TY - JOUR T1 - Trends in dissolved organic matter cycling, sediment microbiomes, and methylmercury production across vegetation heterogeneity in a Great Lakes wetland JF - bioRxiv DO - 10.1101/072017 SP - 072017 AU - Emily B. Graham AU - Joseph E. Knelman AU - Rachel S. Gabor AU - Shon Schooler AU - Diane M. McKnight AU - Diana R. Nemergut Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/05/26/072017.abstract N2 - Recent advances have allowed for greater investigation into microbial regulation of mercury toxicity in the environment. In wetlands in particular, dissolved organic matter (DOM) may influence methylmercury (MeHg) production both through chemical interactions and through substrate effects on microbiomes. We conducted microcosm experiments in two disparate wetland environments (unvegetated and vegetated sediments) to examine the impacts of plant leachate and inorganic mercury loadings on microbiomes, DOM cycling, and MeHg production in the St. Louis River Estuary, which has a legacy of mercury contamination. Overall, our research reveals the greater relative capacity for mercury methylation in vegetated over unvegetated sediments in this environment. Further, oligotrophic unvegetated sediments receiving leachate produced more MeHg than unamended microcosms, pointing to the role of organic matter and vegetation patterns as an important control on MeHg production in these sediments. We also show that while leachate influenced the microbiome in both environment types, sediment with high organic carbon content was more resistant to change than oligotrophic sediment. Our work supports emerging research suggesting that Clostridia may be important methylators in oligotrophic environments. We demonstrate changes in community structure towards Clostridia and metagenomic shifts toward fermentation as well as degradation of complex DOM and MeHg production in unvegetated microcosms receiving leachate. Together, our work shows the importance of wetland vegetation in driving MeHg production in the Great Lakes region and provides evidence that this may be due to both enhanced microbial activity as well as differences in the composition of microbiomes associated with higher DOM levels. ER -