Re: CO2 in nature

[Thomas Barr <tcbiii at earthlink_net>]

> With all the on going talk about CO2 supplementations in the home
> aquarium, I keep wondering how plants in lakes, rivers, streams, ponds
> etc. get their CO2.

There's plenty of water and few plants. Go look at most weed choked ponds
and lakes. Most have algae and are not what many would imagine they'd like
in their tank.
If you add loads of plants into a small box and add a good amount of light,
the CO2 is removed rapidly.
But a huge lake or a river where the volume is much larger, drops in the CO2
is less. Substrate and bacterial respiration also adds to the waters.
If the lake is very shallow with large surface area, then a good deal of the
CO2 can be exchanged with the surface and there's plenty of light etc and
also a productive bottom layer producing CO2 from decomposition.

Ground water such as springs will often have very high levels of CO2. Some
of the most idyllic plant places in nature have high CO2 and nutrients,
stable conditions while having low algae.
 
> I assume that aquatic plants wouldn't get as much CO2 in the "wild" as
> in the aquarium.

Depends on where. Some waters are rich in CO2 or are lotic (moving) waters
that are constantly being renewed.
 
> I also assume that most (or some) CO2 must come from groundwater.  So
> could plants in a aquarium get enough CO2 from daily water changes for
> normal growth found in nature?

In some systems. Many plants in nature and most of the one's we keep are
emergent and amphibious so CO2 is not an issue so much.

Some plants grow till the CO2 is out and then just sit there. They simply
grow slower. This is fine if they have enough CO2 not to die from lack of
carbon skeletons to make their metabolites.
Some plants are able to only get 4 hours of light a day, or some plants are
able to get enough CO2 for 3 hours a day etc. Both have the same problem of
getting enough light or CO2 to make it through.
So they simply shut down, wait and grow slow.

Thing is, folks see a plant sitting there and think it's fine even if it's
not growing actively or has any holes etc or other deficiency signs.

But a slower growing plant is a good place for algae to grow.
Some plants use HCO3(Egeria/Hornwort), a few C4(Hydrillia, Orcutt grass) and
one uses CAM(Isoetes-night time temporal CO2 uptake) to concentrate CO2
levels. But _all_ of these plants do better when CO2 gas/carbon source is
added.
 
> I have a ten gallon planted tank without CO2 addition and I notice O2
> bubbles on leaves after I change about 1/3 of the water.  Any thoughts?
> Sean Meister

The tap often has lots of CO2. It also is often colder than tank water.
When you warm waters that have gas dissolved in them, the gas becomes super
saturated and so does the tank if you do a water change. So O2 and CO2 both
are in excess after a water change generally, which is a good thing for tank
and plants. 

Adding CO2 gas all the time gives the same effect often.

What you have noticed is a good thing. Try measuring the tap before it
equilibrates and see if the CO2 is higher and the PO4, NO3 etc
Ask the water company for their measurements of these two also.

Regards, 
Tom Barr