The Analysis of the Photosynthetic Apparatus of Fresh-water Phytoplankton: Problems — Progress — Perspectives

Freshwater habitats have to cope with dynamic changes in nutrient availability, temperature and light. Most freshwater habitats become increasingly eutrophicated with the result of high primary production. High „standing crop” of pigmented phytoplankton cells absorb PAR efficiently in the upper surface layer leading to a steep light gradient characterised by dynamic changes in light quality and quantitiy. In addition, freshwaters are charged with organic carbon from waste waters or from natural sources. In many cases these compounds themselves absorb visible light („gilvin“) leading to strong attenuation of light, especially when the waters are shallow and turbid [1]. The light climate together with changes in nutrient availabily have selective influence on the growth rates of the different phytoplankton taxa leading to very fast changes in phytoplankton population structure during the year.