Seasonal variations of <i>microcystis</i> species and toxic heptapeptide microcystins in lake suwa

Abstract

Abstract Seasonal changes in species composition of Microcystis and concentrations of toxic heptapeptide microcystins, were investigated in Lake Suwa from June to October in 1991. Microcystins‐RR and ‐LR were the main components of the toxins contained in bloom samples of Microcystis and a very little quantity of ‐ YR was detected through this period. The high amounts of microcystins were estimated during the exponential growth phase of the bloom from June 11 to July 20. The highest concentrations of microcystins‐RR and ‐LR were estimated as 121 and 81.6 μg/100 mg cells on July 20, 1991, respectively. While the higher amounts of the toxins were estimated when M. aeruginosa predominated, the lower amounts were estimated during the predominate period of M. viridis . Since the dissolved inorganic nitrogen (DIN) concentration may well affect the dominance of M. aeruginosa and M. viridis , the production of the toxins by Microcystis may be associated with the DIN concentration. © 1993 John Wiley &amp; Sons, Inc.