Document Type



Phytoplankton, Mississippi River, Discharge, Nutrients, Chlorophyll


In 1986 we studied phytoplankton in the mid-reaches of Pool 8, which is a typical navigation pool of the Upper Mississippi River. During years of normal discharge, the areas studied usually become distinctly different from each other (ranging from free-flowing river to stagnant marsh) as the ice-free season progresses. These differences among sites did not occur during our study because the discharge into Pool 8 during 1986 was about 85% greater than the 10-yr mean discharge (1972-1982). Moreover, differences among areas were not observed with respect to physical and chemical characteristics such as photic zone depth, temperature, dissolved nitrogen and phosphorus, and silica. Accordingly, the phytoplankton assemblages and standing crops, which were characteristic of eutrophic waters, remained similar for all study areas. The phytoplankton was dominated by centric diatoms (Melosira granulata, M. italica, Stephanodiscus astrea, and Cyclotella meneghiniana), which comprised about 70% of the total cell volume. Aphanizomenon flos-aquae, Cryptomonas ovata, and U lothrix subconstricta were the most abundant non-diatoms; however, dense blooms of Aphanizomenon that normally occur in the Upper Mississippi River did not occur during the summer of 1986. Of the physical and chemical characteristics studied, discharge and temperature were most highly correlated with phytoplankton cell volume and chlorophyll a. In contrast, phosphorus and nitrogen were not correlated with phytoplankton standing crop.

Publication Date

March 1993

Journal Title

Journal of the Iowa Academy of Science





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© Copyright 1993 by the Iowa Academy of Science, Inc.



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