Thesis (doctoral)--Universitätsdruckerei, Bern, 1982. / "Inauguraldissertation der Philosophisch-Naturwissenschaftlichen Fakultät der Universität Bern zur Erlangung der Doktorwürde ... von der Philosophisch-Naturwissenschaftlichen Fakultät auf Antrag von Herrn Prof. Dr. H. Oeschger Angenommen, Bern, den 8. Juli 1982." Includes bibliographical references.

Thesis (Ph.D.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on July 7, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Soil Science, Department of Renewable Resources, University of Alberta. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 88-93). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Rhode Island, 2006. / Typescript. Includes bibliographical references (leaves 175-188).

No description available.

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Mar. 4, 2009). Includes bibliographical references (p. 21-28).

Over the course of my PhD, I developed the analytical capability to measure calcium isotopes at the University of Cambridge and analyzed calcium isotopes in a range of fluids and minerals in modern and past environments. After discussing my methodological development, I report my work in the glacial precursor to the Dead Sea. Here, the calcium isotope composition of aragonite varies synchronously with lake level fluctuations over the last 70,000 years. My numerically reconstructed lake calcium budget led me to conclude that 20,000 years ago, the Dead Sea was wetter than modern conditions, rather than colder and drier, as had previously been proposed. The primary focus of my PhD research was understanding the sedimentary sink for carbon. The formation of authigenic carbonate in marine sediments is caused by the microbial degradation of organic matter. I used pore fluid measurements and a numerical model to identify zones of authigenic carbonate precipitation. This knowledge was then combined with an understanding of the microbial processes that occur beneath the seafloor to determine the link between microbial activity and authigenic carbonate formation. Two processes, sulfate reduction and the anaerobic oxidation of methane were determined to be the main drivers of authigenic carbonate precipitation. In order to assess the importance of the carbon isotope signal imparted by each of the two identified processes, I created Artificial Neural Networks to predict the areal extent of authigenic carbonate precipitation and the dominant microbial process driving the precipitation. My ANNs identified that 37% of the modern seafloor is precipitating authigenic carbonate, which leads to a flux of 1.2*10^12 moles of carbon per year, of which 88% is due to the anaerobic oxidation of methane, and 12% is due to sulfate reduction. This represents 2-3% of the modern global carbon deposition, however I was able to show that this would be significantly higher in the geological past when ocean conditions were vastly different to how they are today. Finally, I conclude by proposing that some variations in the global carbon cycle in the past can be explored by linking marine calcium concentrations to authigenic carbonate formation and the flux of alkalinity from the seafloor.

Marine sediments play an important role in the global carbon cycle, where they are ultimately important for recycling of carbon. At the sediment-water interface carbon is in constant movement both into and out of the sediment. However some environments are more important for the natural storage of carbon. Over long time scales this process has a role in climate regulation. Measuring the total O2 uptake represents a good proxy for the turnover of organic material at the sediment surface in oxygenated sediments, and equally the release of O2 represents benthic primary production. Many important biological processes are regulated by the availability of O2 at the seabed including: fauna composition and activity, phosphate exchange, nitrogen cycling and burial of organic material. Understanding of the rate and efficiency at which carbon turnover is occurring in marine sediments provides a valuable insight to the regulatory role they play in climate control. Investigation of marine sediments is best done in situ where possible, and the development of benthic “landers” has allowed measurements to be conducted at the sediment-water interface. Most recently, a novel approach known as “Eddy Correlation” (EC) has been developed. It allows quantification of the O2 exchange across any surface from simultaneous measurements of vertical velocity flow and oxygen concentration within the benthic boundary layer. The large sediment area accounted for; the high measuring frequency and the non-invasive nature are theoretical advantages over traditional methods such as benthic chamber incubations and O2 microprofiles. This study has shown that it is difficult to achieve consistent and improved measurements using EC compared to traditional methods due to the complex nature of the equipment and data analysis. Data does suggest that EC can be a strong complimentary tool for benthic carbon exchange studies. This project presents the first use of this technology across a range of benthic environments, from temperate coastal sediments and maerl beds to high-Arctic sediments and sea-ice. The method has allowed accurate quantification of the benthic remineralisation rates and carbon turnover efficiency in the coastal and maerl environments, but less so for the more complex under sea ice and cold Arctic environments. Rates presented agree well with other published studies documenting the use of this state-of-the-art technology.

Despite the importance of tropical rivers to the global carbon cycle, the nature of carbon cycling within these watersheds has been dealt with by only a handful of studies. The current work attempts to address this lack of information, using stable isotope and concentration measurements to constrain sources and sinks of carbon in two Peninsular Malaysian watersheds. The basins are located on the central-western and northeastern coasts of the Malaysian Peninsula, and are drained by the Langat and Kelantan Rivers, respectively. Water samples were collected from three points along the two rivers twice a month, in addition to the sampling of groundwater in adjacent aquifers. Principal component analyses (PCA) on water chemistry parameters in the Langat and Kelantan Rivers show the dominance of geogenic and anthropogenic influences, grouped in 4 to 6 components that comprise over 50 % of the total dataset variances. The geogenic input is reflected by components showing strong loadings by Ca, Mg, Mn, Si, and Sr, while anthropogenic influences via pollution are indicated via strong loadings by NO3, SO4, K, Zn and Cl. The carbon isotope and concentration data appear unrelated to these groups, suggesting that the riverine carbon cycle in both locations is dominated by other factors. These may include alternative sources of organic pollution, or inputs from the local vegetation and soils. The mean riverine 13CDOC of -27.8 ± 2.9 ‰ and -26.6 ± 2.2 ‰ in the Langat and Kelantan Basins, respectively, are consistent with the dominance of C3-type vegetation in both watersheds. Riverine 13CDIC signatures approach C3-like values at high DIC concentrations, with measurements as low as -19 ‰ in the Kelantan Basin and -20 ‰ observed in the Langat Basin, consistent with a biological origin for riverine DIC. However, the average 13CDIC in river water is 13C-enriched by about 10 ‰ relative to the expected C3 source in both rivers, and this 13C- enrichment appears to be largest with smaller DIC concentrations. Because of the overpressures of CO2 in the rivers, entrainment of isotopically-heavy atmospheric CO2 is not a likely explanation for the observed 13C-enrichment. Theoretically, dissolution of carbonates could be an alternative source of 13C-enriched carbon, but this lithology is scarce, particularly in the Langat watershed. The increase in DIC downstream and generally high pCO2 values in most river sections argues against aquatic photosynthesis as a primary causative factor for the observed isotopic enrichment. This elimination process leaves the speciation of riverine DIC and the evasion of CO2 as the most likely mechanisms for 13C-enrichment in DIC, via isotope fractionation during HCO3- hydration and CO2 diffusion. Potentially, methanogenic activity could also be, at least partially, responsible for the 13C-enrichment in DIC, particularly immediately downstream of the Langat Reservoir, but due to the absence of empirical data, this must remain only a theoretical proposition. The aquatic chemistry and dissolved carbon data suggests that pollution discharge into the Langat and Kelantan Rivers is the major factor that is responsible for the considerable CO2 overpressures and high DIC and DOC concentrations in the river waters, particularly in the downstream sections. This pollution is likely of biological origin, via sewage and palm oil mill effluent (POME) discharge, and therefore isotopically indistinguishable from natural C3 plant sources. Carbon budgets of the Langat and Kelantan River show CO2 degassing to be a significant mechanism of fluvial carbon loss, comprising roughly 50 %, or more, of the total riverine carbon export in both watersheds. The remainder of the river carbon is transported to the ocean in the form of DIC, DOC and POC in broadly comparable proportions. However, the combined riverine carbon export from the Kelantan and Langat Basins amount to 2 % or less of the total carbon sequestration of the watersheds. Thus, most of the sequestered carbon is returned to the atmosphere via respiration, with smaller amounts incorporated into ecosystem biomass . These results highlight the complexity of carbon cycling in tropical rivers, and agree with previous studies in showing riverine systems to be more than simple conduits of carbon from the land to the ocean.

Coastal nutrient loading is a growing concern in urbanized communities and has led to alterations in above- and belowground processes throughout estuarine systems. Mangrove forests are highly productive coastal habitats that exhibit large carbon stocks contained mostly to the deep soils. Since nutrient enrichment has been found to increase mangrove aboveground growth, it’s presumed that nutrient enrichment will also increase belowground respiration rates. Disturbances in soil nutrient content may alter the mangrove carbon cycle by increasing the amount of CO2 lost to the atmosphere from enhanced microbial and root respiration. In this study, soil respiration responded greatest to nitrogen enrichment, but pneumatophore root respiration responded greatest to phosphorus enrichment. Nutrient limitation can shift between different ecological processes and responses to nutrient enrichment tend to be system specific in tidally influenced ecosystems. Understanding the implications of coastal nutrient loading will improve ecosystem models of carbon exchange and belowground processes. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection