Daechung reservoir is the major source of drinking water supplied to Daejeon city, Sejong city and Chungchung provinces. Contamination of source water by odorous compounds are one of the problems related to the water quality management, especially in Korea where surface water is used as drinking water. Geosmin (1,10-trans-dimethyl- trans-9 -decalol) and 2-MIB (2-methyl isoborneol : 1,2,7,7-tetramethyl-exo- bicycloheptan-2-ol) are commonly recognized earthy-musty odor compounds produced by algae causing serious problems to the drinking water purification facilities.
In this study, spatial and temporal distribution of the odor compounds, geosmin and 2-MIB were investigated along with the development of phytoplankton in the Daechung reservoir from July 2012 to October 2013. Concentration and frequency of detection of both compounds were increased from April to October which was related to cyanobacterial bloom periods. Detection frequency of 2-MIB was higher at stations 1 (Jangkye) and 2 (Chooso) located at upstream than at stations 3 (Hoenam), 4 (Choodong), 5 (Dam) and 6 (Mooneui) located at downstream of Daechung reservoir. While occurrence of 2-MIB showed sporadic pattern, geosmin was detected concomitantly with the cyanobacterial development regardless of stations. However, concentrations of odor compounds were not directly related to the number of cyanobacteria. Concentration of both cyanobacteria and geosmin were decreased similarly according to the depths of water. It is well documented that certain species of cyanobacteria are involved in the production of odor compounds at certain periods of their development. Result of Pearson correlation analyses show that geosmin concentration exhibited significant correlation with the count of Anabaena macrospora and Aphanizomenon flos-aquae. On the other hand, 2-MIB concentration showed a significant correlation with the count of Anabaena smithii.