ANAEROBIC HABITATS 



25 



surface. These water-basins represent the typical habi- 

 tat of the sapropelic fauna. 



TABLE 2 



Oxygen Context of the Water at Various Depths ix a Small Shallow 

 PoxD (AccoRDixG TO Wetzel, 1928). 



(Wetzel's figures for his pond No. 11 have been averaged for each 



month.) 



*Iu mud of bottom. 



Similar conditions are found occasionally in relatively 

 large and deep fresh water basins. A large artificial 

 lake, heavily polluted by waste material from factories, 

 recently described by Liebmann (1938), represents an 

 interesting case of this sort. To the same class of habi- 

 tats belong sewage disposal plants. The contents of 

 septic tanks and similar installations are typically 

 anaerobic. 



The bottom deposits of the oceans seem to be large- 

 ly anaerobic, if we disregard the uppermost layers. The 

 deeper strata have repeatedly been reported to be de- 

 void of free oxygen (Moore, 1931; ZoBell and Anderson, 

 1936; ZoBell, 1939). In some cases oxidation-reduction 

 potentials have been found which indicate that at least 

 some deposits are even markedly reducing. Our knowl- 

 edge concerning the vertical distribution of bottom in- 



