GLERL EEGLE Nitrogen Cycling Read Me

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).  



References

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.
