O2 pearling

Subject: "string of pearl" bubbles really O2?
> Just out of curiosity, has anybody ever really checked to see if
> rising from underwater plants are really O2 - or just CO2?  

Well, I can't think of a way to catch the bubbles and then test 
what they are, but I _have_ tested O2 levels during periods that 
the plants are pearling and when they are not.  I have also tested 
O2 levels where plants pearl and those where they do not.  

The highest O2 level I've ever found in a tank without pearling 
(and in tanks without CO2 injection) is just about saturation.  In 
tanks where pearling is taking place, the O2 level is invariably 
above saturation.

> 1. I've never noticed these bubbles in a plant tank without CO2 
> no matter how intense the light.

In a tank with very bright light and without CO2 injection, you 
often _do_ see pearling, but only for a very short period of time, 
when the lights first come on.  Then the plants use up the 
available CO2 in the water, and can no longer efficiently 
photosynthesize... no matter _how_ much light you shine on them.
> 2. The way streams of bubbles seem to be emitted from a single p
> leaf sure seems unlikely.

Pearling is a sign of a break in the plant tissue.  You will not 
see streams of bubbles coming up from any undamaged plant surface. 
 To find O2 bubbles on undamaged leaves look carefully on the 
undersides of broad leafed plants. _These_ bubbles are often 
evident even in tanks  with O2 levels right around saturation, so 
this phenomenon can often be observed even in tanks without CO2 
> 3.  It just plain LOOKS like the bubbles that rise from the bott
> glass of seltzer water!

Any colorless gas  rising through water will look similar.  The 
reason CO2 rises from seltzer water is the same reason O2 escapes 
from the aquarium... The water is supersaturated with that 
particular gas.

Karen Randall
Aquatic Gardeners Assoc.
Boston, MA