system have occurred in regions that would be classified as 

 "oligotrophic" according to the normal criteria. 



In the following report we will attempt to address some of the interac- 

 tive effects of two types of contaminant loadings, phosphorus and heavy 

 metals, which might not be discerned by conventional limnological methods. 

 The research was originally initiated in an attempt to explain the apparent 

 differential influence of phosphorus enrichment on particular species of 

 phytoplankton advected through zones of phosphorus pollution. Loadings, 

 biological availability, and biological pathways of this nutrient in the 

 Great Lakes system are of particular interest because it is the primary 

 nutrient controlling eutrophication. Most undesirable anthropogenic modi- 

 fications of the Great Lakes ecosystem are directly related to increased 

 phosphorus loadings resulting from increased population densities, intro- 

 duction and widespread usage of phosphorus containing detergents, and poor 

 land management practices. In the course of this investigation we found 

 that the mechanism allowing differential sequestering of phosphorus was 

 intimately assotiated with heavy metal concentration in the water and that 

 the same mechanism could permit excessive uptake of certain toxic metals. 

 Since this bioaccumulation mechanism could have both effects on the aquatic 

 ecosystem and potential effects on human health we have attempted to deter- 

 mine some of the factors involved. 



Since the problem we are dealing with has not, to our knowledge, been 

 previously investigated in the context of large lake limnology and since 

 some of the methods we have adopted have not been widely employed in water 

 quality investigations it would perhaps be helpful to give a brief chronolo- 

 gical outline of the development of this investination before discussing re- 

 sults. 



During an investigation of Saginaw Bay, one of the more grossly polluted 

 regions within the Great Lakes ecosystem, it became apparent that certain 

 species of phytoplankton were surviving transport out of the bay into Lake 

 Huron. This was unexpected because the species involved have high nutrient 

 requirements which cannot be satisfied in Lake Huron. We hypothesized that 

 populations within the bay were taking up phosphorus in gross excess of 

 their immediate physiological requirements and subsequently surviving trans- 

 port out of the nutrient-rich environment by using these internal stores. 

 In order to verify this hypothesis we examined the internal cellular con- 

 stituents of these populations by analytical electron microscopy. This ana- 

 lysis confirmed the presence of internal stores of phosphorus in the form of 

 polyphosphate bodies. X-ray analysis further showed that the polyphosphate 

 bodies also contained appreciable quantities of lead. Subsequent field ob- 

 servations in areas subjected to combined phosphorus enrichment and heavy 

 metal contamination indicate that the phenomenon observed in Saginaw Bay is 

 common in other parts of the Great Lakes system. Laboratory studies were 

 also carried out to determine if other metals behave in the same manner as 

 Pb. 



173 



