The influence of the coagulant PAX-18 on Planktothrix agardhii bloom in a shallow eutrophic fishpond

For the first time in the Czech Republic, the PAX-18 coagulant has been used to restore a eutrophic fishpond. The polyaluminium hydrochloride coagulant was applied repeatedly to a shallow eutrophic fishpond in spring 2005. Two cylindrical plastic enclosures were used to isolate parts of the pond as untreated controls. Selected environmental variables were measured in situ. Water samples were analyzed regularly for nutrients, chlorophyll a concentration and phytoplankton abundance and structure with special focus on Planktothrix agardhii. The PAX-18 treatment led to a marked increase in the N/P ratio and changes in the structure and abundance of phytoplankton in the fishpond and P. agardhii blooms were eliminated in the fishpond. By contrast, P agardhii dominated the phytoplankton in the control enclosures, as it bad in the fishpond in 2004, prior to the PAX-18 treatment.