Chapter XVIII 



MICROBIOLOGY OF INLAND WATERS 



Frequent reference has been made to conditions in inland seas, lakes, 

 and limans in the preceding chapters. The general relationships of organ- 

 isms to each other and to the environment are much the same in inland 

 bodies of water as in the oceans, although there are certain qualitative and 

 quantitative differences. The latter are probably no greater in magni- 

 tude, however, than the differences which exist between different parts 

 of the ocean. Though each environment may have unique features, fun- 

 damental observations of conditions in one body of water often help to 

 explain conditions in another. A few of the outstanding microbiological 

 features of certain unique bodies of inland water are outlined on the fol- 

 lowing pages. A key to the periodical literature is also given. 



The Black Sea: — Peculiar hydrographic conditions, coupled with 

 microbiological activities, render nine-tenths of the Black Sea virtually 

 uninhabitable by any form of life except bacteria. Since the influx of 

 fresh water from precipitation and land drainage exceeds evaporation, the 

 density of the surface waters (salinity about i6°/oo) is sufficiently less than 

 that of bottom water (salinity up to 23°/oo) that there is little vertical 

 mixing. As a result, the oxygen content of the water below the photo- 

 synthetic zone is renewed only very slowly. 



The oxygen which does penetrate the water is effectively consumed by 

 bacteria either directly or indirectly, so that there is little or no oxygen 

 present at depths exceeding 200 meters. The lower limit of animal life 

 appears to be from 130 to 190 meters. At greater depths, only anaerobic 

 bacteria are active. In the oxygen-poor waters immediately below the 

 photosynthetic zone, bacteria consume oxygen while oxidizing the organic 

 matter which is raining down from the productive surface layers. Sulfur 

 bacteria are also believed to be instrumental in the utilization of oxygen in 

 the zone wherein the overlying oxygenated water merges with deeper 

 H2S-containing water. The abiogenic oxidation of H2S likewise helps to 

 deplete the oxygen content of the water. 



The H2S results partly from the anaerobic decomposition of albumi- 

 nous compounds. More is believed to result from the bacterial reduction 

 of sulfate. According to Daniltchenko and Tschigirine (1926), sulfate 

 reduction is most intense on the bottom of the Black Sea where the con- 

 centration of H2S sometimes reaches 6000 ml./L., calculated at 760 mm. 

 pressure and 0° C. It was in the Black Sea where sulfate-reducing bac- 

 teria were first demonstrated by Zelinski (1893). Since that time sulfate 

 reducers have been observed in the Black Sea by numerous investigators. 

 ISSATCHENKO (1924) found vigorous sulfate reducers, presumably Desulfo- 

 vibrio desulfuricans or D. aestuarii, in all samples examined. Some of the 

 samples were collected from depths as great as 2,1 18 meters. The cultures 

 produced from 0.3 to 0.5 gm. of H2S per liter of media in the laboratory. 



IssATCHENKO (1929) asscrtcd that H2S-producing bacteria are respon- 

 sible for the formation of ferrous sulfide in the Black Sea. According to 



