Relationship between concentrations of odorous compounds and biomass of phytoplankton and actinomycetes in freshwater ponds of Beijing, China

The odorous compounds including geosmin and 2-methylisoborneol (MIB) were detected in intensively cultivated freshwater ponds in Beijing, China, by coupling head space solid-phase microextraction with gas chromatography mass spectrometry (GC-MS). Moreover, the biomass of phytoplankton and actinomycetes in the fishponds were determined simultaneously, and the relationship between the concentrations of these odorous compounds and the biomass of phytoplankton and actinomycetes was assessed. The results showed that among the odorous compounds detected, geosmin was the main one, and concentrations of 1.22-35.58 ng l⁻¹ were found in all fishponds. Besides, MIB with 1.39-6.00 ng l⁻¹ was found in parts of fishponds. Six phyla and 22 genera of algae were observed in the fishponds with a biomass of 17.33-178.34 mg l⁻¹, among which dominant phyla were Bacillariophyta and Euglenophyta. Four genera of actinomycetes with a gross biomass of 0-76 × 10⁴ ind l⁻¹ were found in the fishponds, of which Streptomyces spp. was the dominant genera. This indicated that geosmin concentration in fishponds was related with the total biomass of the dominant algae. The results showed that Melosira spp. and Cyclotella spp. were the main microalgae to cause off-flavor in Beijing's intensively cultivated freshwater ponds in summer and autumn, while Euglenophyta and other algaes played a small role in causing off-flavor.