Evaluating the contribution of physicochemical parameters to two common off-flavor compounds in a drinking water reservoir
Type of DegreeMaster's Thesis
Fisheries and Allied Aquacultures
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Off-flavors, such as 2-methylisoborneol (MIB) and geosmin, are compounds that produce an earthy or musty taste and odor, which can negatively impact drinking water treatment and aquaculture products. Although these compounds were first identified as secondary metabolites of actinomycetes, cyanobacteria are considered to be the primary cause of off-flavors in freshwater lakes and ponds. Humans can detect off-flavors at very low concentrations (10 and 30 ng/L for MIB and geosmin, respectively), and, although not a health risk, off-flavors can promote distrust between consumers and water utilities. Removal of these compounds requires a large financial investment and is not guaranteed. Controlling ecological factors that promote off-flavor production may be more cost-effective in addition to improving the ecosystem as a whole. Due to their ability to produce toxins, cyanobacteria have been under particular scrutiny, and environmental factors promoting cyanobacterial blooms are relatively well known. Using some accepted paradigms surrounding cyanobacterial production, I conducted two limnocorral experiments that manipulated physicochemical conditions aimed at influencing phytoplankton community structure and, thereby, off-flavor production. The first experiment was conducted during fall 2013 and consisted of an unbalanced factorial design with four nitrogen-to-phosphorus (N:P) ratios and three nitrogen levels. I found that the addition of both N and P promoted MIB and effects were associated with cyanobacterial and diatom biovolume. The second experiment was a complete factorial design conducted during summer 2014 using the nutrient concentrations from the fall experiment that were found to best promote off-flavor. I also manipulated limnocorral mixing frequency to potentially affect growth and off-flavor production of diatoms, taxa not usually associated with off-flavor production. I found that MIB was positively correlated with diatoms, and negatively correlated with green algae and cryptophytes. I also found that geosmin was positively correlated with cyanobacteria. MIB and geosmin showed no concurrent trends throughout the second experiment, suggesting that different management approaches are required for each off-flavor compound. In general, off-flavors increased in both experiments under elevated nutrient conditions. Diatom biovolume was consistently correlated with MIB production, but contributions of cyanobacterial biovolume to off-flavors appeared to vary seasonally. These results indicate that lake managers should consider year-round control of nutrient loading and mixing patterns to better eliminate MIB and geosmin.