significant reduction in flux occurred following addition of rotenone (about 

 1 ml of saturated solution in ethyl alcohol). Note that reduction of the 

 flux in the control cell reflects the progressive approach toward an equili- 

 brium concentration of silicon in overlying water. In another set of ex- 

 periments, tubificid worms and Pontoporeia were added to cores so as to in- 

 crease the natural population densities by about a factor of two. As can be 

 seen in Table 3, these additions did not result in a significant increase in 

 the silicon flux. In retrospect, it appears likely that the addition of 

 Chironomid larvae would have produced the increase in the flux. 



Our results suggests an important role for benthos in the cycling of 

 silica (and possibly other nutrients) in the Great Lakes. As silica is a 

 major and probably limiting nutrient for the diatom productivity, it is im- 

 portant to understand the role of benthos and Chironomid larvae in particu- 

 lar in nutrient regeneration and the possible effect of aquatic pollutants 

 on their interaction with sediments. 



ACKNOWLEDGEMENTS 



The author wishes to acknowledge the help of Cheryl Hoyt, Karen Husby, 

 Kjell Johansen, John Krezoski, and Maranda Willoughby in various aspects of 

 field and laboratory work. Great Lakes Research Division Contribution Num- 

 ber 254. 



REFERENCES 



Brkovic-Popovic, I., and M. Popovic. 1977a. Effects of heavy metals on 

 survival and respiration rate of tubificid worms: Part I - Effects on 

 survival. Environ. Pollut. 13: 65-72. 



Brkovic-Popovic, I., and M. Popovic. 1977b. Effects of heavy metals on 

 survival and respiration rate of tubificid worms: Part II - Effects on 

 respiration rate. Environ. Pollut. 13: 93-98. 



Edgington, D.N., and J. A. Robbins. 1975. The behavioral of plutonium and 

 other long-lived radionuclides in Lake Michigan: II. Patterns of depo- 

 sition in the sediments. IAEA Symposium on the Environmental Effects of 

 Nuclear Power Generation, (IAEA-SM/198/40), l^elsinki, Finland, June, 

 1975. 



Edgington, D.N., and J. A. Robbins. 1979. History of plutonium deposition 

 in Lake Erie sediments. Twenty Second Annual Conference on Great Lakes 

 Research of the International Association for Great Lakes Research, 

 Rochester, New York, April 30 - May 3, 1979. Abstacts p. 49. 



Graneli, W. 1977. Sediment respiration and mineralization in temperate 

 lakes. Ph.D. Dissertation, Institute of Limnology, University of Lund, 

 Sweden, Summary 9 pp. 



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