Category: Student Database

Iowa stream sites and watersheds evaluated in this study

Iowa stream nitrate and the Gulf of Mexico

Student Database

Author: Jones, Christopher S.; Nielsen, Jacob K.; Schilling, Keith E.; Weber, Larry J. Description: The main objective of this work was to quantify and update the U.S. Midwest agricultural state of Iowa’s contribution of nitrate-nitrogen to the Mississippi River stream network against the backdrop of the ongoing problem of Gulf of Mexico hypoxia. To achieve this objective, we used stream nitrate and discharge data collected from 1999 until 2016 at 23 Iowa stream sites near watershed outlets, along with publicly-available data for sites downstream of Iowa on the Missouri and…

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Methylmercury decomposition in sediments and bacterial cultures: involvement of methanogens and sulfate reducers in oxidative demethylation

Student Database

Author: Oremland, R. S.; Culbertson, C. W.; Winfrey, M. R. Description: Demethylation of monomethylmercury in freshwater and estuarine sediments and in bacterial cultures was investigated with CH(3)HgI. Under anaerobiosis, results with inhibitors indicated partial involvement of both sulfate reducers and methanogens, the former dominating estuarine sediments, while both were active in freshwaters. Aerobes were the most significant demethylators in estuarine sediments, but were unimportant in freshwater sediments. Products of anaerobic demethylation were mainly CO(2) as well as lesser amounts of CH(4). Acetogenic activity resulted in fixation of some CO(2) produced…

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Mercury contamination in three freshwater US locations

Methyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted Ecosystems

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Author: Marvin-DiPasquale, Mark; Agee, Jennifer; McGowan, Chad; Oremland, Ronald S.; Thomas, Martha; Krabbenhoft, David; Gilmour, Cynthia C. Description: We examined microbial methylmercury (MeHg) degradation in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), three freshwater environments that differ in the extent and type of mercury contamination and sediment biogeochemistry. Degradation rate constant (kdeg) values increased with total mercury (Hgt) contamination both among and within ecosystems. The highest kdeg’s (2.8-5.8 d-1) were observed in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of…

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Simultaneous determination of mercury methylation and demethylation capacities of various sulfate-reducing bacteria using species-specific isotopic tracers

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Author: Bridou, Romain; Monperrus, Mathilde; Gonzalez, Pablo Rodriguez; Guyoneaud, Remy; Amouroux, David Description: The use of species-specific isotopic tracers for inorganic and methyl mercury has allowed the simultaneous determination of the methylation and demethylation potentials of pure culture of isolated sulfate-reducing (SR) bacterial strains using low Hg species concentration levels (7 µg/L (199)Hg(II), 1 µg/L Me(201)Hg). A major advantage of the method reported here is that it can be used to follow simultaneously both the degradation of the species added but also the formation of their degradation products and thus…

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Mercury released to the atmosphere historical

All-time releases of mercury to the atmosphere from human activities

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Author: Streets, David G.; Devane, Molly K.; Lu, Zifeng; Bond, Tami C.; Sunderland, Elsie M.; Jacob, Daniel J. Description: Understanding the biogeochemical cycling of mercury is critical for explaining the presence of mercury in remote regions of the world, such as the Arctic and the Himalayas, as well as local concentrations. While we have good knowledge of present-day fluxes of mercury to the atmosphere, we have little knowledge of what emission levels were like in the past. Here we develop a trend of anthropogenic emissions of mercury to the atmosphere…

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Detailed assessment of the kinetics of Hg-cell association, Hg methylation, and methylmercury degradation in several Desulfovibrio species

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Author: Graham, Andrew M.; Bullock, Allyson L.; Maizel, Andrew C.; Elias, Dwayne A.; Gilmour, Cynthia C. Description: The kinetics of inorganic Hg [Hg(II)(i)] association, methylation, and methylmercury (MeHg) demethylation were examined for a group of Desulfovibrio species with and without MeHg production capability. We employed a detailed method for assessing MeHg production in cultures, including careful control of medium chemistry, cell density, and growth phase, plus mass balance of Hg(II)(i) and MeHg during the assays. We tested the hypothesis that differences in Hg(II)(i) sorption and/or uptake rates drive observed differences…

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Mercury pollution sources and cycle

Mercury as a global pollutant: sources, pathways, and effects

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Author: Driscoll, Charles T.; Mason, Robert P.; Chan, Hing Man; Jacob, Daniel J.; Pirrone, Nicola Description: Mercury (Hg) is a global pollutant that affects human and ecosystem health. We synthesize understanding of sources, atmosphere-land-ocean Hg dynamics and health effects, and consider the implications of Hg-control policies. Primary anthropogenic Hg emissions greatly exceed natural geogenic sources, resulting in increases in Hg reservoirs and subsequent secondary Hg emissions that facilitate its global distribution. The ultimate fate of emitted Hg is primarily recalcitrant soil pools and deep ocean waters and sediments. Transfers of…

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Legacy phosphorus used in agriculture in China

Quantitative evaluation of legacy phosphorus and its spatial distribution

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Author: Lou, Hezhen; Zhao, Changsen; Yang, Shengtian; Shi, Liuhua; Wang, Yue; Ren, Xiaoyu; Bai, Juan Description: A phosphorus resource crisis threatens the security of global crop production, especially in developing countries like China and Brazil. Legacy phosphorus (legacy-P), which is left behind in agricultural soil by over-fertilization, can help address this issue as a new resource in the soil phosphorus pool. However, issues involved with calculating and defining the spatial distribution of legacy-P hinder its future utilization. To resolve these issues, this study applied remote sensing and ecohydrological modeling to…

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Global mercury cycle

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

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Author: Obrist, Daniel; Kirk, Jane L.; Zhang, Lei; Sunderland, Elsie M.; Jiskra, Martin; Selin, Noelle E. Description: We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environmental Hg data were previously lacking; integration of these data into global and regional models is continually improving estimates of global Hg cycling….

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The herbicide glyphosate is a potent inhibitor of 5-enolpyruvylshikimic acid-3-phosphate synthase

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Author: Steinrucken, H. C.; Amrhein, N. Description: The broadspectrum herbicide glyphosate (N-[phosphonomethyl]-glycine), which causes the accumulation of shikimic acid in plant tissues, inhibits the enzymatic conversion of shikimic acid to anthranilic acid in a cell-free extract of Aerobacter, aerogenes 50% at 5 to 7 uM concentrations. Of the four enzymes involved in the transformation, only 5-enolpyruvylshikimic acid-3-phosphate synthase is inhibited by the herbicide. Subject headings: Enzymes; Glyphosate; Metabolism; Physiology; Weeds; Plants; Eukaryotes Publication year: 1980 Journal or book title: Biochemical and Biophysical Research Communications Volume: 94 Issue: 4 Pages: 1207-1212…

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