Has anyone here fully read Diana Walstad's book?

[Brenden Mitchell]

I've been keeping planted aquariums for about a year now. I initially got into the hobby because I love plants, and not until very recently have I started keeping fish. I am a biology student and have almost finished my bachelor's, so this is a huge interest in my life. 

The first tank I ever did was a dirt substrate tank, capped with gravel. This made inherent sense to me, because I was trying to grow aquatic plants exactly as they are in the wild. 
I had great success with the dirt tank, and eventually just let it grow wild and continued making newer tanks, with the idea of keeping fish in mind. 

Anyway, I currently have a 10 gallon tank with a dirt substrate, and it was an experiment. I was told that you can't use soils that are rich in organic fertilizers, because they are too "hot" and will never settle into a safe environment. I have found that to be false. Within a month the tank was completely stable and had no fluctuations in Ammonia, Nitrite, or Nitrate. I had to purposeful dose fertilizer to get a Nitrate reading. I now have fish in there and even though I am feeding them plenty, my Nitrates are actually staying less than 20 ppm for the last two weeks and seem to be fairly stable at that point. I may end up having to do a water change every few weeks or so at this rate.

All this to say, in Walstad's book Ecology of the Planted Aquarium she describes a unique relationship that is counter to what I see promoted by most people.

Quote

“The truth is plants cannot keep ammonia out. For ammonia diffuses freely across the cell membranes of all organisms (plants, fish, etc) [62]. Because NH3 is a gas without an electrical charge, it diffuses freely across the lipid bilayer of cell membranes. In contrast, ammonium (NH4+) has an electrical charge, and therefore, cannot cross the lipid bilayer without help (membrane transporters, enzymes, etc)."

Plants prefer Ammonia and Nitrite much more than Nitrate, because they must metabolize Nitrate back into Nitrite or Ammonia to use them. 

Quote

“Aquatic plants can use ammonium (NH4+), nitrite (NO2-) or nitrate (NO3-) as their nitrogen source. Many aquatic plants have been found to prefer ammonium over nitrates, and this preference is substantial. For example, Elodea nuttallii growing in a mixture of ammonium and nitrates, removed 50% of the initial ammonium after 8 hr but few nitrates (Fig. VII-1). Only when much of the ammonium was gone (at 16 hr), did it begin to take up nitrates."

However, our nitrifying bacteria that we try to cultivate with our filters actively produce Nitrates as a waste product, due to them receiving energy from the conversion of Ammonia > Nitrites > Nitrates. 

This seem to mean that we have two forces which are counterproductive in our planted aquariums. We have plants and large colonies of nitrifying bacteria in a struggle for resources. This would then cause a build up of Nitrate, which we remove with water changes because the plants do not prefer it and are slow to consume it. 

Walstad also explains the process of how anaerobic bacteria can turn Nitrate back into Nitrite.

Quote

“Nitrate respiration is a common bacterial process carried out by a variety of ordinary bacteria under anaerobic conditions. The reaction whereby bacteria use nitrate (NO3-) for respiration is:

NO3- + 2H+ + 2e- ⇒ NO2- + H2O

Unlike denitrification where nitrite is further converted to the gases (N2O and N2), nitrites are the endproduct of this reaction. Nitrate respiration is a major anaerobic process carried out by a wide variety of ordinary bacteria. Thus, in an extensive survey [28] of sediment and soil bacteria, about 80% of the bacteria capable of growing under anaerobic conditions were nitrate-respiring bacteria (produced nitrites when isolated and cultured). The remaining 20% of the anaerobic bacteria were denitrifying bacteria (i.e., produced N2 but no nitrites when isolated and cultured with nitrate).”

Unless I'm missing something, this means that an excess of nitrates, produced by filters, unwanted by plants, is in danger of being converted back into nitrite, which would then be taken up by plants, converted by bacteria back into nitrate, or removed by water changes. 

This seems like a counterproductive loop. It actually seems like removing the filter would be better for the ecosystem. 

Is anyone else more knowledgeable about this? I find this incredibly fascinating.

[flyingcow]

Not necessarily more knowledgeable, and certainly not an expert, but a few things:

- Plants take up Ammonium, not Ammonia.  These exist in a certain equilibrium based on pH and temperature. This means at a higher pH, plants might not be able to take up ammonium fast enough for it to not become a toxic environment

- Also, she notes in the book that plants take up ammonium preferentially to nitrate, but that doesn't mean they necessarily grow better with ammonium. 

- for Nitrate respiration to occur, you need an anaerobic environment. These usually only happen in very deep substrates, and it's very possible for an anaerobic environment to become an anoxic environment and the same heterotrophs that can respite no3 in the anaerobic environment now start making h2s, which is bad news bears.

So striking a balance where you have nitrifying bacteria and plants both doing their jobs, you get a resilient and stable tank.

[Brenden Mitchell]

I didn't realize the balance of Ammonium vs. Ammonia aspect. That makes sense. I was under the impression that the plants themselves were converting the Ammonia to Ammonium inside their tissues. So as the plants take up Ammonium, this leaves more room for Ammonia to be converted to Ammonium in the environment? 

I found the section where she explains this in the book just now, I must have missed it on my first read through. 

Quote

“Ammonia is one of the most important and common pollutants of aquariums. Fish and bacteria excrete ammonia as a waste product of their metabolism. Ammonia (NH3), which is toxic, exists in equilibrium with non-toxic ammonium (NH4+) in the following reaction:

NH4+ + OH- ⇔ NH4OH ⇔ NH3 + H2O

The percentage of ammonia in a solution with a given N concentration changes dramatically with pH. Typically, there is a 10 fold increase in ammonia for every 1 unit increase in pH as NH4+ converts to NH3 in the above equilibrium reaction. For example, if the pH increases from 7.0 to 8.0, the % of N that is NH3 increases from about 0.33% to 3.3%, while the % of N that is NH4+ correspondingly falls from 99.7% to 96.7% [53]. Thus, the higher the pH, the greater the NH3 concentration and toxicity of a given concentration of inorganic nitrogen.”

Do you happen to know how deep of a substrate is suggested before anaerobic conditions start to occur? I have seen some tanks that have tons of gravel or sand. I saw a video just yesterday from Father Fish on YouTube, he had a tank which had at least 6" of sand with no soil at the bottom which had been undisturbed for 10 years. So I would assume you'd need more than that, or perhaps a soil with lots of mud or clay so that there was little to no circulation. 

[flyingcow]

On 10/9/2022 at 3:24 PM, Brenden Mitchell said:

I didn't realize the balance of Ammonium vs. Ammonia aspect. That makes sense. I was under the impression that the plants themselves were converting the Ammonia to Ammonium inside their tissues. So as the plants take up Ammonium, this leaves more room for Ammonia to be converted to Ammonium in the environment? 

bingo. But the uptake of ammonium is going to be concentration dependent, so you'll need to be a higher ammonia concentration to get enough ammonium for uptake (that's bad).

On 10/9/2022 at 3:24 PM, Brenden Mitchell said:

Do you happen to know how deep of a substrate is suggested before anaerobic conditions start to occur? I have seen some tanks that have tons of gravel or sand. I saw a video just yesterday from Father Fish on YouTube, he had a tank which had at least 6" of sand with no soil at the bottom which had been undisturbed for 10 years. So I would assume you'd need more than that, or perhaps a soil with lots of mud or clay so that there was little to no circulation. 

I don't. I decided it was too complex for my simple brain, and I was too likely to screw it up, so I actively try to avoid anaerobic conditions. But with 6" of sand, I bet there's some anaerobic stuff going on down in the deeper parts of it.

[Patrick_G]

On 10/9/2022 at 11:30 AM, Brenden Mitchell said:

Unless I'm missing something, this means that an excess of nitrates, produced by filters, unwanted by plants, is in danger of being converted back into nitrite, which would then be taken up by plants, converted by bacteria back into nitrate, or removed by water changes. 

There's no danger unless your level of ammonia exceeds the capacity of the bacteria to process it. A lot of that bacteria lives in the filter media, but it's ok to remove the filter as long as the remaining bacteria in the tank can handle the amount of Ammonia being produced.