Discussion 



The available evidence suggests that the formation of sulphide in Ain-ez-Zauia 

 and in the other three lakes examined was most probably due to bacterial reduction of 

 sulphate. Sulphate reduction may also have occurred in the springs supplying the 

 lakes. There are at least five processes by which this sulphide could be oxidised to 

 sulphur. 



(1) Atmospheric oxidation, which occurs in all sulphate- containing waters ex- 

 posed to air, was undoubtedly responsible for some of the sulphur formed in Ain- ez- 

 Zauia, but is too slow to account for the high sulphur yield. For example, Ain-umm- 

 el-Gelud produced hydrogen sulphide but formed very little sulphur though it was ex- 

 posed to atmospheric oxidation. 



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