If we take into account that the rest of the population destroys only 

 around 20% of the total organic matter (especially algae and invertebrates), 

 it is easy to calculate the correlation between bacterial biomass and de- 

 struction. The production of bacterial biomass was 30% of the amount of 

 destroyed organic matter (expressed as carbon). By means of pure cultures 

 it was demonstrated that the correlation between these data (K x coefficient) 

 ranged from 25-35%, which proves the reality of our calculation of bacterial 

 production by means of the data on heterotrophic assimilation of C0 2 . 



Also in the bottom sediments a great amount of organic matter is decom- 

 posed in aerobic or anaerobic conditions according to the redox potential 

 through the activity of aerobic or anaerobic organisms or both. In this re- 

 servoir, the bottom layers are very well supplied with dissolved oxygen, 

 and oxygen deficits are only observed in the flood areas in which the rH 2 

 fluctuates from 10-12, and sulfate reduction and methane formation pro- 

 cesses are most intense. The rH 2 is 10-17 in the peat slimes and 5-20 in 

 the sandy ones with small amount of debris. In such conditions aerobic de- 

 struction of organic matter prevails. 



The mean number of bacteria by direct count is 0.5-30 billion/g of wet 

 slime. Fifteen years ago, when the amount of organic matter from the re- 

 cently flooded areas was high enough, a very strong production of methane 

 gas derived from the activity of methane-producing bacteria was observed 

 and, especially in winter season, the big bubbles of this gas induced the 

 death of fish by asphyxiation. The methane formation process at this time 

 has sharply decreased. 



To determine the destruction of organic matter in the bottom sediments, 

 the oxygen consumption of a column of slime isolated in a glass tube (Hayes 

 and MacAulay, 1959) was used, and the balance of C0 2 extracted from the 

 slime into the water (Romanenko and Romanenko, 1969) was employed to deter- 

 mine the aerobic decompositon of organic matter. 



The results showed that 74,000 ton C as organic matter are decomposed 

 in the slime by aerobic processes during the navigable period, which means 

 20 g C/m 2 . Nearly 10 g C/m 2 are decomposed in anaerobic conditions. This 

 means that 23% of the organic matter is destroyed in the water mass. 



The loss of organic matter through the lower outlet was calculated ac- 

 cording to oxidizability and water balance as 179,000 ton C by Kuznetsov 

 and Bezler (1971). 



For the balance (Table 3) of the input and expenditure of organic 

 matter in the ecosystem of the Rybinskiy reservoir, taking into account 

 only the most important parameters, we can say that as a whole, in this eco- 

 system, the input of organic matter is 826,000 ton C or 199.9 g C/m 2 . 



By bacterial destruction or outlow through the outlet, the expenditure 

 of organic matter is 838,000 ton C, so the difference is -8400 ton C. If 

 we discount the loss of organic matter through the outlet (837,000 - 

 179,000), it is possible to see that the purification effect due to the 



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