Re: Bubbles During Water Changes

To: aquatic-plants at actwin_com
Subject: Re: Bubbles During Water Changes
From: mark.fisher at tpwd_state.tx.us
Date: Wed, 19 Feb 97 12:53:14 cst

     >You would need more than 3-4 ppm of CO2 to keep your plants bubbling 
     >for 2-3 days.  3-4 ppm is very low.  I got a 7ppm reading before I 
     >started adding CO2 and my plants didn't do any bubbling of the kind.  
     >Only after a water change did they do that. 
     
     I don't understand your point.  If my plants pearled at 3-4 ppm CO2 
     and yours didn't at 7 ppm CO2, then I would have to say photosynthesis 
     was limited by something other than CO2 in your tank.
     
     I, too, have noticed the effect of water circulation/plant agitation 
     on bubble production, and I believe Paul is impishly trying to get us 
     to discuss the effect of agitation on the PRANDTL BOUNDARY LAYER and 
     O2 saturation, that rascal ;-)
     
     Basically, the Prandtl boundary layer is a layer of still water 
     surrounding a plant leaf.  On an unagitated leaf, this layer is 
     relatively thick, and during photosynthesis this layer can become 
     saturated with O2, even if the surrounding tank water is unsaturated.  
     O2 produced by the leaf is not completely dissolved in the Prandtl 
     layer, and forms a bubble.
     
     On an agitated leaf, the layer is much thinner, almost nonexistent.  
     Unsaturated aquarium water is in much closer contact with the plant 
     leaf, and O2 produced by the leaf can dissolve into the water column 
     before it can form a bubble.
     
     I suppose we could also see an O2 bubble getting smaller as it rises 
     to the surface and dissolves in an unsaturated aquarium, but they are 
     too fast for me, and besides, my ruler is too big.  This would be a 
     good homework assignment for Paul :-)
     
     How about it?  A or F?