Nitrate and ammonia uptake in the apex of the New York Bight1

Abstract

Nitrate and amMonia uptake were measured under seasonally extreme conditions in the apex of the New York Bight. Uptake velocities were highest in spring and summer under bloom conditions, low in winter, and lowest in fall. Uptake was saturated at 50 µEinst·m‒2·s‒1 or less throughout the year and was inhibited at high light intensities. Total inorganic nitrogen uptake was regulated by light intensity throughout the year, and the form of nitrogen taken was regulated by ammonia inhibition of nitrate uptake. Doubling times of the particulate nitrogen pool and the depletion times of the nitrate and ammonia pools proved to be sensitive indicators of the termination of a spring bloom (silicate‐limited) and a summer bloom (possibly nitrogen‐limited). Comparison of turnover times with the flushing time of the apex showed that blooms were impossible in fall and winter and were likely in spring and summer. Similar turnover times of all pools in summer suggest a quasi‐steady state between phytoplankton growth, grazing, and nutrient regeneration; perturbation of this steady state may allow nutrient‐limited conditions for phytoplankton growth to occur.