Dissolved organic matter (DOM) is crucial to carbon and nutrient biogeochemical cycling in the marine environment because it helps fuel heterotrophic microbial activity by providing substrates for degradation and remineralization. This study shows that substantial production of DOM in Texas estuaries can result from the solar radiation-enhanced dissolution (photodissolution) of particulate organic matter (POM). Experimental results showed that 0.4-6.6 mg C L⁻¹gsed⁻¹ of dissolved organic carbon (DOC) and 0.03-0.93 mg N L⁻¹gsed⁻¹ of total dissolved nitrogen (TDN) can be produced from irradiated sediment suspensions within 24 hours, and further that photodissolution may augment DOC and TDN loads in Texas estuarine waters by as much as 3-85% and 4-75%, respectively. Photodissolution can also enhance the optical thickness of the water column via the release of chromophoric dissolved organic matter (CDOM), which may subsequently further enhance photochemical processes in surrounding waters. Photoproduced CDOM appears to be of relatively high molecular weight and dominantly exhibits humic-like fluorescence, suggesting that photodissolution primarily occurs for humic moieties. Photodissolution was also observed for sterilized sediment suspensions, indicating that photochemical degradation of POM is the primary pathway of DOM production during photodissolution, as opposed to microbial mediated degradation or stimulation of benthic primary production by benthic phytoplankton or algae. Environmental and mechanistic factors controlling the extent of photodissolution in Texas estuaries may include sediment desiccation, water organic content, and sediment characteristics (organic content and lability of POM). Desiccated-rewetted sediments suspended in artificial seawater under solar irradiation produced ~40% more DOC and TDN than wet sediments, indicating the sediment dry-wet cycle may alter the 3-D structure of sediment grain matrices and thus might be a major controlling factor of photodissolution in salt marsh systems. The organic content of water used in sediment suspensions did not significantly influence DOC or TDN photoproduction by itself, but the combined influence of water organic content and sediment dry-rewet event played a substantial role in controlling the extent of photodissolution. In contrast to the results in artificial seawater, wet sediments produced slightly more DOC ([Delta]DOC=0.10 mg C gsed⁻¹) and substantially more TDN ([Delta]TDN=0.14 mg N gsed⁻¹) than dry-rewetted sediments in organic-rich Nueces Marsh water during 24 hours of photoincubation. Photodissolution dominantly produced humic-like DOM even though biologically labile organic matter was available in sediments, indicating that photochemical reactions preferentially occur with humic-like rather than protein-like organic matter. DOC and TDN production during photodissolution was strongly proportional to the amount of POC in sediment suspensions. On average, 69.2 ± 11.0 mg C of DOC and 9 ± 3.1 mg N of TDN was produced from 1 g of organic carbon in sediment suspensions after 24 hours of photodissolution. / text

Legacy mine sites are of concern due to their prevalence and associated environmental and human health risks. The United States Bureau of Land Management estimates as many as 500,000 abandoned mine sites in the US (BLM, 2017). Sites requiring costly management and long-term response to the environmental hazardous risks can be designated to a National Priority List (NPL) by the Environmental Protection Agency (EPA) under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) (EPA, 2017). One such site, located in Central Arizona, is the Iron King Mine Humboldt Smelter Superfund Site (IKMHSSS). The site was designated to the NPL in 2008 due to concerns regarding the size of the tailing pile, the proximity of contaminated materials to the town of Dewey-Humboldt and waterways, and the dangerous concentrations of arsenic (As) and lead (Pb) of the tailings (EPA, 2017). Remediation efforts have been ongoing since the designation of the site to the NPL, including sampling, yard soil removal, and distribution of information to the local community regarding risks from the site. The University of Arizona Superfund Research Program (UA SRP) has conducted greenhouse and phytostabilization studies of the site in an attempt to understand the processes and mechanisms employed to stabilize the tailings materials as well as reduce dust emissions from the tailings to the town of Dewey-Humboldt (Gil-Loaiza et al., 2016). This effort has successfully demonstrated a reduction of dust emissions (Sáez, 2016), however chemical changes to the tailings due to phytostabilization are the focus of this research. This work attempts to ascertain whether adverse effects from the method of phytostabilization are observed in the pore waters of the tailing material, in particular the potential for contamination of water sources by mobilized As through chemical or microbiological means. Recent studies have proposed potential mechanisms that can promote mobilization of As by dissolved organic matter (DOM) (Mladenov et al., 2015). Heterotrophic microbial respiration under O2 limited conditions can cause the reduction of Fe3+ to Fe2+, enhancing desorption or dissolution of As from Fe containing minerals (Hasan et al., 2007). Additionally, DOM competes with As for sorption sites at mineral surfaces (Grafe et al., 2002). In this study, batch and column experiments were used to investigate the mechanisms of sequestration and release of As in compost amended mine tailings. Mine tailings were reacted in triplicate in the presence and absence of DOM using plain tailings and radiated tailings for microbiological control and under anoxic and oxic conditions at timescales from ranging from 3 to 900 hours for batch experiments and 1 to 900 pore volumes in column experiments. The highest As release to pore waters was observed under anoxic conditions in the presence of DOM both with microbial activity inhibited and uninhibited through 60Co gamma irradiation after 3 and 910 h of reaction. The release of As from batch experiments was lowest in the control treatment with no DOM added to tailings in both anoxic and oxic treatments after 24 h. Column flow-through experiments were also carried out to better understand the kinetic biogeochemistry of the tailings interacting with DOM. Columns were completed under suboxic conditions to best mimic field scenarios. To test the effect of microbes, control tailing samples were sterilized by 60Co gamma irradiation prior to flowing DOM. Pore volumes (PV) were collected using fractionation equipment from 1 to 900 PVs. The release of As was highest in the presence of DOM after approximately 40 PVs when As release began increasing to its maximum release of 50 μmol l-1. No significant difference between irradiated and non-irradiated tailings was observed in either irradiated or non-irradiated tailings. Lowest release of As to effluent solutions was in the absence of DOM. These results were consistent with the findings from batch experiments. Batch and column experiments show that DOM influences the mobilization of As from mine tailings, and demonstrates the potential risk to proximal ground water resources in the absence of attenuation processes between the oxidized tailings and groundwater.

Master of Science / Department of Geology / Saugata Datta / Elevated levels of dissolved arsenic (As), iron (Fe) and manganese (Mn) are seen in the shallow, anoxic groundwaters of southeast Bangladesh on the Ganges- Brahmaputra- Meghna River delta. Over the past decade the mechanisms of As release have been widely debated. It is understood that As can sorb onto Fe-bearing minerals and can be subsequently released when reactions, such as microbially driven processes, occur. This study takes a multi disciplinary approach to understand the extent of the natural reactive barrier along the Meghna River and to evaluate the role of the natural reactive barrier in As sequestration and release in groundwater aquifers. River water and groundwater interactions occur in the hyporheic zone, which is defined as the transient subsurface region where river water and groundwater mix. The natural reactive barrier can develop within the hyporheic zone, where Fe-bearing minerals accumulate with a potential for As sorption, along with reworking and re-deposition of sediments along the riverbank. Shallow sediment cores, and groundwater and river water samples were collected from the east and west banks of the Meghna River in Jan. 2016. Groundwater and river water samples were tested for total dissolved Fe, Mn, and As concentrations; δ₂H, δ₁₈O isotopic ratios. Fluorescence spectroscopic characterization of groundwater organic matter provided insight into the hydro-geochemical reactions active in the groundwater and the hyporheic zone. Eight sediment cores of ~1.5 m depth were collected ~10 m away from the edge of the river. Vertical solid-phase concentration profiles of Fe, Mn, and As were measured by four different methods (hand-held XRF, and ICP-OES analysis of 3 digestions: aquaregia (HNO₃: HCl 1:3), 1.2 M HCl, and 1 M NaH₂PO₄ + 1 M L-ascorbic acid extractions). Enrichment of solid phase Fe, Mn, and As and the presence of possible Fe and Mn oxides in the sediments illustrate the existence of an natural reactive barrier at this reach of the Meghna. HCl extractions of sediment revealed solid-phase As accumulation along the west riverbank reaching concentrations of ~1500 mg/kg. Aqueous geochemical results showed the highest dissolved As concentrations in shallow wells (<30 m depth), where organic matter was fresh, humic-like, and aromatic. Humic-like dissolved organic matter present in the groundwater may enhance Fe oxide dissolution. Microbial reduction of organic matter prompts the reduction of Fe³⁺ to Fe²⁺, causing As to mobilize into groundwater. This study quantified the extent of As accumulation in the sediments along a 1 km stretch of the Meghna River. These findings contribute to the understanding of geochemical processes involved in As release into groundwaters from sediments within a fluvial deltaic environment.

One of the key processes in the carbon cycle on our planet is the degradation of dissolved organic matter (DOM) in aquatic environments. The use of organic matter by bacteria links energy from DOM to higher trophic levels of the ecosystem when bacteria are consumed by other organisms. This is referred to as the microbial loop. In this thesis I examined if the communities were functionally redundant in their ability to utilize organic matter, or if variation in bacterial composition and richness is of importance. To test this overarching question several experiments were conducted that include methods such as illumina sequencing of the 16S rRNA gene for taxonomic identification of bacterial communities, flow cytometry to follow the growth of communities and spectroscopic measurement to describe the composition of the organic matter pool. Initially we demonstrated how to optimally sterilize organic matter for experimental studies in order to preserve its natural complexity. In further experiments we found that bacterial communities are redundant in their utilization of organic matter and can maintain optimal performance towards a range of organic matter pools. Related to this we found that pre-adaptation to organic matter played a small role as communities performed equally well regardless of their environmental history. We saw a small effect of richness and composition of bacterial communities on the efficiency of organic matter use, but conclude that this is of minor importance relative to abiotic factors. Still, we also show that organic matter can put strong selection pressure on bacterial communities with regards to richness and composition. Additionally we found that the supply rate of a carbon compound greatly influenced the energy utilization of the compound, i.e. a higher growth rate can be maintained if substrate is delivered in pulses relative to a continuous flow. Finally we conclude that the variation in bacterial communities is unlikely to have a major influence on carbon cycling in boreal lakes, but to enable a finer understanding, the genetics underlying the carbon utilization needs to be further explored.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22429号 / 工博第4690号 / 新制||工||1732(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 清水 芳久, 教授 田中 宏明, 教授 米田 稔 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Indiana University-Purdue University Indianapolis (IUPUI) / Phosphorus (P) is essential for aquatic life; cycling between both inorganic and organic forms to maintain an ecological balance. Its addition into P-scarce freshwaters, either through terrestrial (external) or sedimentary (internal) loading, may disrupt this balance causing blooms of phytoplankton to flourish, often resulting in harmful environmental and anthropogenic consequences. Accordingly, reduction of external P loading has been commonly implemented with a recent focus on sediment-bound legacy P that is mobilized into the water column during dynamic redox conditions. Mobile P species have been identified as both inorganic and organic, with the former representing the most bioavailable fraction, and the latter serving as a source for labile P in freshwaters when in high demand, particularly during blooms. Missisquoi Bay in Lake Champlain, VT experiences harmful cyanobacterial blooms driven by internal P loading and has been the target of numerous geochemical and hydrological studies. This thesis describes a high-resolution investigation of both the organic P and organic matter compositions of the bay with respect to mobility, reactivity, and bioavailability using Fourier Transform-Ion Cyclotron Mass Spectrometry (FT-ICR MS). Sediment from Missisquoi Bay was extracted with a diverse set of reagents, resulting in fractionation of both organic matter and organic P, and illustrating the distribution of various labile and recalcitrant compounds. Many of these molecules are associated with porewater or easily extractable mineral surfaces providing a link to the benthic organic matter and phosphorus fractions available to microorganisms. Additionally, the organic chemistry of the bay was investigated seasonally from May 2017 to January 2018 revealing biological processing from the spring runoff season through the post-bloom summer season. The transition from late summer to under ice conditions in winter was less severe with a higher commonality between both organic matter and organic P compounds, suggesting reduced biological and abiotic degradation. Moreover, short-term anoxic incubations of sediment cores from each season revealed the presence of diverse organic signatures from sorption processes, and a significant contribution of benthic microbial activity to the benthic organic geochemistry.

The microbial origin of methane produced from sedimentary basins is a subject of great interest, with implications for the global cycling of carbon as well as natural gas exploration. Despite the growing body of research in sedimentary basin methanogenesis, few studies have sought to understand the subsurface microbial communities that produce methane, the metabolic pathways involved in the decomposition of ancient organic matter, or the components of ancient organic matter that are consumed. This research examined shale-derived dissolved organic matter (DOM) as a potential substrate to support a subsurface methanogenic community in a known microbial shale gas reserve, the Antrim Shale in the Michigan Basin, USA. Experiments were conducted that enriched fermentative and sulfate-reducing microbial communities from Antrim Shale formation waters. Additionally, 1H NMR spectroscopy was used to characterize shale-derived DOM solutions before and after they were used as growth media for fermentative and sulfate-reducing microbial communities, and to characterize the DOM of the Antrim Shale formation waters. The results of the enrichment studies demonstrate that both fermentative and sulfate-reducing microbial communities from the Antrim Shale are capable of growth using shale-derived DOM as their only source of organic carbon; further, the production of methane in a fermentative enrichment demonstrates that methanogenesis can be supported by shale-derived DOM alone. The 1H NMR characterization studies of the shale-derived DOM solutions before and after growth revealed subtle but detectable differences in DOM compositions, indicating the production and consumption of DOM components by the fermentative and sulfate-reducing microbial communities. Characterization analyses of Antrim Shale formation waters suggest that salinity and microbiological activity may influence the liberation of aliphatic and aromatic compounds from shale. The DOM characterization studies also suggest that carboxylic acids may be consumed by methanogenic communities in the Antrim Shale, and aromatic compounds may be produced by the enriched microbial communities and the communities present in the Antrim Shale.

No description available.

Intensely managed and modified catchments in the Great Lakes are linked to eutrophication and hypoxia of receiving water bodies downstream, resulting in water quality impairment, and adverse impacts on aquatic ecology. While much focus has been on the role of phosphorous and nitrogen, dissolved organic carbon (DOC) plays a complex and critical role in lake biogeochemical cycles, as it influences the interations between nutrients and contaminants in water and soil through processes of mobilization, transport, biological uptake, and deposition. Human-dominated landscapes have a range of consequences on DOC dynamics as catchment hydrology, plant cover, and nutrient inputs are altered in these environments. As such, the objectives of this study were to identify the controls and drivers of DOC quantity and DOM quality in the Spencer Creek watershed, which is the largest contributor of water to Cootes Paradise that ultimately drains into Lake Ontario. The 159 km2 study area of the catchment is complex, as the present landscape is composed of a mosaic of various land uses including agriculture, forest, wetland, urban, and industrial regions. Flow alterations contribute to the complexity of the watershed as there are managed reservoirs and alterations in water courses. From 2016- 2018, hydrometric data was collected across 9 monitoring sites, along with surface water samples that were analyzed for DOC concentration and optical properties. Results indicate differences in flow magnitudes and stream DOC between dry and wet conditions, where concentrations during wet conditions were significantly higher compared to dry. Additionally, there was substantial variation in DOC concentration and quality across the Spencer Creek watershed. DOC concentrations were found to be the lowest at groundwater influenced sites in the headwaters of the watershed, and the highest in the mid-catchment region where DOC quality was strongly influenced by wetland sources. The reservoir-influenced sites showed relatively intermediate concentrations of DOC, with quality that exhibited strong microbial signatures. At the outlet, DOC concentrations were attenuated and DOC quality was intermediate between allochthonous and autochthonous end members, reflecting upstream mixing processes. These processes were presented as a conceptual model of water and DOC movement through the Spencer Creek watershed. The implications of this research suggest that with anticipated wetter and warmer conditions DOC concentrations would increase in the watershed. The repercussions of increased DOC concentrations overall imply a decrease of terrestrial carbon storage, and greater input into more reactive and susceptible pools, which may result in further water quality degradation. Overall, the findings from this research provide insight into the fate and transport of water and DOC in a complex, managed catchment in the Great Lakes region, with the aims of providing key information for local stakeholders. / Thesis / Master of Science (MSc)

As anthropogenic nutrient loads threaten the health of the Chesapeake Bay, lotic processes throughout its headwaters may buffer increased nitrogen inputs by converting them to stable forms, ultimately through denitrification to N2 gas. However, the temporal environmental factors controlling baseflow nitrogen retention are poorly understood, particularly temperature, shading, and dissolved organic matter dynamics. This study therefore attempts to elucidate the effects of these environmental variables on nitrogen cycling within the Fair Hill Natural Resources Management Area (Fair Hill), a forested watershed within the Piedmont physiographic province of the Chesapeake Bay. As expected, groundwater and allochthonous organic matter inputs set the foundation for lotic biogeochemistry at Fair Hill, creating a nutrient-limited, heterotrophic reach. Within this setting, three temporal "hot-moments" of in-stream nutrient processing were observed: the release of ammonium and phosphate during the warm - but shaded - growing season; nitrate uptake during autumnal leaf-fall; and a unique spike of nitrate uptake and respiration-induced degradation of labile organic matter during a drought. Consequently, the baseflow capacity of this headwater stream to buffer nutrient exports to the Chesapeake Bay constantly varies throughout the year in response to light availability, temperature, and in-stream organic matter dynamics. / Master of Science / Throughout the Chesapeake Bay watershed, ecological processes known as nitrogen retention can naturally remove nitrogen pollution from small streams (a.k.a. headwater streams), and hence the Chesapeake Bay watershed. However, in-stream nitrogen retention varies throughout the year due to seasonal changes in temperature, shading (as leaves grow in the spring or fall off in the fall), and the amount and type of organic matter in the stream. This study examines how these three variables (temperature, shading, and dissolved organic matter dynamics) affect nitrogen retention in a headwater, forested stream within the Fair Hill Natural Resources Management Area (Fair Hill) located in the Piedmont region of the Chesapeake Bay watershed. As expected, groundwater and organic matter inputs set the foundation for in-stream conditions at Fair Hill, creating an environment with low concentrations of nitrate and phosphate (thus causing the stream to be nutrient-limited), while also creating a heterotrophic environment, which is an environment where more oxygen is consumed by microbes than produced by algae and plants. Additionally, three seasonal patterns regarding in-stream nutrient dynamics were observed at Fair Hill. Firstly, in-stream ammonium and phosphate concentrations increased during the warm - but shaded - growing season. Secondly, in-stream nitrate concentrations decreased when leaves fell in the fall. Thirdly, during a drought, in-stream nitrate removal increased while in-stream organic matter became more degraded. Consequently, in-stream nutrient retention at Fair Hill varies constantly throughout the year in response to light availability, temperature, and in-stream organic matter dynamics.