Denitrification riddle

"Jimmy Chen" wrote in message ...
I understand (I believe) how DSB and plenums work. By creating an anoxic
zone where bacteria are forced to pull oxygen out of the nitrate molecule,
leaving inert nitrogen behind.

Plenum and DSB actually works in very different ways. The ideal behind the
water layer for plenum is to double the O2 zone by doubling the surface, but
in turn limits the available O2-lacking zone. DSB however, pushes for plenty
of O2-lacking zone, hence the depth.

Could you please explain this "double the 02 zone" little better?
I do not get it...

What baffles me is if the oxygen cant get the anoxic zone, how in blazes
does the water and nitrate get there in order to be denitrified? Or is it
that the anoxic zone incubates this sort of bacteria, which then finds its
way into the water column, but still goes for the nitrate rather than
oxygen as thats all it knows?

This post by Rob may help ...
http://www.escribe.com/pets/reefkeepers/m13461.html

Interesting:
"There is a basic misconception that the lack of measurable oxygen
means that there are no infauna present. That is simply not true. In
detailed studies of the relative meiofaunal density with depth and oxygen
concentration show that fauna are typically found well below the depth of 0
oxygen concentration, although the relative abundance falls quickly after
the oxygen concentration becomes low."

And wow! In the next part he is saying about what I have imagined:

"Since very few animals can live in anoxic sand, burrows to the bottom of the
substrate are prima facie evidence that we don't have an anoxic layer in the
lower portion of the sand.

That is simply not true -- many organisms are incapable of living in the
anoxic layer but make extensive use of the nutrients being regenerated in
those zones. Some species (e.g., Arenicola) gain almost all of their
nutritional requirements by ingestion sulfide-rich sediments from anoxic
zones and subsequently expel the reduced deep sediments onto the surface
around their burrow in the form of fecal castings. These worms make short
trips into the inhospitable reduced layers to feed and then return to oxic
zones for respiration and digestion of the bio-organic layers on the
reduced sediments. "

Who is Rob Toonen ? I should be probably ashamed now knowing who is he... :-)
He definitely sounds like some good college professor :-)