# Uptake rates



## dennis (Mar 1, 2004)

From http://www.aquaticplantcentral.com/forumapc/showthread.php?t=12059&page=2 Quote:
Originally Posted by *plantbrain*
_ 
20-30ppm is a good target overall for NO3.
Try 20ppm a week, if things get to 40ppm(again, that assumes no uptake by plants all week long, I'd expect 7-20ppm uptake for a week), _

Some questions:
So 20mg/l would be the max uptake of a fully planted aquarium running under non-limiting conditions?
How much impact does plant mass have on this? Also, is there a good way to measure plant mass in an aquarium?
Would this be a constant uptake rate(given non-limiting conditions) or would the rate taper off some as the plants filled their reserve stores?
My questions have nothing to do with fertilization or beating algae Nor am I interested in finding the sweet spot, avoiding water changes, etc.

I am curious from a purely physiological point of view the uptake rates of nutrients. I know that will be difficult to answer as plant mass and species will play a big role (I assume). I am also not considering given conditions on a given day as I am assuming an established tank with no limiting conditions. A tank that has had a stable supply of excess nutrients, all nutrients including light and CO2, for 2-3 weeks should show a consistent uptake rate regarding either a daily or weekly base.

What is a good way of describing how planted a tank is? Estimated volume? Area of substrate covered? Any ideas?


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## dennis (Mar 1, 2004)

http://www.siu.edu/orda/igc/proceedings/01/larson.pdf

Experiments conducted by growing plants with high levels of NO3 present in a hydroponics solution tested the uptake rates of several terrestrial plants and Ceratophyllum demersum. It was found tha the C demersum had an average uptake of 2ppm NO3 per day/per gram of plant mass. I don't know if this is dry weight though but I assume it must be.

Back to Google.


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## Laith (Sep 4, 2004)

Very interesting paper...

One of the figures given is that hornwort reduced the Nitrate ppm from 350 to 75 in nine days. That's 30ppm per day! They don't mention what the mass of hornwort was but using their 2ppm/day/gram it must have been 15g of dry weight (I have problems visualizing how big a mass of plant this is, wet, as I don't have a clue to the usual difference between wet and dry weight).

These uptake rates are very high. I know that hornwort is known as a Nitrate hog but let's assume that other aquatic plants average let's say 25% of the hornwort uptake. That means that the uptake rate would be 0.5ppm per day per gram of plant.

Seems high doesn't it? I don't know what the average difference is between wet and dry weights but it seems that in a well planted 55g tank the NO3 uptake rate would be much higher than the 2-4mg/l/day figure that's commonly used.


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## plantbrain (Jan 23, 2004)

The highest rates I've measure in my tanks was 8ppm a day.
But....the more typical ranges are around 3-4ppm a day with good conditions.
Each plant has it's preferences, the generalization is just that, a generalization based on experience and testing as well.

We test and experiment to make generalizations about the world around us.
Then we don't have to test any more if it works well.



Regards, 
Tom Barr


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## almond (Mar 5, 2006)

hmm....i know ppm = parts per million.
But is there another simpler explanation? Im sorry if i sounded silly. i just want to have a better understanding.


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## Elkmor (Mar 30, 2005)

1ppm approx equal to 1mg/l


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