re: NO3 losses

["roger" <roger at spinn_net>]

I feel like I'm following a thread that few people really
care
about, so I'll be brief.

Tom wrote:

> Consider when folks raise their lighting levels up.
> They change nothing in their gravel/filtration etc.

> Before, they never had to add NO3.

> Now with increased lighting and hence increased plant
growth
> suddenly the
> plants are taking up much more NO3.

> The substrate is relatively similar in both cases.
> So if denitrifying bacteria were doing a significant
amount of
> NO3 removal
> in a planted tank, why was this not the case at lower
light?

Increasing plant growth rate and seeing a drop in NO3 levels
in
the tank says doesn't say much about the presence, absence
or
relative importance of denitrification.

Consider this:

With low light setup the aquarist adds 6 mg/l per week of
NO3
through fish feeding.  Plants take 2 mg/l per week and
denitrifying bacteria take 2 mg/l per week.  That leaves 2
mg/l
per week of NO3 that builds up.  Bacterial consumption is
50%
of the total.

The aquarist increases the light and CO2 and the plant
growth
triples.  Now the bacteria are taking 2 mg/l per week and
the
plants are taking 6 mg/l per week for a total of 8 mg/l per
week of NO3 loss.  If the aquarist is still only adding 6
mg/l
per week then the nitrate level drops.  Eventually the
aquarist
has to add NO3 to make up the difference or nitrogen
deficiency
will set in.  Bacterial consumption hasn't changed;
denitrification is still 25% of the total NO3 loss.


Roger Miller