Dynamics of the water bloom-forming Microcystis and its relationship with physicochemical factors in Lake Xuanwu (China).
OBJECTIVE
China's freshwater subtropical shallow lakes are increasingly eutrophic and susceptible to production of heavy growths or water blooms of cyanobacteria. One example was the heavy water bloom that occurred for the first time in Lake Xuanwu, in 2005, an urban lake located in Nanjing city. The aim of the present study was to determine dynamics of water bloom dominating Microcystis in this lake. Meanwhile, the relationship between environmental factors and Microcystis populations was also analyzed.


METHODS
Molecular detection, using quantitative polymerase chain reaction, was used in this lake to study the dynamics of the cyanobacterial community, its Microcystis populations, and the microcystin-producing Microcystis genotypes from August 2005 to November 2006.


RESULTS
It was shown that Microcystis wesenbergii and Microcystis aeruginosa were the main components of the cyanobacterial blooms in Lake Xuanwu, and they coexisted with species of the filamentous cyanobacterial genera Anabaena, Planktothrix, and Anabaenopsis. Microcystis cells were detected during the entire survey period and in all sample sites. The cell abundance of Microcystis ranged from 3.6 × 10(2) cells ml(-1) to a peak of 3.8 × 10(6) cells ml(-1). The ratio of mcyB-containing Microcystis subpopulations to the total Microcystis varied, ranging from 0.1% to 12.8%. The abundance of Microcystis containing the mcyB microcystin gene was shown to be significantly correlated with concentrations of total phosphorus and phosphate.


CONCLUSIONS
Water temperature was the primary factor affecting Microcystis abundance in the lake, and phosphorus loading was shown to be a main factor in governing the growth of both microcystin-producing genotype and total Microcystis population. Higher Microcystis cell counts at the bottom of the water column before and after appearance of water blooms in Lake Xuanwu suggested that Microcystis numbers in the water column, especially at the bottom of the water column, play an important role in forming the next water bloom.
Xu
Yao
Y
College of Geography Science, Nanjing Normal University, Nanjing 210046, China.
Wang
Guoxiang
G
Yang
Wenbin
W
Li
Renhui
R
D002681:China; D004784:Environmental Monitoring; D005068:Eutrophication; D005618:Fresh Water / Q000737:chemistry*; D046931:Microcystis / Q000235:genetics / Q000254:growth & development*; D012621:Seasons; D013696:Temperature; D014873:Water Pollutants / Q000032:analysis*; D014876:Water Pollution / Q000706:statistics & numerical data
D014873:Water Pollutants