188 Marine Microbiology 



mud, we added 'I'l CaSOr2 H.O + 0.05% Na.SO, 10 H.O + 0.05% 

 MgSOrT H2O. The brackish water had a saHnity of 4/'rr; the sea 

 water 3.5 per cent. Source of ILS was desulfuricatiou by desul- 

 furizers Hxing within the mud. 



Eh and pH measurements were made in situ during more 

 than one year. For pH we used the Argosonde of Dr. Ingold 

 GmbH, Frankfurt/Main, with glass electrode, and the pocket pH 

 meter t)'pe 54/RT of Wissenschaftl.-Technische Werkstaetten in 

 Weilheim/Oberbayern. For Eh, we have constructed a Pt-elec- 

 trode in a glass tube which could be stabbed into the sediment or 

 lowered into the water at different levels. The conducting con- 

 nection from the calomel electrode to the substrate was made by 

 a glass tube drawn out into a capillary and filled with KCl agar. 

 The pH meter was type MV 11 of Clamann and Granert, Dresden. 

 For every result, only measurements which could be reproduced 

 were evaluated. 



The development of the typical biocenosis was watched 

 through microscopic changes in the water and the sediment, by 

 microscopic observations and by isolation of microbes in enrich- 

 ment and pure culture. 



About four months after the beginning of the experi- 

 ments, at room temperature of about 18-20 C, the development 

 of color in the sulfureta became visible because of red and 

 green-sulphur microbes, Cyanophyceae, and sulfur-precipitation 

 which were the same under marine and limnic conditions. In 

 some of our aquaria, a pronounced horizonal stratification was 

 present in the water above the sapropelic sediment, in others it 

 was lacking. The specific conditions are not )'et known, but we 

 believe that small differences of temperature and thermic stream- 

 ings witliin the waterbody mav be of importance. In the first case, 

 a bacterial plate, 4-10 mm thick, was formed some cm above 

 the mud-surface (Fig. 1), composed mainly of Chloromicrobes, 

 sometimes also of purple-sulfur microbes. Within the plate, Eb 

 shifted up from low values below to about + 500 mV ( Fig. 2 ) . 

 In the mud, rH- values were 6.1-6.3, within the plate 10-22 and 

 about 10 cm above 25-32 with only small differences between 

 limnic and marine conditions (Table 1). 



^ Brackish water from a bav of the Baltic Sea near Greifswald, 



