DF-excitation spectroscopy of phytoplankton: relationship between dynamics of algal populations and discharge
Delayed fluorescence (DF) as a measure of photosynthetic activity occurs only in living cells. The application of excitation spectroscopy of the DF to analyse phytoplankton populations bases on the fact that the different algae classes differ in pigment composition and therefore show different excitation spectra when excited by monochromatic light. Known limnological phenomena can be investigated in detail because this method allows a dense sampling. DF-excitation spectroscopy is used to investigate the relationship between the dynamics of algae population and the discharge in the river Danube. The discharge and the flow velocity, respectively, are important factors influencing the chlorophyll concentration: It seems that autochthonous phytoplankton growth in the river Danube occurs only when flow velocities are < 1.4 m · s-1. Increasing discharge during the vegetation period leads to shifts in phytoplankton composition: Green algae become more frequent. The most probable sources of these green algae are side arms of the Danube located upstream.