Browsing by Subject "Sulfur"

Now showing 1 - 8 of 8
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    Abiotic transformations of pesticides in prairie potholes
    (2012-08) Zeng, Teng
    The prairie pothole region (PPR) is among the most extensively altered ecosystems on Earth. This region covers approximately 780,000 km2 of central North America, and contains numerous glacially formed wetlands embedded in an agricultural landscape. These wetlands, commonly known as prairie pothole lakes (PPLs), provide essential ecosystem services. Over the last 150 years, agricultural drainage has resulted in severe loss of native prairie wetlands. The remaining PPLs continue to be threatened by nonpoint source pesticide pollution from agriculture. Currently, little is known about the fate and persistence of pesticides in PPLs. In this work, the abiotic transformations of commonly used pesticides in PPL sediment porewaters and surface water were explored. Chloroacetanilide and dinitroaniline pesticides were found to react rapidly with naturally abundant reduced sulfur species (i.e., hydrogen sulfide and polysulfides) in sediment porewaters via nucleophilic substitution and reduction reactions, respectively. Dissolved organic matter (DOM) was also found to play a vital role in the reductive transformation. Next, the photodegradation of a suite of pesticides was investigated in PPL surface water under both simulated and natural sunlight. Enhanced pesticide removal rates pointed to the importance of indirect photolysis pathways involving photochemically produced reactive intermediates such as singlet oxygen and triplet excited-state DOM. Finally, the sedimentary sulfur speciation was examined by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Sulfur species in PPL sediments were found to consist of organic (di)sulfides, sulfonate, sulfate, and the mineral pyrite. Notably, the fractional abundances of reduced and oxidized sulfur species fluctuate on a seasonal basis.
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    Ecology of Giant, Sulfur-Oxidizing Thioploca Bacteria in Great Lakes Sediments
    (2021-06) McKay, Elizabeth
    Microorganisms play a key role in regulating the cycling of carbon, oxygen, nitrogen, sulfur, and other important elements in aquatic ecosystems. Thioploca is a giant, filamentous bacteria that oxidizes sulfide and reduces nitrate, coupling the nitrogen and sulfur cycles in its benthic habitats. Thioploca can achieve high abundances in marine sediment where it is known to alter nitrogen and sulfur dynamics by removing toxic sulfide and recycling fixed nitrogen back into the sediment and water column. Thioploca can also achieve high abundances in freshwater sediments; however, its distribution and biogeochemical function are poorly understood in freshwater environments, making it difficult to determine how it impacts elemental cycling in these habitats. To analyze Thioploca abundance, factors affecting its distribution, and its biogeochemical function in the Great Lakes, I quantified Thioploca biomass and water column and sediment characteristics at 33 sites that spanned a gradient of depth and trophic conditions in the Apostle Islands region of Lake Superior and Green Bay in Lake Michigan. Sediment cores were also collected at eight of my study sites to analyze vertical Thioploca biomass distribution and sediment chemistry. Thioploca was common in both the Apostle Islands and Green Bay and reached biomasses of up to 250 g/m2 wet weight at some sites. While PCA and logistic regression analysis indicated that Thioploca may be more likely to be present under eutrophic conditions, Thioploca was also common and abundant at some oligotrophic sites in the Apostle Islands. Thioploca was more abundant in fine-grained than coarse-grained sediment, suggesting Thioploca distribution may be linked to depositional areas of lakes. At most sites, Thioploca was most abundant in the top 5 cm of sediment. Ammonia profiles in some sediment cores appear to indicate possible ammonia consumption in sediment layers with Thioploca, which suggests these freshwater Thioploca may interact with benthic nitrogen cycling differently than marine species of Thioploca. My results, along with other reports from the Great Lakes, suggest that freshwater Thioploca may be widespread throughout the Great Lakes. At the abundances observed, Thioploca is likely significantly influencing nitrogen and sulfur cycling in these areas, although many questions remain about Thioploca’s biogeochemical functioning in freshwater environments, including how it achieves high biomass in low sulfur environments, whether it reduces nitrate to ammonia or N2, and whether it promotes the recycling of fixed nitrogen or acts as a fixed nitrogen sink.
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    The effects of sulfur and selenium on glucoraphanin and seleno-methylselenocysteine concentrations in broccoli (Brassica oleracea L. italica)
    (2015-05) Doberstein, Annie
    Glucosinolates (GLSs) are sulfur-containing secondary metabolites produced by broccoli (Brassica oleracea subsp. italica) and other cruciferous vegetables. GSLs exist for use in plant defense, but are gaining research interest for their role in cancer prevention. Glucoraphanin (GR) is a particular glucosinolate found in broccoli that has great health benefit potential. Seleno-methylselenocysteine (SeMSC) is another compound unique to broccoli when it has been exposed to selenium during plant growth, and is also of interest for its chemopreventive potential. To understand the relationship between root fertilization of sulfur and selenium on GR and SeMSC concentrations in a production environment, we exposed a low-GR ("Green Magic") and a high-GR ("Beneforte") broccoli to sulfur (0 - 34 kg.ha��) and selenium (0 - 3.36 kg.ha��) fertilization treatments in the field. GR and SeMSC concentrations depended upon cultivar, treatment, and environmental factors."Beneforte" consistently delivered the highest GR concentration, and "Green Magic" the lowest, and "Beneforte" GR concentrations were less affected by the presence of Se treatments than "Green Magic". "Beneforte" also accumulated higher concentrations of SeMSC overall than "Green Magic". A colder, wetter spring in 2013 led to reduced sulfur uptake and lower concentrations of GR overall, while a warmer, drier climate during later Se applications increased Se uptake and subsequent SeMSC concentrations. Contrasting, a warmer, dryer spring the following year gave way to increased sulfur uptake and greater GR concentrations, and wetter, cooler conditions during Se applications negatively impacted SeMSC concentrations overall. To assess the efficacy of foliar Se fertilization as an alternative to root application, the same two varieties were grown in a greenhouse and were subjected to one of four sodium selenate treatments (0 - 93.74 mg Se.plant�). Again, Se significantly affected the concentration of GR in "Green Magic", but not in "Beneforte". Overall, a weak relationship between GR and SeMSC concentrations give a promising outlook to the ability to maximize GR and SeMSC for ultimate benefit upon consumption of broccoli. This is especially true in "Beneforte", where GR concentrations remain relatively stable in the presence of Se, but still allow Se uptake and SeMSC formation.
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    Impact Of Increased Temperature And Atmospheric Carbon Dioxide On Mercury And Sulfur Speciation In Peatland Soils
    (2018-08) Krupp, Anna Lucia
    Environmental mercury (Hg) pollution exists as a global public health issue without any localized borders. Volatile Hg emissions travel freely throughout the atmosphere, allowing anthropogenic point-source industrial emissions to have truly global impact. Recent research demonstrates that climate change may further impact the extent of environmental mercury pollution through increased production of monomethylmercury, more commonly known as methylmercury (MeHg), by various microorganisms within the soil, including sulfate-reducing bacteria, iron-reducing bacteria and methanogens. Continued research on the subject is warranted to fully understand the impacts of climate change on the environmental biogeochemical cycling of Hg and MeHg on various natural systems. Increasing global temperatures and levels of atmospheric CO2 could significantly increase the net conversion of Hg to MeHg by sulfate-reducing and iron-reducing bacteria in systems particularily vulnerable to climate change such as ombrotrophic peatbogs, leading to an increased size in the net MeHg pool overall. The Supplementary Files attached to this thesis document include the following files: raw data (SPRUCE_2012_2014_2015_2016_Peat_Final_Data.xlsx), untransformed multiple linear regression values (Regression_Non_Transformed.xlsx), log transformed multiple linear regression values (Regression_Log_Transformed.xlsx), maximum value calculations (Max_Calculations.xlsx), and fitted XANES data for 2012 (SPRUCE-2012-fit7-tidy.xlsx), 2015 (SPRUCE-2015-fit4-tidy.xlsx), and 2016 (SPRUCE-2016-fit4-tidy.xlsx).
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    A New Insight Into The Geochemistry Of Sulfur In Low Sulfate Environments
    (2018-08) Fakhraee, Mojtaba
    As an essential element for life, sulfur plays an important role in the biosphere, hydrosphere, atmosphere and lithosphere. Studies of sulfur cycling have been traditionally concentrated on modern marine environments with 28mM of sulfate, yet its importance in low sulfate environments such as large freshwater systems as well as the oceans of the geologic past (>0.5 billion years ago) cannot be neglected. This thesis, through modeling and theoretical approach, aims to provide a new insight into several aspects of sulfur cycling in low sulfate environments. For example, it is widely assumed that water-column sulfate is the main sulfur source to fuel microbial sulfate reaction in sediments. While this assumption may be justified in high-sulfate environments such as modern seawater, I show that in low-sulfate environments mineralization of organic sulfur compounds can be an important source of sulfate and sedimentary sulfide. The results in this thesis indicate that in low sulfate environments (<500 µM) the in-sediment production of sulfate can support a substantial portion (>50%) of sulfate reduction. Extrapolating the results to Archean oceans with tens of µM of sulfate, modeling results reveal that sulfite generated by mineralization of organic sulfur could fuel microbial S reduction in the absence of ambient sulfate, and hydrogen sulfide generated by mineralization of reduced organic S compounds could provide a pathway to pyrite that bypassed the microbial reduction of sulfate or sulfite. Reproducing isotopic records in the sedimentary sulfides from the rock record, modeling results show that in the low sulfate (<10 µM) environment of the Archean oceans (2.5-4 billion years ago), oxygen could have accumulated to up to 25 µM, while being consistent with the sulfur isotopic composition in Neoarchean rocks. A mass balance model coupled to a sediment diagenesis model suggests that seawater sulfate concentrations during the Proterozoic Eon (0.5-2.4 billion years ago) remained below 1.5% of modern values (<500 µM), and possibly as low as 100 µM. Using exploratory modeling of sulfur cycling, I also constrain the geochemical factors that control the fluxes of methylmercury from modern freshwater sediments. Modeling results identify oxygen, sulfate, and organic matter as leading geochemical parameters. They also suggest a critical level of oxygen at the sediment water interface, below which methylation rate dominates demethylation rate, resulting in an efflux of methylmercury into overlying water.
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    Split application of sulfur and potassium and their leaching potential for corn grown on irrigated soils
    (2013-09) Bonde, Andria Jansen
    Irrigated coarse textured soils have the potential to produce high yielding crops but are also likely to leach out fertilizer nutrients before they can be utilized. Few studies have considered split fertilizer applications of sulfur (S) and potassium (K) on coarse textured soils. Eight fertilizer studies, four S and four K, were conducted to assess how split applications of S and K fertilizers affect plant uptake, corn grain yield, and the leaching potential over the growing season. Each site had four at planting (AP) and four in-season (IS) fertilizer rates applied for a combination of 16 different fertilizer treatments. Various plant tissue, remote sensing readings, and soil samples were taken to assess nutrient availability and movement through the soil profile. Suction cup lysimeters were used in select treatments to monitor soil pore water concentrations. Single or split applications of S and K fertilizers did not increase grain yield. Significant differences among different AP and IS rates were found for early plant and ear leaf S and K concentrations, but these were unable to predict grain yield. Normalized difference vegetation index or SPAD chlorophyll readers did not prove to be indicators of final corn grain yield in either S or K studies. Plant NDVI data was able to predict biomass in K studies. Lysimeter data from S studies suggest increased S concentration towards the end of the growing season but provided no advantage of split application of S fertilizer to avoid S losses. Lysimeter data suggested early season K movement and in most sites and IS fertilizer application had the greatest effect on end of the growing season pore water K concentration. Because of potential early K movement, split applications may be advised for farmers growing corn on coarse textured soils to avoid K losses.
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    Use of metagenomics and metatranscriptomics to determine the influence of organic sulfur compounds on the sulfur cycle in the sediment of a low-sulfate freshwater system
    (2020-08) Hyde, Emily
    The sulfur cycle is an important and complex biogeochemical cycle involving both inorganic and organic species in both oxic and anoxic environments. However, due to the lack of research regarding the sulfur cycle in freshwater systems, the contributions of organic sulfur compounds to the sulfur cycle are underappreciated. Recent studies have suggested organic sulfur compounds likely fuels sulfate reduction, especially in low-sulfate oligotrophic freshwater systems, through a possible cryptic sulfur cycle. To determine the contributions that organic sulfur compounds may have in this environment, we used Lake Superior sediment to analyze for the presence of and expression of sulfur cycling genes. In these metagenomes, we found genes for sulfur reduction, oxidation and organic sulfur compound degradation. Metabolic pathway analysis showed presence of not only organic sulfur compounds contributing to the sulfur cycle, but tetrathionate, thiosulfate, and polysulfides playing a role as well. Using Lake Superior sediments, we also conducted sediment incubations to measure the biotransformation capability of sulfur-containing amino acids, sulfonates, and an analog for a common sulfolipid. Taurine and sodium dodecyl sulfate produced higher sulfate values in incubations, suggesting that microbes prefer sulfonates over sulfur-containing amino acids, in addition to a possible partiality towards oxidized organic sulfur compounds over reduced forms regarding sulfate production. The preference of sulfonates is supported by the commonality of taurine genes present as well as the low, but present transcription values of sulfoacetaldehyde degradation. While sulfur-containing amino acids do not produce sulfate values near that of sulfonates or sulfolipids, there are still present and transcriptionally active genes that can contribute to sulfate reduction in the system. Regarding methyl-sulfurs, metatranscriptomic data shows that methyl-mercaptan (intermediate within dimethyl sulfide and methionine degradation) degradation is transcriptionally active across genomes. By combining biotransformation incubation data, metagenomics, and metatranscriptomics, we analyzed how methylated sulfurs, sulfur-containing amino acids and sulfonates can fuel a sulfur cycle in a low-sulfate environment, informing us on how pathways may have operated in our Earth’s geologic past.
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    Utilization of synchrotron radiation X-ray microscopy, micro-probe, and spectroscopy to characterize the carbon, sulfur, and iron speciation of particles from buoyant, deep-sea hydrothermal plumes in the Mid-Cayman Rise
    (2017-04) Kamermans, Brandi
    The purpose of this study was to investigate the geochemical inputs to rising hydrothermal vent plumes of the Mid-Cayman Rise. To assess processes that modulate hydrothermal fluxes to the deep ocean at the Mid-Cayman Rise, the speciation of Fe, S, and C was measured for particles and aggregates using: (1) microprobe S 1s and Fe 1s X-ray absorption near edge structure (XANES) spectroscopy, (2) microprobe X-ray fluorescence (XRF) chemical mapping, and (3) scanning transmission X-ray microscopy (STXM) based C 1s and Fe 2p XANES. The Mid-Cayman Rise is an ultraslow spreading center located in the Caribbean Sea. The Mid-Cayman Rise hosts two hydrothermal vents that produce geochemically diverse fluids: (1) Beebe, the deepest (5000 ± 50 meters) known high-temperature (398 oC) vent site with high iron and sulfur, and (2) Von Damm (2300 ± 50 meters) with fluids at 110 to 200 oC (Kinsey and German, 2013). My samples were collected with a newly developed instrument, called the SUPR (SUspended Particle Rosette) (Breier et al., 2014). The SUPR was developed for high-precision collection of deep-sea samples, and it also made it possible to collect samples for complementary research efforts. Carbon XANES of Von Damm fluids reveal the presence of biomolecules such as proteins, lipids, polysaccharides, and chitin in plume particles. Iron 2p imaging and XANES indicate that nanoparticulate Fe minerals are associated with particulate organic C (POC). Sulfur 1s XANES and chemical mapping data reveal the presence of sulfonate, sulfone, and ester sulfate, as well as elemental S, and indicate that microbial processes and chemical oxidation occur in the subsurface or in the near vent samples. In the Von Damm particles, a shift from strongly reduced to oxidized, including the appearance of intermediate S-bearing functionalities, suggests turbulent mixing of Von Damm fluids with seawater provide oxic and pH neutral conditions where chemical and biological interactions can occur. The Fe 1s XANES observations capture trends that suggest particles within the Von Damm and Beebe Vents could be sourced from chemical processes within the plume and physical entrainment processes from multiple sources.