source deterioration and implementing management strategies which will con- 

 trol or eliminate the particular problems. In many cases management strate- 

 gies are clearly evident and considerable success has been obtained by their 

 implementation. Perhaps the clearest case of success is the restriction of 

 use of certain chlorinated hydrocarbon pesticides which has reduced the con- 

 tamination levels of Great Lakes fish. In the Great Lakes system primary 

 productivity is clearly controlled by phosphorus availability and efforts 

 are underway to limit inputs of this material to the system. This limita- 

 tion has proven more difficult to implement and positive effects, to this 

 point, have not been dramatic. 



As we become more familiar with the characteristics of the Great Lakes 

 ecosystem it becomes more and more apparent that effective management will 

 demand a detailed understanding of ecosystem characteristics and functional 

 relationships in order to develop management strategies which can control 

 subtle and multiplicative causes of ecosystem deterioration. Consideration 

 of the unique characteristics of the Laurentian Great Lakes leads to the 

 conclusion that these bodies of water may present the most demanding chal- 

 lenge to effective water quality management found in any freshwater system. 

 Several considerations are involved in this conclusion: 



1. In their pristine state the Laurentian Great Lakes were an 

 almost perfectly exploitable system. They were a source of 

 water which could be utilized without extensive treatment 

 and supported a fishery for very highly valuable species. 

 They were also a source of aesthetic enjoyment and recrea- 

 tional activities for a significant portion of the popula- 

 tion. Minimal levels of perturbation led to disproportion- 

 ately large damage to the resource potential compared to 

 other systems. 



2. The Great Lakes are a geologically ^^ery young ecosystem, com- 

 pared to most large lakes of the world. The fauna and flora 

 are unique but have not had time to develop stable adaptations 

 to their environment. Such communities might be expected to 

 be particularly susceptible to environmental perturbation and 

 this expectation has been realized in the history of biological 

 changes observed. 



3. The Great Lakes are ^^ery long residence-time systems compared 

 to most other freshwater biotopes. This means that introduced 

 contaminants may have very prolonged effects. 



4. Because of the great dilution volume of the Great Lakes con- 

 taminants may be present in quantities so low that they are 

 difficult to measure by conventional chemical methods although 

 their effects may be crucial to the biota. 



5. It is quite clear that the classification and perception of 

 water quality developed for other freshwater systems is not ap- 

 propriate for the Great Lakes. Paradoxically, drastic and 

 possibly irreversible modifications of the Great Lakes eco- 



172 



