716 Marine Microbiology 



demand, the latter being determined experimentally (2). The 

 quantity of microbe cells in the North Caspian silts was also 

 shown to be proportionate to the amount of organic substance. 



This fact proves once more that bacteria participate in the 

 process of regeneration of bio-microelements. The transition of 

 biogen elements from sediments into water in the Azov Sea is 

 quicker than in the North Caspian Sea. 



The quantity of labile organic substance in the Azov Sea 

 sediments (on the average) is 2.4 times greater than in the 

 sediments of the North Caspian Sea. The five days' biological 

 oxygen demand is also higher: 27.2 mg O^ per g of natural sedi- 

 ment in the Azov Sea against 6.25 mg O.- per g of natural sedi- 

 ments in the North Caspian Sea. The number of bacteria in the 

 Azov Sea sediments is correspondingly higher. 



Theoretical calculations show that the regeneration rate of 

 biogens is such that it can ensure the development of 340 mg/m^ 

 phytoplankton per day in the summer period at a depth of 7 m 

 (a 5 m deep photosynthetic layer: this actually takes place in the 

 summer period). 



Anaerobic reactions are of particular importance for the pro- 

 cess of decomposition of organic substance in sediments. Anaero- 

 bic processes precede the transition of biogens from silt into wa- 

 ter. 



Sediments being kept without an access of oxygen prior to 

 the beginning of the observations, were found to transmit into 

 water 1.5 to three times as much biogen elements as sediments 

 being kept aerobically. 



In the Azov Sea, under high temperature and restricted con- 

 ditions (less than 3 ml O^/L) in summer, the content of am- 

 monium nitrogen salts and phosphates in the near-bottom water 

 increases by two to three times. Such greatly inhibited oxygen 

 conditions near the Azov Sea bottom were found to have formed 

 during stable periods of calm weather favouring the warming up 

 of the upper water layers only. At the same time the difference 

 in the density of different water layers results in their stabilization, 

 which impedes the mixing still further. 



If, in addition, there is a difference in the salinity of water 

 layers (as a result of the inflow of water from the Black Sea or 



