24 ANAEROBIC HABITATS 



inorganic oxidations will then rapidly reduce the oxygen 

 content of the deeper soil layers, Ege (1916) found the 

 oxygen tension of the air 30 cm. below the surface of a 

 field to be 153 mm. of mercury ; 6 and 11% hours after a 

 rainfall it had decreased to 64 and 46 mm. respectively ; 

 after 36 hours, however, it had risen again to 129 mm. 



Rainwater itself entering the soil loses considerable 

 amounts of oxygen in a relatively short time as shown by 

 Merker's (1926) laboratory experiments. This loss is 

 probably due primarily to biological oxidations. The 

 oxygen deficiency so set up, is, according to this author, 

 responsible for large numbers of earthworms coming to 

 the surface after a rainfall. 



Other terrestrial habitats where oxygen deficiencies 

 can be expected are large masses of decomposing leaves, 

 compost and similar aggregations of decaying organic 

 material. 



It is quite possible that in many soils anaerobic or 

 near-anaerobic conditions prevail locally. This seems 

 to be indicated by the many reports of anaerobic bacteria 

 in soils (f,or a summary, see Waksman, 1932). To what 

 extent such conditions may influence the soil fauna re- 

 mains to be investigated. 



2. WATER BASINS 



A. Bottom of water basins. In nature small and usu- 

 ally shallow ponds and bogs frequently occur that are 

 rich in decaying organic material. An analysis reveals 

 that the bottom mud of these ponds and the water layers 

 in immediate contact with it are frequently oxygen-free 

 and contain hydrogen sulfide (the *'Faulschlamm" of 

 Lauterborn, 1908, 1916 and of Wetzel, 1928). The 

 results of a study of one such habitat are presented in 

 Table 2. The prevalence of anaerobic conditions is here 

 largely caused by micro-organisms which develop in the 

 decaying organic matter and which consume oxygen 

 faster than it can be replaced through diffusion from the 



