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Re: anaerobic substrates


First Dr. Dave wrote:

> >>BAD THINGS that can happen;
> >>
>
> >

Then Steve Pushak wrote:

> >I'd like to add one or two (dozen) points to Dave's excellent remarks.
> >All substrates are anaerobic (or more correctly anoxic, without
> >free oxygen) below about a half inch of the surface.
>
>

and then Tony Greer wrote:

> Aerobic substrate zones in static water bodies, particularly
> in the presence of plants -  and certainly moving water bodies -  can be
> extensive.

So I'm adding:

I suspect that most of us have substantially aerobic substrates.  The
plants themselves tend to oxygenate their root zones.  I doubt strongly
that burrowing snails could live long in a substrate free of oxygen and
their burrowing action (bioturbation) would tend to mix aerated water into
the substrate. And of course there are those of us using substrate
heating, UGF, RUGF and so on to promote at least some circulation in the
substrate -- discouraging anaerobic conditions.

However, a substrate that is predominantly aerobic may still contain zones
capable of supporting anaerobic bacteria.  I've read that obligate
anaerobic bacteria can be found within nearly "microscopic" flocs in fully
aerated sea water and I suspect that would happen in aquaria as well.
Anaerobic microenvironments will develop within pore spaces containing
labile organic material while adjacent pores still contain free oxygen.

So we can get the good points of anaerobic substrates (trace elements
availability, root hair development) and the good points of aerobic
substrates (hmmm... what ever those are) in the same substrate.  The
disadvantage to anaerobic conditions result from fairly extreme conditions
where anaerobic bacteria reduce sulfate and carbonate to sulfide and
methane, and those conditions probably won't be common in a substrate that
contains a mixture of aerobic and anaerobic microenvironments.

Of course, if your substrate contains enough labile organic material and
you don't provide for circulation or bioturbation in the substrate then
anaerobic conditions can prevail.  As I understand it, this might get so
bad that it exceeds the ability of some plants to keep their roots
supplied with oxygen, and the roots will die.

Incidentally, I've noticed filaments extending up from the substrate
around some of my Cryptocoryne wendtii that grow in fine gravel or sand.
Could these be something like cyprus knees -- a mechanism for the plant to
promote the oxygen supply to its roots?


Roger Miller

In Albuquerque, where fine homes are built of mud and straw.