Hi everyone.
My first post here, and I hope you don't mind me contributing to this conversation. I'm very interested in this topic, having just started learning about the "el natural" (Walstad, though I'm sure she wasn't the first to make such aquariums) approach to planted tanks. So I was discussing this stuff in another forum, and Carissa linked to this interesting thread.
Quote:
Originally Posted by Tom Barr
Most every plant out there also prefers a ratio of NH4:NO3, not this either or business for optimal growth.
|
Do you happen to have some references for the studies about this ratio, or what might be the optimum such ratio, for aquatic plants? My understanding so far is that aquatic plants are quite different to terrestial plants in this regard, though I don't know enough about it to understand why the differences exist.
Quote:
Originally Posted by Tom Barr
If you look at the cited reference from Diana Walstad's book, the figure starts off at 2 ppm of NH4, pretty darn toxic.
Then once the level drops to 0.5 ppm of NH5 or close, the rate slows way down.
At that same time, the rate of NO3 uptake starts. and it never stops even when the NH4 is still present.
So under our typicaly aquarium conditions, that graph supports that NO3, not NH4 is actually preferred in Egeria. One plant also is hardly evidence that all 300 species prefer the same conditions as well.
Note, the experiment was also done in absence of any algae spores etc, sterile conditions............our tanks have algae spores and bacteria growing on all surfaces. When you factor such issues into the real world field test vs a controlled lab setting, the results often are no longer significant.
Poor interpretation of graphs can lead to poor conclusions also.
It depends on where on the graph you are discussing.
At one end of the graph, yes, there appears to be preferences for NH4 vs NO3.
However, at the other end of the graph, this relation is reversed.
And that is the end that applies to us and aquariums.
Most research is this way, you have things change through time, space and concentrations etc. You need to be able to apply the research you read and support the argument that you make.
Tom Barr
|
Agreed that data must be interpreted correctly, or at the very least sensibly, to give a useful result. But I suggest respectfully that you might need to check that graph again. I've just been staring at it (and at the original paper it was copied from - the joys of having access to a university library). And I draw a different conclusion to you.
I agree that a study of one species doesn't necessarily apply to all species, and I haven't checked the original references for the following figure in Walstad's book, which list 29 plants that prefer ammonia and 4 that prefer nitrate.
Note that both figures are in this article, as Figure 1 and Table 1 respectively:
Aqua Botanic - Plants and biological filtration
Anyway, the graph showing data for elodea nuttallii starts off with 2ppm of nitrate and ammonium, and the ammonia is reducing quite fast. The nitrate isn't reducing at all. This continues until the 16-hour mark, when the ammonium is at 0.5ppm and the nitrate still at 2ppm. At this point, the nitrate also starts reducing, but slightly slower than the ammonium is reducing. This continues until the 32 hour mark, when the nitrate is at about 1.5ppm and the ammonium at about 0.1ppm. From this point the ammonium level is constant and the nitrate level decreases slightly faster than before. At the 64 hour mark, the end of the plot, the nitrate is at 0.5ppm and thr ammonium still at 0.1ppm.
I believe that this shows that the plant in question, in the conditions it was in, preferred ammonium over nitrate at least until the ammonium concentration was 1/20th of its original value (0.1ppm). It was only at this point that the nitrate consumption was faster than any ammonium consumption.
I would also guess, by the way, that the experimenters didn't have a way to measure ammonium accurately below 0.1ppm, and that this is why the graph tails off like that, with the ammonium levels constant and low, but not zero. It doesn't seem likely to me that the plants would suddenly stop taking in ammonium altogether.
A quick googling suggests that modern instruments, like the one described here:
Nitrogen Trichloride
can measure ammonium accurately down to around 0.05mg/l. Which makes a lowest value of 0.1mg/l from a study done 18 years ago seem plausible, as instrumentation has probable improved in that time.
My conclusion from this graph is that the plant studied prefers ammonium to nitrate in all conditions where the ammonium level is equal to or less than the nitrate level, though when the ammonium concentration is below 0.5mg/l for a nitrate concentration of 1.5-2mg/l, the preference is slight. When the ammonium gets very low (undetectably low?), the rate of nitrate consumption increases slightly.
I am personally increasingly inclined to rely on plants to remove ammonia from my aquariums rather than on massive "artificial" biological filtration. It will always be a combination of things, of course, but it seems to me that the plants are more reliable and less likely to fail very suddenly than the filter. If the powerhead driving the trickle filter on my largest tank (a measly 30 gallons, I know it's tiny compared to many, but all I can fit) dies, the plants will still grow (yay plants
. And once I move my tanks over to getting a lot more natural light rather than artificial light, I won't even be relying on electricity to make them grow well. It seems like a much more stable system to me. (Maybe this is just my lack of experience showing here, though
)
Anyway, thank you for having a most interesting discussion in public where people can contribute.
Helen