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Water chemistry in tanks vs rivers

> Date: Sat, 7 Mar 1998 06:59:04 +1000
> From: David Aiken <d.aiken at eis_net.au>
> Plants and algae grow when there are enough of *all* the necessary
> nutrients available. If one nutrient is not available in sufficient
> quantity, growth slows or stops.

Yup, I've got that.  I guess I just have trouble thinking that there was 
excess phosphate available in this river.  I have heard before concern 
about high nitrate levels in natural bodies of water.  Is it common for 
phosphate (or some other source of phosphorus) to be plentiful in these 
water bodies?

> Now, the big difference between streams and aquariums. A plant in a
> stream is bathed in a constantly changing flow of water. It doesn't
> matter that nutrient levels are lower than we have in an aquarium
> provided the water keeps flowing, bringing a fresh supply of nutrients
> every second. In a tank there is a fixed and limited supply of water with
> no new supply of nutrients except those added by fish waste and the
> aquarist. Assuming nothing is being added, a plant in a stream which came
> into contact with 1,000 gallons of water a day would have the same
> nutrient exposure as a plant in a 10 gallon aquarium when the nutrient
> levels were 1% of the levels in the aquarium (basically because it's
> exposed to 100 times the water as the plant in the aquarium). Others have
> already made this observation in response to the question that started
> this thread but I hope that putting it in numerical terms like this might
> help anyone who hasn't grasped the point to understand it.
> That is also the reason why a 10ppm nitrogen level in a river has an
> astronomically greater impact than a 10ppm nitrogen level in an aquarium.

As you say, others have maed this point before, and at first I accepted it 
as sounding logical.  After some thought though it just doesn't make sense 
to me.

I can see how *maintaining* small concentrations in an aquarium would be 
very difficult due to the consumption of that plants in a small amount of 
time being a higher proportion of the total amount of that nutrient in the 
water, but if one *does* maintain a given concentration then I really don't 
see what difference the total water volume makes.

If a plant in my tank, and another in the river both have 10ppm of nitrate 
in the water that they are touching, and if both are in sufficient current 
that new, 10 ppm water is alays flowing over them, then why should it 
matter if there is another billion gallons upstream or not?

The very act of seeking sets something in motion to meet us;
something in the universe, or in the unconscious responds as if
to an invitation.  - Jean Shinoda Bolen