Re: Forms of nitrogen in the aquarium

On Tuesday, May 28 Christopher L. Weeks <c576653 at cclabs_missouri.edu> wrote:

>Subject: Forms of Nitrogen in the aquarium
>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?
I can't think of very many animals that would produce urea in an aquatic
environment.  Mammals and sharks produce it.  Birds and reptiles and many
insects produce uric acid which suits them even better to arid environments
because uric acid crystallizes out at low concentrations and this allows
the animal to remove water from its urine without the urine becomming
concentrated.  Freshwater fish and amphibians mostly produce ammonia.

The studies I mentioned didn't use urea, but I added some urea to several
of my plant tanks a year or two ago and saw a rapid growth response by the
plants. I got about the same amount of growth from the addition that I
would expect if I had added the same molar concentration of nitrate. (just
an empirical observation; I didn't make any measurments.)  I was interested
to see that my ammonia test kit did not indicate any ammonia after the urea
was added.   Urea is a relatively cheap source of nitrogen, and when plants
use it, there aren't any anions or cations left over to change the pH.
Since plants seem to be able to take up urea quite readily, I wouldn't
think that in a normal planted aquarium there would be only traces of urea
present, even if there was some animal in the tank that produced it.

By the way, I got the urea from a bottle on the shelf of our chemical
stockroom, not from where you might be thinking.  I am pretty big on DIY,
but I already tried that when I was 15 years old, and it almost killed a
test male guppy.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
In cool, humid, Mississippi where we finally got some rain!