Researches on Nitrifying Bacteria 



421 



2) Between ten and fifteen days: for depths of 50, 80, 185, 

 325 and 500 m. 



3) Fifteen days: for depths of 0, 120, 356, 526 and 650 m. 

 The first group includes only the depths of less than 100 m, 

 the last includes a majority of depths over 300 m and the second 

 group is intermediary with nearly equal representation of great 

 and shallow depth. Certainly depth cannot be the sole determi- 

 nant, which explains the exception in the second group and 

 third; however, depth seems to play an important role in the 

 distribution of the bacteria. 



It is worth noting that all the sediments studied have proven 

 capable, in this selective medium, of transforming ammonium 

 salts into nitrates. 



Variations in Nitrification Activity in 

 Relation to the Depth of Sediment 



Let us now consider the results of a single sediment in rela- 

 tion to the sediment depth. By using cores of 0.5 to 1.0 m in 

 length, it has been possible to compare various horizons. Figure 3 

 represents a typical example obtained from sample area No. 235: 



S/ P 



E 

 O 





TIME (days) — > 



Fig. 3. Nitrification in the upper (S) and lower (P) portion of a sediment 



core. 



