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Abstract Title: Understanding Environmental Controls on Fluvial Periphyton Composition and Effects on Mercury Cycling
Presenter Name: Spencer Washburn
Company/Institution: Oak Ridge National Laboratory
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling
Co-Authors: Spencer Washburn,Scott Brooks,Grace Schwartz,Scott Painter,Saubhagya Rathore,Alyssa Carrell,Melissa Cregger

Abstract Information :

Periphyton biofilms play an important role in the biogeochemical cycling of mercury (Hg) within watersheds, but relatively little is known about what environmental physicochemical factors (e.g., nutrient concentrations, disturbance regime) impact the methylation and demethylation potentials of the complex consortia of microbiota within these biofilms. For example, nutrient conditions impact periphyton productivity and composition, but nutrient driven changes to the Hg-methylating microbial community within fluvial periphyton are poorly characterized. To address this knowledge gap, we conducted a translocation experiment, across multiple seasons and quantified the effects of physicochemical factors on the net Hg methylation and monomethylmercury (MMHg) demethylation potentials of periphyton and the production of specific low molecular weight thiol compounds within biofilms. Using a natural gradient of nutrient concentrations between two locations within the Hg-impacted East Fork Poplar Creek (Oak Ridge, Tennessee, USA) we assessed periphyton community composition and Hg methylation potential in biofilms colonized under relatively low and high nutrient concentrations. The impacts of altering the nutrient regime to which an established periphyton community is exposed was assessed via physical translocation. Application of our transient availability model, developed for quantifying Hg methylation kinetics in biofilms, will allow us to quantify the impact of seasonally variable physicochemical factors on periphyton methylation rates. Sequencing data will be utilized to evaluate the relative impacts of community structure and interaction within the periphyton microbiome that drive variations in observed rates of Hg transformation. By providing insights into the environmental controls on the community composition and function of complex fluvial biofilms, this work aims to improve our understanding of how future anthropogenic activity, including land use change and runoff management practices, will impact the production of MMHg within stream ecosystems.

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