Phytoplankton growth and phosphate uptake (for P limitation) by natural phytoplankton populations from the Loosdrecht lakes (The Netherlands) 1

Phosphate uptake capacity of natural phytoplankton populations was used as a physiological indicator of P limitation in the Loosdrecht lakes. During a substantial period of the growth season of 1983, P‐limited growth was observed in Lake Breukeleveen and Lake Loosdrecht, but P limitation was less severe in the latter. In Lake Breukeleveen the maximum initial phosphate uptake rate ( V m ) varied between 0.3 and 5.7 µ g P( µ g Chl) −1 h −1 during P‐limited growth, whereas in Lake Loosdrecht, V m varied between 0.3 and 2.1 µg P( µ g Chl) −1 h −1 . Both at the end of June and the beginning of July, growth was not P limited in either lake. Phytoplankton in Lake Loosdrecht was not limited by phosphorus in September. The frequent occurrence of P limitation led to the prediction that reduction of the P loadings of Lake Loosdrecht will result in a reduction of the phytoplankton biomass.