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(-1) of total plankton biomass, ng . L(-1) of lake water, and mu g . g(-1) of Microcystis 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 (r = 0.60-0.77), total and total dissolved phosphorus concentration (r = 0.46-0.59), pH (r = 0.38-0.58), and chlorophyll a (r = 0.25-0.59). Surprisingly, there was no relationship between MC-LR concentration and water temperature (range: 7 degrees-24 degrees C, r = -0.13 to 0.02) and a negative correlation with nitrate concentration (r = -0.27 to -0.34). In two synoptic surveys examining spatial variability, MC-LR concentrations were quite variable (CV of 185 and 36% between sampling sites for Coal and Little Beaver lakes, respectively). 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 G-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.