TROPHIC STATUS OF TWO GLACIAL LAKES, WEST AND EAST OKOBOJI, IN NORTHWEST IOWA. U.S.A.

The lentic water system formed by the West and East Okoboji lakes and the Big Spirit lake was sampled in four stations spread through the Okoboji lacustrine system on October 9th, 1994. In these samples were determined chemical and biological parameters as depth, Secchi’s depth, temperature, pH, dissolved oxygen, electrical conductivity. The content of chlorophyll A between both lakes was also studied, including a comparison in zooplankton. In contrast with the shallow stations, in the deepest stations it was observed stratification due to the presence of thermoclyne and oxiclyne. For the comparison of chlorophyll between both Okoboji lakes, a one-way ANOVA test was applied. Results showed that there were statistically significant differences at 2-meter depth among the stations in both lakes but not in surface waters. Later, a Duncan Multiple Range test was performed to examine the nature of these differences. It showed that only Station SP in East Okoboji differed from the other three with respect to chlorophyll A. The zooplankton comparison showed no differences either in the presence of cladocerans calanoyds and ciclopoyds, or in the total amount of zooplankton. The behavior among the stations only showed statistically significant differences in ciclopoyds