The ocean emission and subsequent oxidation of dimethylsulfide (DMS) provides a source of sulfate in the atmosphere, potentially affecting the amount of solar radiation reaching the Earth's surface through both direct and indirect radiative effects of sulfate aerosols. DMS in the ocean can be quite variable with season and location, which in turn leads to high spatial and temporal variability of ocean DMS emissions. This study tested currently available observational and empirically-based climatologies of DMS concentration in the surface ocean. The exploration of the existing parameterizations mainly reveals the limitations of estimating DMS with an empirical model based on variables such as chlorophyll and mixed layer depth. The different algorithms show significant differences in spatial pattern, and none correlate strongly with observations. There is considerable uncertainty both in terms of the spatiotemporal distribution in DMS concentration and flux, as well as in the global total DMS flux. The present research investigates the influence of DMS on sulfate aerosols and radiative fluxes given different DMS climatologies in the fourth generation of the Canadian Global Atmospheric Climate Model (CanAM4.1). In general, the response in the radiative flux seems to follow the variation in the global mean flux of DMS linearly. Differences in the spatial and temporal structure of oceanic DMS have only a secondary effect on the radiative changes. The overall response of the atmosphere to the presence or absence of structure of DMS in space and time is distinctly smaller compared to the possible uncertainty of this response associated with the magnitude of the annually averaged global flux. / Graduate / 0425 / 0725 / 0416 / jetesdal@uvic.ca

Carbon storage was compared between two perennial biomass energy systems, namely switchgrass (Panicum virgatum L.) and short-rotation willow Salix alba x glaffelteri L.) at 2 adjacent sites, and further compared with a corn cultivation, a 20-year-old abandoned field, and a mature hardwood forest, in southwestern Quebec. Aboveground carbon results indicated that switchgrass and corn had significantly greater carbon levels than willow at the less fertile site, but no significant differences were detected at the more fertile site. Root carbon results indicated that corn had significantly lower carbon levels than both perennial systems to a depth of 30 cm at both sites. However, switchgrass had significantly greater root carbon levels beyond 30 cm compared with willow and corn, and beyond 45 cm compared with the forest and abandoned field. These findings indicate that deep-rooted perennial grasses such as switchgrass have the potential to sequester carbon at deeper soil layers. Soil carbon results showed that at the more fertile site, willow was associated with significantly greater soil carbon levels than switchgrass. Moreover, both perennial crops had soil carbon levels that were greater than for corn, the abandoned field, and the forest. In contrast, at the less fertile site, no significant differences in soil carbon were detected between the various plant systems examined. The results of this study suggest that the perennial energy crops used, when grown on relatively fertile soils, have the potential to substantially increase soil carbon levels compared with conventional agricultural and/or forest systems. Consequently, when these crops are grown on less fertile soils, their added advantage of increasing carbon storage is lost.

Net ecosystem exchange of CO$ sb2$ (NEE) and CH$ sb4$ flux were measured at five sites within a boreal peatland near Thompson, Manitoba, from June through September, 1994. Sites were chosen to represent the different plant communities present along a productivity gradient where the water table was at or near the peat surface. Methane emissions, water table depth, and peat temperature were measured on weekly basis, while the relationship between photosynthetically active radiation (PAR) and net ecosystem exchange of CO$ sb2$ was determined three times during the field season, and then used to develop net ecosystem production (NEP) models at each site. Porewater methane was sampled for $ rm delta sp{13}C/ sp{12}C$ isotopic analysis once a month. / Among the sites, after PAR, light CO$ sb2$ flux was primarily controlled by sedge biomass and water table position, while dark CO$ sb2$ flux was controlled by peat temperature. From early June to late August, the five sites consumed approximately 1 to 2 g $ rm CO sb2$-C m$ rm sp{-2}d sp{-1}$. Seasonal CH$ sb4$ fluxes ranged between 16 and 456 mg $ rm CH sb4 m sp{-2}d sp{-1}$, and were higher than fluxes measured at other boreal sites in the same latitude. Seasonal average NEP was a good predictor of seasonal CH$ sb4$ fluxes from the sites (r$ sp2$ = 0.50), providing a model which estimates CH$ sb4$ flux based on site productivity alone. Stable carbon isotope analysis indicates root exudates that stimulate methanogenesis are an important control on this relationship, as is a high water table, particularly in its influence on the depth of the CH$ sb4$ oxidizing layer in the peat. These results suggest NEP measurements have the potential to be used in remote sensing applications to estimate CH$ sb4$ flux from wetlands, but that their use may be restricted to inundated sites.

Upland environments are important sources of mercury (Hg) to downstream wetlands and water bodies. Hydrology is instrumental in facilitating Hg transport within, and export from watersheds. Two complementary studies were conducted to assess the role hydrological processes play in controlling Hg mobility and transport in forested uplands. A field study compared runoff and Hg fluxes from three, replicate hillslope plots during two contrasting spring snowmelt periods, in terms of snowpack depth and timing. Hillslope Hg fluxes were predominately flow-driven. The melting of soil frost significantly delayed a large portion of the Hg flux later into the spring following a winter with minimal snow accumulation. A microcosm laboratory study using a stable Hg isotope tracer applied to intact soil cores investigated the relative controls of soil moisture and precipitation on Hg mobility. Both hydrologic factors control the mobility of contemporary Hg; with greatest Hg flushing from dry soils under high-flow conditions.

Uranium contamination of soils and groundwater at Department of Energy facilities across the United States is a primary environmental concern and the development of effective remediation strategies is a major challenge. Bioremediation, or the use of microbial enzymatic activity to facilitate the remediation of a contaminant, offers a promising in situ approach that may be less invasive than traditional methods, such as pump and treat or excavation. This study demonstrates for the first time the successful biomineralization of uranium phosphate minerals as a result of microbial phosphatase activity at low pH in both aerobic and anaerobic conditions using pure cultures and soils from a contaminated waste site. Pure cultures of microorganisms isolated from soils of a low pH, high uranium- and nitrate-contaminated waste site, expressed constitutive phosphatase activity in response to an organophosphate addition in aerobic and anaerobic incubations. Sufficient phosphate was hydrolyzed to precipitate 73 to 95% total uranium as chernikovite identified by synchrotron X-ray absorption spectroscopy and X-ray diffraction. Highest rates of uranium precipitation and phosphatase activity were observed between pH 5.0 and 7.0. Indigenous microorganisms were also stimulated by organophosphate amendment in soils from a contaminated waste site using flow-through reactors. High phosphate concentrations (0.5 to 3 mmol L-1) in pore water effluents were observed within days of organophosphate addition. Highest rates of phosphatase activity occurred at pH 5.5 in naturally low pH soils in the presence of high uranium and nitrate concentrations. The precipitation of uranium phosphate was identified by a combination of pore water measurements, solid phase extractions, synchrotron-based X-ray spectroscopy, and a reactive transport model. The results of this study demonstrate that uranium is biomineralized to a highly insoluble uranyl phosphate mineral as a result of enzymatic hydrolysis of an organophosphate compound over a wide range of pH, in both aerobic and anaerobic conditions, and in the presence of high uranium and nitrate concentrations. The nonreductive biomineralization of U(VI) provides a promising new approach for in situ uranium bioremediation in low pH, high nitrate, and aerobic conditions that could be complementary to U(VI) bioreduction in high pH, low nitrate, and reducing environments.

Vegetation sampling is an effective exploration technique in areas of transported cover where other techniques have been of limited success. Several plant species were sampled along transects across 9 known Au ore bodies; Triodia pungens was found give a Au, As, ±Zn, ±S, ±Ce and ±La signature which represented mineralisation through cover materials and Eucalyptus brevifolia was found to give a geobotanical and ±Ca, ±Mg, P, S and Zn signature of underlying geological structure. The Hyperion prospect was used as a ‘blind’ target as there was no background information available until after interpretation was carried out. Mineralisation was located at the contact between granite and dolerite, biogeochemical signatures from E. brevifolia and Acacia bivenosa showed areas of change in ±Au, Ba, Ce, ±Cu, La, ±Mn, Nd, P, S, Sm, Y and Zn which corresponded to this contact. All species in the Pine Creek Orogen were able to present areas elevated in Au, As, ±Zn, ±S, ±Mo and ±Cu which provide future drilling targets. Biogeochemical sampling was able to determine the location of mineralisation at each site and identify underlying substrate changes, however, background knowledge relating to regolith, geology, hydrology and geophysics are important in aiding the interpretation of the elemental data as each component of the substrate influences the elements which a plant will uptake. Mineral exploration in Australia has been driven by the search for large ore deposits close to the surface. This has led to the need to develop technologies for detecting mineral deposits under cover, which can be up to several hundred metres of transported sediments. The aim of this research was to test the feasibility of using vegetation biogeochemical sampling over known Au deposits within semi-arid and arid terrains. Biogeochemical sampling has the advantages of being cost effective, sustainable, environmentally friendly and relatively easy to perform. Nine field sites were covered, 4 in the Tanami Region (Coyote, Larranganni, Hyperion and Titania), 4 in the Pine Creek Orogen (Johns Hill, Great Northern, Glencoe and McKinlay) and 1 in the Gawler Craton (Tunkillia). At each of these sites the dominant species were sampled and the elemental concentrations of the plant were analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to test if they were able to detect buried mineralisation. In general, all species identified as being deep rooted (larger trees, paperbarks and spinifex) were able to detect mineralisation in each location within multi-element dispersion haloes centring over the projected ore body. Variations were dependant upon species differences and root structures, groundwater influences, and the potential for detrital contamination. In arid Australia, Triodia spp. were shown to be ideal for closely spaced tenement/prospect scale exploration, and Heteropogon spp. show similar trends for the humid tropics. Eucalyptus/Corymbia spp. are more suitable for widely spaced regional sampling exploration as they amalgamate a wider signal with strong groundwater influences. It was found that all plant species were effective at expressing buried mineralisation in a multi-element suite (pathfinders: Au, As, S, Zn, +(Ce/La), _Mo and _Cu) through cover in these terrains provided care was taken with sampling and interpretation. Regolith materials, botanical properties and landforms are essential background knowledge for determining the effectiveness of biogeochemical sampling. Plants with deep root systems with little lateral spread are ideal for prospect/tenement mineral exploration programs, and plants with wide lateral spreads and large chemical uptake potentials are ideal for regional mineral exploration programs. This exploration strategy would be quick, sustainable and relatively cheap compared to other methods of exploration. This is not to say that biogeochemical sampling would be the only tool needed for further mineral exploration in Australia. This process would work best if used in conjunction with other sampling methods like geophysics and some soil sampling techniques. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1351318 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, School of Earth and Environmental Sciences, 2009

Thesis (Ph.D.)--University of Western Sydney, Macarthur, Faculty of Informatics, Science and Technology, 1999. / References: p. 210-233.

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 142-146). Also available in electronic format on the Internet.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 183-197). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 106-118). Also available on the World Wide Web.