SECTION 14 



SIMULATION OF POTENTIAL POLLUTANT-CAUSED CHANGES IN THE ECOSYSTEM, 

 RESULTING FROM THE SENSITIVITY OF AQUATIC ORGANISMS TO TOXICANTS 



N.S. Stroganov 1 



The ecosystem changes in a complex manner from exposure to pollutants. 

 The course of the changes which take place depends both on the properties 

 and quantity of the pollutants and on the features of the system itself. 

 Aquatic organisms have a substantial effect on water properties, but their 

 vital activity, in turn, depends on the physical and chemical conditions of 

 the water body. The effect of seasonal climatic changes are superimposed 

 onto these interdependences. Beside the direct effect of pollutants on 

 aquatic organisms, secondary intermediate effects create a "web" of links 

 and interdependences. 



It is possible to simulate a complex ecosystem using a small volume, in 

 which there are a 1 1 of the basic components characteristic of natural aqua- 

 tic communities. However, such a simulation is expensive, very time-con- 

 suming, and requires the equipping of a large experimental base. Another 

 means of simulation could be based on laboratory tests and conducted ac- 

 cording to a definite plan using representative organisms from basic func- 

 tional groups which take part in the cycling of materials and of organisms 

 which are of interest to industry. 



Aquatic ecosystems were created over a very lengthy period of time, and 

 have acquired a definite qualitative structure, which is disturbed on a 

 small scale by the seasons of the year. The introduction of pollutants, es- 

 pecially toxic substances, drastically disturbs the established order, and 

 the system passes into a new state, which is in response to the new condi- 

 tion. As a rule, the new state of the ecosystem is unstable. The change 

 which has taken place is not desirable for man, his health, or his indus- 

 trial activity. The instability is expressed by the disappearance or de- 

 crease in numbers of commercially important species of organisms and the 

 deterioration of water quality. Considering the fact that aquatic organisms 

 are a major component of the ecosystem and determine the desirable pro- 

 perties of the water body and the productivity of the species useful to man, 

 we turned our attention first and foremost to them, devoting special atten- 

 tion to the sensitivity of these aquatic organisms to toxic substances- 

 responses which can be determined under laboratory conditions. 



biological Faculty of Moscow State University 



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