TABLE 1.

Ambient substrate concentrations and uptake and regeneration rates in surface water

SubstrateConcn (μmol N liter−1)Uptake rate (μmol N liter−1 h−1)Regeneration rate (μmol N liter−1 h−1)
NH4+ (ammonium)0.135 ± 0.0360.077 ± 0.0120.082 ± 0.008
NO3 (nitrate)0.118 ± 0.0120.065 ± 0.0140.147 ± 0.035
Urea0.328 ± 0.0670.013 ± 0.004NDa
Dissolved primary amines (approximately amino acids)0.854 ± 0.2200.055 ± 0.001ND
DON16.2 ± 0.271NDND
PO4−3 (phosphate)0.028 ± 0.002NDND
Dissolved organic phosphate0.635 ± 0.021NDND
Biogenic silicate5.543 ± 0.374NDND
  • a ND, not determined.