Thesis (S.M.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2001. / Includes bibliographical references (leaves 65-72).

During the last deglaciation, 15,000 to 12,000 calendar years ago, global warming and wholesale shifts in regional precipitation patterns produced dramatic changes in vegetation worldwide. Paleobotanical records, namely pollen and macrofossils, have been used not only to reconstruct shifts in plant distributions and abundances, but also to quantify changes in temperature and precipitation amounts or seasonality. In addition to climatic change, during the full glacial period atmospheric CO₂ values had dropped 30% to 200 ppmv compared to the Holocene, preindustrial value of 280 ppmv. Hypothetically, variations in atmospheric CO₂ affect plant water-use efficiency (carbon gained to plant-water transpired) and thus may have modulated vegetation response as climates change. The studies incorporated in this dissertation focused upon carbon isotope and morphological changes in leaves of key functional groups. The studies concentrated on plant species that are abundant in the fossil record and comprise major floral components of past and present vegetation. Key findings include: (1) that shifts in δ¹³C in modern populations along steep environmental gradients seldom exceeds inter-plant variability at a given site, (2) inter-plant and intra-site variability in modern and historic herbarium collections of the C₄ halophytes Altriplex canescens and A. confertilfolia and packrat midden macrofossils of A. canescens excludes their use as a reliable proxy for atmospheric δ¹³C, (3) calcium-oxalate crystals are common component in plant tissue and can have a significantly different δ¹³C value that increases inter-plant variability, especially in C₄ plants such as Atriplex canescens and A. confertifolia, (4) carbon isotope and stomatal density/index measurements of macrofossils from packrat middens show species specific adaptation in ecophysiological processes as atmospheric CO₂ rose from the full glacial, and (5) the greatest adaptation to low atmospheric CO₂ during the last ice age was in the C₃ species and that C₄ and CAM plants showed few changes in their discrimination against ¹³C or in the number of stomata on their leaf surfaces.

A multidisciplinary study the oceanography of the Pontevedra Ria (NW Spain), including hydrography, biogeochemistiy and biogeochemical modelling, has been performed. The hydrographical variability of the Pontevedra Ria was dependent on freshwater inputs and upwelling of nutrient-rich East North Atlantic Central Water from the shelf. Intrusions of the Poleward Current were also detected during winter. A stratified box model approach predicted that upwelling water fluxes into the ria of 2-4x10³ m³ s-1, of which >30% rises to the surface waters inside the ria. Freshwater residence time varied from ~4-9 d in the central ria and 1-4 d in the internal ria. Nutrients concentrations showed a strong fluvial and oceanic signal, with a clear zone of near-bed aerobic remineralisation in the internal ria. Nutrient flux experiments showed that high nutrient fluxes, particularly ammonium (3.5 mg N mˉ² hˉ¹), coincided with period of high water influx to the ria. These were related to stirring of quasi-benthic phytodetrital fluff. Denitrification was a major fate for particulate organic nitrogen in the sediment, averaging 2.5 mg N m ˉ² h ˉ¹ for the spring and dry season. A non-steady state nutrient budget revealed that the central and internal zones of the Pontevedra Ria display different biogeochemical characteristics. Net community production (NCP) based on phosphate uptake was spatially and temporally variable, with rates of 9.6 and 20.2 mg C m ˉ² h ˉ¹ in central and internal rias in spring, respectively, and 30.3 and 29.0 mg C m ˉ² h ˉ¹ in the dry season. Previously unquantified benthic nutrient inputs were important, and up to 25% of NCP was due to the sediment nutrient flux in the dry season. Denitrification calculated with the nutrient budget equalled 1.82 and 5.66 mg N m ˉ² h ˉ¹ in the dry season in the central and internal ria, respectively, and was equal to 27 and 42% of dry season NCP. The robustness of the box model was questioned, and found to be an unsuitable modelling approach for the Rias Bajas. This had clear implications for predicting NCP and net nutrient budgets to the coastal zone. Salinity and temperature were simulated with the commercially-available simulation shell, ECoS, to within the analytical error of the observed data. Inorganic nutrient concentrations and benthic effluxes were qualitatively and quantitatively agreeable with observed data. Phytoplankton growth in ECoS was limited by up to 30% by phosphorus rather than nitrogen, as previously believed. The annual evolution of NCP was successfully reproduced by examining the chlorophyll-normalised rate of organic carbon production. Mean NCP In the spring and dry season was 46.5 and 147 mg c m ˉ² h ˉ¹, which agreed well with the literature. There were clear discrepancies between box model and ECoS-derived nutrient export to the Atlantic ocean. The definitions of constituent uptake and remineralisation processes between the two approaches were examined In the context of biogeochemical modelling and environmental management of the Rias Bajas.

Thesis (Ph.D.)--Indiana University, Dept. of Geological Sciences, 2008. / Title from PDF t.p. (viewed on May 13, 2009). Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4621. Adviser: John M. Hayes.

Thesis (Ph. D., Geology)--University of Idaho, December 2007. / Major professor: Mickey Gunter. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (Ph. D.)--College of William and Mary. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0888. Adviser: Thomas M. Johnson. Includes bibliographical references (leaves 124-135) Available on microfilm from Pro Quest Information and Learning.

The investigations outlined in this thesis were conducted in an attempt to establish the role of biogeography/geobotany, geochemistry and biogeo-chemistry in the detection of copper mineralization in bedrock concealed by transported material. To aid the interpretation of the results a detailed study of the physical background of the study area was necessary. Orientation studies were carried out overmineralized tilloid and mineralized lava, and comprised the mapping and/or recording of vegetation along transects, the establishment of plant species suitable for biogeochemistry and the copper content of various mesh fractions of the soil. Analytical techniques suitable for plant and soil sample analysis were also investigated. A regional biogeo-chemical/geochemical programme was carried out to locate extensions to known mineralization and also additional areas of mineralization. The biogeographical/geobotanical studies reveal the composition of anomalous and background vegetation units and indicate the influence of relief, drainage and lithology on plant species distribution. Over mineralized tilloid two plant species emerge as specific indicators of copper toxicity in the soil. The extent of the overburden limits the use of geobotany as a prospecting tool as vegetation is generally found to reflect overburden and soil types rather than concealed bedrock. Geochemistry, comprising analysis of the -270 mesh fraction of the soil by the acid leaching/atomic absorption spectrophotometry method, is found to give satisfactory results in areas of near surface bedrock. The value of biogeochemistry in areas of thick overburden is discussed, and of the tree and shrub species investigated Phaeoptilum spinosum is found to be the most suitable for further biogeochemical work. Dry ashing/acid digestion followed by atomic absorption spectrophotometry is a suitable method of analysis for plant samples. The limited success obtained in the regional biogeochemical/geochemical survey is probably due to the absence or low grade of mineralization in the tilloid and the lens-like occurrence of mineralization in the lava.

Within the Eastern Goldfields vegetation studies have revealed that distinct associations characterise the different geological units. The relationship may be constant within a given field area but species differences may occur on similar rock types in different areas of the region. The physical and chemical environments are both influential in the establishment of geobotanical relationships; a vegetation association developed over an outcropping rock unit may vary from that growing on the similar unit when soil covered. Similarly, any marked changes occurring in the chemistry of the soil over differing rock types may be revealed by modifications in the plant assemblage. Thus, an increase in the soil metal content over the normal background content may affect the vegetation supported. Soil geochemical anomalies over areas of mineralisation of nickel, copper and arsenic (gold) are not always characterised by recognisable geobotanical relations: where possible relationships are observable, as over part of the Jimberlana Dyke at Norseman, and over a limited area at Kambalda, further work is necessary in similar localities of the region to substantiate them. Biogeochemical analyses may usefully indicate areas where the concentration of metals in the soils becomes anomalous, thus indicating the location of potential mineralisation. The application of the bio-geochemical method may be limited by the non-availability of elements for plant absorption.

Investigations of the vegetation of the Otavi Mountainland in northern South West Africa were undertaken during the period 1970 - 1972. These had two primary objectives; firstly an evaluation of the influence of individual environmental factors on the distribution of vegetation units and secondly, an assessment of the roles of geobotany and biogeochemistry in exploration for copper, lead and zinc ores in the particular environment characteristic of this part of Africa. Regional reconnaissance studies were followed by detailed field investigations involving the collection of soil and plant samples for subsequent laboratory analysis for trace elements. The results of these investigations form the subject of this thesis. The study area is characterised by a sequence of predominantly calcareous rocks, mainly dolomites and limestones, of the Nosib Formation and Damara System, both of Proterozoic age. The more resistant rocks build striking mountain ranges which rise abruptly from broad flat floored valleys which are covered with younger depositional material. The ranges carry forms of Open Low Savanna Woodland, a low tree Savanna in which the trees are relatively closely spaced, while the valleys carry a Low Tree and Shrub Savanna in which the trees are widely to closely spaced in a fairly dense grass cover. The geobotanical investigations disclosed close distributional relationship between vegetation associations and lithological units. They revealed the considerable influence of calcrete and calcareous bedrock on the composition of the vegetation associations. Change of species distribution imparting differences of pattern within vegetation associations and the occurrence of possible indicator plants were discovered in the vicinities of known mineralised areas. The biogeochemical investigations revealed a number of areas with weak anomalies in the copper, zinc and lead contents of the leaves and twigs of the trees and shrubs which were sampled. Some of these anomalies occurred over areas with outcropping mineralised bedrock where they supported and confirmed the geochemical anomalies disclosed by soil sampling. Others having occurred in areas with deep soil and/or thick calcrete cover where geochemical values were either low or weekly anomalous. Overall the results suggested that biogeochemistry provides a complement to geochemistry, that it is capable of detecting mineralised bedrock beneath cover of soil and calcrete.