[Enviro-lunch] This Thurs. 11/2: Stefanie Helmrich

[Nate Bogie]

Dear all,

Please join us this Thursday (11/2) for our speaker, Stefanie Helmrich from
UC Merced.


 Simulating methylmercury production at the sediment-water interface to
improve the water quality in the San Francisco Bay-Delta



*Stefanie Helmrich*

UC Merced



*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 have 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 those measured in incubation experiments. 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.



*Bio: *

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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