Development of cyanobacteria and production of cyanotoxins in Lake Garda: statistical models and predictive power

Though with different species, potentially toxic cyanobacteria are particularly abundant in eutrophic and thermally stable lakes, where they can form huge water blooms with detrimental effects for ecosystem functionality and water exploitation. Since the 1970s, Lake Garda showed a doubling in the concentrations of total phosphorus (TP) measured over the whole water column. During the last 5 years, TP values showed a stabilisation around 18-20 µg P/L. Since the mid 1990s, the increase in the trophic status of Lake Garda was followed by a significant increase of toxic cyanobacteria (mainly Planktothrix rubescens), with the appearance of apparently) non-native species belonging to Nostocales (Dolichospermum lemmermannii). The cell quota of microcystins (MC, hepatotoxins) did show a significant seasonality, while statistical models linking the oncentrations of MC and the biovolume of the dominant cyanobacteria Planktothrix, BV) generally did show only modest differences between Cy different water layers and years. Nevertheless, the overall variations in the cell quota of MC in Lake Garda were much lower if compared with the values measured in many other lakes dominated by Planktothrix, indicating the presence of specific genotypes. A greater sensitivity and reliability in the management strategies aimed at minimising the risks from cyanobacteria should also contemplate the use of specific lake-tailored models linking MCs and BV Cy