POTASSIUM-SALTS INHIBIT GROWTH OF THE CYANOBACTERIA MICROCYSTIS SPP IN POND WATER AND DEFINED MEDIA - IMPLICATIONS FOR CONTROL OF MICROCYSTIN-PRODUCING AQUATIC BLOOMS

Ten metals were assayed in 21 Indian ponds which comprised three group s: (1) eutrophic alkaline ponds containing <2.5 mM potassium and thick growths of Microcystis aeruginosa or Microcystis flos-aquae during mo st of the year, (ii) equally eutrophic alkaline ponds containing >2.8 mM potassium and no detectable Microcystis growth, and (iii) oligo- or mesotrophic ponds with various potassium and hydrogen ion concentrati ons and no persistent Microcystis blooms. The effects of potassium on Microcystis growth were examined in filter-sterilized pond water and i n defined culture media. A 50% reduction in the 10-day yield of cultur ed M. aeruginosa was observed in DP medium and pond water supplemented with 1 and 3 mM KCl, respectively. In contrast, the addition of 2 to 30 mM NaCl did not suppress the growth of M. aeruginosa in either DP m edium or pond water. Both 5 mM KCl and 20 mM KHCO3 in J medium strongl y inhibited the growth of M.flos-aquae C3-9, whereas 5 to 30 mM NaCl h ad no effect and 20 mM NaHCO3 was stimulatory. For pond water cultured with a mixture of M. aeruginosa and the duckweed Wolffia arrhiza, M. aeruginosa dominated in unsupplemented water and W. arrhiza dominated in water supplemented with 4.8 mM KCl. Implications for the ecology an d control of Microcystis blooms are discussed.