It will hopefully be understood when related to the Generic sand system. Ain't going to be easy with some of the evangelists. They are, for the most part, a side loop to the bacterial metabolisms. Derived from this, on an elemental scale, a very important relationship is the carbon and nitrogen cycles. The role of sulfur surprisingly plays a crucial and interesting part in the flux of carbon to and from these cycles.
Carbon dioxide is a certain source, but, bacterial sulfate reduction is a key.
Bacterial sulfate reduction with the release of the end product hydrogen sulfide becomes a significant process in organic degradation at low redox potential. As a result, its contribution to total anaerobic minerlization can be considerable. Since two moles of organic carbon are respired for every mole of sulfate reduced, sulfate reduction consumes large amounts of carbon. This is by far the major sink for organic carbon. Interestingly, denitrification appears to be a very minor sink or carbon.