Phytoplankton Data
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During
the period from 1983 to 1998 a total of 157 phytoplankton taxa were
identified, including 55 diatoms, 53 chrysophytes, 1 xanthophyte, 21
chlorophytes, 12 dinoflagellates, 6 cryptomonads, 7 cyanobacteria, and 2
unknown taxa. In winter the flora was uniformly distributed to the depth
of mixing. Stephanodiscus hantzschii, Ankistrodesmus
spiralis and a small unidentified chrysophyte were the dominate
taxa during this period of the year. During the period of thermal
stratification, phytoplankton are spatially segregated within the water
column to a depth of 200 m (Figure 5).
Nitzschia gracilis was the dominant taxa in the upper 40 m of
the water column. Ankistrodesmus spiralis, Dinobryon
sertularia, Tribonema sp., Rhodamonas lacustris
and Gymnodinium inversum were the dominant taxa from 60 to 100
m. From 120 to 200 m the dominant taxa were the same as during winter.
Concentrations of total chlorophyll were maximum usually
at 120 m during periods of thermal stratification from 1984 to 1999 (Figure 6).
Peak concentrations of total chlorophyll were always less than 2 g/l
however. Total chlorophyll integrated to a depth of 200 m exhibited
cyclic changes between 1979 to 1990. Primary production was low between
1986 and 1990, using the carbon-14 assimilation method. Maximum primary
production occurred between 40 and 80 m during periods of thermal
stratification from 1986 to 1990, (Figure 7)
although relatively high production values occasionally were observed in
near-surface samples. Primary production in August exhibited a similar
cyclic pattern as did total chlorophyll.
