Patterns and Drivers of Carbon Dioxide and Methane Emissions from a Temperate Salt Marsh Creek

Coastal salt marshes are becoming increasingly of interest to carbon cycle researchers due to their ability to sequester and store significant amounts of carbon. Many studies which have focused on vertical greenhouse gas fluxes from marsh soils and at the marsh ecosystem scale demonstrated a heterogeneity of fluxes across the marsh landscape. Within that heterogeneity, there is a lack of information on vertical greenhouse gas fluxes from salt marsh creeks. This study utilized high temporal resolution measurements of CO₂ and CH₄ concentrations within creek water, ecosystem-scale plant phenology, ecosystem-scale CO₂ and CH₄ fluxes, and sediment CO₂ fluxes. We complemented this information with water quality data, meteorological data, and manual water flux measurements to parameterize a model of water-atmosphere fluxes of CO₂ and CH₄ for a salt marsh creek and to assess the patterns and drivers of these fluxes. Creek fluxes for CO₂ and CH₄ were found to vary significantly with tide stage, being highest at low tide and lowest at high tide. Creek fluxes and concentrations of CO₂ and CH₄ in the creek water peaked along with plant greenness in mid-July. Temperature was found to be a significant driver for the concentrations of both CO₂ and CH₄ in the creek, creek CH₄ fluxes lowered with increased concentrations of dissolved oxygen in the creek water, and creek CO₂ fluxes increased with higher water level. Creek CO₂ fluxes were higher than marsh sediment CO₂ fluxes across the whole growing season and made up a substantial portion of the marsh's night time respiration during the period of plant dormancy. Creek CH₄ fluxes were significantly lower than ecosystem-scale CH₄ fluxes across the whole growing season. These results highlight the importance of salt marsh creeks as hotspots for CO₂ emissions but demonstrate their lesser role for CH₄ emissions.