Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 125-140).

Iron oxyhrdroxide exist in a range of crystallinities and subsequent bioavailabilities with the poorly crystalline Fe oxyhrdroxide, ferrihydrite, considered the most bioavailable. Yet, as a result of the instability ferrihydrite it quickly ripens and/or transforms to more thermodynamically stable end-members bringing into question its importance in supporting long-term Fe(III)-reducing microbial communities. Furthermore, while a wide phylogenetic diversity of microorganisms capable of reducing ferrihydrite have been isolated, these organisms show diminished abilities to reduce more stable and dominant crystalline Fe phases. Therefore to address the questions of which microorganisms and what microbial processes are responsible for controlling the reduction of diverse Fe(III) minerals phases, cultivation based approaches using both batch and column-type reactors were employed. Using geochemical and phylogenetic analysis it was revealed that the Fe oxide substrate was important in dictating the mechanisms of Fe(III) reduction, and the structure of the microbial communities. While model dissimilartory Fe reducing microorganisms were capable of reducing ferrihydrite when acetate was provided as a carbon source these organisms did not enrich and were incapable of reducing crystalline Fe(III) oxides. Instead, in enrichments where crystalline Fe(III) oxides were reduced, organisms associated with fermentation and sulfate respiration dominated, this despite using freshwater media low in sulfate (less than 200 µM). In addition, these non-model Fe reducers dominated in ferrihydrite enrichments when carbon compounds other than acetate were given. Interestingly, a strong negative correlation between Fe(III) and sulfate respiration was observed with the canonical thermodynamic view that ferrihydrite should precede sulfate as a terminal electron acceptor being challenged. Further experiments with pure cultures of Desulfovibrio putealis indicated that a catalytic sulfur cycle may be responsible for greater than expected Fe(II) values under low sulfur conditions. These findings, have broad implications in predicting microbially mediated electron flow to oxidized substrates which will dictate the pathways and degree of carbon mineralization and subsequent carbon sequestration within sediments and soils. Further, given the importance of Fe(III)-reducing communities and Fe(II) in the sequestration of both inorganic and organic contaminants, these findings will have direct bearing on contaminant mitigation and remediation. / Engineering and Applied Sciences

A hydrological and biogeochemical study was undertaken at the Mer Bleue bog, Ottawa, Ontario, Canada from May 22, 1998 to May 21, 1999. Basin runoff was generated by groundwater discharge at the peatland margin, and groundwater discharge was controlled by hydraulic gradients and horizontal hydraulic conductivities (Kh). Flux of dissolved organic carbon (DOC) measured at the basin outflow was 8.3 g C m-2 yr-1 and compared to within 23% of DOC flux estimated using a Dupuit approximation of seepage during the ice-free season. Annual DOC flux was 11% of the annual carbon sink. / Flownet analysis showed that seasonal patterns of groundwater flow were controlled by boundary condition changes that resulted from precipitation and evapotranspiration events. A pattern of recharge was most common over the hydrological year, but a discharge pattern was observed during a 40 day groundwater flow reversal. Evaluation of the peatland recharge-discharge function using in situ sodium concentrations and a diffusion model revealed that the peatland is a long-term recharge system. It is hypothesized that peatland biogeochemical function is controlled by long-term recharge despite annual occurrence of groundwater flow reversals.

Contaminated aquatic sediments pose health risks to fish, wildlife, and humans and can limit recreational and economic uses of surface waters. Technical and cost effective in situ approaches for sediment management and remediation have been identified as a research need. Subaqueous in situ capping is a promising remedial approach; however, little is known regarding its impact on underlying sedimentary processes and the feasibility of bioaugmented caps at sites subject to contaminated groundwater seepage. This work specifically addresses (1) the impact of capping on biogeochemical processes at the sediment-water interface, (2) the ability and degree to which indigenous sediment microorganisms colonize an overlying cap, (3) the effect of advective flow direction on redox conditions within a cap, (4) natural contaminant bioattenuation processes within capped sediment, and (5) limitations toward a functional bioreactive in situ cap. Laboratory-scale experiments with capped sediment columns demonstrated that emplacement of a sand-based in situ cap induced an upward, vertical shift of terminal electron accepting processes into the overlying cap while simultaneously conserving redox stratification. Upflow conditions simulating a groundwater seep compressed anaerobic processes towards the cap-water interface. Microorganisms indigenous to the underlying sediment colonized cap material and spatial population differences generally reflected redox stratification. Downflow of oxic surface water through the cap, simulating tidally-induced recharge, created fully oxic conditions within the cap, demonstrating that flow direction strongly contributes to redox conditions. Experiments simulating capped sediment subject to contaminated groundwater seepage revealed a reduction of natural bioattenuation processes with time, stemming from the elimination of labile organic matter deposition to the sediment and a subsequent lack of electron donor. Thus, parent contaminants within groundwater seeps will be subject to minimal biotransformations within the sediment before entering a reducing cap. A bioreactive cap, inoculated with microorganisms capable of reductive dehalogenation, was established to reductively dechlorinate tetrachloroethene present in the groundwater; however electron donor amendments to sediment effluent were required to achieve complete dechlorination of tetrachloroethene to non-toxic ethene. Results from this work improve understanding of biogeochemical and bioattenuation processes within capped aquatic sediments and should aid in the development of active capping technologies.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 124-142).

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 69-72). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 156-175).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 51-57). Also available on the World Wide Web.

Thesis (doctoral)--Chalmers Tekniska högskola, 1972. / "Akademisk avhandling för filosofie doktorsexamen i kemi ... fredagen den 2 juni 1972 ... Chalmers tekniska högskola."

With a burgeoning population, increasing land area, and the emergence of new megacities, urban areas have the ability to alter biogeochemical cycles across great scales. Though cities are hotspots of pollution, these concentrated population centers present an opportunity to reduce the human footprint and provide a model of sustainability. Creating sustainable cities requires an understanding of urban biogeochemical cycles of nutrients, such as carbon (C), nitrogen (N), and phosphorus (P). Studies in urban areas, however, often include measurements at only a few sites, either in an urban-rural comparison or as an anchor along an urban-rural gradient. In my dissertation work, I deployed a network of sites across the greater Boston area to measure several key biogeochemical processes: 1) rates of carbon dioxide (CO2) efflux through soil respiration, 2) atmospheric inputs and soil solution concentrations of N, P, and organic C, and 3) rates of N mineralization and nitrification in soils. I found that urban soil respiration is driven by landowner management and that respiration from urban residential soils produces almost 75% of the CO2 as fossil fuel emissions in these areas during the growing season. I also found that mean fluxes of inorganic N in throughfall are double rural rates and vary more than threefold throughout the urban area, exhibiting rates at some urban sites which are as low as rural rates. These rates are driven by vehicular N emissions and local fertilizer inputs, and are decoupled from rates of soil biogeochemical cycling of C and N. Finally, I found atmospheric fluxes of organic N equaling almost 40% of total atmospheric N inputs, atmospheric inputs of organic C on par with rural rates, atmospheric inputs of P similar to rates of P in parking lot runoff, and an enhancement of nutrient inputs to urban ecosystems by the urban tree canopy. My dissertation work highlights the need for a more thorough understanding of biogeochemical fluxes in cities, provides further impetus for the development of a more holistic, multifaceted understanding of urbanization, and suggests that urban areas should be studied as systems unto themselves, rather than strictly in comparison to rural areas.