THE LEVEL OF THE COMMUNITY AND THE ECOSYSTEM 



The most greatest problem of the present, the problem of clean water, is 

 connected not with the processes of individual and population levels, but 

 with the synecological processes, since water quality is a function of the 

 combined living activity of aquatic organisms. Therefore, the final crite- 

 ria in assessing toxicant effects on an aquatic population as a whole, i.e., 

 criteria of "normalcy" and "pathology", are the processes taking place with- 

 in complex biological formations, the community and the ecosystems. 



Toxicant inputs into a natural ecosystem leads to a rather specific 

 situation, the major features of which may be characterized as follows: 



1. The toxicant is directed not towards a single target 

 organism as it is under experimental conditions in aquarium, 

 or in the whole in vitro system, where the isolated "toxicant- 

 organism" relationship is artificially created, but rather, 

 the toxicant effects on variety of targets; 



2. As a result of spectrum of action, its concentration is dis- 

 persed and the real dose per organism is not equivalent to 

 the present projected concentration; 



3. The toxicant quantity per biological organism depends on popu- 

 lation density, biomass, species diversity, the presence of 

 the most susceptible organisms consuming the given toxicant, 

 and on many other factors; 



4. Immediately after entering an ecosystem, the toxicant is at- 

 tacked by active lower organisms, begins to undergo biodegrada- 

 tion by various exoenzymes, and is intercepted by species sus- 

 ceptible to accumulation; 



5. A decrease in concentration as a result of the process of de- 

 toxication, dispersion, physico-chemical destruction, and sorb- 

 tion of the toxicant promotes phase reactions, which may be 

 responsible for both inhibition and stimulation of vital activ- 

 ity of aquatic organisms. 



Thus in an aquatic ecosystem, the toxicant encounters the system func- 

 tioning as a whole: it is a negatively eutropic system, and the toxicant is 

 an entropic factor destroying life. Between the entropic factor, and the 

 system inclined toward negative eutrophy, a struggle starts. In the system 

 a counteraction grows in an effort to destroy the entropic factor. This 

 creates its specific quality buffering, described in the works of M.M. 

 Kamshilov (1973). The system consumes and transforms the toxicant, but only 

 within certain limits. When this potential of resistance is exhausted, a 

 toxic effect is manifested. 



Because of this situation, bodies of water with varying trophic status 

 have varying degrees of resistance to toxicants, and varying rates of 

 transition to the state of disturbed balance. Generally, the richer in life 



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