>Magister Scientiae - MSc / Salt pans are a characteristic feature of many dry deserts. The microbial communities inhabiting salt pans are thought to be particularly complex and are generally dominated by halophilic microorganisms. Although saline pools are frequently found within the hyper-arid Namib Desert, the microbial communities of these saline sites have been scarcely investigated. The aim of the present study was to characterise the archaeal, bacterial and cyanobacterial diversity inhabiting these extreme saline pools using three culture independent molecular techniques (DGGE, T-RFLP and 16S rRNA clone libraries). The physiochemical results, mainly the conductivity readings recorded from the sampling sites, indicated that the Gobabeb (103.0mS/cm) region was less saline than the two Swakopmund [(Sps01) (150.0mS/cm) and Sps02 (180.0mS/cm)] sites. Results obtained from DGGE and T-RFLP data were in agreement for both bacterial and cyanobacterial analysis indicating that the Gobabeb site was more diverse than the two Swakopmund sites (Sps01 and Sps02). In comparison, the archaeal community profiles for DGGE and T-RFLP analysis were in agreement illustrating that the archaeal community were more abundant in the two extreme Swakopmund saline sites. Phylogenetic data obtained from 16S rRNA gene clone libraries identified halophilic phylotypes (Rhodothermaceae, Idiomarinaceae Puniceicoccaceae and Cyanobacteria/Chloroplast, Family VII) normally associated with salt rich sites. In addition, a large number of unclassified taxa were identified. To conclude, the study highlighted the presence of a rich microbial diversity present within the salt pans of the Namib Desert and establishes a platform for future investigations. / National Research Foundation

Microbial mats have played an important role in the carbon (C) and nutrient cycles since the Archean Eon and modern mats are important contributors to the biogeochemistry of intertidal wetlands. Microbial mats are flat assemblages of microbes that are currently found in many unvegetated habitats globally. Intertidal salt pans are a common habitat for microbial mats, however little is known about the distribution of microbial mats within the intertidal landscape. Understanding the spatial distribution of microbial mats is critical to developing quantitative estimates of the impacts of microbial mats on their ecosystems. We photographically measured the presence and density of microbial mats within 1 m2 quadrats across a landscape scale (~1000 Ha) on the Gulf Coast of Florida. The wide variety of metabolic processes that are found within microbial mats makes the net biogeochemical impacts of the microbial mats highly variable as well. To explore the biogeochemistry associated with microbial mats, we measured a suite of soil attributes under microbial mats and compared those measurements to nearby soils without microbial mats. We found that microbial mats are found on soils with biogeochemical attributes that are significantly different than soils without microbial mats. Soil organic matter, nitrate concentration, and soil temperature significantly increased in soils under microbial mats; pH was significantly lower in soils under microbial mats. Also notable was although the concentration of soil organic matter was higher, the bioavailability of that organic matter was significantly lower. Microbial mat presence is correlated with geomorphic variables such as proximal boundaries, as well as neighboring vegetation and other microbial mats.

Thesis (D.Sc.)--University of Adelaide, Dept. of Geology and Geophysics, 2002. / "April 2002" Includes bibliographical references and list of the publications and papers submitted.

Thesis (M.S.)--State University of New York at Binghamton, Department of Geological Sciences and Environmental Studies, 2008. / Includes bibliographical references.

The playas of the Salt Basin in Trans-Pecos Texas are natural laboratories for the study of the hydrodynamic, hydrochemical, and sedimentologic properties of the unsaturated zone under the conditions of evaporation from a shallow water table. Water beneath the salt-flat surface moves upward from the saturated zone, through a thick capillary fringe, to the unsaturated zone where it is removed by evaporation. Daily temperature fluctuations change soil suction values and seasonal variations in temperature alter the thickness of the capillary fringe. There is little change in the chemical composition of the pore water as it moves from below the water table to the capillary fringe because the filled pore spaces of the capillary fringe prevent evaporation from taking place. However, an enrichment in the heavy isotopes of hydrogen and oxygen in the groundwater, as compared to area precipitation, suggests that evaporation may have occurred earlier along the flow path. As water moves from the top of the capillary fringe into the unsaturated zone, evaporation in the partially-filled pore spaces increases the total dissolved solids content. According to the increase in chlorinity, the brine has lost over 60% of its original volume by the time it has moved to within 20 cm of the surface. Evaporation in the unsaturated zone further enriches the brine in deuterium and oxygen-18. Gypsum precipitation in the unsaturated zone depletes the shallow pore water in calcium and sulfate, relative to chloride, and forms white patches, enterolithic bands, and discontinuous lenses of pure gypsum. The sediments are made almost entirely of gypsum and dolomite. The high magnesium-to-calcium molar ratio in the brines and the poorly ordered nature of the dolomite mud in the sediment column indicate that the salt-flat dolomite formed by the alteration of a calcium carbonate precursor. A lack of lateral continuity in sediment structures and a change in sediment character from massive below the water table to laminated above indicate that the shallow salt-flat sediments were formed by vadose-zone processes rather than by sedimentation in an ancient lake. / text

Master of Arts / Department of Geography / Jida Wang / Monitoring salt pans is important especially for agricultural management in arid or semi-arid regions because salt pans can negatively affect human life, wildlife, and ecology. Some of the harmful impacts of salt pans are accelerated desertification, cropland loss, economic downturn, wildlife loss, and forced migration of humans and animals due to salt storms. Spectral salt pan indices based upon remotely sensed data (using spectral properties of Landsat-8 imagery) suggested in previous studies vary by location. In other words, the spectral configuration of a salt index for a given location may not be readily applicable to another location due to spatial heterogeneity of salt components across the continental surface. Using Landsat-8 OLI imagery and climate data sets, this study aims to develop a mapping framework which can effectively extract salt pans and salt playas under various spectral conditions in different geographic locations. Based on training samples selected in eight major salt pans/playas in North America, Central Asia, Africa, and Australia, the mapping framework was designed to include the following steps: i) a conservative salt index to highlight potential salt-covered regions, ii) a calibrated support vector machine (SVM) to extract high-salinity areas in the mask regions, and iii) a posterior quality assurance/ quality control (QA/QC) with assistance of auxiliary datasets (e.g., surface slope and land covers) to eliminate commission errors and refine the extracted saltpan areas. The developed mapping framework was validated in the arid endorheic regions across the western United States, with a total area of 699 thousand square kilometers. Both qualitative and quantitative assessments of the results show reliability of the developed framework. The overall accuracy of the extracted salt pans prior to QA/QC is 97%. The final product after QA/QC achieves an overall accuracy of 99.95% and a Kappa statistic of 0.99.According to the results of salt pans areas and endorheic basins areas, it can be concluded that two aforementioned variables of this study are positively correlated to each other, and 1.10 percent of the entire case study area is covered by salt pans. The accuracy of the results suggests a potential that the mapping framework, together with the collected training sample and algorithms, may be applicable to identify salt pan and salt playa regions across the Earth’s land surface.

"April 2002" Includes bibliographical references and list of the publications and papers submitted. Pt. 1: section 1. Ostracod taxonomy and ecology -- section 2. Limnology of salt lakes -- section 3. Ostracod palaoecology - Quaternary environments -- section 4. Palaolimnology - Quaternary paleoenvironments and geology -- pt. 2: section 5. Geochemistry of ostracod shells -- section 6. Palaeoceanography Contains the majority of the author's scientific publications. Aims at reconstructing Quaternary paleoenvironments, mostly from the Australian region, using the fossil remains of organisms as well as new geochemical techniques.

"April 2002" / Includes bibliographical references and list of the publications and papers submitted. / 2 v. (various pagings) : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Contains the majority of the author's scientific publications. Aims at reconstructing Quaternary paleoenvironments, mostly from the Australian region, using the fossil remains of organisms as well as new geochemical techniques. / Thesis (D.Sc.)--University of Adelaide, Dept. of Geology and Geophysics, 2002