THE COMPLEXITY OF MERCURY CYCLING: STUDYING THE METHYLATION WINDOW AND ASSESSING TWO REMEDIATION TECHNIQUES IN TWO AQUATIC ENVIRONMENTS

Abstract
   In California, the gold rush era and atmospheric deposition have caused mercury (Hg) contamination in surface waters. Methyl mercury (MeHg), the organic form of Hg, is formed by anaerobic bacteria bioaccumulates in the food chain, posing health risks for wildlife and humans consuming contaminated fish, seafood, and rice. This dissertation examined the factors contributing to MeHg production in two different aquatic environments: Hodges Reservoir (a lake-like environment), and Cache Creek Settling basin, CCSB (a wetland-like environment), alongside two Hg remediation techniques: hypolimnetic oxygenation system (HOS) and coagulation with metal-based salts. In Hodges Reservoir, wet years extended the methylation window from late spring to fall, while dry years closed it early in May. After HOS implementation, oxygenation suppressed the methylation window by inhibiting anaerobic bacteria activity. In CCSB, coagulant-treated soils under rewetting conditions were not a source of Hg, but elevated organic matter loading opened a short-lived methylation window. Fluorescence spectroscopy of dissolved organic matter quality correlated with MeHg production, suggesting its potential for monitoring. Overall, oxygenation and controlling organic matter loadings offer viable strategies to mitigate Hg contamination in aquatic ecosystems.

Biography
   Naivy is a PhD Candidate in the Environmental Systems graduate group at UC Merced, joining Dr. Beutel’s Lab in 2019. She is from Mexico City and has a Bachelors of Science in Geological Engineering from the National Autonomous University of Mexico (UNAM). At UC Merced, she also earned a MS in modeling nutrients removal in constructed wetlands. Naivy’s interests are related to environmental engineering, specifically surface water quality, treatment wetlands, limnology, biogeochemistry, and natural resource solutions.