Electron micrographs of sectioned material from control cultures and all 

 treatments were analyzed by stereology to quantify polyphosphate body abun- 

 dance under the conditions tested and to determine other changes in cellular 

 structure which might be induced by the treatments. Sectioned material was 

 also subjected to X-ray analysis to verify polyphosphate body composition 

 and metal accumulation. The results of this analysis is given in Table 1. 



Preliminary results from work currently in progress indicates that heavy 

 metal stress results in increased polyphosphate body formation in Plectonema 

 boryanum Gom. (Figures 9-11). These results further indicate a differential 

 effect depending on the degree of direct toxicity of the metal to the alga 

 subjected to the stress. In Plectonema Pb and zinc cause an approximately 

 10-fold increase in polyphosphate bodies per cell after 3 days exposure. 

 Copper and cadmium treatments result in a ca. 5-fold increase, but increased 

 apparent cellular damage at the ultrastructural level. 



DISCUSSION 



Our results are indicative of the complex and poorly understood cellular 

 level interactions which may occur in algal populations of large lakes sub- 

 jected to nutrient and toxicant contamination. Previous reports in the 

 literature suggest polyphosphate accumulation may be triggered by several 

 types of nutrient imbalance (see Sicko 1974 for review). It is important to 

 note that the mechanism may be triggered either by deficiency in some criti- 

 cal nutrient in the presence of excess exogenous phosphorus (Lawry and 

 Jensen 1979), stress invoked by excess levels of micronutrients, or simply 

 by the restoration of excess exogenous phosphorus to cells previously 

 stressed by deficiency of this nutrient. 



Any or all of these conditions are apt to be present in mixing zones 

 where contaminated stream flows enter the Laurentian Great Lakes. It is 

 thus highly probable that rapid uptake of phosphorus in these areas is not 

 directly related to the immediate growth potential of the algal populations 

 affected. This is illustrated by our results from Saginaw Bay (Figure 4). 

 The normal water circulation of the bay is counterclockwise with water exit- 

 ing the bay along the southern shore (segments 3 and 5 in Figure 4) being 

 replaced by Lake Huron water entering the bay along the northern coast 

 (Danek and Saylor 1977). The primary source of nutrient enrichment and 

 heavy metal contamination is the Saginaw River (Smith et ^. 1977) which en- 

 ters the far southwestern tip of the bay. In this case polyphosphate bodies 

 are much more abundant in phytoplankton populations taken at stations down- 

 stream, in the sense of the average current vector, of the source than in 

 other segments of the bay. It further appears that phosphorus bound in this 

 form is transported out of the bay since polyphosphate bodies are found at 

 stations near the mouth of the bay. The eventual fate of this material in 

 the Lake Huron system cannot be determined on the basis of our observations. 

 We would speculate, however, that at least two effects may occur. The first 

 is that phosphorus bound in this form may eventually be reutilized allowing 

 the survival of phytoplankton populations which are usually restricted to 

 eutrophic areas in the open waters of Lake Huron. Other investigations 

 (Stoermer and Kreis, in press) have shown that populations which appear to 



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