Implications of Vegetation Shifts on Greenhouse Gas Production in a Coastal Salt Marsh

Abstract:

Methane production in salt marshes is understudied, although these anaerobic environments store vast amounts of carbon and may release large quantities as climate shifts. Studies show ranges of salt marsh methane emissions that vary widely from 0.4–160 g CH₄ m^-2 y^-1. CH₄ production in salt marshes is governed by several variables. Due to high sulfate concentrations in these environments, less CH₄ is expected to form and escape from the subsurface. However, vascular plants allow greater amounts of CH₄ escape from subsurface porewater and produce more labile organic carbon substrates, which support higher rates of microbial decomposition. Coastal salt marshes are also dominated by various vascular plant species both native and invasive which may allow for greater amounts of CH₄ formation and escape than previously thought. To better understand CH₄ dynamics in coastal salt marshes, pore water samples were collected from various depths in Piermont salt marsh, NY (40 ̊00’ N, 73 ̊55’W), a tidal wetland that has been invaded in the last century by Phragmites australis. Dissolved organic carbon lability was measured, previously developed isotope-mass balance equations were utilized, and root depth and density were analyzed from several vegetation zones. Areas dominated by invasive Phragmites australis vegetation contain deeper and denser root zones and are expected to produce more subsurface methane and release more methane than areas dominated by native vegetation types. This study will allow us to identify zones more likely to contribute greenhouse gases to the atmosphere and increase knowledge of CH₄ production and release in coastal salt marshes.