Seasonal and diurnal patterns of NH4+ and NO3‒ uptake were determined for Lake Kinneret phytoplankton. Nanoplankton generally, but not always, had a higher uptake of NH4+ and NO3‒ than did net plankton. Ammonium was always taken up preferentially and the phytoplankton had lower apparent affinity (Ks) for this ion than for NO3‒. However, during the annual dinoflagellate bloom of Peridinium (February–May), when ambient levels of NH4+ were low and those of NO3‒ were high, a considerable portion of the total N flux was derived from NO3‒. The observed daily fluctuations of specific uptake rates for both NH4+ and NO3‒ can be partially explained by changes in light intensity. The finding that NO3‒ was utilized by the dinoflagellates implies that control of the amounts of this nutrient, which is predominantly supplied from watershed sources, could be important in limiting eutrophication in Lake Kinneret.
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Berman et al. (1984) studied this question.