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Measuring Methane Emissions of the Deal Island Peninsula Area Tidal Marshes
Kyle Derby and Brian Needelman, University of Maryland Environmental Science and Technology Department
Tidal marshes are commonly referred to as “carbon sinks” due to their ability to absorb large amounts of carbon dioxide from the atmosphere and store it as carbon in its rich soil organic matter (peat). This is important because atmospheric carbon dioxide is considered by scientists as the primary greenhouse gas linked to global climate change. As a result, marshes provide an opportunity for decreasing greenhouse gases.
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Chamber used to measure how much methane is being emitted from the marsh.
Black Needelrush, one of three species that were monitored for methane emissions. Photo credit: Anne Murray, University of Florida (2000).
the Chesapeake Bay have lower salinities than 18 ppt because the bay is brackish (a mix of salt and fresh water), which makes it more difficult to predict the amount of methane emitted.
To better understand methane production in these brackish marshes, researchers involved with the NOAA NERRS Science Collaborative, with support from the Maryland DNR Power Plant Research Program, measured methane fluxes at four distinct areas of a marsh in the Deal Island Peninsula area. Each area was monitored monthly from April – December 2015. The results of this work determined that certain areas of the study marsh emitted much more methane than others. In particular, the areas of the marsh containing the smooth cordgrass plant (Spartina alterniflora) generated methane gas at a rate 2.7 times higher than the next highest plant type. Researchers calculated that the methane being released in the smooth cordgrass areas offset approximately 46% of the carbon, which would otherwise be stored in the marsh. However, the areas with lower methane release would offset a fairly small amount of the carbon storage. Two areas of black needlerush (Juncus roemerianus) only offset between 11% (the lower elevation areas) and 15% (the higher elevation areas), while the Salt Marsh Hay (Spartina patens) areas only offset 5% of their carbon storage. Other measurements taken alongside methane measurements showed that salinity may not be the primary inhibitor of methane production in the marshes that were studied, as the area with the highest methane production also had the highest salinity, and the areas with the lowest salinity also had the lowest measured methane production.
At the same time that tidal marshes absorb carbon dioxide, however, they also produce another potent greenhouse gas— methane gas—which potentially offsets some of the benefits that marshes provide as carbon sinks. How much methane do marshes produce though, and how does this affect the use of marshes in mitigate greenhouse gas emissions? These were some of the questions at the heart of marsh studies carried out in the Deal Island Peninsula area during 2015.
Smooth cordgrass, the species that dominated areas of marsh where the highest levels of methane emmissions were measured.
Salt Marsh Hay, the plant species that dominated areas where lowest emissions levels were documented.
Marshes produce methane through the presence of microorganisms that release methane as a byproduct when they “eat” organic matter. The amount of methane marshes release is partially determined by the amount of sulfate present, a salt that comes from seawater. Salt marshes that have high levels of sulfate due to high salt inputs produce very little methane. This is because methane-producing
microorganisms cannot compete with microbes that thrive in high sulfate environments. Therefore, the saltier a marsh, the fewer methane producers will be present, and the lower its methane emissions will be. Scientists have been able to determine that a marsh with salinity (saltiness) greater than 18 ppt (parts per thousand) will consistently maintain low methane emissions. However, marshes in