The role of light and nutrients in the phytoplankton production of Lake Wooster

Abstract

Preliminary work had indicated that lakes in this geographic region do not fit productivity models developed for lakes in other areas of the United States. This study was undertaken to investigate the factors controlling phytoplankton productivity in a shallow, turbid lake. Lake Wooster on the campus of Emporia State University, Emporia, Kansas was selected as the study site. Fourteen added nutrient trials were made between October 2, 1987 and November 30, 1989. Composite lake water samples with added concentrations of phosphate ion or nitrate ion were incubated in the lake along with untreated samples. Ammonium ion and a series of trace elements were also tested. Relative light intensity measurements were made between September 21 and November 30, 1989. The phytoplankton productivity of Lake Wooster was extremely variable, however the results were found to be in the range for lakes classified as eutrophic. The lake's productivity was confined to a narrow range, generally from 0.5 m to 1.0 m. The region below 1.0 m was often phosphate limited despite the overall high concentration of total phosphorus found in the lake. Phosphate concentrations and relative light intensity patterns were followed during an algae bloom in the fall of 1989. The chemical, physical and biological interactions in Lake Wooster were found to be complex. During the bloom the productivity reached levels which would place the lake in the hypereutrophic category. Given the very long exchange time for the lake, as nutrients continue to enter, Lake Wooster is likely to reach a state where it will be unquestionably hypereutrophic.