Nutrient status of metalimnetic phytoplankton peaks

The nutrient state of the chrysophyte, Chrysosphaerella longispina, forming a large metalimnetic chlorophyll a peak in Jacks Lake, Ontario, was examined over several summers. Turnover times of phosphate were fast in the epilimnion (minutes) but slow (hours) at the depth of the peak. Long turnover times, high concentrations of polyphosphate, low P debt, low V,,,, and high K, values for phosphorus all indicated that initially the peak was not more P-deficient than epilimnetic phytoplankton. However, with time it became P-deficient and this factor coincided with its demise in August. At no time was the peak population N-deficient. The peak population was not supplied by nutrients from the hypolimnion nor from the mineralization of sedimenting epilimnetic material but instead seemed to have brought cellular reserves of phosphorus when it migrated down from the epilimnion.