Dataset: UConn Seasonal IPT
Deployment: UConn_Tobias_2013-14

Samples were collected at coastal oyster farms in Rhode Island (41 22' 45" N, 71 38' 43" W) and New York (41 16' 9" N, 71 59' 29" W). At both locations, the approximate depth is 2 meters.

Coupled direct denitrification (DNF), direct DNF, and dissimilatory nitrate reduction to ammonium (DNRA) are measured in sediments collected from each site in areas that are influenced by oysters and areas that are not. Seasonally five intact sediment cores are taken from directly underneath oyster growth and from control sites in both farms. Cores are incubated at in situ temperature with no air headspace and 15N-NO3- tracer added to the overlying water. Each core is sacrificed and slurried as a single time point. Water column dissolved inorganic nitrogen (DIN) samples are analyzed colorimetrically for concentration (WestCo SmartChem). N2 isotopologues are measured on the membrane inlet mass spectrometer (MIMS) and are used to calculate rates of both coupled and direct DNF via the isotope pairing method (IPT, Steingruber et al. 2001). Sediment bound 15N-NH4+ enrichment is measured using the azide hypobromide method (Zhang et al. 2007) and are run on the isotope ratio mass spectrometer (IRMS). 15N-NH4+ enrichment is then used to calculate rates of DNRA. Additionally, sediment sub-samples are run on an elemental analyzer (EA) coupled to IRMS for sediment C:N, 15N, and 13C. Finally, in order to constrain the overall 15N mass balance intermediate pools such as NO2 and N2O are also analyzed.

Related references:
Steingruber, S. M., Friedrich, J., Gächter, R., & Wehrli, B. 2001. Measurement of denitrification in sediments with the 15N isotope pairing technique. Applied and Environmental Microbiology, 67(9), 3771-3778. doi:10.1128/AEM.67.9.3771-3778.2001

Zhang, L., M. A. Altabet, T. Wu, O. Hadas. 2007. Sensitive measurement of NH4+ 15N/14N (15NH4+) at natural abundance levels in fresh and salt waters. Analytical Chemistry 79:5297-5303. doi:10.1021/ac070106d