Atmospheric Ammonia Measurements Over A Coastal Salt Marsh Ecosystem Along The Mid-Atlantic Us

Measurements of atmospheric ammonia (NH3) concentrations and fluxes are limited in coastal regions in the eastern U.S. In this study, continuous and high temporal resolution measurements (5s) of atmospheric NH3 concentrations were recorded using a cavity ring-down spectrometer in a temperate tidal salt marsh at the St Jones Reserve (Dover, DE). Micrometeorological variables were measured using an eddy covariance system which is part of the AmeriFlux network (US-StJ). Soil, plant, and water chemistry were also analyzed to characterize the sources and sinks of atmospheric NH3. A new analytical methodology was used to estimate the average ecosystem-scale diurnal cycle of NH3 fluxes by replicating the characteristics of a chamber experiment. This virtual chamber approach estimates positive surface fluxes in continuing strongly stable conditions when mixing with the air above is minimal. Our findings show that tidal water level may have a significant impact on NH3 emissions from the marsh. The largest fluxes were observed at low tide when more soil was exposed. While it is expected that NH3 fluxes will peak when the air temperature maximizes, high tide occurred concurrently with midday peaks in solar irradiance led to a decrease in NH3 fluxes. Furthermore, soil, plant, and water chemistry measurements underpinning the NH3 concentrations and fluxes lead us to conclude that this coastal wetland ecosystem can act as either a sink or a source of NH3. Such measurements provide novel data on which we can base reliable parameterizations to simulate NH3 emissions from coastal salt marsh ecosystems using surface-atmosphere transfer models.Plain Language Summary Coastal wetlands such as salt marshes, mangroves, and seagrasses provide a natural environment for the sequestration and long-term storage of carbon dioxide (CO2) from the atmosphere. As a fertilizer, nitrogen (N) increases the vegetative growth and thus more CO2 may be fixed in plants as biomass representing the short-term storage pool of carbon, therefore reducing its atmospheric level. Salt marshes, in particular, have been identified as being highly effective at carbon sequestration as well as adsorbing and transforming N. However, there are limited atmospheric measurements of ammonia (NH3) concentrations and exchanges in coastal areas of the Eastern and Mid-Atlantic U.S. This pilot study represents one of the few atmospheric measurements of NH3 over temperate tidal salt marshes in the Mid-Atlantic U.S. The high temporal resolution measurements of NH3 concentrations indicated that local sources, such as agriculture and industry, may have a considerable impact on the local atmospheric NH3 concentrations. The results also show that tidal water levels in salt marshes may have a significant effect on NH3 emissions.