Diel periodicity in uptake of nitrate and nitrite by reservoir phytoplankton

Diel periodicity in the uptake of nitrate, and nitrite as measured by the ¹⁵N technique, occurs in reservoir phytoplankton. The time course of changes in the rate of nitrate uptake generally paralleled changes in irradiance. Uptake of nitrate and nitrite occurred in the dark, but at low rates. Periodicity in nitrate uptake needs to be considered in models of primary production where nitrogen is the limiting nutrient.