Source apportionment and odor-producing potential assessment of 2-methylisoborneol in Danjiangkou Reservoir

In recent years, odor problems caused by 2-methylisoborneol (2-MIB) have been frequently reported, posing a prominent challenge to global water quality safety management. Monitoring data showed that in mid-to-late August 2025, the average concentration of 2-MIB at the Taocha Section of the main channel of the South-to-North Water Diversion Middle Route Project reached 29.0 ng/L. To elucidate the biological sources and odor-producing potential of 2-MIB, this study focused on a period of abnormal algal proliferation in the Danjiangkou Reservoir. Methods including morphological identification via microscopy, high-throughput sequencing of the mic gene, and quantitative PCR (qPCR) were comprehensively employed to systematically analyze the cyanobacterial community structure, potential odor-producing taxa, and the spatiotemporal distribution characteristics of mic gene abundance. Morphological identification revealed a cyanobacterial community dominated by Aphanocapsa, Raphidiopsis, and Leptolyngbya. Molecular biological methods further uncovered numerous ecologically significant taxa with low abundance. Planktothricoides and Pseudanabaena were identified as the main potential odor-producing groups. Among these, Planktothricoides accounted for 64.2% ~ 93.3% of the mic gene-carrying community and showed a significant positive correlation with mic gene abundance, leading to the inference that it was the primary contributor to 2-MIB. The mic gene copy numbers ranged from 3.14 × 10⁵ to 2.00 × 10⁷ copies/L, exhibiting significant spatial differences and vertical stratification, with the highest abundance found in the surface water of Taocha Section. This study confirms that combining morphological and molecular biological methods can effectively enhance the accuracy of identifying odor-producing algae and assessing associated risks, thereby providing a scientific basis for the early warning and control of 2-MIB risks in drinking water sources.