Effect of phosphorus fluctuation caused by river water dilution in eutrophiclake on competition between blue-green alga Microcystis aeruginosaand diatom Cyclotella sp.
Yoshimasa Amano , Yusuke Sakai , Takumi Sekiya , Kimitaka Takeya , Kazuo Taki , Motoi Machida
DOI:
Received December 29, 2009,Revised May 25, 2010, Accepted , Available online
Volume 22,2010,Pages 1666-1673
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Tega-numa (Lake Tega) is one of the eutrophic lakes in Japan. For the improvement of water quality in Lake Tega, the Northchiba
Water Conveyance Channel was constructed in 2000, which transfer water from Tone River into the lake. After 2000, the
dominant species of diatoms, mainly Cyclotella sp., have been replacing blue-green algae, mainly Microcystis aeruginosa in Lake
Tega. This transition of dominant species would be due to the dilution, but the detail mechanism has not been understood yet. This
study examined the relationship between phosphorus fluctuation caused by river water dilution to Lake Tega and dominance of algal
species, M. aeruginosa or Cyclotella sp. based on the single-species and the mixed-species culture experiments. The single-species
culture experiment showed that the half-saturation constant and uptake rate of phosphorus were one order lower and seven times higher
for M. aeruginosa than those for Cyclotella sp. These findings implied that M. aeruginosa would possess a potential for the growth
and survival over Cyclotella sp. in the phosphorus limited condition. The superiority of M. aeruginosa was reflected in the outcome of
the mixed-species culture experiment, i.e., dominance of M. aeruginosa, even phosphorus concentration was lowered to 0.01 mg-P/L.
Therefore, it could be concluded that the decrease in phosphorus concentration due to the river water dilution to Lake Tega would be
interpreted as a minor factor for the transition of dominant species from M. aeruginosa to Cyclotella sp.
