Degree Name

Master of Science (MS)

Semester of Degree Completion

1990

Thesis Director

Charles L. Pederson

Abstract

Lake Charleston is a 1.1 billion gallon capacity side channel reservoir which was constructed in 1982 as a public drinking water supply for the City of Charleston in Coles County, Illinois. Past studies of the lake indicated an increase in eutrophication and the capacity to support large algal populations. Recent lake management practices include copper sulfate applications as an algicide and aeration to reduce flavor and odor.

In order to assess present lake status and to evaluate the effectiveness of lake management practices, two lake sites were sampled on a weekly basis from May to October, 1989. Chemical, physical, and phycological analyses followed standard methods (APHA 1985).

Carlson's Trophic State Indices calculated from data on secchi depth (m), chlorophyll a (ug/L), and total phosphorus (mg/L) indicated that Lake Charleston is hypereutrophic. Phosphorus probably limited algal standing crop at site 3 while light was most likely the limiting factor at site 1. Abundance of phosphorus at site 1 was attributed to the circulation of hypolimnetic phosphorus by the aeration unit.

Phytoplankton density has increased by a factor greater than five since 1982. During a bloom in July, bluegreen algae dominated at site 3, however bluegreens never comprised more than fifty percent of total algae at site 1. The inability of bluegreens to dominate at site 1 could have resulted from low pH/high carbon dioxide water circulated from the bottom which would favor dominance by green algae. After copper sulfate treatment in late July, phytoplankton density decreased dramatically and green algae resumed dominance at site 3.

Several chemical, physical, and phycological parameters were significantly correlated. Site specific differences were observed and attributed to the effects of aeration.

Aeration may be a good management option for Lake Charleston with higher carbon dioxide and lower pH levels at site 1 presumably preventing bluegreen algal dominance. Total algal biomass should decrease with continued and/or extended aeration as nutrient concentrations level off and algae become light limited. Copper sulfate, which is toxic to zooplankton, could then be eliminated as a management technique and increased zooplankton populations could possibly provide biological control for phytoplankton. Dissolved oxygen has not yet increased, possibly because of an increase in oxygen demanding substances and a decrease in photosynthesis, both of which are attributable to circulation. With constant aeration, dissolved oxygen should eventually increase and overall lake conditions should improve.

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