Thesis (Ph. D.)--Syracuse University, 2003. / "Publication number AAT 3113254."

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3662. Adviser: Praveen Kumar. Includes bibliographical references (leaves 133-139) Available on microfilm from Pro Quest Information and Learning.

<p> Land-use change has significantly contributed to rising global atmospheric carbon dioxide (CO₂) concentrations by reducing carbon (C) storage and increasing C emissions from soils. Soils represent the second largest C pool on Earth, with drylands comprising approximately 21% of the globe&rsquo;s soil organic carbon (SOC). While research regarding the effects of land-use change on SOC in more mesic regions has typically shown an overall reduction in SOC, it is relatively unclear how the land use change from native vegetation to irrigated cropland will affect SOC dynamics in semi-arid regions. Surface soils (0-10 cm) and subsoils (90-100 cm) of an alfalfa field that has been under irrigation for more than five decades, and of an adjacent unmanaged shrubland were collected at the University of Nevada, Reno Main Station Field Laboratory on the eastern boundary of Reno, Nevada. Soils were fractionated using particle size and density fractionation methods and each fraction was analyzed for C, nitrogen (N) content and C and N isotopic composition. Soil CO₂ concentrations and effluxes were measured monthly in the same sites for the 12-month duration of the study.</p><p> Carbon and N analysis of particle size and density fractions revealed that irrigation and management significantly reduced the amount of C and N in the soil. The amount of C in the labile fractions from both the particle size fractionation and density fractionation was significantly smaller and the relative amount of C in recalcitrant fractions was larger in the alfalfa field compared to the native vegetation. The differences in &delta;¹³C values of both stable and labile soil organic matter reflected differences between dominant vegetation types, but these differences were only significant for density fractions. Both fractionation methods revealed differences in &delta;¹⁵N values between soil types, again reflecting differences in vegetation. An eight-week laboratory incubation at constant temperature and water content revealed that the shrubland soil had a higher potential rate of decomposition than the alfalfa field soil, even though alfalfa SOM had a lower C/N ratio, likely as a result of water limitations at the field site allowing for greater accumulation of labile C in the shrubland soil. Additionally, decomposition of organic matter in the buried A horizon from each site was limited by substrate quality rather than environmental conditions. Land conversion to irrigated agriculture resulted in larger soil CO₂ concentrations and effluxes, especially during the growing season. This was true despite shrubland soils having larger amounts of labile C available for decomposition. The source of respired CO₂ for each soil type remains unclear, though CO₂ &delta;¹³C values reflected differences in &delta;¹³C isotopic values for the SOM and vegetation between the two sites. The results from this study suggest that converting a semi-arid shrubland into irrigated cropland may cause an overall loss of SOC that can contribute to rising atmospheric CO₂ levels, though the relative amounts of recalcitrant C may increase in semi-arid soils following management.</p><p>

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No description available.

Soil-reinforcement technology has become an acceptable approach for constructing earth structures. Development in the industry of polymer based reinforcements (geosynthetics) provided the necessary products to advance this technology Limit state design of soil-reinforced continuum does not account for the characteristic kinematic and constitutive behavior of the different elements that constitute a reinforced-soil mass. In the mean time, finite element modeling, which is a powerful numerical tool, provides a scheme of analysis that is capable of predicting the overall performance of a reinforced-soil continuum. Different finite element models have been reported in the literature for modeling soil/geosynthetic interaction in reinforced-earth structures. However, most of these attempts do not fully represent the possible modes of shear mobilization that may develop along different types of soil/geosynthetic interfaces. Possible numerical problems were also associated with most of these models This research provides a new approach for the finite element modeling of soil/geosynthetic interaction in reinforced earth works. The proposed approach is based on the actual interaction behavior experienced in different experimental and theoretical studies presented in the literature over the past three decades The model was numerically tested versus the results of actual laboratory and field tests conducted on soil/geotextile and soil/geogrid pullout tests. The results of the numerical analyses complied with the actual measurements indicating the reliability of the model. A new computer program, TU-INTERACT incorporating the new model, was developed to simulate the behavior of full-scale reinforced-earth structures. The program was used to perform a class-C prediction for the field behavior of a full-scale test section of a levee located in New Orleans, Louisiana. The numerical model yielded good predictions of the field measurements A parametric study was conducted on virtual scenarios to investigate the effect of the different control parameters of soil/geosynthetic interactions on the overall behavior of reinforced-soil masses, and to further examine the sensitivity of the proposed model to the changes in such parameters. Results of this study yielded logical behavior that conformed with the expected real performance of reinforced earth structures / acase@tulane.edu

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on December 2, 2009. Major professor: Brent G. Hallock, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Agriculture with specialization in Soil Science." "November 2009." Includes bibliographical references (p. 67-71). Also available on microfiche.

The impacts of El Nino Southern Oscillation (ENSO) on precipitation, reference evapotranspiration, and vegetation in a three-state region of central Mexico were investigated using daily weather data from 20 weather stations for the years 1970 through 1990, which included 5 El Nino years, 5 La Nina years, and 11 Neutral years. In addition, two years, 1997 (El Nino), and 1998 (La Nina) of 10-day NDVI composites were analyzed during the growing season (May-Oct) along with precipitation and reference evapotranspiration (ETo) over central Mexico. Regional precipitation trends were analyzed using the normalized rainfall departures. The interannual variation of vegetation cover was analyzed using the NDVI on 10-day and monthly bases. The Food and Agricultural Organization (FAO) Penman-Monteith method was used to calculate ETo. The dynamics of the soil water balance in central Mexico was evaluated according to the method proposed by Thornthwaite and Mather. Analyses indicate that driest conditions occurred within the northern part of the region and during neutral ENSO years. Rainfall amounts during El Nino and Neutral years were not statistically different however, La Nina years were about 30% wetter than N and EN years (0.05 level). The correlation coefficient between NDVI and precipitation was 0.79 in 1997, and 0.52 in 1998, in June and July, respectively. Negative correlation was found between NDVI and reference evapotranspiration during the rainy months of July and August. The spatio-temporal variability of NDVI showed that there was significant statistical difference in NDVI between regions, but not between years. Regional soil water balance determinations indicated that conditions were most favorable in the Southern part of the region for crop growth during La Nina years. In general, soil water deficits were reduced by about 50% during the growing season compared to the annual soil water deficits.

The objective of this study was to evaluate the effects of mesquite overstory removal and modifications of soil properties due to mulching treatments on herbaceous production. The three overstory treatments were complete removal of mesquite overstory with no removal of regrowth, complete removal of mesquite overstory with removal of regrowth and an untreated control. The mulching treatments included applications of chip mulch, commercial compost, lopped-and-scattered mesquite branchwood and a control. Both overstory treatments resulted in an increase of over 20% in total annual herbaceous production. The overstory treatment of complete removal of mesquite overstory with no removal of regrowth had the greatest impact on fall production of native herbaceous species during years of relatively high precipitation, at times increasing production by almost 2-fold. Mulching treatments had no effect on herbaceous production; however, soil pH and plant available phosphorus was affected by some of the mulching treatments.

In the arid Southwest where groundwater levels are rapidly declining, reuse of wastewater for groundwater recharge is currently being practiced. Since this practice is known to improve the chemical and biological quality of wastewater, it has been referred to as Soil Aquifer Treatment (SAT). This study investigated the fate of enteric viruses during SAT in Los Angeles, California, and Tucson, Arizona. The sites differed by both the quality and quantity of wastewater applied to spreading basins. At the Tucson site, secondary treated wastewater was applied. In Los Angeles, some sites received stormwater run-off combined with tertiary treated wastewater and others received only tertiary treated wastewater. A major concern with recharge of groundwater is the possible introduction of disease-causing organisms from inadequately treated wastewater. Although harmful bacteria, viruses, and protozoa may be present in wastewater, viruses cause the greatest concern regarding groundwater contamination due to their small size and long-term survival capabilities in the environment--making them less likely to be removed by the process of soil filtration. Integrating the DNA amplification method Polymerase Chain Reaction (PCR) with cell culture, a new technique called Integrated Cell Culture-Polymerase Chain Reaction (ICC-PCR) was adopted to study the occurrence of viruses after SAT. ICC-PCR was used in this study for the detection of non-cytopathogenic effect (CPE) producing enteroviruses in cell culture lysates. Primers had a sensitivity of 1 PFU/mul in cell culture lysate fluid. ICC-PCR products were confirmed with semi-nested PCR and sequencing of the viral nucleic acid. Two hundred eighty-two CPE negative cell culture lysates were analyzed via ICC-PCR. Twenty-seven of these cell culture lysates were found to be positive by ICC-PCR. These twenty-seven cell culture lysates encompassed four tertiary treated wastewater samples, three reclaimed groundwater monitoring well samples, three deep potable groundwater well samples from the Los Angeles area, two secondary wastewater effluent samples, and one reclaimed groundwater monitoring well sample from Tucson, AZ. Coliphages were detected in the groundwater at the Tucson SAT site more often than indicator bacteria. There was no evident relationship between the occurrence of indicators and isolation of non-CPE producing enteroviruses at the Tucson site.