Water quality and relation to taste-and-odor compounds in the North Fork Ninnescah River and Cheney Reservoir, south-central Kansas, 1997-2003

Cheney Reservoir, the primary water supply for the city of Wichita in south-central Kansas, and its main source of inflow, the North Fork Ninnescah River, were sampled between 1997 and 2003 for sediment, nutrients, and the taste-and-odor-causing compounds geosmin and 2-methylisoborneol (MIB). It is believed that objectionable tastes and odors in Cheney Reservoir result from cyanobacteria (blue-green algae), and there is concern with proliferation of algal growth. Both nutrients and suspended solids affect algal growth and may be a concern for taste-and-odor issues. The transport of nutrients and suspended solids from the North Fork Ninnescah River to Cheney Reservoir was monitored as part of an effort to understand and thereby mitigate algal proliferation. The regression-estimated concentrations of total phosphorus in water entering the reservoir from the North Fork Ninnescah River during 2001–03 exceeded the base-flow, runoff, and long-term goals established by the Cheney Reservoir Task Force. Total suspended-solids concentrations in water from the North Fork Ninnescah River during 2001–03 generally exceeded long-term goals only during periods of runoff.

Water samples from Cheney Reservoir were analyzed for geosmin and MIB, the two most common taste-and-odor causing compounds produced by cyanobacteria. MIB was rarely detected in samples, indicating that geosmin is likely the primary source of objectionable tastes and odors. Anabaena, a cyanobacterial genera often linked to taste-and-odor occurrences, was not statistically related to geosmin in Cheney Reservoir, which indicates that Anabaena abundance is not linearly related to geosmin concentration or that other cyanobacteria are producing geosmin.

Regression models were developed between geosmin and the physical property measurements continuously recorded by water-quality monitors at each site. The geosmin regression model was applied to water-quality monitor measurements, providing a continuous estimate of geosmin for 2003. The city of Wichita will be able to use this type of analysis to determine the probability of when concentrations of geosmin are likely to be at or above the human detection level of 0.01 microgram per liter.