matter); C is the organic matter in consumers; R is the organic matter in 

 reducers and broken down by them; represents bottom sediment and B is the 

 catch of commercial species and insects which migrate out of the system. 



At the present time, the situation is complicated by the fact that com- 

 ponent A consists not only of organic matter washed away from the surface of 

 the land, but also many toxic substances in industrial waste, residential 

 sewage and flood water. If a reservoir is used for commercial purposes 

 (fishing, catching of crabs and mollusks), some of the organic matter is re- 

 moved from the reservoir in the form of commercial species. All industrial 

 reservoirs are populated, particularly around their shores, with insect lar- 

 vae, which leave the reservoir in the imago stage, thus carrying away a por- 

 tion of the organic matter from the reservoir. 



Chemical pollution acts on the entire aquatic ecosystem (living and in- 

 direct) and due to the variety in quality and sensitivity of living compo- 

 nents of the system, restructures it in the direction of greater agreement 

 to the new quality of the environment. This restructuring almost never 

 satisfies the needs of humans. This is because processes of self-purifica- 

 tion are suppressed. Reducers cannot process all of the matter polluting 

 the water in such a short period of time. Water quality decreases and com- 

 mercial species disappear. 



Reducers function in a definite sequence (biologic oxidation, nitrifica- 

 tion in two phases) and if the toxin breaks some link, the entire chain of 

 processes of mineralization is broken. 



We have studied the effects of many toxins of various chemical natures 

 (metals, organometallic compounds, pesticides, antiseptics) and in all cases 

 a common law is observed, as the concentration of the toxin increases, there 

 is a delay in the development and an increase in the population of sapro- 

 phytes and nitrifiers. The delay may be so long that self-purification is 

 practically absent for 2-4 months. Figure 2 shows the variation of the 

 several links of self-purification with concentration of toxins and time of 

 action. 



If this delay in mineralization processes occurs in a river, the pol- 

 luted water flows downstream for 1000-1500 or more kilometers from the 

 source of pollution. Quite naturally, the river carries traces of the ef- 

 fects of the chemical pollutant over this entire distance. Various filter 

 feeders, particularly bivalve mollusks and Cladocera crustaceans, play a 

 great role in processes of self-purification of water. However, they are 

 sensitive to chemical pollution and their population drops quite rapidly, 

 leading to a decrease in the self-purifying capability of the aquatic eco- 

 system with subsequent death of many species. The aquatic ecosystem is 

 simplified to a small number of species and, if the chemical pollution 

 continues to increase, the entire ecosystem may approach zero. This trend 

 in aquatic communities is reported elsewhere (Stroganov 1978). 



Of course, under today's conditions there are no surface natural bodies 

 of water which have responded to pollution by complete death, but some small 

 areas near industrial production facilities have approached this state. 



24 



