# How deep does the dissolved oxygen penetrate?



## _Maq_ (19 Jul 2022)

Oxygen penetrates into sediment's depth from water column. The actual depth of penetration depends primarily on microbial oxygen consumption.
Many people believe that oxygen penetrates down to the very bottom of their tanks. Some believe differently. I don't want to open another, potentially heated discussion on this topic. Both sides should admit that we can only guess. Between oxic zone and that of sulfate reduction (where black sulfides and hydrogen sulfide are generated) there is a suboxic zone where microbes reduce nitrates, manganese and iron.
I want to ask the forumites, esp. present chemists, for help. *Is there a suitable way to determine the depth to which oxygen penetrates?* I've been considering an iron nail inserted vertically into the substrate. Where black coating appears, I'd assume the nail came into contact with hydrogen sulfide. But I wonder, someone would come with a better suggestion?


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## Wookii (19 Jul 2022)

Could the probe of a dissolved oxygen meter not be inserted into the substrate? Perhaps pushing it in at 45 degrees so as to minimise any oxygen rich water being taken down with it?


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## dw1305 (19 Jul 2022)

Hi all,


_Maq_ said:


> Is there a suitable way to determine the depth to which oxygen penetrates?





Wookii said:


> Could the probe of any dissolved oxygen meter not be inserted into the substrate?


I'd guess that @Wookii's suggestion is the only real way of knowing.

You would really want an "Oxidative - Reductive Potential" (ORP) probe and monitor. I think @jaypeecee has <"one of these">?


_Maq_ said:


> *?* I've been considering an iron nail inserted vertically into the substrate. Where black coating appears, I'd assume the nail came into contact with hydrogen sulfide.


You would just need to stir the substrate and sniff it, if you thought that H2S formation had occurred in the anoxic layer, we can sense hydrogen sulphide <"H2S at ppb levels">. <"Sulfur smell after tearing down dirted tank.">


_Maq_ said:


> Oxygen penetrates into sediment's depth from water column. The actual depth of penetration depends primarily on microbial oxygen consumption.
> Many people believe that oxygen penetrates down to the very bottom of their tanks.


Personally I'd make a <"very clear distinction"> between what happens <"in a planted tank"> (and particularly a <"planted tank with emergent vegetation">) and what happens when you don't have plants.

Plants have physiological (<"and morphological">) adaptations to allow them to <"grow in anoxic sediments">*, by transporting oxygen into the rhizosphere.

That is why I'm not too hung-up about what happens in the substrate (or <"what that substrate is">). Over the passage of time when you have plants, and leave the substrate alone, it will <"will mature and function successfully">, pretty much wherever you started.

cheers Darrel

* If the link stops working the reference is: "Hernández-del Amo, E., Dolinová, I., la Ramis-Jorba, G., Gich, F. and Bañeras, L., 2020. Limited effect of radial oxygen loss on ammonia oxidizers in _Typha angustifolia_ root hairs. _Nature Scientific reports_, 10(1), pp.1-13.


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## jaypeecee (19 Jul 2022)

dw1305 said:


> You would really want an "Oxidative - Reductive Potential" (ORP) probe and monitor. I think @jaypeecee has <"one of these">?


Hi @dw1305, @_Maq_ & Everyone,

Yes, I have an ORP/Redox electrode and meter. I also have a copy of Diana Walstad's book, _Ecology of the Planted Aquarium_, which is very helpful regarding water column and substrate ORP/Redox. She provides ORP figures (in mV) down to a substrate/sediment depth of 4.5 cm for a submerged plant, for no plants and an emergent plant. It is presented in graphical form and appears in Chapter IX of the Third Edition of her book. As my interest to date has always been water column ORP, I have not made any substrate ORP measurements. Besides which, the substrate depth of my experimental tank is a mere 2 cm.

Please let me know if I can help in any way!

JPC


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## _Maq_ (19 Jul 2022)

jaypeecee said:


> the substrate depth of my experimental tank is a mere 2 cm.


Still, could you push your probe into that depth and let us know? Ideally, multiple measurements accompanied with pics? It could be a starter in discussing this issue.


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## jaypeecee (19 Jul 2022)

_Maq_ said:


> Still, could you push your probe into that depth and let us know? Ideally, multiple measurements accompanied with pics? It could be a starter in discussing this issue.


Hi @_Maq_ 

It will be _several_ weeks before I get a chance to do what you have requested as it's not a ten minute job! And, I'm confused. The Redox values are available from Diana Walstad's book as I mentioned previously. If you are interested in knowing specifically the depth to which _oxygen_ penetrates into the substrate, you really ought to use an oxygen probe and not just any oxygen probe. It would need to have a tiny sensing tip. 

JPC


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## _Maq_ (19 Jul 2022)

jaypeecee said:


> The Redox values are available from Diana Walstad's book as I mentioned previously.


She merely describes so called redox cascade. Also, quote: _The oxidized microzone is the all-important top layer of sediment. It separates the sediment environment from the aerobic overlying water. Even though it may be only a few mm thick, it is critical._
Still, aquarium hobbyists mostly insist that their substrate is oxygenated much deeper because it's sandy, due to water flow, etc. etc. So I'm seeking a way to solve this question by a suitable *demonstration*. Measuring ORP is a good way to do it.
Not ideal, though. I've been dreaming of a simple way any tank keeper could employ for him/herself to see. Something like my suggestion of an iron nail. (I'll give it a try, definitely.)
For comparison with Walstad, here is a snap from Wetzel - Limnology:




The numbers in Wetzel are much closer to those shared in much of related literature. There's a general consensus that below 200 mV the oxygen is absent.


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## jaypeecee (19 Jul 2022)

_Maq_ said:


> She merely describes so called redox cascade. Also, quote: _The oxidized microzone is the all-important top layer of sediment. It separates the sediment environment from the aerobic overlying water. Even though it may be only a few mm thick, it is critical._



Hi @_Maq_ 

It is Figure IX-3 on page 149, Third Edition of Walstad to which I was referring. I'll also take a look at Wetzel.

JPC


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## _Maq_ (20 Jul 2022)

jaypeecee said:


> It is Figure IX-3 on page 149


I see. Thank you.
But the issue remains. Readers can see that 5 mm deep in the substrate the redox is below +200 mV, but they still think _they_ know better, _their_ sediment is different (sandy), etc.


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## Ria95 (20 Jul 2022)

Though they can be in relation to each other, ORP is different from Dissolved Oxygen. Which  is relevant?
As Darrel alluded to, the level of DO in the substrate is not only dependent on substrate characteristics but the entire system. Low water DO vs supersaturated water will  change what you see in the substrate for example. Grain size/shape can only get you so far, at some point each system needs to be individually approached and improved.  Far as approaches go, experiments are usually set up with a continuous water column and various sampling ports or probes. But  to the question in the title, I can  only ask: How hard are you pushing?


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## jaypeecee (20 Jul 2022)

_Maq_ said:


> But the issue remains. Readers can see that 5 mm deep in the substrate the redox is below +200 mV, but they still think _they_ know better, _their_ sediment is different (sandy), etc.


Hi @_Maq_ 

Please enlighten me as I need to plead ignorance of 'the issue'. Substrate/sediment science is obviously a topic that I know precious little about. Looks like I need to re-visit chapters VIII and IX of Walstad.

Thanks in advance.

JPC


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## _Maq_ (20 Jul 2022)

@jaypeecee , Walstad is not the source I'd recommend, ever. I'll try to fish some better sources from my library.



> @Ria95 Though they can be in relation to each other, ORP is different from Dissolved Oxygen. Which is relevant?


I suppose hobbyists are more interested in DO level, so this is more relevant.


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## jaypeecee (20 Jul 2022)

Ria95 said:


> Though they can be in relation to each other, ORP is different from Dissolved Oxygen. Which is relevant?


Hi @Ria95 

Firstly, I want to say that it's good to see you back on UKAPS!

On one of my freshwater tanks, I continuously monitor ORP* with a Milwaukee MW500 and I occasionally check Dissolved Oxygen with a Salifert O2 Test Kit. I have empirically determined that there is a correlation between DOM** and ORP. In my opinion, it is _very _ important to keep an eye on DOM.

*ORP = Oxidation-Reduction Potential
** DOM = Dissolved Organic Matter

JPC


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## _Maq_ (20 Jul 2022)

Influence of submerged macrophytes, temperature, and nutrient loading on the development of redox potential around the sediment–water interface in lakes
Worth reading, esp. the introduction is good. Don't miss Fig. 2 on page 123.

Edit:
Diffusive boundary layers and the oxygen uptake of sediments and detritus1 | Semantic Scholar
A batch of papers of which I've read only some, so far. All related to our topic.

Second edit:
This one: Oxygen and the spatial structure of microbial communities


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## Ria95 (22 Jul 2022)

_Maq_ said:


> @jaypeecee , Walstad is not the source I'd recommend, ever. I'll try to fish some better sources from my library.
> 
> 
> I suppose hobbyists are more interested in DO level, so this is more relevant.


then you might want to setup separate columns with extraction points and vacuum pumps. In situ measurements will be hard with the DO probes i am aware of as they do better with flow at the membrane. Stagnant water will mess your results up.


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## jaypeecee (22 Jul 2022)

Ria95 said:


> ...then you might want to setup separate columns with extraction points and vacuum pumps. In situ measurements will be hard with the DO probes i am aware of as they do better with flow at the membrane. Stagnant water will mess your results up.


Hi @_Maq_ & @Ria95

I think it's self-evident that acquiring, setting up specialized equipment and conducting these measurements falls way outside the scope of we hobbyists. I'll settle for just reading the cited papers. 

JPC


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## _Maq_ (22 Jul 2022)

jaypeecee said:


> falls way outside the scope of we hobbyists


Correct, I'm afraid. That's why I'd suggested the 'nail' test and encouraged others, esp. chemists, to *suggest something* better. Pleeease. 💪⚗️


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## ElleDee (22 Jul 2022)

Unfortunately I don't know anything about the best way to measure dissolved oxygen in the substrate, but is this an academic question or a practical one?

On a practical level, if someone is having issues with anoxic substrate conditions they won't need the changing color on a nail to let them know they have a problem. If they aren't having problems, then does the amount of oxygen in the soil really matter?

If someone has access to the original paper that Figure IX-3 is referencing I'd love to see it. The abstract mentions that the submerged plant they used had a small root system which seems pretty relevant, but I had a few other questions about the methodology as well.


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## _Maq_ (23 Jul 2022)

ElleDee said:


> is this an academic question or a practical one?
> On a practical level, if someone is having issues with anoxic substrate conditions they won't need the changing color on a nail to let them know they have a problem.


I think this is a practical question. The very way you put the issue suggests so. Anoxic substrate is *a problem*? I think it is not. I think our substrates are predominantly anoxic and yet it brings no problems at all.
It has practical consequences. Perhaps I'm influenced by Czech hobbyists community. In ours, vendors make big business with light, porous substrates which purportedly _help to keep substrate oxygenated_. Hobbyists are afraid to use soft sand because it purportedly _prevents oxygen from penetrating into the substrate_. Many people vigorously vacuum the substrate _to keep it oxygenated_.
I think it would be useful to demonstrate that these and similar practices are based on mistaken assumptions.


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## _Maq_ (23 Jul 2022)

ElleDee said:


> If someone has access to the original paper that Figure IX-3 is referencing I'd love to see it.


This one is rather old a difficult to find. Microsensors have made a huge technological progress since then.


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## Ria95 (23 Jul 2022)

That's pretty much it, without an actual calibrated probe and validated protocol we are at the equivalent of dipping our finger in the aquarium to tell the temperature.  Then arguing with others who have done the same 'temperature measurement'  about the impact of 2 K on plants and fish.  Thus as mentioned in the first post, more hands-on and individualized approaches and improvements are needed when people experience issues.

From what I have read,  the recommendation to vacuum the substrate is  to reduce the amount of detritus in it. Naturally this will lower the oxygen demand in the substrate, opposite to how you would intentionally add organic rich mud and cellulose to the bottom of a Winogradsky column.


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## ElleDee (23 Jul 2022)

_Maq_ said:


> I think this is a practical question. The very way you put the issue suggests so. Anoxic substrate is *a problem*? I think it is not. I think our substrates are predominantly anoxic and yet it brings no problems at all.
> It has practical consequences. Perhaps I'm influenced by Czech hobbyists community. In ours, vendors make big business with light, porous substrates which purportedly _help to keep substrate oxygenated_. Hobbyists are afraid to use soft sand because it purportedly _prevents oxygen from penetrating into the substrate_. Many people vigorously vacuum the substrate _to keep it oxygenated_.
> I think it would be useful to demonstrate that these and similar practices are based on mistaken assumptions.



Ah, ok, that's interesting. It sounds like there are some regional differences that are informing the direction that we approach this question from. 

It's possible that the thinking on this has evolved over the last 15 years, but the current collective wisdom in the US seems to be that sand is just fine (and is pretty popular!) and that anaerobic substrates are primarily an issue for people with dirted tanks. It may be that people are generally mistaken about how oxygenated their soil is, but it's not something that gets a whole lot of attention and is at best a minor factor in substrate selection and maintenance.


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## _Maq_ (23 Jul 2022)

ElleDee said:


> It sounds like there are some regional differences


There are, indeed, and that's one of the reasons I find useful to be here. Not all shared (un)wisdom is spread worldwide.


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