The Effect of Sewage Effluent and Deicing Salt on the Green Alga Selenastrum Capricornutum
Arneson, Susan Rebecca
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The problem. This study was undertaken to evaluate the impact of secondary sewage effluent and highway deicinq salt runoff on a planktonic green alga. Procedure. The test organism, Selenastrum capricornutum, was grown in an algal assay which combined various concentrations of deicing salt and sewage effluent diluted with Des Moines River water. Monthly river and sewage samples were taken from November 1976-March 1977. Growth response was measured with a chlorophyll assay. Findings. Stronger sewage concentrations gave greater responses. The addition of 5,000 mg Cl/l was stimulating in any combination of river water and sewage effluent. It appeared that 10,000 mg Cl/l, while not entirely inhibitory, was slightly toxic since the growth response was less than the lower salt concentration and more like that of straight river water. Statistical analyses indicated that fluctuations in river water composition occurred over time since monthly growth responses differed significantly from each other. November samples gave the lowest chlorophyll values and collections from March usually had the greatest which corresponded to nutrient values determined by chemical analyses of the samples. Conclusions. The addition of both sewage effluent and deicing salt to Des Moines River water had a growth-enhancing effect on tile test alga, Selenastrum capricornutum, in most combinations. Recommendations. Further study should include a year-round survey with more sampling sites and frequent collections to determine present chloride levels and serve as a basis for predicting future trends. Experiments dealing with nutrient spikes ought to be considered. The use of indigenous algal species and in situ observations would be valuable.
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