Abstract
A field survey of the seasonal variation of microcystin (MC) concentration was performed in Gonghu Bay (a total of 15 sampling sites) of Lake Taihu from January to December 2008. Microcystis spp. biomass and intra-/extracellular MCs were significantly correlated with water temperature, suggesting the importance of temperature in cyanobacterial blooming in the lake. Higher MC concentration was found in summer and autumn, and peaks of Microcystis biomass and intra-/extracellular MC concentrations were all present in October. Spatially, risk of MCs was higher in littoral zones than in the pelagic area. There were significant correlations between N or P concentrations, and Microcystis biomass or MC content, suggesting that N and P levels affected MC production through influencing Microcystis biomass. Intra-/extracellular MCs and Microcystis biomass had negative exponential relationships with TN:TP, and the maximum values all occurred when TN:TP was <25. Multivariate analyses by pcca indicated that intra- and extracellular MC concentrations had better correlations with biological factors (such as Microcystis biomass and chl-a) than physicochemical factors. The maximum concentration reached up to 17 µg/L MC-Lreq, considerably higher drinking water safety standard (1 µg/L) recommended who. So it is necessary take measures reduce exposure risk of cyanobacterial toxins human beings.
Highlights
The occurrence of cyanobacterial blooms in eutrophic freshwater bodies has become a worldwide problem[1]
Intra- and extracellular MC concentrations were both at a low level from January to June, but increased dramatically from July to October when water temperature was above 20°C
Environmental control may be the result of control of cyanobacterial growth rate, which in turn is correlated with cellular MC content[16]
Summary
The occurrence of cyanobacterial blooms in eutrophic freshwater bodies has become a worldwide problem[1]. MCs can cause poisoning or death of fish[6], birds[7], and domestic and wild animals[8], as well as illnesses and mortality in humans[9] They can transfer along the food chain[10], affecting human health through chronic exposure[11]. Laboratory and field studies indicated that production of MCs by cyanobacteria is affected by various environmental factors such as light, temperature, and nutrients[19,20,21,22]. Such studies provide valuable information on which environmental conditions most tend to be associated with high MC concentrations; empirical relationships between MCs and environmental factors have seldom been developed. Studies on the interactions between MCs and physicochemical variables are still lacking in Chinese lakes in spite of the abundant presence of cyanobacterial blooms in many eutrophic lakes in China[23,24,25]
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