Toxin-forming species of freshwater cyanobacteria have been detected in all parts of Germany. Because of the high number of lakes (more than 2000) in Baden-Württemberg, in southwestern Germany, only a representative selection of lakes (155) was intensively monitored for mass development of cyanobacteria and the formation of toxins in 1999. Nutrients, dominant algal species, chlorophyll, and toxins were determined from waters with cyanobacterial blooms. Toxin analyses were performed using HPLC, the PP1 inhibition test, and the microcystin ELISA. In 45% of the monitored lakes, the phytoplankton assemblage consisted mainly of cyanobacteria; in an additional 24% of the lakes cyanobacteria were detected. More than 26% of the lakes contained toxigenic cyanobacteria. The highest amount of microcystins detected outside scum areas was 11-560 microg/L. In relation to biomass, cyanobacteria contained up to 1100 microg/g dry matter and up to 2.6 microg/microg Chl a. The dominant form of microcystin detected was microcystin-LR, one of the most toxic known microcystins. The results of the present study have been used to develop a stepwise monitoring scheme for lakes with permanent cyanobacterial populations to protect human health and livestock.
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