re: Homework

>Since it is not likely that these gentle motions inhibit photosynthesis,
>there must be some other explanation.  I have my theory, but I would like
>to hear yours first.

Here's my guess:
Without a current, water forms a thin "boundary layer" or film on the 
surface of plant leaves.
This boundary layer becomes saturated with O2 due to the continual 02 
production by photosynthesis. At some point, the O2 cannot go into solution 
anymore (in the layer) and escapes as a bubble. Gentle motion, as described 
by Paul, should destroy this boundary layer and equalize its O2 
concentration with that of the rest of aquarium. Assuming the rest of the 
water is not saturated, the bubbles stop.

This boundary layer is also the reason why some people suggest a constant 
water current in a planted tank: without a current to break up the boundary 
layer, it become deficient in nutrients and growth is slowed.

Since Paul's plant produces O2 DESPITE the nutrient deficiencies in the 
boundary layer, I assume that the tank has a soil substrate to provide all 
nutrients. Paul?

Mike Eckardt
in Waterloo, where spring is (but shouldn't be) in the air