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Freshwater blooms of harmful cyanobacteria in drinking water source-oriented shallow lakes affect public health and ecosystem services worldwide. Therefore, identifying 2-methylisoborneol (2-MIB)-producing cyanobacteria and predicting the risks of 2-MIB are critical for managing 2-MIB-infected water sources. Previous studies on the potential producers and risks of 2-MIB have focused on reservoirs or have been limited by the ecosystems of phytoplankton-dominated areas. We investigated the producers, distribution, and occurrence of 2-MIB in East Taihu Lake-a drinking water source-oriented shallow lake with macrophyte- and phytoplankton-dominated areas-from August 2020 to November 2021. We observed that Pseudanabaena sp. produces 2-MIB in this lake, as determined by the maximum correlation coefficient (R = 0.71, p < 0.001), maximum detection rate, and minimum false positive/negative ratio exhibited by this genus. Extreme odor events occurred in this lake during late summer and early autumn in 2021, with the mean 2-MIB concentration increasing to 727 ± 426 ng/L and 369 ± 176 ng/L in August and September, respectively. Moreover, the macrophyte-dominated area, particularly the wetland area, exhibited a significant decrease (p < 0.01) in bloom intensity and 2-MIB production during these extreme odor events. Pseudanabaena sp. outbreak was likely owing to eutrophication, seasonal gradients, and macrophyte reduction, considering that temporal trends were consistent with high water temperature, high total phosphorus levels, and low-light conditions. Moreover, 2-MIB production was sensitive to short-term hydrometeorological processes, with high water levels and radiant intensity enhancing 2-MIB production. The risk assessment results showed that the probability of 2-MIB concentration exceeding the odor threshold (10 ng/L) is up to 90% when the cell density of Pseudanabaena sp. reaches 1.8 × 10 7 cell/L; this risk is reduced to 50 and 25% at densities of < 3.8 × 10 5 cell/L and 5.6 × 10 4 cell/L, respectively. Our findings support calls for shallow lake management efforts to maintain a macrophyte-dominated state and control odorous cyanobacteria growth., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Identifying typical odor-causing compounds is essential for odor problem control in drinking water. In this study, aiming at a major water source reservoir in hot and humid areas in southern China, which encountered seasonable odor problems in recent years, an integrated approach including comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS), flavor profile analysis (FPA) and quantitative real-time polymerase chain reaction (qPCR) was adopted to investigate the odor occurrence., Results: The results indicated that earthy-musty odor is blamed to the seasonable odor problems, and it is consistent with the complaints results from consumers. Fifty-four typical odor compounds were investigated in the reservoir and twelve were detected, of which, 2-methylisoborneol (2-MIB) was significantly increased during the odor event. Pseudanabaena sp. is the dominant species in the reservoir, which can be further represented by the number of mic gene with qPCR method ( R 2  = 0.746, P  < 0.001). Oxygen consumption (COD Mn ) and dissolved organic carbon (DOC) have great influence on growth of Pseudanabaena sp., and the release of 2-MIB from the Pseudanabaena sp. cells is affected by temperature and light., Conclusion: Our findings demonstrated that 2-MIB is the odor-caused substance in the reservoir and Pseudanabaena sp. is the main 2-MIB producer, which was confirmed as a benthic filamentous algae. Due to COD Mn and DOC have great influence on Pseudanabaena sp. growth, further measures to reduce the CODMn and DOC input should be performed. We also demonstrated that the 2-MIB release is affected by temperature and light. The risk of sudden increase of 2-MIB will be reduced by raising the depth of water in the reservoir. Our study will improve the understanding of T&O problems in this city, as well as in other hot and humid area.