Forms of Nitrogen in the aquarium

On Tue, 28 May 1996, krombhol at felix_TECLink.Net (Paul Krombholz) says:

> The energy necessary to reduce the absorbed nitrate to ammonium is also not
> a significant amount in the plant's overall energy budget.  Whether the
> available nitrogen is ammonium, nitrite, nitrate, or urea, algae and
> vascular aquatic plants can take it up efficiently.

What provides urea in an aquatic environment.  I was under the impression 
that urea was primarily produced by organisms in arid environments.  Am 
I remembering something wrong?  Was urea mentioned merely because it was 
used in the studies referenced?  Does a small concentration of urea 
result all the time at equilibrium?

just curious,

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Christopher L. Weeks             |             Training Specialist |
                                 | University of Missouri-Columbia |
http://www.missouri.edu/~ccweeks |                Campus Computing |
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