Phytoplankton community structure in the drainage network of a Mediterranean river system (Aliakmon, Greece)

Phytoplankton structure was studied in Aliakmon river basin in April (highf low) and September (lowflow) 1995 in 29 sampling sites. Abundance and bioma ss were generally low and ranged considerably between sites. Benthic diatom s contributed greatly to the suspended algal assemblages whereas trends of potamoplankton development were observed downstream. Limnoplankton and espe cially chlorophytes developed in the areas where lentic conditions prevaile d. The nature of changes in phytoplankton seemed to be both longitudinal an d temporal. Multivariate techniques revealed that areas with distinctive mo rphology, hydrology and anthropogenic inputs tended to have similar phytopl ankton composition although no simple relation with physico-chemical factor s can be shown. Human impact was more obvious on phytoplankton at the lowfl ow period. Generally, discharge played a significant role to the structure of phytoplankton communities.