Using 14 C to investigate methane production and DOC reactivity in northern peatlands

1. Using 14C to investigate methane production and DOC reactivity in northern peatlands Liz Corbett*, Jeffrey P. Chanton, Paul A. Glaser, William T. Cooper, Donald I. Siegel, Mimi Sarkar, Julianna D’Andrilli Department of Oceanography, Florida State University, Tallahassee, FL 32306 *corresponding author: corbett@ocean.fsu.edu • Fen DOC has a lower C:N ratio meaning it is more labile and a better food source for the bacterial community • Cross-plot shows the transition from aceticlastic methanogenesis to CO2 reduction that the bacteria make in the fen with depth, but the constant use of the CO2 reduction at all depths occurs in the bogs • EEMS plots showing UV degradation as DOC travels downstream Introduction Peatlands are a large carbon reservoirs. These ecosystems are saturated with water, and therefore, have an extremely low rate of decomposition. In this way, they have stored and accumulated carbon for over 6,000 years. With the current threat of global warming, they have the potential to become a carbon source to the outside environment by either leaching large amounts of DOC into connecting rivers or by producing CO2 and CH4 into the atmosphere by increased microbial respiration. Purpose of Study • Understand why microbes in a fen environment show a shift from acetate fermentation to CO2 reduction at depth, but microbes in a bog environment utilize CO2 reduction at all depths • Quantify the DOC size reservoirs in the peatland environment • Differentiate between bog and fen DOC • Differentiate between deep and surface DOC • Determine which DOC sizes serve as a microbial food source • Categorize DOC based on size, aromaticity and structure Conclusions • Data suggests that the structure or quality of DOC may differ between the bog and fen environments • Fen DOC is more labile than bog DOC suggesting it as a better food source for bacteria • The concentration of LMW DOC increases with depth suggesting LMW accumulates because it is not utilized by bacteria, whereas HMW concentrations increase as the bacteria metabolize it as a food source • DOC degradation by UV light suggests that the DOC is made • up of aromatic groups • The cross-plot shows a shift in metabolic pathways in the fen but not in the bog • Size Filtration study showing larger concentrations of LMW DOC suggesting bacterial preferentially choose HMW DOC as a resource and leave behind LMW DOC to accumulate • Microbes seem to prefer fen DOC to bog DOC since the 14C value of their respiration products (CO2 and CH4) exactly matches DOC in the fen environments, but only partly matches bog DOC.