Temperature and Moisture Controls on Greenhouse Gas Flux from Coastal Bay Mouth Bar Marsh Sediments

English Abstract:

Wetlands function as carbon sinks when the rates of sequestration outweigh the rates of emissions; however land use and climate changes can degrade sequestration pathways, resulting in an increasing rate of greenhouse gas (GHG) release. To determine the impact of changing climatic conditions on marsh soils with varying levels of inorganic sediment accumulation, this study assesses GHG flux responses within the sediment layers of a coastal bay mouth bar marsh exposed to varying saturation and temperature treatments. Sediment at three depths were collected from a natural cattail zone, two cattail areas degraded by decades of varying silt accumulation, an inorganic mud flat, and a zone of recent sediment removal to expose the underlying natural peat. Sediment was analyzed in the lab for CH₄, CO₂ and N₂O, under 3 temperature (5^oC, 15^oC, or 25^oC) and moisture (field capacity or saturated) conditions. Preliminary results show an increase in CH₄ and CO₂with increasing temperature for both saturated and field capacity conditions. Despite anaerobic conditions, the saturated sediment produced greater GHG fluxes than the drier soils. Soil at depths 0-20 cm and 20-40 cm below surface produced similar fluxes in saturated conditions; however, were different when incubated at field capacity. This indicates GHG fluxes within distinct soil layers have a complex relationship with temperature and moisture in regards to varying levels of exposure to inorganic sediment accumulation.

Keywords: greenhouse gas exchange; marsh; restoration; peat; biogeosciences