192 Marine Microbiology 



disappeared and the conditions of the water were again 

 anaerobic. 



Limnic Conditions (With/without Stirring) 



The ecological conditions were changed in the same manner; 

 pH was lowered and the zone of Eh shift was situated deeper 

 than before; with stirring, it was displaced about 5 mm below 

 the mud-surface. 



With stirring, the heavy metals settled very slowly as a 

 greenish-brown colloidal layer of basic copper carbonate and 

 iion hy dioxide, mixed with sulfides. After 25 days all the pre- 

 cipitated iron and copper-compounds had been reduced to a 

 thin, more solid but still water-containing layer of sulfides, and 

 the sulphuretum was restored. 



Without stirring, the heavy metals were precipitated at first 

 as a mixture of carbonates and hydroxides distributed in the 

 water above the bacterial plate. When the colloidal particles sank 

 down into the range of the bacterial plate, they were reduced 

 to sulfides and the bacterial plate settled nearly to the surface 

 of the sediment. 



In all the experiments with heavy metals, the amount of 

 H2S dissolved in water and the rate of release of H^S from the 

 sediment was not high enough to reduce at once the heavy 

 metals in solution to below toxic concentrations. Most of the 

 microbes living in the water died during the first days, but 

 but the biocenosis of the sediment had not been altered, and 

 from the microbial reservoir of the sediment, the restitution of the 

 sulphureta took place. 



SUMMARY 



The development of sulphureta has been studied under 

 marine and brackish ( nearly limnic ) conditions during two years 

 in model experiments. The wholly developed sulphureta are 

 characterized by a shifting of pH from weakly acid to weakly 

 alkaline values, and of Eh and rHj from rcductixc to oxidative 

 conditions in the direction from the sediment to the water level. 

 The shifting of rHs was influenced by bacterial plates and bv 

 stirring of the water. Addition of solutions of copper and iron- 



