EEGLE Nitrogen Cycling
Water samples were collected from selected stations during 4 cruises (March 1999 and 2000, May 2000, and June 1999) on the R/V Lake Guardian. Water samples were spiked with 4 uM (final concentration) 15NH4+ or an amino acid mixture and incubated in triplicate light and dark 70 mL tissue culture bottles in a decktop, temperature-controlled incubator. In March and May 2000, additional light and dark triplicates were incubated after spiking with 0.4 uM PO4 and either 15NH4+ or an amino acid mixture. Dark bottles were wrapped with aluminum foil.
Initial samples were collected immediately after spiking and filtered with a 0.2 um syringe filter. These samples were analyzed for NH4+ and primary amines using a shipboard HPLC (Gardner and St. John 1991). Remaining filtrates were frozen in 8 mL Wheaton vials for later analysis of atom % 15N-NH4+ by HPLC (Gardner et al. 1995). After incubating for ~24 hours, final samples were collected and processed as described above. Twenty-four hour incubations were selected to allow measurable concentration changes to occur and make light-dark comparisons consistent among stations sampled at varying times of day.
Data is reported as net NH4+ or amino acid flux (uptake or production) in uM h-1. From the atom % 15N-NH4+ measurements, total NH4+ uptake and regeneration rates (in uM h-1) were determined using the Blackburn/Caperon model (Blackburn 1979; Caperon et al. 1979).
Wayne S. Gardner or Mark J. McCarthy
University of Texas at Austin
Marine Science Institute
750 Channelview Drive
Port Aransas, TX 78373
(361) 749-6826 or (361) 749-6730
email@example.com or firstname.lastname@example.org
Blackburn, T.H. 1979. Method for measuring rates of NH4+ turnover in anoxic marine sediments, using a 15N-NH4+ dilution technique. Applied and Environmental Microbiology 37: 760-765.
Caperon, J., D. Schell, J. Hirota, and E. Laws. 1979. Ammonium excretion rates in Kaneohe Bay, Hawaii, measured by a 15N isotope dilution technique. Marine Biology 54: 33-40.
Gardner, W.S. and P.A. St. John. 1991. High-performance liquid chromatographic method to determine ammonium ion and primary amines in seawater. Anal. Chem. 63: 537-540.
Gardner, W.S., H.A. Bootsma, C. Evans, and P.A. St. John. 1995. Improved chromatographic analysis of 15N:14N ratios in ammonium or nitrate for isotope dilution experiments. Mar. Chem. 48: 271-282.