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by Mika Pringle Tolson |
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 TSR&TP fellowship recipient Francisco Rueda gathers data froma weather station in the middle of Clear Lake. Courtesy photo. |
Testing hypotheses is an integral part of the scientific process. Many experiments can easily be executed in the lab, but when the questions involve complex and changing conditions, such as those existing in natural environments, a different approach is needed. Models that simulate natural conditions save both time and money, especially in testing potential strategies of cleaning up toxic substances and ensuring that the cure does not become worse than the problem. |
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| Francisco Rueda, a doctoral student in Civil & Environmental Engineering at UC Davis and TSR&TP fellowship recipient, is developing a model of the fate and transport of particles in complex aquatic environments, using field data from Clear Lake, a system highly contaminated from historic mercury mining. The goal of his research is "to understand the interaction between stratification, topography, and wind forcing in generating the currents in Clear Lake," says Rueda. The ultimate goal is to determine how the currents affect the transport of material within the lake, and thus how mercury draining from the Sulphur Bank Mercury Mine moves around to the rest of the lake. The mine is an EPA Superfund site scheduled to be remediated over the next few years. The capability of modeling the environmental fate of mercury will render valuable information on how to clean it up. |
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| To create his model, Rueda is reviewing and evaluating several existing models. He will incorporate the best features into one three-dimensional mathematical model that will allow us to study how the currents in a complex system develop in response to a variety of conditions. Rueda is calibrating and verifying his model with data collected at Clear Lake. Having an accurate wind map turns out to be the most important factor in simulating currents in the lake, and hence, considerable effort has been put on studying the wind over Clear Lake. By simultaneously measuring wind and water currents, Rueda can plug the wind information into the model and test the outcome of the currents with the actual data from the lake. The most significant function of the model is predicting how particles are transported in the water, and thus how mercury moves through the ecosystem. When acid rock drainage containing high levels of mercury flows into the lake, it forms a flocculent material just above the sediment where bacteria convert the inorganic mercury to methylmercury, the toxic form that bioaccumulates. This material (floc) becomes a methylmercury rich medium that has a neutral buoyancy and can be easily transported by currents. |
 Currents in the lake are measured with the Acoustic Doppler Current Profiler (ADCP). Courtesy photo. |
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| "The floc seems to be the substrate where the transformation of mercury from inorganic to the organic form is taking place. If you are able to model how the currents are picking up and transporting the floc, you are in a position of addressing the question of where the mercury is going and what kind of transformations it will most probably undergo," says Rueda. The next step will consequently be to develop another module that can simulate the fate of the mercury, whether it ends up bioaccumulating in fish or settles back into the sediments. |
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| Rueda’s model will provide another valuable tool for testing the impacts of potential remediation strategies. Before expensive options are implemented, they can be tested in the model to simulate what happens to the mercury in the lake. Although it has been developed with data from Clear Lake, the model is not site-specific. As Rueda says, "Results from studies at Clear Lake could be applicable to any other place having problems with mercury contamination," which covers a lot of ground not only in California, but throughout the world. |
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 Rueda and Porter Anderson (Vector Control of Lake County) prepare to use the ADCP to measure currents at various points in Clear Lake. |
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Francisco Rueda can be reached via email at fjrueda@ucdavis.edu |
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