are the dominant species of phytoplankton in spring and autumn, but during 

 July and August the blue-green algae are predominant. 



Primary productivity of organic matter was determined by the C method 

 (Steeman Nielsen, 1952). The intensity of photosynthesis in the water mass 

 correlated well with water transparency according to Secchi disc readings 

 (Romanenko, 19/3a) according to the formulas: 



F m = F| x 0.7 x 3 1 x 1000, where 



F = Phytoplankton primary producti vity/m 2 /24 hours 



Fj = Phytoplankton primary productivity in a water sample 

 integrated according to depth, exposed at surface 

 illumination during 24 hours. 



1 = Secchi disc transparency. 



The gross phytoplankton primary productivity (mean for several years) 

 ranged from 100 to 500 thousand ton C for the whole water body; for the sur- 

 face it changed from 30 to 150 g C/m 2 (Figure 2), with a mean of 76 g C/m 2 . 

 Long-term (meaning for several years) fluctuations in the intensity of 

 photosynthesis depended on meterological factors during the year, rate of 

 outflow, and an increase in the reservoir drainage zone. Estuaries of 

 large rivers are the most productive areas. As a rule, the primary produc- 

 tivity is 1.5-2.0 higher than in the central area. In all, 0.05-0.20% 

 energy from solar radiation penetrating the water is used by the algae. 

 Solar radiation is used less effectively during the spring when there are 

 few phytoplankton and the water temperature is low (0.02-0.07%). During 

 the blue-green algae bloom in July and August, given the highest water temp- 

 eratures, it is used considerably more effectively (0.37%). 



By using the data of chemical oxygen demand (COD) and the water balance, 

 the total input of allochthonous organic matter was calculated by Kuznetsev 

 and Bezler (1971). According to their data, 4.75 x 10 3 ton C as organic 

 matter enters the reservoir with the melted ice and snow. Since this reser- 

 voir is located in a low populated region, and the pollution of it as a re- 

 sult of man's activity is not great, the input of organic matter by such 

 sources as wastewaters can be neglected. The input of organic matter due 

 to atmospheric precipitations, in particular in winter with snow on the re- 

 servoir surface, is 680 ton C, which is only 0.5% of the value of primary 

 productivity (Romanenko and Bezler, 1971). An additional input of organic 

 matter is also due to rainfall precipitation during summer months. There- 

 fore, it is necessary to consider all these sources of organic matter to- 

 gether, because each of them isolated represents a very small input of allo- 

 chthonous organic matter. 



The total bacterial assimilation of C0 2 and hydrocarbonate (hetero- 

 trophic assimilation of C0 2 and chemosynthesis) were determined by the C 



123 



