Salt Marsh Denitrification Provides a Significant Nitrogen Sink in Barnegat Bay, New Jersey

Denitrification in salt marshes can be an important removal mechanism for inorganic nitrogen, particularly in coastal estuaries subject to high nutrient loading and eutrophication. Barnegat Bay, New Jersey has had high nutrient loading in the northern part of the Bay and has exhibited symptoms of eutrophication. The first goal of this study was to examine seasonal denitrification, other N fluxes, and sediment oxygen demand in salt marshes of Barnegat Bay where inputs and concentrations of nutrients vary spatially within the Bay. Second, differences in N process rates among emergent vegetated marsh and permanently flooded isolated ponds were investigated. Finally, the percentage of the N load to the Bay removed by denitrification in the salt marshes of Barnegat Bay was calculated. It was hypothesized that denitrification rates would be the highest in summer and depend on water-column nutrient concentration. In addition, denitrification rate would be higher in vegetated marsh than in inundated ponds because of the aerobic/anaerobic interfaces present in marshes required by coupled nitrification-denitrification. Denitrification rate was three times greater in July than in October (p < 0.05). There were significant differences among marshes in N fluxes related to local availability of nutrients in the water column. Denitrification rates in vegetated marsh on thin sediment layers were more variable than in ponds. Overall, denitrification removed an average of 27.9% +/- 6.9% of the total N load transported to the Bay, highlighting the important ecosystem service that the marshes provide to the Bay.