VARIABILITY OF THE HEPATOTOXIN MICROCYSTIN-LR IN HYPEREUTROPHIC DRINKING WATER LAKES

The patterns of occurrence of the peptide hepatotoxin microcystin-LR (MC-LR) was studied in three hypereutrophic hardwater lakes (Coal, Driedmeat, and Little Beaver) in central Alberta, Canada, over three open-water seasons. MC-LR concentration was based on high-performance liquid chromatography detection and expressed as mu g/g of total plankton biomass, ng/L of lake water, and mu g/g of Mycrocystis aeruginosa Kuetz. emend. Elenkin. MC-LR was highly variable temporally (differences up to 3 orders of magnitude) within each lake over an individual year, between years in an individual lake, and between lakes in any year. Seasonal (within-year) changes in MC-LR concentration (expressed in the preceding units) were positively correlated to the abundance and biomass of the cyanobacterium M. aeruginosa, total and total dissolved phosphorus concentration, pH, and chlorophyll a. Surprisingly, there was no relationship between MC-LR concentration and water temperature and a negative correlation with nitrate concentration. In two synoptic surveys examining spatial variability, MC-LR concentrations were quite variable. Spatial distribution of MC-LR on any one day was correlated with the abundance and biomass of M. aeruginosa. Over a 24-h period, MC-LR concentration in M. aeruginosa decreased more than 6-fold at night relative to daytime concentrations. In general, analytical and within-site variation of MC-LR was relatively small (CV < 4 and 9%, respectively) but greatest both within and between years in a lake followed by diel and spatial variation.