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You searched for subject:(monomethylmercury). Showing records 1 – 3 of 3 total matches.

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Texas A&M University

1. Keach, Sara Elizabeth. Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia.

Degree: MS, Oceanography, 2007, Texas A&M University

A study of monomethylmercury (MMHg) concentrations in the water and sediment of the hypoxic zone in the northeastern Gulf of Mexico was conducted on several cruises between April 2004 and May 2005. Surface water MMHg concentrations were low and constant throughout the sampling period. Bottom water concentrations displayed a seasonal trend: maximum MMHg concentrations were in June/July 2004, decreased to a minimum in October 2004, and in May 2005 concentrations had begun to increase. MMHg concentrations and MMHg as a percent of THg in surface sediment (0-2 cm) also followed this trend. Bottom water dissolved oxygen and temperature displayed inverse relationships with bottom water MMHg concentrations. This correlation between dissolved oxygen and MMHg is typical for low-oxygen waters, but the relationship between temperature and MMHg is relatively unique. A possible explanation is that warmer summer temperatures inhibited bacterial methylation. Stratification intensity (quantified as N2) was strongly correlated with bottom water MMHg concentrations, indicating either increased methylation at the pycnocline or that the pycnocline inhibited vertical mixing, thus limiting MMHg to the bottom water. Benthic flux estimations indicate that sediment release of MMHg could be a significant source of MMHg to bottom water. The presence of an oxygenated layer in the surface sediment could have played a role in inhibiting MMHg flux during oxic conditions; a decrease in the thickness of this layer under hypoxic conditions likely allowed MMHg to diffuse into the bottom water. Dissolved oxygen seemed to play an important role in controlling sediment MMHg concentrations with highest methylation rates in sediment under hypoxic water. Overall, sites closest to the Mississippi River mouth displayed the highest MMHg concentrations. Further research will need to be done in this area to fully characterize the relationship between biogeochemical parameters and MMHg concentrations. Advisors/Committee Members: Gill, Gary (advisor), Santschi, Peter (advisor), DiMarco, Steven (committee member), Rooker, Jay (committee member).

Subjects/Keywords: monomethylmercury; hypoxia

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APA (6th Edition):

Keach, S. E. (2007). Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/6003

Chicago Manual of Style (16th Edition):

Keach, Sara Elizabeth. “Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia.” 2007. Masters Thesis, Texas A&M University. Accessed November 27, 2020. http://hdl.handle.net/1969.1/6003.

MLA Handbook (7th Edition):

Keach, Sara Elizabeth. “Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia.” 2007. Web. 27 Nov 2020.

Vancouver:

Keach SE. Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia. [Internet] [Masters thesis]. Texas A&M University; 2007. [cited 2020 Nov 27]. Available from: http://hdl.handle.net/1969.1/6003.

Council of Science Editors:

Keach SE. Monomethylmercury concentrations on the eastern Texas-Louisiana shelf during the formation, peak, and disappearance of hypoxia. [Masters Thesis]. Texas A&M University; 2007. Available from: http://hdl.handle.net/1969.1/6003

2. Agather, Alison M. Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters.

Degree: PhD, Environmental Sciences PhD, 2018, Wright State University

Mercury (Hg) is a global pollutant toxic to humans and wildlife. Monomethylmercury (MMHg) is a bioavailable compound that bioaccumulates and biomagnifies in food webs. Humans are primarily exposed to MMHg from seafood consumption (Sunderland 2007), and high quantities of the neurotoxin lead to reduced neurocognitive functioning in adults and the children of exposed mothers (Cohen et al. 2005, Yokoo et al. 2003). Negative effects from MMHg accumulation on the health of humans and wildlife requires a more complete understanding of the chemistry and microbiology driving Hg methylation in both marine and freshwater systems. This work focuses on water column distribution, speciation, and methylation of Hg. The aims of this dissertation are three-fold: (1) characterize the speciation and distribution of Hg in the western Arctic Ocean; (2) examine seasonal variations in Hg speciation, methylation, and demethylation, and the microbial communities of Hg methylators in Crystal Lake, Ohio; and (3) quantify Hg methylation rates and characterize methylating microbial communities in waters on the continental shelf of the northwest Atlantic Ocean. While Hg methylation has been studied for decades, this work is built upon recent improvements in Hg detection limits, and newly discovered genes responsible for Hg methylation. In conjunction with U.S. Arctic GEOTRACES (GN01), the western Arctic Ocean was sampled in the summer of 2015. Although Hg concentrations in the Canada and Eurasian Basins were low relative to the Atlantic and Pacific Oceans, higher MMHg concentrations were observed in Arctic seawater that recently interacted with continental margins. We estimate that the Arctic Ocean receives 4–71 kmol Hg yr−1 from the Bering Strait, which is likely to interact with sediments of the shallow continental shelves before entering into the Arctic Ocean. This is potentially important, because while the estimated atmospheric input to the Arctic Ocean is ~400 kmol Hg yr−1, inflowing Hg from the Bering Strait may still be an important source of Hg that can be methylated on the Chukchi Shelf. Mercury methylation potentials were measured in a stratified freshwater system, Crystal Lake, in Dayton, Ohio (objective2). Mercury methylation occurred in both oxic and anoxic portions of the water column, but methylation potentials were greatest at the oxic/anoxic boundary layer. Mercury methylating genes were found throughout the water column and had the greatest copy number in the hypolimnion. Similarly, previous marine work showed that sediments and the microbial communities therein are large sources of MMHg to near shore marine systems (Fitzgerald et al. 2007), which led to methylation and demethylation studies along the northwest Atlantic shelf (objective #3). Greater abundance of Hg methylating microbes were observed in water overlying sediment as opposed to shallower waters, but methylation potentials did not significantly differ. Together, these results suggested that (1) Archaea may be responsible for Hg methylation in oxic waters; and (2)… Advisors/Committee Members: Hammerschmidt, Chad (Advisor).

Subjects/Keywords: Biogeochemistry; Environmental Science; Limnology; Oceanography; Monomethylmercury; MMHg; Mercury Methylation; Hg methylation

…filtered monomethylmercury (black squares) and dimethylmercury (open triangles… …monomethylmercury (MMHg, C). Black dots indicate sample depth. ............................. 97… …Hg0) differs from monomethylmercury (MMHg) due to chemical differences… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Agather, A. M. (2018). Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters. (Doctoral Dissertation). Wright State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=wright154522079626445

Chicago Manual of Style (16th Edition):

Agather, Alison M. “Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters.” 2018. Doctoral Dissertation, Wright State University. Accessed November 27, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright154522079626445.

MLA Handbook (7th Edition):

Agather, Alison M. “Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters.” 2018. Web. 27 Nov 2020.

Vancouver:

Agather AM. Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters. [Internet] [Doctoral dissertation]. Wright State University; 2018. [cited 2020 Nov 27]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=wright154522079626445.

Council of Science Editors:

Agather AM. Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters. [Doctoral Dissertation]. Wright State University; 2018. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=wright154522079626445

3. Klaus, Jaclyn Elizabeth. In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio.

Degree: MS, Earth and Environmental Sciences, 2014, Wright State University

Periphyton are of ecological importance because of their critical role at the base of aquatic food webs as primary producers and as a significant source of energy to higher trophic levels in many stream ecosystems. This study examined the toxicity of mercury (Hg) to fluvial periphyton with in situ chemical exposure substrates. Two endpoints were used to measure toxicity of either total Hg or monomethylmercury (MMHg) to periphyton: periphyton biomass and metabolic activity, as a function of Hg concentrations in either periphyton or their exposure to the contaminants from two contrasting sediment types, a low-organic, sandy sediment type (SC) and a high-organic, fine-grained sediment (WD). MMHg and total Hg accumulation was greater in periphyton exposed to sandy SC sediment, whereas our results indicated periphyton growth and metabolic activity may be reduced when exposed to organic-rich WD sediment. These results suggest that the organic content of sediment is a driving factor influencing the exposure and toxicity of MMHg and total Hg to stream periphyton, thus limiting or altering a crucial food source for primary consumers. Advisors/Committee Members: Hammerschmidt, Chad (Advisor).

Subjects/Keywords: Biology; Aquatic Sciences; Chemistry; Environmental Science; Periphyton; MMHg; monomethylmercury; ecotoxicology; primary producer; metabolic activity; biomass; toxicity; sediment; biofilm; in situ

monomethylmercury (MMHg), which bioaccumulates and biomagnifies within aquatic food webs (… …world (up to 23000 ng/g, Covelli et al., 2001). MMHg in sediments Monomethylmercury… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Klaus, J. E. (2014). In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio. (Masters Thesis). Wright State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=wright1409918494

Chicago Manual of Style (16th Edition):

Klaus, Jaclyn Elizabeth. “In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio.” 2014. Masters Thesis, Wright State University. Accessed November 27, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1409918494.

MLA Handbook (7th Edition):

Klaus, Jaclyn Elizabeth. “In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio.” 2014. Web. 27 Nov 2020.

Vancouver:

Klaus JE. In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio. [Internet] [Masters thesis]. Wright State University; 2014. [cited 2020 Nov 27]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=wright1409918494.

Council of Science Editors:

Klaus JE. In situ measurement of mercury ecotoxicological effects on stream periphyton in southwest Ohio. [Masters Thesis]. Wright State University; 2014. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=wright1409918494

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