voirs. To do this, let us discuss the main elements of the problem, in 

 order to note paths for their solution. 



In each reservoir, the quality of water is formed by all aquatic or- 

 ganisms. They pass through their bodies the entire mass of water of the re- 

 servoir, enriching it by many products of their metabolism and, simulta- 

 neously, changing the gas and mineral composition of the water. In the 

 cycle of matter, some organisms play a determining role while others play a 

 subordinate or even hardly noticeable role. Bacteria, protozoa, algae, and 

 all invertebrate animals - the filter feeders - play a significant role. 



A reservoir is a multicomponent system, consisting of living organisms 

 and the water itself, containing various chemical substances in the mole- 

 cular and supermolecular states, as well as the bottom, which contains a 

 number of organisms and silt particles. The number of species is usually 

 several hundred or even thousands in such reservoirs as Lake Baikal, while 

 the number of individual substances is not precisely known, but it must be 

 assumed that there are also several hundreds, or perhaps even thousands. 

 For example, some of the large rivers pick up along their way not only 

 several hundreds of different chemical compounds and ions, depending on the 

 geochemical status. of the watershed, but also several hundreds of chemical 

 compounds from industrial enterprises, cities and population centers, water 

 transport, and atmospheric precipitation. The complete chemical composi- 

 tion of such waters is unknown. We know indirectly that it includes a long 

 list of substances. 



This tremendous number of components in the water system is in total 

 interaction and interrelation. The quality of water is a resultant of these 

 many interrelationships. It is practically impossible to consider them all 

 at the present time. Therefore, we must distinguish the most important 

 determining components. This approach to determination of the regularities 

 of behavior of an aquatic system is simplified, but is necessary in order to 

 solve the problems of standardization of water quality which have been set 

 before us. 



Among aquatic organisms, three main functional groups must be distin- 

 guished: 1) producers - organisms which create organic matter in their 

 bodies by the process of photosynthesis, utilizing mineral substances dis- 

 solved in the water (salts and gases); 2) consumers, transformers - organ- 

 isms which construct their bodies by consuming organisms of groiup 1. This 

 group includes phytophages and organisms which feed on the phytophages, 

 i.e., predators; and 3) reducers. A large group of organisms (bacteria, 

 protozoa, fungi) decompose the waste substances from the vital activity of 

 other organisms as well as dead organisms, to mineral substances once more. 



In each of these groups there are many species which follow each other 

 in a regular sequence during the seasons of the year. The specific composi- 

 tion of each functional group changes depending on the specifics of the re- 

 servoir, its geographic position,, climate, nature of bottom, hydrologic and 

 hydrochemical modes. For the full cycle of matter in the reservoir, the 

 specific composition of the functional groups (1-3) is of no great signifi- 

 cance, while for commercial organisms (their nutrition, growth, breeding), 



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