Re:Bubbling plants

     Long ago in one of my marine science classes, the lab instructor 
     demonstrated the carbonate-bicarbonate buffering system of seawater by 
     placing a pH probe in a container of sea water (pH 8.2) then bubbling 
     nitrogen gas into the water.  This, he explained, would drive off the 
     CO2 from the water and the carbonate-bicarbonate equilibrium would 
     shift, causing a pH change.  (Nitrogen gas is inert and will not 
     affect the pH by itself).
     After a few minutes of nitrogen bubbling, the pH changed 
     dramatically--it shot up to around 10 (as I recall--it's fuzzy), and 
     then once the nitrogen was turned off and regular air was bubbled 
     through, the pH dropped back down to 8.2.  (8.2 is the normal pH of 
     sea water).  The nitrogen drove off all the O2, as well.
     Doesn't this empirically demonstrate that an excess of one gas can 
     drive off the others?  Or is it just that the sea water was exposed to 
     nothing but nitrogen (I'm sure there was a layer of nitrogen gas over 
     the surface of the sea water, as well) and it reached a new 
     equilibrium--100% N2, 0% CO2 and 0% 02?  If this is the case, then 
     excess 02 (or CO2) in our aquariums would probably NOT displace other 
     gases, as they are not in equilibrium with the atmosphere.  BTW, I'm a 
     biologist, not a chemist.