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Current applications of the critical loads concept are geared primarily towards targeting emission control strategies at a national and international level. In the UK maps of critical loads for freshwaters are available at 10km2 resolution based on a single representative site in each grid square. These maps do not take variations of water chemistry within mapping units into account and are therefore of limited use for application to non-mapped sites. This thesis describes the development of an empirical statistical model, which uses nationally available secondary data, to predict freshwater critical loads for catchments lacking the appropriate water chemistry information. A calibration exercise using data from 78 catchments throughout Scotland is described. Water chemistry for each catchment has been determined and each catchment is characterised according to a number of attributes. Multivariate statistical analysis of these data shows clear relationships between catchment attributes and water chemistry and between water chemistry and diatom critical load. The key variables which explain most of the variation in critical load relate to soil, geology and land use within the catchment. Using these variables (as predictors) in a regression analysis diatom critical load could be predicted across a broad gradient of sensitivity (R2adj = c. 0.8). The predictive power of the model was maintained when different combinations of explanatory variables were used. This accords the model a degree of flexibility in that model paramaterisation can be geared towards availability of secondary data. There are limitations with the model. These relate to the nature of the predictor variables and the ability of the model to predict critical loads for more sensitive sites. Nevertheless the ability of the model to differentiate between sensitive and non-sensitive sites offers considerable scope for environmental managers to undertake national inventories of catchment sensitivity and specific assessments of individual catchments.

Thesis (PhD) -- University of South Australia, 1999

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 (Ph. D.)--University of Melbourne, 1991. / Typescript (photocopy). Includes bibliographical references.

Presented as thesis (Ph. D.)--University of Wisconsin--Madison, 1918. / Reprinted from Journal of the American Chemical Society. Part 1: vol. XL, no. 8 (Aug. 1918), p. [1184]-1187. Part 2: vol. XL, no. 8 (Aug. 1918), p. [1168]-1184. Part 3: vol. XL, no. 5 (May 1918), p. [793]-796. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

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Thesis (M. Sc.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on June 18, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Ecology, Department of Biological Sciences, University of Alberta. Includes bibliographical references.

No description available.