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) measurementusing an in situ pulse light fluorometer were investigated inorder to validate this method for monitoring the vertical andhorizontal chlorophyll a (chl. a) distribution in lakes. Thecorrelation between chl. a and IVF was poor in the upper epilimnion(0–5 m) of a mesotrophic lake. The IVF of algal culturesand natural phytoplankton is very sensitive to changes in thelight environment. The response of the IVF to rapid light fluctuationsdepends on the amplitude of the light intensity and the lightconditions to which the algae were exposed before the onsetof light fluctuations. The variability of the ratio IVF:chl.a concentration makes a permanent calibration of the IVF againstchl. a necessary. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP), Second International Workshop heldat the National Oceanographic Institute, Haifa, Israel in April–May1984.