The Phytoplankton Spring Outburst and its Conditions in Lake Erken (Sweden) 1

Pechlaner, R.

Limnology and Oceanography 15(1): 113-130


ISSN/ISBN: 0024-3590
DOI: 10.4319/lo.1970.15.1.0113
Accession: 068500722

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In Lake Erken a conspicuous peak in the standing crop and production rate of phytoplankton occurs regularly in the ice-out period. The environmental changes associated with this outburst were studied in spring 1960. The availability of radiant energy is the key factor for the instigation of the phytoplankton "explosion," but some lag in the response of the algae to the increase of radiation is caused by the necessity for light adaptation even when the intensities of photosynthetically usable energy are still very low. The growth rates of phytoplankton as measured by cell volume and by chlorophyll content are similar. The specific growth coefficient (in log. units per day) of the dominant species Stephanodiscus hantzschii pusillus is considerably higher (0.09) than that of the entire assemblage of algae (0.065). Two weeks after ice-out the biomass, production rate, and relative photosynthetic efficiency (carbon uptake per unit biomass and unit radiation) of phytoplankton decrease sharply. Depletion of inorganic nutrients, especially nitrogen, is apparently the main cause for the end of the spring bloom. Grazing affects only a small fraction of the phytoplankton; exploitation of diatoms by the zooplankton is negligible during the spring outburst.