In Situ Benthic Nutrient Flux and Sediment Oxygen Demand in Barnegat Bay, New Jersey

The U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection, measured sediment oxygen demand (SOD) and benthic nutrient fluxes throughout Barnegat Bay, New Jersey. SOD was determined in situ using chambers equipped with optical dissolved oxygen sensors. The benthic nutrient fluxes of ammonia (NH3), nitrite + nitrate (NO3- plus NO2- ions; here, referred to as NO32), soluble reactive phosphorous (SRP), and dissolved silica (SiO2) were measured with in situ equilibrium dialysis samplers. Measurements were made at nine stations around the periphery and at three mid-Bay locations from August 2012 to October 2013. The SOD ranged from -1.5 to -8.4 g of oxygen (O-2) m(-2) d(-1). The SOD rates varied as a function of water temperature and followed the van't Hoff rate equation for change in reaction rate with temperature, with a temperature coefficient (Theta) that varied among sites and averaged 1.083. The highest SOD rates in the bay were measured near the mouth of the Toms River embayment. Concentrations in the upper 1 m of sediment pore water were found up to 23 mg N L-1 for NH4+ and 6.7 mg P L-1 for SRP. Maximum measured fluxes into the overlying water were 3.0x10(-2) g NH3-N m(-2) d(-1), 7.0x10(-4) g NO32-N m(-2) d(-1), 1.9x 10(-3) g Pm-2 d(-1), and 3.6x10(-3) g SiO2 m(-2) d(-1). Using the measured benthic N and P fluxes, daily nutrient inputs derived from sediment recycling are shown to be comparable in scale to freshwater tributary inputs to the bay.