Carbon Substrates and Iron Oxides Influence Methane Production and Iron Reduction in Salt Marsh Sediments

Coastal wetlands are major emitters of methane; however, the controlling factors of methane production are not well known, especially in salt marshes. Delaware salt marshes contain abundant iron minerals, which may inhibit or promote methane production, depending on the conditions and the microbial populations present. In anoxic salt marsh sediments, methanogens may be outcompeted by iron reducing bacteria they may engage in a syntrophic relationship with them via interspecies electron transfer (IET). Different organic carbon substrates, which may be seasonally variable in salt marsh sediments, can also promote methane production by through distinct methanogenic pathways. Sediment collected from the Great Marsh in Lewes, Delaware was incubated with four carbon substrates and two iron minerals in this study. Carbon substrates for hydrogenotrophic (H2/CO2), acetoclastic (acetate), and methylotrophic (trimethylamine (TMA), dimethyl sulfide (DMS)) methanogenesis were investigated along with two controls. The iron treatments were either hematite, ferrihydrite, or an iron-free control. The results show an increase in methane production in each of the treatments but the most methane production was found in TMA and H2/CO2 incubations. Methane production in ferrihydrite treatments was delayed compared to hematite, likely due to competition from iron reducing bacteria. The results of this experiment shed light on the potential interactions between iron reducers and methanogens and how the presence of different carbon substrates and iron oxides influence methanogenesis.

Presentation Preference: Poster

Primary Presenter: Samantha Reynolds, Millersville University of Pennsylvania (sjreynol@millersville.edu)

Authors:

Sunita Shah Walter, University of Delaware  (suni@udel.edu)

Kaleigh Block, University of Delaware  (kblock@udel.edu)