SPATIO-TEMPORAL PATTERN OF ODOROUS COMPOUNDS AND ITS INFLUENCING FACTORS IN THE CANAL OF THE MIDLE-ROUTE OF SOUTH-TO-NORTH WATER DIVERSION PROJECT

In order to recognize the spatiotemporal dynamics of odorous compounds in nine sampling sites along the main canal of the Middle Route of South-to-North Water Diversion Project, we monitored six odorous compounds, phytoplankton communities, physicochemical parameters every month, from September 2018 to August 2019. Results showed that the average concentration of 2-methylisoborneol was (7.431±9.631) ng/L, which exceeded the olfactory threshold in summer. The mean concentrations of β-cyclocitral and β-ionone were (12.371±12.800) ng/L and (11.973±20.643) ng/L, respectively, and β-ionone exceeded its olfactory threshold in autumn. The average concentration of dimethyl-trisulfide was (173.014±302.047) ng/L, which was not detected in winter and spring. Geosmin and dimethyl-sulfide did not surpass the olfactory threshold in the whole year along the MRP. The seasonal variance of six odorous compounds were greater than the spatial difference in MRP. Redundancy analysis showed that COD_Mn had a significant negative relationship with dimethyl-sulfide and dimethyl-trisulfide. β-Cyclocitral, β-ionone, dimethyl-sulfide and dimethyl-trisulfide were significantly correlated with nitrate, and Chl.a had a remarkable positive relationship with β-cyclocitral and β-ionone. Nitrate, COD_Mn and Chl.a were the influencing factors to predict the dynamic change of odorous compounds. There was a significant positive correlation between the concentration of 2-methylisoborneol and geosmin with Chrysophyta sp. and Anabaena pseudoanabaena. There was a time overlapping between the cell density of Microcystis sp. and the concentration of β-cyclocitral and β-ionone. Microcystis sp. had 13.8% explanatory weight to the concentration of β-ionone. There was a correlation between dimethyl-sulfide and dimethyl-trisulfide with Pyrrophyta sp. and total cells density. These findings reveal that the odourous problem in the main canal of MRP is generally not serious, but algae is an important contributor to the odorous compounds. In order to prevent the odorous problem, it is necessary to pay attention to the algae community composition and its dynamic variations in summer and autumn.