Dr Reddy's work on uptake efficies for nutrient removal by aquatic plants

[Tom Barr]

http://wetlands.ifas.ufl.edu/publications/PDF-articles/96.pdf

this should be accessible for folks.

Regards,

Tom Barr

 

[ceg4048]

Hi Tom,
When I first saw that this article was only 4 pages I sighed in relief because I reckoned I would only have to take half as much aspirin as I normally do after reading a typical Reddy journal. The more I read and re-read though the more confused I got so I was hoping you could clarify a few things.

I realize the test was performed within the context of possible large scale industrial application of sewage treatment and not in terms of aquariums but I noted that the comparison was between some floating plants, which I imagine have better access to CO2 at the surface, with our E. densa and Hydrocotle submerged in which I guess was a non-CO2 supplemented tank, possibly in bright sunlight.

The other thing I felt was "unfair" was that both SAMs were left alone without a substrate, but I understand that he wanted to eliminate any sediment effects.

The baffling thing though is how to explain the wildly different Summer curves of the two SAMs. I'm not sure how to interpret that at all. If most of the NH4 reduction was being done by bacteria in both cases shouldn't their NH4 curves be the same? How does this show that E. densa was better at NH4 uptake than Hydrocotyle at summer temperatures? If a plant removes NH4 doesn't that leave less for the bacteria to nitrify? Shouldn't that be reflected in an NO3 curve as shown by the hydrocotyle?

On page 3 paragraph 2 he concludes that E. densa is good at NH4 removal but poor at overall N removal - but I can't see how he reached that conclusion; if the rise in NO3 was so high doesn't that mean it was the bacteria consuming the NH4, not so much the E. densa?

Wouldn't it have been standard practice to do a "control" where no plants were in a tank to see the curves of that tank to determine the effect of the bacteria alone?

Of course, if he says E. densa is good at NH4 removal then I have to accept it but I'm having trouble believing it, because the data seems very conflicting. Could you help clarify?

Cheers,

 

[Tom Barr]

I realize the test was performed within the context of possible large scale industrial application of sewage treatment and not in terms of aquariums but I noted that the comparison was between some floating plants, which I imagine have better access to CO2 at the surface, with our E. densa and Hydrocotle submerged in which I guess was a non-CO2 supplemented tank, possibly in bright sunlight.

True, these are issues and uncertainties.
We must be careful in applying things, but if you assuem that CO2 is non limiting..........and plenty of light(recall 600 micrmols or there abouts is a max range) etc..........then you can scale things down.

The other thing I felt was "unfair" was that both SAMs were left alone without a substrate, but I understand that he wanted to eliminate any sediment effects.

The baffling thing though is how to explain the wildly different Summer curves of the two SAMs. I'm not sure how to interpret that at all. If most of the NH4 reduction was being done by bacteria in both cases shouldn't their NH4 curves be the same? How does this show that E. densa was better at NH4 uptake than Hydrocotyle at summer temperatures? If a plant removes NH4 doesn't that leave less for the bacteria to nitrify? Shouldn't that be reflected in an NO3 curve as shown by the hydrocotyle?

On page 3 paragraph 2 he concludes that E. densa is good at NH4 removal but poor at overall N removal - but I can't see how he reached that conclusion; if the rise in NO3 was so high doesn't that mean it was the bacteria consuming the NH4, not so much the E. densa?

Wouldn't it have been standard practice to do a "control" where no plants were in a tank to see the curves of that tank to determine the effect of the bacteria alone?

Of course, if he says E. densa is good at NH4 removal then I have to accept it but I'm having trouble believing it, because the data seems very conflicting. Could you help clarify?

Cheers,

Removing the plants will influence the bacteria, so you cannot do this easily.
They are linked and correlated.

No, the curves would not be the same.
The curve represents a rate.
The rates are different obviously summer vs winter.

The other thing is the NO3 build up. While NH4 is rapidly oxidized, NO3 is not, it's anoxically reduced.
So the result from adding 12 ppm of NH4 is a lot of NO3.
This is due to the bacteria, not plant uptake.

Some plant uptake does take place, but not much according to this.

There's only one submersed plant here, Egeria. Pennywort is a floater.
And like is the case here in CA, it grows well in cooler temps.

The Hyacinth curve is very different summer/winter, but the Egeria is pretty much the same.

So the Hyacinth removes more NO3 and NH4 over all, but only in the warm summer, in the winter, having the diversity, Egeria and Penny wort will give consistent removal of NH4/NO3 but less NO3 overall in the winter.

NH4 is easy to convert.
Removal of NO3 is another matter.

Still, you can see that at high levels of NH4, bacteria are doing most of the work.
Not the plants so much unless it's Hyacinth.

Yes, I see your point about the removal by Egeria vs the results about NH4.
It suggests the opposite.

However, if you consider the totals, how much NO3 builds up?
Start at 12ppm.

It goes up to 18-19ppm.
So NO3 was about 6-7ppm produced.

Now how about the original 12ppm of NH4?

So 12ppm - 7ppm of NH4= 5-6ppm of NH4 removal in about 4-5 days.
The other plants take up both NO3/NH4.

Something to ponder when folks claim that plants take up just NH4 or prefer it.
The above suggest that all the other plants will take up both and do so rather fast.

As far as the raw data, adding 12 ppm of NH4 is hardly realitistic in our aquariums.
When you add very low levels of NH4, that's another matter and you can see from the bacterial actions, that 0.2ppm of NH4 will be gone in a matter of a couple of hours in an aquarium.

However, notice how the curves go flat as they near zero for NH4, but not so much for NO3. This is more applicable to our tanks and suggest that at normal NH4 levels in our tanks, that NO3, not NH4 is preferred.

At least if you used this study to make the argument.

Regards,
Tom Barr

 

[paludarium]

When you add very low levels of NH4, that's another matter and you can see from the bacterial actions, that 0.2ppm of NH4 will be gone in a matter of a couple of hours in an aquarium.

Hi Tom,

So the aquatic plants may not even have a chance to take up NH4 in the pressence of rapid nitrification, does it mean that daily dosage with 0.2ppm of NH4 is safe in our planted aquarium without algae issues?

BTW the dissolved O2 content of the water under large-leaf floating plants is low, so... removal of NO3 by the denitrification process cannnot be ruled out.

Regards,
Erich