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Understanding Hydrogen's & Vegetation's Link to Methanogenesis in Tidal Marshes

Speaker: David Pal, Graduate Student
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E225
Date/Time: Friday, March 1, 2013, 12:00 p.m. - 1:00 p.m.

Abstract:

Full title: Understanding Hydrogen’s and Vegetation’s Link to Methanogenesis in Tidal Marshes: Capturing Subsurface Dynamics and Flux Measurements to Predict Methane Emissions

Methane emissions from wetland soils have been shown to be one of the largest natural sources of methane into the atmosphere. Methane gas, being the second most important greenhouse gas after carbon dioxide, and wetlands covering almost 6% of the Earth’s surface, demonstrates that wetland methane production has an important role in the radiative forcing of our climate. Wetlands, being mainly constructed and planned environments, allow for the control and regulation of methane flux into the atmosphere by artificially altering the conditions within the soil. Two relationships that will be explored are hydrogen-methane dependencies and vegetation-methane controls.

Methane production in wetland soils occurs from a series of microbial processes, originating at fermentation and ending with methanogenesis. These fermentation reactions consume root exudates and other soil carbon sources to produce hydrogen, and various organic molecules. After a series of fermentation steps of particular interest, in the soil there are small organic molecules (e.g. acetate, carbon dioxide), and hydrogen gas. These small molecules with hydrogen can be consumed or produced to form methane. There are two distinct methane production pathways, acetotrophic methanogenesis and hydrogenotrophic methanogenesis, and both have different relationships to hydrogen concentrations.

Vegetation has been shown to be a gas conduit between below and above the surface. The roots ventilate gas from the soil and injecting different gases and nutrients below the surface. The ventilation rate depths may correlate with root depth, density and activity; all of which can differ between plant species. By measuring these rates and densities, it may become possible to better understand how plants can regulate subsurface dynamics through the ventilation of essential gases like hydrogen.

Through peeper sampling and flux measurements, it is possible to gather enough information and begin to understand the dynamics of hydrogen and methane gas with depth and season. Additionally, it is a goal of this project to be able to synthesize this information into a model that would allow us to predict how changing vegetation and soil characteristics would affect methane production.