Seasonal occurrence and toxicity of Microcystis in impoundments of the Huron River, Michigan, USA

Occurrence and toxicity of Microcystis spp. were measured by ELISA in three impoundments of the Huron River in southeast Michigan, USA. Assays were conducted weekly from June through October 2005. Additional samples were collected to assess microcystin concentrations throughout the drinking water treatment process at the Ann Arbor Water Treatment Facility. Water column stability, nutrient concentrations, and N:P ratios were examined as potential predictors of phycocyanin and microcystin. Microcystin was found in two of the impoundments at seasonally varying concentrations. Microcystis presence was associated with N:P ratios between 40 and 80 by moles, and toxin levels typically peaked one to two weeks after a peak in phycocyanin. The toxin was also detected at low levels at all stages of the drinking water treatment process. Freezing and thawing water samples prior to analysis yielded maximum microcystin assay concentrations. Experiments indicated that the competitive ELISA method is susceptible to false negative reporting. This is the first report of algal toxins in this catchment, and results demonstrate that sensitive and rapid analytical methods offer the chance to link the dynamics of toxin production with environmental conditions.