The concentration of NH4
+ in the solutions of NH4
15NO3 and 15NH4NO3 decreased
significantly over time (Fig. 1A,B) with nearly identical regression equations. In addition,
the NH4
+ concentrations at the end of the longest time interval in the two label treatments
were indistinguishable (about 50 AM). Nitrate was also depleted over time in both labeled
nutrient treatments, with similar regression equations (Fig. 1C,D). The NO3
concentrations
at the end of the largest time interval both averaged about 150 AM. The major differences
between NH4
+ and NO3
depletion were that (a) NH4
+ was reduced more quickly in the water
and to a lower concentration by the algae than NO3
, and (b) the variability in the nutrient
concentrations was higher for NO3
than for NH4
+ throughout the entire experiment.