substrate heating

I think the answer to te questio is probably going to be E.  all of the 
above.  I think that the main reason that substrate heating does any good at 
all is that it stimulates bacterial growth in the substrate.  Under natural 
conditions you would have a cycling of the microbiological "flora" within 
the mud, some populations grow and some crash.  I think that the substrate 
heating may favor some of the bacteria that are needed in the tank.  If you 
don't heat you will have the same results.  But if you heat, and then the 
heating goes out, then you may experience a population crash or at least a 
change in the eclogy of the substrate.  Micriobiological ecology is a very 
new field in trying to explain what is going on in the wild...if anyone else 
has any comments on this please feel free.

I am not biased...I am a microbiologist-John Davis in now freezing Texas