Denitrification Capacity of a Natural and a Restored Marsh in the Northern Gulf of Mexico.

Anthropogenic pressures, such as diking, construction of dams, and oil spills negatively impact coastal marshes creating growing pressure to preserve and to restore salt marshes due to their critical role in permanently removing nitrate runoff through denitrification as well as other ecosystem services they provide. This study determined denitrification rates across a typical northern Gulf of Mexico salt marsh landscape that included a natural marsh, a tidal creek, and a 21-year-old restored salt marsh. Denitrification capacity, measured with the isotope pairing technique on a membrane inlet mass spectrometer, was comparable across the sites despite significant differences in above and below ground characteristics. Total extractable ammonium concentrations and sediment carbon content were higher at the natural marsh compared to the restored marsh. Hydrogen sulfide concentrations were highest at the creek compared to the vegetated sites and lowest at the restored marsh. This suggests that marsh restoration projects reestablish nitrogen removal capacity at rates similar to those in natural systems and can help to significantly reduce nitrogen loads to the coastal ocean.