Changes in Nitrogen Cycling Processes Along a Salinity Gradient in Tidal Wetlands of the Hudson River, New York, USA

Rising sea levels and stronger storm surges may expose tidal freshwater wetlands to saline waters, possibly leading to increased sulfate reduction and higher sulfide (H2S) concentrations. To better understand the effects of salinity on nitrogen cycling, porewater chemistry and sediment profiles of H2S and dissolved oxygen (O-2) were measured along a salinity gradient in the Hudson River (New York, USA). Additionally, laboratory experiments exposed freshwater sediments to varying salinities after which sediment O-2 and H2S dynamics along with nitrification and denitrification were measured. Overall, sites with higher salinities had lower oxygen availability (both as concentration and oxic sediment depth) and higher sulfide concentrations. Both nitrification and denitrification were depressed at higher salinities suggesting that exposure to saline water may alter nitrogen cycling of tidally influenced wetlands in the brackish region of the Hudson River estuary which may result in reduced retention of nitrogen.