacteria, and freshwater inputs from the Mississippi River system have been shown to stimulate new production by alleviating nitrogen (N) limitation in the northern Gulf of Mexico (GoM). Stable carbon (delta13C) and nitrogen (delta15N) isotopes were used to investigate whether these sources are utilized differentially by coastal and marine pelagic food webs. Particulate organic matter (POM), Trichodesmium, and zooplankton were collected from the Mississippi River plume and Loop Current (LC) which were detected using remote sensing data. Stable isotope values were used to separate coastal and marine water masses and environmental data (salinity, nutrient and pigment concentrations) allowed me to relate variability to the degree of freshwater influence. Published food web data from these two environments were then assessed to establish whether isotopic baseline shifts observed in our data occur at an ecosystem level. Isotope values of the POM and zooplankton were found to be significantly different between coastal and marine water masses. This was not the case for Trichodesmium whose isotope values were not significantly different between the two water masses. We found that marine water masses (sal > 35) exhibited silicate concentrations, cyanobacterial pigments and DIN: P that suggest an increased abundance of diazotrophs. In contrast, coastal water masses (sal < 35) exhibited increased diatom pigments and molar C:N indicating terrestrial sources fuel phytoplankton production. When published food web data were compared, we found producer and consumer delta15N values were enriched in the coastal compared to the marine environments. This work suggests that differences in delta15N values within my data set and published data reflect a shift in the use of biologically available N where higher trophic levels are sustained by diazotrophic activity in marine environments versus those supported by terrestrial sources in coastal ones. Food webs that have been constructed without considering Trichodesmium as a significant source of organic matter in the GoM should be reconsidered. By re-evaluating published data, this research gives insight into the early life ecology of larval fishes and works to help answer questions about the structure and function of pelagic food webs.Item Effect of variation in freshwater inflow on phytoplankton productivity and community composition in galveston bay, texas(2009-05-15) Thronson, Amanda MaeFreshwater inflows are essential to the health of estuaries and minimum discharge levels must be maintained in order to sustain a healthy ecosystem. Due to the predicted 50% increase in urban population growth along the Texas coastline by the year 2050, water regulators and managers are faced with the challenge of meeting human needs, while maintaining essential freshwater inflows into estuarine ecosystems. Galveston Bay is of particular concern because 10 million people currently living within its watershed. Freshwater inflows into Galveston Bay during 2006 were determined by using daily discharge data from a United States Geological Survey (USGS) sampling gauge in the Trinity River. Changes in water quality parameters, primary productivity, and phytoplankton community structure in response to freshwater inflows, were monitored monthly to determine how the phytoplankton community responded to inflow events. Freshwater inflow into Galveston Bay during 2006 was indicative of a low-inflow year, with seven large (>7,000 ft.3 sec-1) inflow events occurring throughout the year. There were significant differences in phytoplankton biomass (Fm), photosynthetic efficiency (alpha), and photosynthetic potential (yield) of the phytoplankton community, between wet (January-April and October-December) and dry (May-September) months. Significant differences in the biomass of phytoplankton groups also occurred with cyanobacteria being present in higher concentrations during the dry months and diatoms & dinoflagellates during the wet months. Low flow periods favored cyanobacteria, which lead to decreased secondary productivity, while pulsed inflow events resulted in enhanced secondary productivity by favoring diatoms and dinoflagellates. Resource Limitation Assays (RLAs) indicated that nitrogen was a potential limiting nutrient in Galveston Bay during spring/summer, with light limitation of phytoplankton communities possibly occurring near the mouth of the Trinity River. This study demonstrates the role of freshwater inflows in determining the primary productivity and community composition of the phytoplankton in Galveston Bay over an annual cycle. Inter-annual studies are needed to elucidate the impact of freshwater inflows in years with higher inflows to Galveston Bay and determine which of these impacts need to be incorporated into water management decisions to maintain a healthy ecosystem.Item Effects of Biochar Recycling on Switchgrass Growth and Soil and Water Quality in Bioenergy Production Systems(2012-07-16) Husmoen, Derek HowardIntensive biomass production in emerging bioenergy systems could increase nonpoint-source sediment and nutrient losses and impair surface and groundwater quality. Recycling biochar, a charcoal byproduct from pyrolysis of biomass, provides potential sources of mineral nutrients and organic carbon for sustaining biomass productivity and preserving soil and water. Yet, research is needed to verify that recycling of pyrolysis biochars will enhance crop growth and soil and environmental quality similar to black carbon or biochar derived from burning of biomass in tropical or Terra Preta soils. The experimental design of this study consisted of 3 replications and four biochar rates (0, 4, 16, and 64 Mg ha-1) incorporated in both a sandy loam and clay soil with and without fertilizer sources of N, P, and K. The sandy loam and clay soils were studied in separate experiments within a set of 24 box lysimeters seeded with switchgrass. Simulated rain was applied at 50 percent and 100 percent establishment of switchgrass for each soil type. Runoff and leachate were collected and analyzed for total and dissolved N, P, K and organic C. After the second rain event, each soil type and the accumulated switchgrass was sampled and analyzed. In the Boonville soil, biochar applied at 64 Mg ha-1 decreased switchgrass emergence from 42 percent to 14 percent when compared to soil alone. In the Burleson soil, 64 Mg ha-1 biochar had no effect (P > 0.05) on biomass production or leaf area index (LAI). Fertilizer N, P, and K had no effect (P > 0.05) on switchgrass emergence for either soil, but did increase (P < 0.001) N, P, and K uptake, biomass production, and LAI. Increasing rates of biochar increased (P < 0.001) runoff concentrations of DRP during each rain event for both the Boonville and Burleson soils. Four rates of biochar receiving supplemental N, P, and K fertilizer also resulted in greater runoff concentrations of DRP. Emergence tests under increased heat showed electrical conductivities of soil-water solutions to be as high as 600 microS cm-1, even after biochar was washed with acetone and water to remove residual oils and tars and soluble salts. Increasing biochar rates decreased soil bulk density and increased pH and SOC in the 0- to 5-cm depth of soil. As a result of high nutrient recovery during pyrolysis (58 percent of total N, 86 percent of total P and 101 percent of total K), high rates of biochar applied at 64 Mg ha-1 increased mass losses of TN, TP, and TK from both soils. Yet, the mass balance of nutrients showed a surplus of N, P, and K at 64 Mg ha-1 biochar, which suggests some nutrient inputs are not plant available and remain in soil. Careful management of biochar, especially at high rates with these high nutrient contents, is critical when trying to improve soil fertility while protecting water quality. ?Item Estimation and Fate of New Production in the Marine Environment(2014-06-03) McInnes, Allison SkinnerThe fate of carbon in the ocean determines both the amount of CO_(2) that can be sequestered and the amount of sustainable biomass. Compartmentalization into new and regenerated production allows a first order estimate of carbon available to the local community versus the amount exported. The goal of this project was to study sources and sinks of production in order to test the general hypothesis that new production is underestimated in the marine environment. Specifically we looked at pulsed new nutrients and the effect on the ecosystem, the effect of currents on our measurements and estimates of export (equivalent to new production), and finally development of a new method which will allow in situ determination of new production in the majority of the global ocean. Specifically, the role of a Pacific herring spawn was investigated as an important stimulant to ecosystem wide carbon and nitrogen cycling in Simpson Bay, Alaska. A consistent pattern was observed each year: a large bloom in June corresponded to the timing of the herring spawn and low nutrients, low phytoplankton diversity, and high POC concentrations; elucidating a previously unidentified pulse of new nutrients to the system. Estimates of carbon export are affected by the physical environment. The model presented and validated herein is used to improve our understanding of C export by including the effect of horizontal transport. We show that measurements of export to shallow water traps are less impacted by currents than deep traps. Spatial extent of variable primary production necessary to affect deep water traps is greater, as such, over half of the traps analyzed in this study are affected by up-current productivity regimes. A method to simultaneously quantify the C and N fixing community in the same sample was developed, eliminating many assumptions introduced when using different techniques and incubations. Cultured and environmental samples were successfully hybridized using TSA-FISH. Strong correlations between positively tagged community abundance and ^(14)C/^(15)N measurements are presented. The findings of this work support the general hypothesis that new production is under-accounted for in marine systems.Item Evaluating the technique of using nitrogen retention as a response criterion for amino acid studies in the horse(Texas A&M University, 2007-09-17) Antilley, Teri JillSix Quarter Horse yearling fillies were used in a duplicated 3 x 3 Latin square designed experiment to evaluate the technique of nitrogen retention as a response criterion for amino acid studies in the horse. The yearlings were paired by age and randomly assigned to one of three concentrates fed with a medium quality Coastal Bermudagrass hay throughout the study. Diets were fed at approximately 1.9% of horse body weight per day, divided into twice daily feedings with a 60:40 concentrate: hay ratio. With the exception of lysine and threonine, proposed amino acid requirements for yearling horses were calculated using nutrient to calorie ratios of gilts weighing 80-120 kg and gaining 325 g/d. Diet A was amino acid sufficient, as provided by a soybean meal-based concentrate. Diet B was amino acid deficient, with a cottonseed hull-based concentrate. Diet A and Diet B were isonitrogenous, containing approximately 12% crude protein. Diet C used the identical concentrate as Diet B, with synthetic essential amino acids and cysteine orally dosed to match the amino acid levels in Diet A. Nitrogen retention was not different between Diet A and Diet B. Diet C resulted in differences from Diets A and B in nitrogen retention; however, differences were a consequence of nitrogen intake. Nitrogen retained as a percent of nitrogen absorbed was lower (P < 0.05) for Diet B than for Diet A, for data not accounting for endogenous fecal and urinary losses. There were no differences in nitrogen retained as a percent of nitrogen absorbed for horses fed Diet C, when compared to either Diet A or Diet B, for data not accounting for endogenous losses. It was concluded that differences in nitrogen retained as a percent of nitrogen absorbed were observed between amino acid sufficient diets and amino acid deficient diets. However, horses fed amino acid deficient diets and orally dosed with synthetic amino acids, likely require some modified dosage level to achieve the same or higher values in nitrogen retained as a percent of nitrogen absorbed as those values for amino acid sufficient diets.Item Fate of nitrogen in on-site surface application systems(2005-08) Wheeler, Joshua L.; Fedler, Clifford B.; Borrelli, John; Green, Cary J.With the ever increasing suburban growth, the need for expanding currently available public utilities such as wastewater treatment systems become very difficult. An alternative to expanding these public utilities, such as wastewater treatment lines, is to install on-site wastewater treatment and disposal systems. Unfortunately, this can create other problems. First of all, the areas where these systems are usually installed are more rural areas where the source of drinking water is groundwater. In fact, 86 percent of the United States’ domestic water sources come from groundwater and it accounts for 24 and 95 percent of the urban and rural drinking water supplies, respectively. In some cases, these fresh water sources become compromised when on-site wastewater treatment systems either fail or are improperly operated. On-site systems that utilize surface application of the treated wastewater is one area of concern when you consider the nitrogen applied, how the nitrogen cycle is involved, and how uniform this nitrogen gets applied to the surface. The objectives of this research were to investigate the range in uniformity that can occur from using the currently available sprinklers in the various designed systems and how that uniformity affects the application of nitrogen to the surface application system. The potential nitrogen leached to groundwater was calculated and compared between the same sprinkler in systems that use no overlap versus systems that use up to head-to-head spacing. Head-to-head spacing can significantly reduce the amount of excess nitrogen that could potentially leach to groundwater by as much as 58 lb of nitrogen per acre per year, or 22 % of the nitrogen applied for the sprinklers analyzed. It was concluded that proper attention to the design and maintenance of on-site surface applications systems can provide an environmentally sound treatment and disposal system for wastewater.Item Fate of nitrogen in on-site surface application systems(Texas Tech University, 2005-08) Wheeler, Joshua L.; Fedler, Clifford B.; Borrelli, John; Green, Cary J.With the ever increasing suburban growth, the need for expanding currently available public utilities such as wastewater treatment systems become very difficult. An alternative to expanding these public utilities, such as wastewater treatment lines, is to install on-site wastewater treatment and disposal systems. Unfortunately, this can create other problems. First of all, the areas where these systems are usually installed are more rural areas where the source of drinking water is groundwater. In fact, 86 percent of the United States’ domestic water sources come from groundwater and it accounts for 24 and 95 percent of the urban and rural drinking water supplies, respectively. In some cases, these fresh water sources become compromised when on-site wastewater treatment systems either fail or are improperly operated. On-site systems that utilize surface application of the treated wastewater is one area of concern when you consider the nitrogen applied, how the nitrogen cycle is involved, and how uniform this nitrogen gets applied to the surface. The objectives of this research were to investigate the range in uniformity that can occur from using the currently available sprinklers in the various designed systems and how that uniformity affects the application of nitrogen to the surface application system. The potential nitrogen leached to groundwater was calculated and compared between the same sprinkler in systems that use no overlap versus systems that use up to head-to-head spacing. Head-to-head spacing can significantly reduce the amount of excess nitrogen that could potentially leach to groundwater by as much as 58 lb of nitrogen per acre per year, or 22 % of the nitrogen applied for the sprinklers analyzed. It was concluded that proper attention to the design and maintenance of on-site surface applications systems can provide an environmentally sound treatment and disposal system for wastewater.Item Freshwater contributions and nitrogen sources in a South Texas estuarine ecosystem : a time-integrated story from stable isotope ratios in the eastern oyster (Crassostrea virginica)(2012-05) Bishop, Karen Anne; McClelland, James W.; Dunton, Kenneth H.; Walter, BenjaminChanges in freshwater inputs due to water diversions and increased urbanization may alter the function and properties of estuarine ecosystems in South Texas. Freshwater and nitrogen inputs from the Mission and Aransas rivers to the federally designated Mission-Aransas National Estuarine Research Reserve (Mission-Aransas NERR) have received considerable attention in the past few years. However, freshwater inputs from two rivers (the San Antonio and Guadalupe rivers) that combine and drain into a neighboring bay (San Antonio Bay) may also provide a substantial nitrogen source to Aransas Bay, which is within the boundaries of the Mission-Aransas NERR. In order to study the influence of the San Antonio and Guadalupe rivers, an oyster species, Crassostrea virginica, was chosen to provide time-integrated information about freshwater contribution as a nitrogen source within the bays. Chapter One addresses variations in isotope values ([delta]¹⁵N and [delta]¹³C) in oyster adductor muscle tissue from 2009-2011 along a sampling transect from the head of San Antonio Bay through Aransas Bay. Stable carbon isotope values increased linearly from approximately -25 % to -17 %, while stable nitrogen isotope values decreased from approximately +16 % to +10 % along this transect. The patterns in stable carbon and nitrogen isotope values are consistent with substantial mixing of river-supplied water and nitrogen from San Antonio Bay into Aransas Bay. Variations in nitrogen isotopic signature between periods of sustained drought and flood conditions were relatively small, suggesting that riverine nitrogen contributions were similar regardless of the amount of freshwater inflow observed during the time frame of this study. Chapter Two addresses the isotopic equilibration time for adult oyster adductor muscle tissue using a year-long transplant experiment (November 2010-November 2011). Full representation of ambient water isotopic composition in oyster adductor muscle tissues was determined to occur roughly a year after transplant. Oyster adductor muscle could therefore be useful for long-term monitoring of nitrogen contribution from freshwater sources, and would be valuable to include in concert with water sampling and analysis of other tissues that have shorter integration rates for a comprehensive view of an estuarine system.Item Increased temperature effects on fish-mediated nutrient cycling in an East Texas stream(2017-11-07) McWilliams, Jessica Lynn; Hargrave, Chad W.The unprecedented rate of global warming is an inevitable outcome of anthropogenic CO2 release into the atmosphere and complex climatic feedbacks. In ectotherms, increasing temperature may increase metabolic rates, which could enhance the energy demands of individuals and should accelerate resource acquisition. Population size and fish biomass were measured seasonally in a small second order stream over a 10-year period to examine seasonal variation in these parameters. I examined effects of increased temperature on nitrogen and phosphorus excretion in the four most abundant fish in this stream system. These fishes represent three functional feeding guilds common to many temperate stream ecosystems and comprise approximately 80-90% of the fish community. I developed temperature dependent nitrogen and phosphorus excretion models for fishes and applied these models to daily average temperatures in the stream. I then simulated climate warming (+2, +4, & +6°C) to examine the potential effects of increased temperature on fish-mediated nutrient dynamics in a southern temperate stream ecosystem. I found that increased temperature does increase nutrient cycling and nutrient flux within aquatic ecosystems; however, these effects appear to be tied to population size, biomass in addition to seasonal temperature. With increased temperature effects in spring and autumn having the greatest effect, when temperatures are cool and fish abundance and biomass is also greatest.Item Nitrogen and phosphorus nutrition for semi-dwarf castor (Ricinus communis L.) production in West Texas(2012-08) Wallace, Sean M.; Trostle, Calvin S.; Auld, Dick L.; Wheeler, Terry A.In general technical nitrogen and phosphorus requirements have not been established for castor in the United States. Brazil and India have each shown nutrient requirements for castor although the climate, soil types, cultivars, and cultivation techniques are vastly different than what would be used regionally in the United States. Our objective is to measure yield response to nitrogen fertilization on irrigated castor in West Texas. Field tests were conducted 2010-2011 at Lubbock, TX (Texas Tech University Quaker Research Farm, and Texas AgriLife Extension and Research Farm), and 2010 at Pecos, TX (Texas AgriLife Research Farm), using an RCDB layout with five replication of five treatments (0-40-80-120-160 lbs/A of N added in the form of UAN). Spring soil samples were collected from each plot (0-6”, 6-12”, 12-24”, 24-36”, and if possible 36-48”, 48-60” depths) and analyzed for nitrate and ammonium nitrogen, and additionally Melich III phosphorus for phosphorus test sites. The 2011 drought reduced the yields enough to likely overshadow possible significant differences. The 2010 TTU Quaker Research Farm Site showed significant increases in yield from the 80 and 120 lbs/A N vs. the 0 lbs/A N treatment (P = 0.05), with soil test to the 36” depth showing an accumulation that averaged around 45 lbs/A of nitrate nitrogen. The 2010 AgriLife Lubbock Research Farm site soil test results show large accumulations of soil nitrate nitrogen to the depth of 36” averaging near 150 lbs/A, with no significance differences between N treatments. The 2010 AgriLife Pecos Research Farm site soil test results also showed large accumulations of soil nitrate nitrogen to the depth of 36” averaging near 250 lbs/A. Yields for this site were low and differences were not meaningful, significant differences between treatments were found between the 0 and 40 lbs/A treatment vs. the 160 lbs/A treatment (P = 0.05). The sites with low levels of rainfall and irrigation showed N treatments ineffective at increasing yield. Test sites with higher levels of rainfall and irrigation show the treatments of 80-120 lbs/A of nitrogen to significantly increase the yield. High subsoil nitrate nitrogen levels masked any yield response to nitrogen fertilizers. Overall, the fields appear to have adequate P levels for most. Unlike typical recommended 0-6” soil tests for P, moderate levels of P were also measured at 6-12” for Quaker 2010 & Quaker 2011, and Lubbock 2011. For the Quaker 2010 & Quaker 2011, and Lubbock 2011 sites when subsoil P at 6-12” is added to 0-6” then the combined soil P became 25 to 39 ppm, or in the lower range of moderate P to a higher moderate range soil P. Only one test site showed any positive response to P fertilization Quaker 2010 testing 19 ppm P 0-6” or combining with the 6-12” sample of 10 ppm P totaling 29 ppm P. The recommendation for this 29 ppm P would be the addition of 20-40 lbs P2O5 fertilizer.Item Phophorus and nitrogen leaching losses during turf establishment(Texas A&M University, 2004-09-30) Hay, Francis JohnConcerns over water quality have led to required removal of 50 % of dairy manure phosphorus (P) from the impaired Bosque River Watershed. Application of composted dairy manure (CDM) to sod and moving P off the watershed with sod has prompted a study using box lysimeters to determine NO3--N and P leaching from transplanted sod grown with CDM and inorganic fertilizer as well as sprigs top-dressed with CDM. Treatments were applied to lysimeters filled with a silica sand medium. Three leaching events were imposed, leaching 0.07 to 0.09 % of the total P applied and 0.09 to 1.43 % of total N applied. Concentrations of P in leachate averaged 0.04 to 0.25 mg L-1. Top-dressed CDM on sprigs leached statistically greater amounts of NO3--N than both transplanted sod treatments and greater P than the fertilizer grown sod. After the third leaching event, all treatments received an additional application of P, 100 kg ha-1 as CDM for manure-grown sod and sprigs, 50 kg ha-1 as triple superphosphate for fertilizer-grown sod. An additional three leachings were imposed. Top-dressed sprigs and transplanted sod leached similar amounts of P following the additional P application. Applied nutrients appeared to stay mainly in the sod layer and in the sand medium just below the sod layer. Top-dressed CDM appears to exhibit greater leaching losses of NO3--N than transplanted manure-grown sod and greater N and P losses than transplanted fertilizer grown sod.Item Preparation and characterization of nitrogen doped carbon nanotube electrode materials(2006) Maldonado, Stephen; Stevenson, Keith J.This dissertation describes the preparation and characterization of nitrogen doped carbon nanotube films by a chemical vapor deposition (CVD) process. Thorough description of the preparation method is given. A variety of techniques are used to demonstrate the relationship between the physicochemical properties and electrochemical properties of nitrogen doped carbon nanotubes, shedding insight to the influence of nitrogen doping on observed electrocatalysis phenomena. Chapter 1 comprises a general overview of the presented material and scope of the work. Chapter 2 details the CVD preparation of nitrogen doped carbon nanotubes. Scanning electron microscopy, thermal gravimetric analysis, and x-ray photoelectron spectroscopy are used to demonstrate the degree of control afforded by the CVD process over the resultant properties of the prepared carbon nanotubes. The direct preparation of carbon nanotube films on a current collector is shown. Chapter 3 consists of a thorough characterization and comparison of nitrogen doped carbon nanotubes and non-doped carbon nanotubes. Transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy demonstrate the increased disorder caused by nitrogen doping into the graphitic lattice structure of carbon nanotubes. X-ray photoelectron spectroscopy highlights the existence of multiple carbon-nitrogen surface functionalities that change in relative abundance as the nitrogen content is varied. Titration analyses indicate that nitrogen doped carbon nanotubes are basic and acquire a cationic surface charge in solutions of neutral pH. Chapter 4 presents a collection of voltammetric responses of several outer-sphere and innersphere redox probes. The similarities and differences between the responses at non-doped carbon nanotube electrodes and nitrogen doped carbon nanotube electrodes are noted and discussed in the context of the conclusions of the physical characterizations. A detailed mechanistic analysis of the O2 reduction process at nitrogen doped carbon nanotube electrodes is presented. Chapter 5 details continuing work with carbon nanotube materials for fundamental and applied studies.Item Response of nitrogen and phosphorus leaching and soil properties to applications of biosolids during turfgrass establishment(Texas A&M University, 2005-02-17) Kerns, James PatrickRegulations for total maximum daily loads require management of phosphorus loading from farms and municipalities. This study evaluated environmental impacts of a system for using and exporting the phosphorus in composted dairy manure (CDM) and composted municipal biosolids (CMB) through turfgrass sod. Responses of soil physical, chemical, and biological properties within and below the sod layer were monitored during turfgrass establishment in two experiments under greenhouse conditions. During turf establishment in column lysimeters, phosphorus and nitrogen leaching from an amended surface layer through soil were evaluated. In addition, growth of turf was related to the observed changes in soil nutrients and properties. In the first experiment, four replications of a factorial design comprised three soil types (USGA greens sand, Windthorst fine sandy loam [fine, mixed, thermic Udic Paleustalf], Houston black clay [fine, smectitic, thermic, Udic Hapustert]), two dairy manure rates ( 200 kg P ha-1, 400kg P ha-1), and two turf species (St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze var. Raleigh) and Tifway 419 Bermudagrass (Cynodon dactylon [L.] Pers. x C. transvaaleensis Burtt-Davy). Columns received three separate leaching events in which a 9-cm depth of distilled water was applied. A similar experimental design was implemented for Experiment 2 in January 2004. Treatments consisted of the same three soils and three volume-based rates of CDM and CMB (0, 150, 250 cm3 L-1) during establishment of St. Augustinegrass turf. Columns received one pore volume of distilled water on three separate occasions. In both experiments, soil physical properties (bulk density, water infiltration rate, and water content) and microbial populations were unaffected by CDM or CMB. Applications of CDM at P-based rates utilized in the first experiment yielded no variation of leaching loss among rates of P or N. Most of the P applied was retained in the top 10 cm of soil. When large volume-based rates were used, leaching losses of P and N varied among CDM or CMB application rates. Leaching losses were only observed in the USGA sand and were highest for the 250 cm3 L-1 rate of CDM or CMB. Regardless of compost source, applications of organic amendments at volume-based rates can increase leaching loss of P and N on sandy soils. However, if P-based rates are used there is little risk for leaching loss of N and P during sod establishment.Item Selective reduction of nitrogen dioxide by ammonia(Texas Tech University, 1972-12) Cheng, Yang-lehNot availableItem Soil microbial community structure and allocation are critical drivers of ecosystem functioning(2015-08) Averill, Colin; Hawkes, Christine V.; Bennett, Phillip; Juenger, Thomas; Keitt, Timothy; Leibold, MathewThe functioning of terrestrial ecosystems is entirely dependent on the activity of autotrophic primary producers and microbial decomposers, and how they are affected by climate, mineralogy and anthropogenic change. Ecosystem ecology has classically focused on how allocation and community composition of plant primary producers may alter predictions of future ecosystem functioning in the face of environmental change. Little attention has been paid to allocation and community composition of microbial decomposers. The functioning of microbial decomposers has been considered implicitly, in the context of plant traits; primarily plant biomass chemistry. However, soil microbial communities represent a vast diversity of taxa spanning multiple kingdoms of life and an array of functional groups. It is not only likely, but probable that understanding ecological aspects of soil microbial community structure, activity, and allocation will fundamentally change how we understand and predict ecosystem function in the future. In chapters 1-3 of this dissertation, I explicitly considered how microbial activities varied based on microbial community structure and the resulting impacts for biogeochemical cycling. Specifically, in chapters 1 and 2, I manipulated the relative abundance of symbiotic root fungi to demonstrate that competition between symbionts and free-living decomposers for nitrogen slowed soil carbon cycling. In chapter 3, I scaled how nitrogen is partitioned between plants, mycorrhizas and free-living decomposer microbes to demonstrate how shifts in microbial community structure could explain how forests productivity is sustained over centuries. In chapter 4, I developed a microbial allocation framework that explicitly considers microbial resource environments. I demonstrated that past microbial allocation frameworks based on plant ecological mechanisms cannot explain allocation patterns of decomposer microbial life. Throughout this dissertation I attempt to put soil microbial life in an explicit ecological context that challenges current understanding of ecosystem process and will allow for deeper understanding and prediction of ecosystem functioning. Incorporating microbial community structure, allocation, and simple ecological mechanisms into models will improve the predictive power of ecosystem ecology.Item The effect of various amino acids as nitrogen source on biofilm formation of Aeromans spp.(2012-12) Price, Rachael; Jeter, Randall M.; Zak, John; Rumbaugh, Kendra P.; Hamood, Abdul N.For generations, scientists have studied microorganisms in their planktonic form to discover basic information about microorganisms and to perform more detailed experiments, including testing the effectiveness of antimicrobial agents. The term biofilm was defined and the concept of the biofilm was formulated very recently. Therefore, relatively little is known about biofilm growth in otherwise well-characterized microbial species. This would be a minor issue if microbial growth within a biofilm was similar to planktonic growth, but this is not the case. The difference in microbial growth within a biofilm compared to that of planktonic bacteria is immense. The perspective on uses for and treatments of biofilms are changing as we learn more about microorganisms within biofilms. For this reason, it is important to further explore the bacterial biofilm. A correlation between biofilm growth and nutrient environment has previously been observed but needs clarification. In this thesis project, I have isolated an Aeromonas environmental strain from the playa lake in Maxey Park in Lubbock, TX and analyzed the effect of varied nutrients, specifically nitrogen source, on biofilm formation of the environmental Aeromonas strain, comparing its biofilm formation capabilities to those of a reference Aeromonas hydrophila ATCC 7965 strain with the crystal violet assay. I have also assessed the accuracy of the crystal violet assay in quantifying cell concentrations by observing crystal violet absorbance of planktonic Aeromonas cells. Both the environmental Aeromonas isolate and the reference ATCC 7965 Aeromonas strain formed thicker biofilms in the presence of rich nutrient environments as compared to the more dilute nutrient environments. Our data suggests that Aeromonas ATCC 7965 is a more effective biofilm-former than the environmental isolate. It also reveals extreme variance in biofilm formation of both Aeromonas strains observed in the presence of different amino acids as nitrogen source. Finally, our assessment of the accuracy of the crystal violet assay and the calibration curve demonstrated the limitations of a common technique used in preliminary biofilm research.Item The significance of ammonium adsorption on lower laguna madre (texas) sediments(2009-05-15) Morin, Jeffery PeterThe work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations.Item Trophodynamics of the benthic food webs in the Chukchi and Beaufort Seas, Alaska(2013-12) McTigue, Nathan David; Dunton, Kenneth H.The Chukchi and Beaufort Sea shelves host diverse and productive seafloor ecosystems important for carbon and nitrogen cycling for the Arctic Ocean. The benthic food web transfers energy from primary producers to high trophic level organisms (e.g., birds, fish, and mammals), which are important for cultural practices and subsistence hunting by Native Alaskans. This work focuses on the trophic ecology of arctic food webs through use of several different approaches. First, variation in the natural abundance of stable carbon and nitrogen isotopes facilitated the identification of trophic pathways and, subsequently, allowed the comparison of trophic guilds and food webs from the Chukchi and Beaufort Seas. Compared to water column and sedimentary organic matter end-members, second trophic level grazers and suspension feeders were conspicuously ¹³C-enriched throughout the Chukchi Sea, which supports the hypothesis that microbial degradation of organic matter occurred prior to metazoan assimilation. Second, food web recovery from disturbances caused by exploratory oil drilling at the seafloor that had occurred approximately 20 years prior were assessed in both the Chukchi and Beaufort Seas. Based on isotopic trophic niche overlap between organisms common to drilled and reference sites in the Chukchi and Beaufort Seas, the oil drilling sites had similar food web structure, indicating recovery from the activity associated with the drilling process. Third, photosynthetic pigment biomarkers were used to better understand the diagenetic process, specifically focusing on how both microbial and metazoan grazing pathways degrade organic matter in relation to seasonal sea ice retreat in the Chukchi Sea. The benthic macrofaunal and microbial food web caused rapid degradation of organic matter upon the initial pulse of microalgal food sources to the seafloor. These diagenetic pathways are linked to the ¹³C-enrichment of residual organic matter, which corresponds to the stable isotope values measured in the benthic macrofauna. Lastly, high-precision liquid chromatography and spectrophotometry were compared for estimating sedimentary pigments in the marine environment. Substantial differences in pheopigment (chlorophyll degradation products) concentrations were observed between the two techniques, suggesting the need for revisions to the monochromatic spectrophotometric equation that relates absorbance to pigment concentrations. One pheopigment, pheophorbide, was found to interfere with the accuracy of the spectrophotometric equation and caused the overestimation of pheopigments.