Species composition and seasonal succession of phytoplankton were analyzed in a lowland river located in South Banat (Ponjavica, Serbia). As a result of human activity, a network of irrigation channels was built on the Ponjavica River's upper and lower courses. These channels reduce the water level in the river and help to create favorable conditions for accelerated eutrophication processes. Eight phytoplankton divisions with 444 taxa were present. Physical and chemical testing of water, phytoplankton abundance and biomass, as well as chlorophyll a concentration showed a high level of eutrophication. Cyanobacterial biomass developed in 2002 with dominance of Microcystis aeruginosa and Aphanizomenon flos-aquae.Changes in phytoplankton composition were observed during 2008, characterized by the appearance and dominance of Cylindrospermopsis raciborskii when this species accounted for more than 85% of the total phytoplankton biovolume. The change in dominant phytoplankton functional groups was observed: codons H 1 and M characterizing summer in 2002 were replaced by codons S N and S 1 in 2008. This study compares the presence of C. raciborskii with other phytoplankton species in relation to water quality parameters. High abundance of this species correlated positively with biochemical oxygen demand and turbidity, and negatively with NO 3 -N concentrations during the study period.
This study contributes to the issue of pollution of the National Park Ponjavica. Besides, literature data and WHO clearly point out harmfulness of cyanobasterias and their toxins and implicate the necessity of legislation concerning determination and monitoring of these toxins in our country. Method used for quentification of mycrocystin-LR was shown to be sensitive, selective, rapid and simple and could be recommended for routine determination of this toxin.
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