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DIURNAL PERIODICITY IN THE PHYTOPLANKTON ASSEMBLAGE OF A HIGH MOUNTAIN LAKE 1
Author(s) -
Tilzer Max M.
Publication year - 1973
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1973.18.1.0015
Subject(s) - stratification (seeds) , phytoplankton , morning , photosynthesis , noon , light intensity , water column , environmental science , evening , algae , diel vertical migration , oceanography , diurnal cycle , atmospheric sciences , biology , geology , ecology , botany , physics , nutrient , optics , seed dormancy , germination , astronomy , dormancy
Diurnal changes in phytoplankton stratification and photosynthesis were studied at all seasons. The dominant flagellates usually ascend in the evening and at night and migrate downward with increasing light intensities. Maximum migratory speeds are higher than 1 m hr −1 and almost independent of cell size. The vertical stratification pattern of flagellates is the result of varying upward and downward migrations, but the vertical stratifications of nonmotile species depend on the turbulence of the water. Over the day the mean photosynthesis of the entire water column varies in about the same proportions as the input of light energy. At a given depth algae seem to be adapted to the daily mean value of light intensity. Near the lake surface, around noon (1000–1400 hours), photosynthesis is considerably reduced due to downward migration, light saturation, and light inhibition—all caused by high light intensities—but at greater depths the utilization of light energy frequently is increased. During low light periods (early morning, evening) suboptimal light intensities in deeper layers of the lake cannot be utilized as effectively. By phototactic vertical migrations, the diurnal shifts of light energy utilization can be partly compensated.