PHYTOPLANKTON AND NUTRIENTS IN THE RIVER STRYMON, GREECE

Phytoplankton species composition, biomass, diversity, nutrients and c hlorophyll alpha were studied at monthly intervals from December 1991 to December 1992 in a selected area of the river Strymon. SRP ranged f rom 53 to 182 mu g(-1) l(-1) and DIN from 265 to 850 mu g(-1) l(-1). N utrient values do not indicate strong anthropogenic effects. Chlorophy ll alpha ranged from 1.0 to 35.3 mu g(-1) l(-1) and followed the tempo ral distribution of total phytoplankton biomass. Phytoplankton biomass exhibited maxima in winter - spring and summer (6.8 g m(-3) in Decemb er 1991, 4.8 g m(-3) in April 1992 and 9.3 g m(-3) in August 1992) com posed mainly of diatoms, chlorphytes, cyanophytes and dinophytes. Nano plankton was the most important component of phytoplankton biomass (69 .5%) revealing increased values in winter and early spring. Phytoplank ton diversity ranged from 0.8 to 3.2. The hydrological conditions in t he river Strymon seem to be appropriate for the algae to reproduce the mselves in the running water and so, to develop as a true potamoplankt on. However, significant populations of phytoplankton must have been c arried out from the Kerkini reservoir, situated at the north of the sa mpling station. The phytoplankton species composition and their period icity in the river resemble those of typical, large, lowland and nutri ent - rich rivers of Europe.