Biogenic Decalcification??
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Biogenic Decalcification??

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Biogenic Decalcification??
Old 03-30-2011, 02:17 PM   #1
 
Biogenic Decalcification??

Has anyone heard of this? Does anyone know anything about it?
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Old 03-30-2011, 02:48 PM   #2
 
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Reportedly, some plants deplete calcium carbonate in the water to meet their carbon needs (= biogenic decalcification), so the water has less buffering capacity, leading to pH fluctuations.

I'm not certain this is accurate(?), hopefully someone who knows more aquatic plant physiology and water chemistry will respond to this thread!
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Old 03-30-2011, 02:56 PM   #3
 
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Originally Posted by DKRST View Post
Reportedly, some plants deplete calcium carbonate in the water to meet their carbon needs (= biogenic decalcification), so the water has less buffering capacity, leading to pH fluctuations.

I'm not certain this is accurate(?), hopefully someone who knows more aquatic plant physiology and water chemistry will respond to this thread!
That's part of it. The other thing that happens is that the plants that do this "discharge" limescale in the process so they get covered in a white kind of dusty film.

I have it happening in my tank now and not sure how to combat it. I've read that they need extra carbon/CO2 to stop doing it. Not sure and that's why I'm looking for answers.

BYRON... Where are you????
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Old 03-31-2011, 11:29 AM   #4
 
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In that other thread I suggested this white deposit was due to the minerals in the water, and I believe I mentioned having read about it somewhere but couldn't lay my hands on it. Now that the proper term has been mentioned, I found it. Diana Walstad mentions biogenic decalcification in her book Ecology of the Planted Aquarium.

First: bicarbonates, or perhaps more scientifically correct as hydrogen carbonate (HCO3-), is an intermediate form of carbonic acid. Bicarbonates are higher in hard alkaline water. Plants can obtain carbon from CO2 (carbon dioxide) or bicarbonates, though they often have a preference. Most of those in aquaria are soft water plants that prefer CO2 because it is less work for the plant to extract the carbon. Plants such as Vallisneria, Egeria, Elodea and Myriophyllum (to name only a few) which naturally occur in hard water are better at using bicarbonates. Some, such as the mosses, the pygmy chain sword, Ceratopteris, Ludwigia, and several others cannot use bicarbonates at all. [There is a list if you're interested in Walstad, p. 97, with the reference to the scientific study that determined this.]

Interestingly, many of the amphibious plants [the bog or marsh plants like Echinodorus, Cryptocoryne, etc] cannot use bicarbonates well, and it is hypothesized that they use the aerial strategy (emersed leaves) to supplement their carbon uptake.

Plants use bicarbonates much less effectively than algae. This is probably part of the reason that algae tends to be worse in hard water compared to soft, all else being equal.

Now with the background understood, I will cite directly from Walstad to define biogenic decalcification since this is highly technical and beyond my comprehension:
Some bicarbonate users polarize their leaves during bicarbonate uptake. Polarized bicarbonate uptake has been described for Potamogeton lucens. The plant excretes H= (acid) on the leaf's underside to generate a pH of about 6. The acidity converts bicarbonate to CO2, which diffuses into the leaf to be used for photosynthesis. In order for the plant to maintain its internal charge balance, H= is taken up by the plant on the leaf surface resulting in a high, localized pH (about 10) and a high hydroxide (OH-) concentration.

The OH- combines with calcium bicarbonate [Ca(HCO3)2] in the water causing the precipitation of calcium carbonate (CaCO3) on the top of the leaf. In hard, alkaline water, this reaction, which is called "biogenic decalcification," may be so great that crusts of precipitated CaCO3 may weigh more than the underlying plant. I have seen CaCO3 deposited as small white "pimples" on the leaves of Egeria densa and Ludwigia repens when they were grown in hardwater under intense light.

Some aquatic plants (e.g., Myriophyllum spicaytum and Vallisneria spiralis) that use bicarbonates do not polarize their leaves during bicarbonate uptake.
There we are.

Byron.
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Old 03-31-2011, 11:50 AM   #5
 
Thanks for the info Byron. It sounds exactly like what is happening in my tank. My Val. is doing it the worst and yes it's only on the one side - which I thought was weird. So far my pH hasn't fluctuated at all. It's still at 8. I'm assuming that's because my water is so hard that there's plenty of buffer there to offset what's happening. I'm going to add some more CO2 this weekend and see if that helps. From what you've said/quoted and from what I've read elsewhere, if I give them enough CO2 they won't have to use the bicarbonates in the water to convert to CO2. We'll see how it goes. If you have any other suggestions I'd love to hear them. :)
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Old 03-31-2011, 12:18 PM   #6
 
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Originally Posted by desico View Post
Thanks for the info Byron. It sounds exactly like what is happening in my tank. My Val. is doing it the worst and yes it's only on the one side - which I thought was weird. So far my pH hasn't fluctuated at all. It's still at 8. I'm assuming that's because my water is so hard that there's plenty of buffer there to offset what's happening. I'm going to add some more CO2 this weekend and see if that helps. From what you've said/quoted and from what I've read elsewhere, if I give them enough CO2 they won't have to use the bicarbonates in the water to convert to CO2. We'll see how it goes. If you have any other suggestions I'd love to hear them. :)
Nothing to add at the moment. As I mentioned, I've never had this issue, with my very soft water out of the tap. If I come across something, I'll try to remember to mention it. Keep us posted.

Byron.
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Old 04-01-2011, 02:12 AM   #7
 
If anyone is interested in understanding the chemistry I might be able to help, I think I understand what you quoted by Walstead Byron, but I'd like to work it out on paper, but not unless there is interest in it. I may also be able to estimate its potential effect on your tank Desico. I'm only learning the chemistry now, but I think I know the correct equations to do so.
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Old 04-01-2011, 01:02 PM   #8
 
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Originally Posted by Aqua Jon View Post
If anyone is interested in understanding the chemistry I might be able to help, I think I understand what you quoted by Walstead Byron, but I'd like to work it out on paper, but not unless there is interest in it. I may also be able to estimate its potential effect on your tank Desico. I'm only learning the chemistry now, but I think I know the correct equations to do so.
If you want the references and don't have the Walstad book, I can provide them. Just ask. She cites several studies within that brief passage I cited. B.
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Old 04-02-2011, 12:22 PM   #9
 
I do not have the book, but I've just added it to my list of books to buy ;) Sounds like a great resource.
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