Measuring Greenhouse Gas Fluxes Due to Ebullition in a Freshwater Estuarine Wetland

Methane (CH₄) and nitrous oxide (N₂O) are potent greenhouse gases (GHGs) with global warming potentials 28-36 and 265-298 times greater than carbon dioxide, respectively. Wetlands are the greatest natural source of CH₄, estimated to contribute approximately 32% of global CH₄ emissions and are also one of many natural sources of N₂O. These gases are emitted through multiple pathways, but ebullition – random bubbling events – is the least studied of these pathways. Previous studies in saltwater and freshwater wetlands in subarctic, tropic, and subtropical climates have highlighted the significance of ebullition relative to the other pathways. However, the contributions of ebullition to GHG emissions from freshwater estuarine wetlands in temperate zones remain largely unquantified. The goal of this study was to measure the summertime CH₄ and N₂O flux due to ebullition at varying water depths in a temperate freshwater wetland – the Old Woman Creek National Estuarine Research Reserve in Ohio. Flux measurements were conducted with inverted-funnel passive gas-traps to collect gas for approximately 2.85 days. Two traps were used at each of three different water depths, twice during summer (June and July). In June, the median CH₄ flux was 20.880 mg CH₄ m^-2 d^-1 and the median N₂O flux was 0.107 mg N₂O m^-2d^-1. In July, the median CH₄ flux was 51.625 mg CH₄ m^-2 d^-1 and the median N₂O flux was 0.000 mg N₂O m^-2d^-1. The fluxes for both CH₄ and N₂O have no significant correlation with the depth of the water or the month. The results suggest that ebullition is a substantial source of CH₄ but is a small source of N₂O in this wetland and, in principle, other temperate freshwater wetland sites.