MEASUREMENT OF DAILY PRIMARY PRODUCTION USING 24-H INCUBATIONS WITH THE C-14 METHOD - A CAVEAT

Computer simulations and experiments with cultured and natural phytopl ankton were used to study C-14 uptake kinetics and budgets over 24 h i ncubations. There was good agreement between experiments and simulatio ns. After 24 h incubations and depending on the starting time of incub ations, net C-14 uptake varied by a factor of 2 in the laboratory and by a factor of 3 in the field. Both simulated and experimental data sh owed lowest C-14 accumulation for incubations starting at sunrise (i.e . dawn-to-dawn incubation), while highest values corresponded to incub ations beginning at sunset. Recommendations for field studies are as f ollows. For samples collected at night, incubations can be started at any time, but should be conducted for a full 24 h after dawn. Samples collected after dawn should be incubated for 24 h, and C-14 accumulati on should be corrected in order to obtain dawn-to-dawn values.