Abstract
Lake Chaohu, which is a large, shallow, hypertrophic freshwater lake in southeastern China, has been experiencing lake-wide toxic Microcystis blooms in recent decades. To illuminate the relationships between microcystin (MC) production, the genotypic composition of the Microcystis community and environmental factors, water samples and associated environmental data were collected from June to October 2012 within Lake Chaohu. The Microcystis genotypes and MC concentrations were quantified using quantitative real-time PCR (qPCR) and HPLC, respectively. The results showed that the abundances of Microcystis genotypes and MC concentrations varied on spatial and temporal scales. Microcystis exists as a mixed population of toxic and non-toxic genotypes, and the proportion of toxic Microcystis genotypes ranged from 9.43% to 87.98%. Both Pearson correlation and stepwise multiple regressions demonstrated that throughout the entire lake, the abundances of total and toxic Microcystis and MC concentrations showed significant positive correlation with the total phosphorus and water temperature, suggesting that increases in temperature together with the phosphorus concentrations may promote more frequent toxic Microcystis blooms and higher concentrations of MC. Whereas, dissolved inorganic carbon (DIC) was negatively correlated with the abundances of total and toxic Microcystis and MC concentrations, indicating that rising DIC concentrations may suppress toxic Microcystis abundance and reduce the MC concentrations in the future. Therefore, our results highlight the fact that future eutrophication and global climate change can affect the dynamics of toxic Microcystis blooms and hence change the MC levels in freshwater.
Highlights
Harmful cyanobacterial blooms pose a threat to freshwater ecosystems used for recreation and drinking water supply because cyanobacteria can synthesise toxic secondary metabolites, such as cyanotoxins [1,2,3]
Sites 1–3 were located in the eastern part of Lake Chaohu, sites 4–6 were located in the centre of the lake, and sites 7–9 were located in the western part of the lake (Figure 1)
These results were supported by the Pearson correlation and stepwise multiple regressions analyses that showed total phosphorus, water temperature and dissolved inorganic carbon were the primary variables regulating the variations in Microcystis population dynamics and MC concentrations during the bloom season
Summary
Harmful cyanobacterial blooms pose a threat to freshwater ecosystems used for recreation and drinking water supply because cyanobacteria can synthesise toxic secondary metabolites, such as cyanotoxins [1,2,3]. Microcystis populations are usually composed of toxigenic and non-toxigenic strains in the aquatic system [13,14,15]. The successive replacement of toxigenic and non-toxigenic strains during the development of cyanobacterial blooms has been suggested to be the cause of the changes in MC levels [18]. It is not possible to distinguish between toxigenic and non-toxigenic strains of Microcystis using traditional techniques, such as morphological and pigment analyses. Quantitative real-time PCR (qPCR) has been developed and widely used to estimate toxic Microcystis genotype abundance in natural populations based on specific MC synthetase genes (mcy) [19,20,21,22,23]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call