Microcystin in Missouri reservoirs

During summers (May-Aug) 2004-2006, 177 Missouri reservoirs were sampled monthly at open pelagic locations to assess regional patterns in microcystin concentration, frequency of occurrence over successive summer seasons and relations with environmental factors. Microcystin was detected in 58% of Missouri reservoirs and 23% of samples (n = 1402). Total microcystin concentrations, measured by enzyme-linked immunosorbent assay, ranged from <= 0.1 to 21 mu g/L. Concentrations >= 1 mu g/L were detected in 10% of reservoirs and exceeded the human health concern limit of 20 mu g/L once in a single sample. Microcystin occurred throughout summer, with maximum concentrations in individual reservoirs observed in each month. Occurrence was consistent across years, with about one-half of Missouri reservoirs having detectable microcystin each summer. Eleven reservoirs with microcystin maxima >= 1 mu g/L were sampled multiple seasons; of these, 8 had detectable microcystin each summer, which indicates that short-term surveys can identify water bodies with the greatest potential for toxin production. Eutrophic reservoirs in northern Missouri had the greatest microcystin occurrence and concentrations. Reservoirs with detectable microcystin had significantly (p < 0.01) greater nutrient and chlorophyll values and significantly shallower Secchi depths than reservoirs without detection. All correlations, however, had r-values <= 0.35, and bivariate plots indicated nonlinear trends. Cylindrospermopsin was measured by enzyme-linked immunosorbent assay in 36 reservoirs once in late summer 2006; 14% had small detectable levels (total concentrations <1 mu g/L). This is the first report of cylindrospermopsin in Missouri.