ZoBell — 108 — Marine Microbiology 



The foregoing data on the rate of oxygen consumption by aquatic 

 bacteria should suffice to indicate that the abundant bacterial fiora of 

 bottom deposits may play an important role in depleting dissolved oxygen 

 in lake bottoms. Not only is all of the oxygen consumed in most bottom 

 deposits faster than it can be replaced by diffusion from the atmosphere or 

 photosynthetic processes, but there is generally an oxygen deficit in bot- 

 tom deposits as shown by the spontaneous oxygen-absorbing capacity (see 

 Table XXX). ZoBell and Feltham (1942) estimated that there are 

 enough bacteria in the topmost i.o cm. of each square meter of Mission 

 Bay mud to consume from 8.4 to 25.2 mgm. of oxygen per day at 20° C. 



Bacteria in various lake deposits examined by Miyadi (1934) con- 

 sumed from 0.42 to 1.26 mgm. of oxygen per gram of mud in 60 hours at 

 15° C. In general, muds having the highest organic-carbon content and 

 those under water containing the least dissolved oxygen exhibited the 

 largest biochemical oxygen demand. Waksman and Hotchkiss (1938) 

 likewise found the oxygen consuming capacity of bottom deposits to be a 

 function of the organic content. The biochemical oxygen demand of bot- 

 tom deposits from the Woods Hole region was found to be from 0.08 to 

 2.83 mgm. of oxygen per gram in 14 days at 25° C. 



KusNETZOW and Karzinkin (1931) attributed the zones of dimin- 

 ished oxygen tension in Lake Glubokoje to bacterial activity, after ob- 

 serving that the disappearance of oxygen corresponded with large bac- 

 terial populations. This conclusion has been substantiated by more 

 recent observations of Kusnetzow (193 56) who found that heterotrophic 

 bacteria are the chief agents responsible for the depletion of oxygen from 

 lake bottoms. Methane- and hydrogen-oxidizing bacteria were regarded 

 by Kusnetzow as also being very important. 



Gases in bottom deposits : — Because of the relatively large bacterial 

 populations and high content of organic matter in bottom deposits, it is 

 primarily in or immediately above bottom deposits that the most oxygen 

 is consumed. Likewise it is primarily in or near bottom deposits that 

 other gases are produced or transformed by bacteria. 



Under anaerobic conditions appreciable quantities of methane and 

 hydrogen may be produced from the decomposition of organic matter. 

 According to Waksman (1941a), the anaerobic oxidation of organic mat- 

 ter by aquatic bacteria results in the formation of methane, hydrogen, 

 H2S, and organic acids besides CO2, phosphate, and ammonia, whereas 

 under aerobic conditions organic matter is decomposed with the formation 

 of CO2, phosphate, ammonia, and sulfate. 



The gaseous products resulting from the anaerobic decomposition of 

 lake muds observed by Allgeier et al. (1932) consisted of from 65 to 85 

 per cent methane, 3 to 30 per cent CO2, i to 3 per cent H2 and from 3 to 22 

 per cent N2. The catabolic H2S had probably combined with mineral 

 constituents to give metallic sulfides. 



DtJGGELi (1936) reported that the gas produced in deep muds from 

 Red Lake in Switzerland consisted largely of methane and N2 with lesser 

 quantities of H2, CO2, and H2S. 



Very little work has been done on methane production in marine muds 

 but there is voluminous literature on the factors which influence the bac- 

 terial production of methane in industrial wastes, soil, and under labor- 

 atory conditions (Barker, 1936a, b; Buswell, 1936). The general oc- 

 currence of methane in natural gas which is usually associated with an- 



