This investigation has been made to see whether there is a correlation between microorganisms present and the water content and temperature of four Denton County, Texas, sandy soils.

This thesis is concerned primarily with the growth and detection of soil microorganisms in ten Denton County, Texas, soils antagonistic to a specific gram-positive and a specific gram-negative bacterial organism.

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Ph. D.

Free energy changes of oxidative inorganic nitrogen transformations in acid and basic media were calculated and interrelated. The free energy values of reactions involving nitrification were not always found to be in agreement with those reported in the literature. The primary reason for the deviations was that the pH of the medium had often not been considered in formulating these reactions. It was also found that thermodynamically, hyponitrous acid and nitrous oxide might well be intermediates in the process of nitrification. The existence of hydroxylamine as an intermediate between ammonia and/or ammonium ion and nitrite was not supported by the data obtained. It was shown that in acid solutions nitrite may thermodynamically undergo three reactions; it may decompose to nitric oxide, oxidize to nitrate or be reduced to nitrous oxide. In alkaline solutions nitrate seems to be the only product. Ammonia volatilization and water evaporation from the soils investigated followed different functions and may be independent of each other. The functions were not affected by differences in soil texture, soil water, speed and relative humidity of air flowing over the soil surfaces. Ammonia losses from finer-textured soils were proportional to their original soil pH's. Norfolk fine sandy loam, pH 6.7, lost most ammonia indicating that soil texture is also an important factor in ammonia volatilization. A linear relationship was observed between rate of ammonia applied (up to 600 ppm) and ammonia volatilized. The rate of ammonia volatilization followed a first-order reaction. Deviations from a first-order reaction were observed when higher levels of ammonia were applied. In regard to mechanisms of ammonia adsorption by soils it was found that at low concentrations, ammonia adsorption followed Langmuir's monomolecular adsorption theory. The differential slopes obtained for different sections of the curves were related to reactions involving "hydrogen", exchange sites and physical adsorption. The S-shaped curve obtained for high concentrations suggests the formation of polymolecular layers. Ammonia adsorption by neutral and basic soils also gave a typical Freundlich adsorption isotherm and furthermore closely simulated the behavior of a buffer medium. In fine-textured soils the amount of ammonia retained was inversely related to the original soil pH. The subsequent difference in adsorption capacity for ammonia between Yolo loam and Davidson clay, and between the buffer medium and Norfolk fine sandy loam seems to indicate that kind and amount of salt and/or weak acid may have a greater effect on ammonia adsorption than pH. Between texture groups, texture appears to exert a major influence on ammonia adsorption capacity. / Ph. D.

The herbicide simazine (2-chloro-4,6-bis(ethylamino)- 1,3,5-triazine) was found to have an inhibitory effect on nitrification in pure and mixed cultures of the nitrifying bacteria. Simazine concentrations of 6 and 9ppm inhibited the rate of nitrification in soil perfusion units, and an abnormally high level of nitrite nitrogen was observed in the herbicide treatments. The herbicide had no effect on the growth of Nitrosomonas europaea in shake flask culture, but did inhibit the growth of Nitrobacter agilis. The addition of yeast extract to the culture medium did not reverse the inhibition. Simazine did not inhibit the respiration of N. agilis even at a 100ppm concentration. Five organisms were isolated which could utilize simazine as a sole source of carbon and nitrogen. Pure cultures of these organisms were made and several were identified. / Master of Science

Microcosm studies determined that the indigenous microflora of the subsurface Groseclose clayey loam did not metabolize TBA, but TBA degradation was stimulated by the addition of the Pseudomonas sp., VT100. The indigenous subsurface microflora of the Fredrick clay metabolized TBA in soil microcosms that contained 10 to 500 mg/liter TBA. The addition of Pseudomonas sp., VT100, to the Fredrick clay enhanced the rate of TBA degradation in the l0 and 500 mg/liter TBA treatments, and reduced the time required for the initiation of TBA degradation. The indigenous Fredrick clay microflora reduced the growth and TBA degrading potential of the Pseudomonas sp. The addition of yeast extract and acetate to the Groseclose clayey loam allowed the indigenous microflora to initiate TBA degradation and enhanced TBA degradation in the sterile Groseclose clayey loam inoculated with Pseudomonas sp., VT100. We hypothesize that the native TBA-degrading microflora competed with the Pseudomonas sp. in both soils. A 1.0 mM molybdate amendment stimulated TBA degradation by the indigenous microflora but reduced the rate of TBA degradation by Pseudomonas sp., VT100, in subsurface soil microcosms. A TBA-degrading Alcaligenes sp. was isolated from the Fredrick clay. Limited TBA degradation was observed in one of three deep subsurface coastal plain soils after 220 days of incubation. / Master of Science

A microcosm study was performed to investigate the biodegradation potential of BTX compounds in unsaturated soils under aerobic and anaerobic conditions. Toluene was used as a model compound at concentrations of 100 to 200 mg/L. An uncontaminated, groseclose soil ranging in depth from 0 to 18 feet was used in order to observe differences in microbial degradation abilities in shallow subsurface environments. Several metabolic groups were investigated including aerobes, denitrifyers and sulfate reducers. Bacterial densities of these groups were determined at each soil depth. Physical and chemical parameters of the subsurface environments were also investigated to observe their impact on microbial biodegradation potentials. These included changes in soil particle size, moisture content, and pH with increasing depth. Substantial toluene biodegradation took place in some, but not all soils under both aerobic and denitrifying conditions. Biodegradation rates varied considerably among aerobes and denitrifyers in similar environments. In acidic, poorly drained clay soils of 3, 6 and 9 feet, denitrifyers readily degraded toluene while aerobic microorganisms were unable to mineralize the compcund. Evidence of toluene biodegradation by anaerobic bacteria including sulfate reducers was also observed in moist, clay soils although the rates were much slower. Currently, in situ bioremediation techniques for benzene, toluene and xylene compounds almost always rely on indigenous, aerobic organisms to degrade the contaminants. However, results of this study indicate that aerobic organisms capable of biodegradation may not exist in some subsurface environments, even in soils very close to the surface. The physical/chemical properties of unsaturated environments have significant impacts on microbial capabilities as well as the biodegradation potential of contaminants. / Master of Science