This study aimed to examine 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 experiment. The single-species
culture experiment revealed 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. The superiority of M. aeruginosa in the
phosphorus limited condition was reflected in the outcome
of the mixed-species culture experiment, i.e., dominance
of M. aeruginosa in all of phosphorus levels ranged from
0.01 to 0.5 mg-P/L. Therefore, the phosphorus fluctuation
caused by river water dilution to Lake Tega would not
influence the transition of dominant species from M.
aeruginosa to Cyclotella sp. even phosphorus concentration
was decreased as low as 0.01 mg-P/L. Although
the influence of the Si:P mass ratio was also discussed,
Cyclotella sp. never became a dominant species despite the
fact that the Si:P mass ratio was more than 95, which was a
condition promoting the growth of diatoms. The transition
of dominant species in Lake Tega was considered as a
consequence of either event, i.e., decreasing concentrations
of various substances by dilution or increasing the
concentrations by the supply from the North-chiba Water
Conveyance Channel, or their interaction. Further experiments
as well as field investigations would be required
to understand the rule of dilution for the improvement
of water quality and of the critical factor determining
dominant species in the phytoplankton community in Lake
Tega.
This study aimed to examine the relationship betweenphosphorus fluctuation caused by river water dilution toLake Tega and dominance of algal species, M. aeruginosaor Cyclotella sp. based on the single-species andthe mixed-species culture experiment. The single-speciesculture experiment revealed that the half-saturation constantand uptake rate of phosphorus were one order lowerand seven times higher for M. aeruginosa than those forCyclotella sp. The superiority of M. aeruginosa in thephosphorus limited condition was reflected in the outcomeof the mixed-species culture experiment, i.e., dominanceof M. aeruginosa in all of phosphorus levels ranged from0.01 to 0.5 mg-P/L. Therefore, the phosphorus fluctuationcaused by river water dilution to Lake Tega would notinfluence the transition of dominant species from M.aeruginosa to Cyclotella sp. even phosphorus concentrationwas decreased as low as 0.01 mg-P/L. Althoughthe influence of the Si:P mass ratio was also discussed,Cyclotella sp. never became a dominant species despite thefact that the Si:P mass ratio was more than 95, which was acondition promoting the growth of diatoms. The transitionof dominant species in Lake Tega was considered as aconsequence of either event, i.e., decreasing concentrationsof various substances by dilution or increasing theconcentrations by the supply from the North-chiba WaterConveyance Channel, or their interaction. Further experimentsas well as field investigations would be required
to understand the rule of dilution for the improvement
of water quality and of the critical factor determining
dominant species in the phytoplankton community in Lake
Tega.
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