AMMONIUM EXCRETION RATES IN KANEOHE-BAY, HAWAII, MEASURED BY A N-15 ISOTOPE-DILUTION TECHNIQUE

Ammonium ion uptake and excretion rates were measured in water samples taken from Kaneohe Bay, Oahu, Hawaii, by monitoring the 15N/(15N+14N) isotope ratio in dissolved ammonium ion in incubated samples which had been spiked with 15N-labeleled crops of microzooplankton (organisms passing a 0.333 mm mesh gauze), but the actual excretion was due primarily to smaller organisms (less than 0.035 mm in nominal diameter). Preliminary results indicate that excretion rates were substantially higher during the night than during the day, and that on the average daily uptake and excretion of ammonium ion were roughly in balance. © 1979 Springer-Verlag.