Wetlands are important habitats that serve many ecosystem functions in part because they typically exhibit a zone of biogeochemical transition between aerobic and anaerobic conditions. This transition creates a rich tapestry of biogeochemical transformations that can affect the fate of many contaminants. Mercury is a contaminant of great concern and its fate, speciation, and transport are linked intrinsically to wetland conditions. Optical characterization has proven useful in identifying dissolved organic matter (DOM) sources and transformation processes, thus providing a powerful tool for understanding biogeochemical cycling in wetlands. In this study, surface waters were collected from wetlands located in the Cosumnes River Preserve (CRP), the Yolo Bypass Wildlife Area, the Cache Creek Settling Basin and upstream watersheds in California to characterize DOM quality and composition so as to infer biogeochemical conditions and processes affecting mercury methylation. Several vegetative or other wetland types were included: domestic (Oryza sativa) and wild (Zinzania) rice production, emergent cattail (e.g., Typha spp), submergent wetland plants (e.g., Ludwigia and Egeria densa) and mining-affected streams. All samples were analyzed for DOM concentration, optical properties using absorbance and fluorescence spectrometry, and methylmercury (MeHg) concentration. A subset were analyzed for DOM fractionation. Unique fluorescence signatures were identified for water from different habitat types and related to MeHg concentration and/or production. This presentation will highlight the differences in organic matter characteristics among these wetland habitats and potential effects on mercury cycling.

Relationships between dissolved organic matter and mercury cycling in California ecosystems affected by historic mining

253rd National Meeting (2017)

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