Quote:
Originally Posted by Carissa
I think maybe the bottom line is that this graph doesn't provide enough data to make the assumptions that are being made. All it's telling us is that if you happen to have a tank with 2ppm of ammonia and 2ppm of nitrates, the plants will use much of the ammonia first. Maybe, this could be generalized to say that if you have a tank with equal amounts of ammonia and nitrates, this would occur. But what if we started with 0.5 ppm of ammonia and 20 ppm of nitrates (a more realistic situation in an aquarium)? Plants are very good at adapting to their circumstances, so my guess would be that you would see what could be interpreted as a definite nitrate preference under those circumstances....in other words, the ammonia wouldn't be reduced to near 0 before nitrate started being used, both would probably be used concurrently.
|
The discussion above, around and below table 2 in
Aqua Botanic - Plants and biological filtration
answers some of these questions, assuming the research done is good (I haven't bothered to look up the refered papers to check the original research).
As I see it, the more interesting things in that discussion are the following:
- as little as 0.02ppm ammonia was enough to inhibit nitrate uptake by duckweed, so that plant at least prefers ammonia so much that it basically won't consume nitrate at all unless there is no ammonia available
- looking at table, 2, the variation in speed of uptake of ammonia is much larger than that of nitrate. It takes hardly more time for the plant to remove 26mg/l of ammonia than it does to remove 0.025mg/l. But for the nitrate the duration to remove 26mg/l is much longer than to remove 0.025mg/l (actually, the detail of that set of data is interesting - looks like there is some kind of threshold around 6.4mg/l of nitrate above which the time taken to remove it is roughly proportional to the amount of nitrate there is, whereas below that point it isn't proportional at all, and for ammonia looks like in the range of that experiment there was no point at which the time taken increased linearly with the amount of ammonia, which is also odd).
Carissa I think that that table 2 actually answers our earlier question about whether plants can cope with a sudden large change in the amount of ammonia available, by the way. If other plants behave like duckweed (of course I don't know whether they do), then a planted tank could presumably deal with a large amount of ammonia (dead fish?) about as easily as the more usual tiny amounts of ammonia. Which is reassuring for me
