A 



BOD. , = *— - — - 

 tot . Za, - a,, 



a 1 = BOD for 3 days, 

 ao = BOD for 6 days. 



Heterotrophic Assimilation of C02 



Heterotrophic assimilation of CO2 is assimil ition of carbon dioxide by 

 heterotrophic organisms. As early as 1921, it was shown by A.F. Lebedev 

 and later by Wood and Werkmann (1936) that heterotrophic organisms assimi- 

 late a small amount of CO2 in their metabolism. 



Until the present time, this phenomenon was described only in the 

 experiments performed at the Institute of Biology of Inland Waters, Academy 

 of Sciences, USSR (Romanenko, 1964; Sorokin, 1964). By this work it has 

 been shown that a certain amount of carbon dioxide is assimilated per 

 given increase in biomass of bacteria. It has also been found that there 

 is a direct proportionality between assimilation of CO2 and respiration. 

 As a result, it has been established that the ratios between oxygen con- 

 sumption, increase of bacterial biomass, and assimilation of CO2 is equal 

 to 1000:100:7 (mg O2, mg C, mg C). It should be realized, of course, that 

 this correlation is not as strict as may be found in chemistry and physics. 

 However, it may be used for the determination of productivity of bacterial 

 biomass (Kutnetsov oX al., 1966). With the exception of meromictic lakes 

 in the zones above the layer of hydrogen sulphide, heterotrophic assimila- 

 tion of CO2 prevails over chemosynthesis in water bodies. Heterotrophic 

 assimilation of CO 2 in waters of varying types in shown in Table 4. 



TABLE 4. MEAN MID-SUMMER VALUES OF HETEROTROPHIC ASSIMILATION OF C0 2 IN 



WATER BODIES OF VARIOUS TYPES 



Type of Water- Assimilation of C0 2 , Character of 

 Body g C/1/day Water 



Oligotrophic 0.1-1.0 Very Clean 



Mesotrophic 1-5 Clean 



Eutrophic 5-70 Dirty 



10-200 Very Dirty 



The high sensitivity of the radioactive carbon method enables the 

 determination of the smallest values of CO2 assimilation. The method is 

 as follows. 50-70 ml of water is placed in a bottle to which 1 ml of Re- 

 labeled carbonate, NaH 14 C03, is added having a specific activity of 

 1-5 x 10 6 imp/min under the Geiger counter. The bottles are placed in 

 lightproof bags, and the samples are incubated at the temperature of the 

 water-body for 24 hrs in oligotrophic and mesotrophic waters, 6-12 hrs may 



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