An in situ pulse light fluorometer for chlorophyll determination as a monitor for vertical and horizontal phytoplankton distribution in lakes

Methodological problems with in vivo, fluorescence (IVF) measurement using an in situ pulse light fluorometer were investigated in order to validate this method for monitoring the vertical and horizontal chlorophyll a (chl. a) distribution in lakes. The correlation between chl. a and IVF was poor in the upper epilimnion (0-5 m) of a mesotrophic lake. The IVF of algal cultures and natural phytoplankton is very sensitive to changes in the light environment. The response of the IVF to rapid light fluctuations depends on the amplitude of the light intensity and the light conditions to which the algae were exposed before the onset of light fluctuations. The variability of the ratio IVF:chl. a concentration makes a permanent calibration of the IVF against chl. a necessary