The Eutrophic Status of Ten Central Iowa Lakes

Abstract

The problem. To date little work has been done determining the eutrophic status of small central Iowa lakes. The purpose of this study is to (1) determine the eutrophic status of ten central Iowa lakes; (2) compare and contrast any differences between the lakes located within the Wisconsin Glacial drift and those lakes located outside of this area; and (3) compare and contrast any differences between natural and man-make lakes. Procedure. During the spring of 1975, the fall of 1975 and the spring of 1976, composite water samples were taken from the euphotic layer of each lake. Each water sample was then subjected to various tests including: alkalinity, free carbon dioxide, specific conductance, pH, nitrate and nitrite nitrogen and ortho and meta phosphate. After autoclaving, each water sample was innoculated with a test algae, Selenastrum capricornutum, and incubated under set conditions. Cell counts and algal dry weights were determined. The algal dry weights and seasonal changes in lake alkalinity were correlated to the eutrophic status of each lake. Findings. After incubation, all the samples from the man-made lakes had moderate algal dry weight values while the algal dry weight values of the samples from the natural lakes were higher. In general, the lakes located within the Wisconsin Glacial drift had higher chemical parameters than those located outside of this area but this did not seem to have any effect on the general eutrophic status of any lake studied. Conclusion. Of the lakes studied the man-made lakes are mesotrophic while the natural lakes are eutrophic. Recommendations. It is suggested that further studies on these lakes be more quantitative, employing more frequent samplings and including nutrient budgets and turnover to aid in developing a plan to improve water quality.