for which a confident difference is established between the initial and 

 final oxygen content in bottles. The sensitivity of the oxygen methods 

 conducted by a skillful specialist may reach 0.05 mg O2/I . 



Destruction of organic matter expressed in terms of oxygen is equal to: 



°H " °k = °n ""a/ 1 /day 



where: 



Oh - initial oxygen content (mg/1), 



0^ - final oxygen content, 



On - oxygen consumption. 



Approximate summer values for respiration of the aquatic ecosystems in 

 water-bodies of various trophic degree are indicated in Table 3. 



TABLE 3. OXYGEN CONSUMPTION FOR RESPIRATION OF ORGANISMS IN 

 WATER-BODIES OF VARIOUS TYPES (SUMMER VALUES). 



Type of Water- Approximate Values of Oxygen Quality of 

 Body Consumption, mg 02/1/day Water 



Oligotrophy 0.05-0.1 Clean 



Mesotrophic 0.1-0.3 Good 



Eutrophic 0.3-3 Bad 



With organic pollution 3-10 Very Bad 



Total BOD 



In sanitary microbiology, instead of daily oxygen consumption, the 

 value of total BOD, i.e., quantity of oxygen which may be used by the 

 microflora for oxidation of all the fractions of easily degradable or- 

 ganic matter, is often used (Lapshin, 1952). The experiments are per- 

 formed at a constant temperature of 20 °C. 



Water from the bottom sampler is poured into a flask, its tempera- 

 ture is adjusted to 20 °C, and filled with a syphon into 6 100-150 ml 

 bottles. In a case of low oxygen content, the water is saturated with 

 oxygen by bubbling air through it. In two bottles, the initial content of 

 oxygen is measured by Winkler method, the remaining two are analyzed for 

 BOD. Bottles to be incubated are placed in water and ground covers with 

 the tested water (water lock) are fixed on them. 



The difference in oxygen content between the initial water and at the 

 amount present after 3 days is designated as BOD3, and after 6 days as 

 BODs. The total BOD is determined by the formula: 



66 



