Thesis (M.S.) in Civil Engineering--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 98-106).

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (M.S. - Natural Resources)--University of Arizona. / Includes bibliographical references (leaves 42-46).

No description available.

Superoxide, a reduced form of dioxygen is produced in natural waters from abiotic thermal processes such as iron(II) oxygenation photochemically, and biologically in natural waters. Superoxide is highly redox-active due to the presence of an unpaired electron and plays an important role in the geochemical cycling of trace metals and degradation of organic pollutants in natural waters. It also has a significant effect on the physiology of aquatic microorganisms and has been implicated in the growth of toxic microalga in coastal areas of Japan, Australia and Canada. The generation of superoxide by both biotic and photochemical pathways is described in this thesis and attention given to selected reactions of superoxide in simulated natural waters. Particular attention in this work has been given to the interaction of superoxide and iron and the impact of this interaction on iron availability to Chattonella marina, a red-tide phytoplankton frequently associated with fish-mortalities in Australia and Japan. Superoxide production from both phototchemical and biological sources is measured using a highly sensitive chemiluminescence technique and the effect of superoxide production on iron transformation under various environmental conditions is investigated by employing spectrophotometric techniques with high sensitivity and temporal resolution. The intermediacy of superoxide in iron acquisition mechanism by C. marina is also investigated using a radioisotope labeling technique. Our experimental results show that superoxide in natural waters is produced via reduction of dioxygen. The reduction of dioxygen takes place by transfer of electrons by the photo-excited quinone moieties present in natural organic matter or by reductases located on the outer cell membrane of organisms' surface. The experimental results suggest that the fate of iron in marine waters is closely related to the superoxidedioxygen redox couple. Superoxide can reduce a wide range of organically complexed iron(III) species to the more soluble iron(II) redox state, thus affecting its bioavailability. A simple kinetic model for redox-cycling of iron in the presence of superoxide is developed. In addition, by coupling the model for redox-cycling of iron with the forms of iron acquired by C. marina, a generalized mathematical model for iron acquisition is presented which satisfactorily describes all results obtained.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 313-329).

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 190-194).

Environmental change is currently regarded as one of the greatest threats to water resources. Limited knowledge of hydrological processes prevents from adequate characterization of systems behaviour to future changes. Geochemical and isotope tracers are considered reliable tools to study physical processes, but tracer studies are often constrained by the temporal and spatial variability in the tracer response and coarse data sets. Novel automatic sampling devices and inexpensive laser spectroscopy made higher-resolution stable isotope tracer data feasible. This thesis presents approaches to integrate geochemical tracer data, high-resolution stable isotope tracer data and process dynamics observed in the field into lumped conceptual rainfall-runoff models to study catchment hydrological processes at different scales. The use of such process-based data successfully aided model conceptualization and calibration in the quest for simple water and solute transport models with improved representation of process dynamics. In particular, high-resolution isotope data could identify temporally and spatially variable flow pathways to assess diffuse pollution transport, which otherwise might have been lost. This work showed that pollutants in some catchments are likely to rapidly discharge into the stream and due to geological properties reside over longer periods in deeper groundwater systems. In other words, changes to these systems today are likely to show an immediate effect fading persistently over decadal time periods. Such knowledge is important if catchment remediation and recovery has to be assessed from a management point of view such as for example targeting measures and cost-effective land management to improve water quality status.

No description available.

No description available.