Chapter VI 



91 



Bottom Deposits 



water interface is comparable with that of the underlying mud. The bac- 

 terial content of the water decreases sharply above this mud-water transi- 

 tional zone. 



In bottom deposits of fresh-water lakes, Henrici add McCoy (1938) 

 found from a few thousand to 500,000,000 bacteria per ml. Direct counts 

 were even higher. Rubentschik et al. (1936) demonstrated 3 billion 

 bacteria per gram of mud from limans near Odessa. Issatchenko (1937) 

 found a maximum of 1 1 billion bacteria per gram of mud from the Kara 

 Sea. These Russian workers employed the direct microscopic technic. 

 Most of the bacteria were adsorbed upon sediment particles, a condition 

 which tends to make plate counts lower than direct microscopic counts 

 because large numbers of bacteria may be adsorbed to a single particle 

 which may give rise to only one colony on a plate. The tendency for bac- 

 teria to be adsorbed by marine bottom deposits has been emphasized by 

 the studies of Waksman and Vartiovaara (1938). 



Other general observations on the bacterial content of bottom depos- 

 its have been made by Williams and McCoy (1935), Duggeli (1936), 

 BuTKEViCH (1938), Hartulari (1939), and Elazari-Volcani (1943). 



Vertical distribution of bacteria in mud : — Wherever profile series have 

 been examined, a progressive decrease in the bacterial population of bot- 

 tom deposits from the surface downward has been observed (Lloyd, 

 1931(2; Reuszer, 1933; ZoBell and Anderson, 19366; ZoBell and 

 Feltham, 1942). The decrease is most rapid in the topmost few centi- 

 meters of sediment, below which the decrease is more gradual or even 

 sporadic. This is illustrated by the data in Table XXVI. 



Table XXVI. — Number of bacteria per gram of mud (wet basis) in diferent core strata 

 (from ZoBell, ig42b): — 



Significant numbers of viable bacteria have been found in marine sedi- 

 ments at all depths sampled. Waksman ei al. (1933c) reported the occur- 

 rence of bacteria down to a depth of 90 cm. Rittenberg (1940) demon- 

 strated the presence of numerous bacteria throughout the length of 

 several cores, some of which were longer than 350 cm. The numbers of 

 bacteria found varied greatly from core to core. The abundance of bac- 

 teria decreased from the surface dowTiward, although in certain sediments, 

 zones or strata of high bacterial population were found beneath strata of 



