SIZE-FRACTIONATED PRIMARY PRODUCTIVITY 

 IN LAKE MICHIGAN NEAR THE KEWAUNEE 

 NUCLEAR POWER PLANT 



STEPHAN I. ZEEMAN* and RALPH GRUNEWALD 

 Department of Botany and the Center for Great Lakes Studies, 

 The University of Wisconsin, Milwaukee, Wisconsin 



ABSTRACT 



Primary productivity rates were measured at the site of the Kewaunee Nuclear 

 Power Plant from Aug. 26, 1975, to July 23, 1976. Productivity was determined 

 for three size fractions by sequential filtration through 64-, 10-, and 0.45-jUm 

 porosity filters. Total unfractionated productivity was also measured. Univariate 

 analysis of variance showed no difference (P > 0.05) between pre- and 

 postcondenser productivity rates of the unfractionated samples. Multivariate 

 analysis of variance applied to size-fractionated samples detected lower rates 

 only when there was a AT across the condenser. These differences were caused 

 by changes in the <10- and >64-/jm fractions. Average productivity rates for the 

 year at the postcondenser station were within 13% of those at the precondenser 

 station. Chlorophyll a values were within 4% of precondenser values. It was 

 concluded that, although individual phytoplankton may be killed by passage 

 through the cooling system, populations suffer no permanent damage. Both 

 productivity rates and chlorophyll a concentrations for the net plankton 

 (>64 ixm) averaged over 55% of the sum of the three fractions. The 10- to 64-^<m 

 fraction averaged about 12% for productivity and 24% for chlorophyll, but the 

 values for the <10-jUm fraction were about 30 and 20% of the sum of the 

 fractions for productivity and chlorophyll, respectively. Assimilation numbers 

 (milligrams of carbon per milligram of chlorophyll a per cubic meter per hour) 

 were generally low (<3) for the unfractionated plankton. For the size- 

 fractionated samples, the two larger fractions were most often low, and the 

 <10-jUm fraction had numbers >3 on 44% of the sampling dates. 



*Present address: Marine Science Program, University of South Carolina, 

 Columbia, S. C. 



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