Phytoplankton Community Structure in the Drainage Network of a Mediterranean River System (Aliakmon, Greece)

Phytoplankton structure was studied in Aliakmon river basin in April (highflow) and September (lowflow) 1995 in 29 sampling sites. Abundance and biomass were generally low and ranged considerably between sites. Benthic diatoms contributed greatly to the suspended algal assemblages whereas trends of potamoplankton development were observed downstream. Limnoplankton and especially chlorophytes developed in the areas where lentic conditions prevailed. The nature of changes in phytoplankton seemed to be both longitudinal and temporal. Multivariate techniques revealed that areas with distinctive morphology, hydrology and anthropogenic inputs tended to have similar phytoplankton composition although no simple relation with physico-chemical factors can be shown. Human impact was more obvious on phytoplankton at the lowflow period. Generally, discharge played a significant role to the structure of phytoplankton communities.