[Enviro-lunch] this Thursday (11/2): Stefanie Helmrich, "Simulating methylmercury production at the sediment-water interface to improve the water quality in the San Francisco Bay-Delta"

[Lixia Jin]

[cid:5E34BAB9-9FB4-4679-8DAB-10ED774F4AC4 at home]
Dear all,
Please join us this Thursday for our speaker, Stefanie Helmrich from UC Merced.

Stefanie Helmrich
Environmental systems, UC Merced

Simulating methylmercury production at the sediment-water interface to improve the water quality in the San Francisco Bay-Delta
 Abstract: Mercury (Hg) in the environment poses a significant threat to human and ecological health, and is a major contaminant of concern for water quality in California. Methylmercury (MeHg) is the most toxic form of Hg and bioaccumulates in fish and higher organisms. The San Francisco Bay-Delta received significant amounts of inorganic Hg from the Sierra Nevada foothills due to historic gold mining and anoxic sediments in wetlands in the Delta are hotspots for bacterially driven MeHg production. Environmental conditions that influence the net methylation of Hg are known, but quantification of water-column concentrations of MeHg is still difficult because of the high cost of collecting data over detailed spatial and temporal scales. However, quantification of MeHg concentrations is important to plan mitigation and remediation measures. Computer simulations can provide a tool to predict Hg and MeHg concentrations over a range of hydrologic conditions and improve understanding of hydrogeochemical and biological processes controlling Hg and MeHg transport and fate. As such, I am developing a mechanism-based reactive-transport model to simulate the mercury cycle at the sediment-water interface. As a first step, I am investigating how to utilize incubation experiments with isotopically labeled tracers to parameterize (de)methylation reactions in the model. A considerable number of incubation experiments has been carried out in the last two decades. However, the assumptions made in calculating (de)methylation rate constant, and the conditions of the incubation experiments differ between studies. I am assessing the suitability of the reported rate constants for use in a generalized kinetic model and I will assess the selected rate constants by comparing simulated MeHg concentrations with in incubation experiments measured MeHg concentrations. It is important to note that the kinetic rates and the corresponding rate constants are empirical in nature, however, the thermodynamic framework is not empirical. The model development will yield new insights and the mechanistic model can be applied to sites with the same environmental conditions to simulate MeHg concentrations at the sediment-water interface.
Biography: Stefanie is a second year Ph.D. student and her research aim is to develop and scale up a biogeochemical reaction-transport model for simulating the fate of mercury. Before Stefanie came to UC Merced, she graduated with a Master of Science in Water Management from Technical University of Dresden in Germany and she did an internship at the Lawrence Berkeley National Lab. Her master thesis focused on two-dimensional surface-runoff simulations coupled to a channel network model to predict flooding in urban areas. As an intern at the Berkeley Lab Stefanie used SJRWARMF to simulate the fate of mercury on the watershed scale.

When: Nov. 2nd, Thursday, 12pm – 1pm
Where: SE2-302

Coffee will be provided and please bring your own mugs.
We look forward to seeing you,

Organizers for 2017-18: Nate Bogie and Lixia Jin
Faculty coordinator: Asmeret Asefaw Berhe
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