CARBON STORAGE AND RELEASE IN PIERMONT MARSH; A CONTINUING STUDY

More research needs to be done to quantify the amount of carbon stored and on the processes that cause carbon degradation and release from tidal wetlands. To further investigate the carbon dynamics in these marshes, samples were collected and analyzed from Piermont Marsh, a brackish, tidal wetland along the Hudson River Estuary a few miles north of New York City. Sampling sites were determined by vegetation and location. Plant root analysis done on a core taken from a Phragmites australis dominated site located in the marsh interior indicated that live Phragmites australis roots existed down to 300 cm. The amount of greenhouse gases both produced and released by the marsh were measured with concentration and stable isotope values of CO₂ and CH₄. Isotope-mass balance equations were used to determine the amount of CO₂ produced from methanogenesis (CO_2-meth) and the amount of CH₄ escape. It was determined that methanogenesis occurs mostly at depths below 100 cm while sulfate reduction occurs at the surface. Almost all of the methane was lost from the subsurface of the marsh with little evidence of methane oxidation. Interior marsh sites dominated by introduced Phragmites australis had the greatest amount of CO_2-meth (49.8 ± 10.9 mM) followed by sites dominated by native mixed vegetation (Spartina patens, Schoenoplectus americanus, and Eleocharis parvula) (43.8 ± 10.4 mM) and lastly the mudflat location dominated by native Eleocharis (19.3 ± 8.9 mM). These findings were possibly due to the influence of labile substrates from plant roots. Phragmites australis has a deeper and denser root system than native vegetation that might leach labile dissolved organic carbon (DOC) into the subsurface as optical analyses and FT-ICR-MS results showed Phragmites DOC to be more reactive than DOC from native vegetation. This research provides a deeper understanding on carbon production and release in marshes, including estimates on how much Piermont marsh sequesters, determining how much carbon dioxide and methane is being produced by methanogenesis, and finding how much the invasion of Phragmites australis has impacted the production of methane.