From stagnancy to deoxygenation

[wooden_reefer]

If you put just $10 in your account, it will still be there 20 years from now even if you don't put more money into it, provided there is no bank fee and interest.

How does stagnate water become deoxygenated? Many people equate the stagancy with deoxygenation.

I think aerobic microbial activity at the surface or one end of any stagnate water still need to be present for any stagnate water to become deoxygenated.

I am thinking about aerobic activity at one section is needed to support anaerobic activity in another.

The aerobic activity does not have to be nitrification but can be.

Is there non-biological phyiscal phenonenon that depletes oxygen slowly in stagnate water? Any surface phenonenon?

 

[ctenophors rule]

if you have water in a glass, greatly agitate it( shake it, air stone, etc) when your done take a D.O. reading and oxygen levels will be sky high. tommorow around the same time dissolved oxygen levels will be lower.

i think it has to do with the excess microscopic diatomic molecules of oxygen stratifying themselves out of the water sample. the two hydrogens have their oxygen and they dont hold onto the rest.

hope this helps

 

[billsreef]

The typical stagnant pool of water contains various life, even if microbes, and it's that life using up the oxygen that causes the water to oxygenate There could also be some chemical deoxygenation if there are any oxidizable compounds present.

 

[dots]

http://www.merriam-webster.com/dictionary/Stagnant

http://www.epa.gov/volunteer/stream/vms52.html

I think you are confusing the terms, and trying to relate them to a third. Do you have a specific question to a biological process, as it seems?

Here are some things to get you going:

"Dissolved Oxygen" is the key term here. Oxygen is introduced via churning, moving, and other physical interaction between the air/water surface boundries.

DO, has a maximum saturation limit based on temperature. See link.

Oxygen is an "Oxidizer" which helps break down waste materials.

Remember, Oxygen is a by product of plants....even underwater.

Low flows also means less thermal exchange.....lower evaporation, higher temps....lower DO concentration.

The money analogy is not correct, Oxygen interacts and is part of a biological system and should be considered as such. The only way this would be equal is if it were at a temp of Absolute 0.

Again, your question seems to be in regards to another much larger topic.....what would that be?

 

[Joe Pusdesris]

Erm, how about buoyancy? Oxygen is less dense than water, so it rises to the surface unless mixed. [/guess]

 

[wooden_reefer]

http://www.merriam-webster.com/dictionary/Stagnant

http://www.epa.gov/volunteer/stream/vms52.html

I
Again, your question seems to be in regards to another much larger topic.....what would that be?

How does slow flow create low oxygenation? This is the implication.

There must also be consumption of the even limited oxygen in the water.

What consumes the limited oxygen in slow moving water?

What I am driving at is nitrification in close proximity needed to deplete O2 so as to allow denitrification? Certainly, if there are other aerobic activities that consume O2 other than nitrification, nitrification will not be required to deplete the limited amount of O2 in slow flow.

 

[billsreef]

How does slow flow create low oxygenation? This is the implication.

It's not that the low flow directly creats low oxygenation, it's that the low flow prevents the water from becoming well oxygenated.

There must also be consumption of the even limited oxygen in the water.

Correct. This is how the water becomes lower in O2 than it started out.

What consumes the limited oxygen in slow moving water?

At a bare minimum, bacteria and protozoans. In some areas, also higher life forms such as copepods, nematodes, and even up to fish.

What I am driving at is nitrification in close proximity needed to deplete O2 so as to allow denitrification? Certainly, if there are other aerobic activities that consume O2 other than nitrification, nitrification will not be required to deplete the limited amount of O2 in slow flow.

Yes, there are other aerobic process to drive down O2 content other than nitrification

 

[KarlBob]

Erm, how about buoyancy? Oxygen is less dense than water, so it rises to the surface unless mixed. [/guess]

Nope. Most oxygen in water is dissolved. Each individual oxygen molecule is surrounded by water molecules. Some oxygen molecules that happen to reach the surface may leave the solution and float off into the atmosphere, but at the same time, the occasional molecule of oxygen from the atmosphere will impact the surface and go into solution

In a perfectly sterile glass of water, barring any agitation, the dissolved oxygen will be evenly distributed. Random collisions with water molecules will push the oxygen molecules all over the place.

A bubble of oxygen is a different story; it's not in solution, and it will rise to the surface unless friction with the side of the glass (and the thin film of water between the bubble and the glass) is strong enough to hold it in place.

 

[wooden_reefer]

Nitrification is not the only aerobic activity in a tank, certainly. There are others.

In regions (micro-regions) of very slow flow, how dominant is nitrification as the process that consumes O2?

What I am driving at is still the question, how does stagnant water become deoxygenated? Whereever nitrification is the dominant process that consumes O2 (when there are few others), nitrification must be present to consume O2. Since ammonia or nitrite is needed for nitrification, besides O2, ammonia and nitrite presence or absence in areas nearby may affect denitrification.

Conditions and substances needed for aerobic activities are needed to deplete O2 even in stagnant water, to become deoxygenated downstream in micro spaces. Is this true?

 

[Joe Pusdesris]

Nope. Most oxygen in water is dissolved. Each individual oxygen molecule is surrounded by water molecules. Some oxygen molecules that happen to reach the surface may leave the solution and float off into the atmosphere, but at the same time, the occasional molecule of oxygen from the atmosphere will impact the surface and go into solution

In a perfectly sterile glass of water, barring any agitation, the dissolved oxygen will be evenly distributed. Random collisions with water molecules will push the oxygen molecules all over the place.

A bubble of oxygen is a different story; it's not in solution, and it will rise to the surface unless friction with the side of the glass is strong enough to hold it in place.

Hm, I thought that since oxygen was not polar it was held in solution by dispersion forces which were rather weak. This weak hold would encourage it to resume gaseous state. Isn't the equilibrium of dissolved oxygen much much lower than both saturation point and what we keep our tanks at?

I have only had very basic chemistry, so I don't really know.

 

[KarlBob]

I am thinking about aerobic activity at one section is needed to support anaerobic activity in another. The aerobic activity does not have to be nitrification but can be.

This part is essentially correct. Room temperature water exposed to air in an open container contains too much oxygen for obligate anaerobes (anaerobic critters that cannot "switch gears" between aerobic and anaerobic metabolisms) to survive. Except in the case of something like a "red tide" event, open water in an aquarium can't support the anaerobic bacteria that carry out denitrification.

The key is the phrase "open water." Water inside live rock is far from "open." The convoluted passages and tight spaces in live rock greatly restrict the distribution of oxygen. Aerobes on the surface of the live rock, and at the edges of the internal passages, use up lots of oxygen. Facultative anaerobes (able to "flip-flop" between aerobic and anaerobic metabolisms) use up the oxygen that gets past the aerobic bacteria. Deep inside a piece of live rock there's very little oxygen in the water, no matter how much flow and agitation the rest of the tank receives.

This is one of the reasons why denitrification is slower than nitrification. Just like oxygen, it takes a long time for nitrate to filter into live rock, and for dissolved nitrogen gas to make its way out.

 

[wooden_reefer]

Hm, I thought that since oxygen was not polar it was held in solution by dispersion forces which were rather weak. .

What takes O2 out of solution? Is there non-biological processes (may be just surface phenonenon) that causes the O2 to leave the solution and becomes unavailable?

 

[KarlBob]

Hm, I thought that since oxygen was not polar it was held in solution by dispersion forces which were rather weak. This weak hold would encourage it to resume gaseous state. Isn't the equilibrium of dissolved oxygen much much lower than both saturation point and what we keep our tanks at?

Now we're getting to the edge of my knowledge, too. I'm pretty sure you're right in saying that in still (non-agitated) water, the equilibrium point of dissolved oxygen is much lower than its saturation point. The water in our tanks is not still, though; it's often highly agitated. I'm not certain how much higher the equilibrium point of agitated water is than still water.

 

[KarlBob]

What takes O2 out of solution? Is there non-biological processes (may be just surface phenonenon) that causes the O2 to leave the solution and becomes unavailable?

Yes: evaporation. At equilibrium, though, the rate of oxygen molecules getting bumped out of solution is equal to the rate of oxyen molecules being knocked into solution from the air.

 

[wooden_reefer]

Yes: evaporation. At equilibrium, though, the rate of oxygen molecules getting bumped out of solution is equal to the rate of oxyen molecules being knocked into solution from the air.

Such equilibrium won't affect the concentration of dissolved O2. Many things chemical are at equilibrium.

Yes, IMO super-saturation likely is not a factor in a tank.

 

[KarlBob]

I suppose some dissolved oxygen probably reacts with things (like waste) in the water, but I suspect that aerobic critters use up a lot more oxygen than reactions with junk in the water.

 

[Mattik]

Just like water can only dissolve so much Ca before it begins to precipitate out of your water column, water can also only hold so much oxygen.

Many have said in this thread that agitation is the primary means by which oxygen is dissolved in water, which is partially correct. The other means is by biological processes that convert CO2 to O2....primarily photosynthesis by algae and plant life within the water.

Similarly, there are other processes which consume oxygen by converting it to CO2. Such processes are 1) oxygen breathers like fish and other animals (including microscopic), and 2) the decay of dead plant and animal tissue, which use up oxygen to create PO4 (phosphate) as well as the "stinky molecules" like hydroxides and sulfates, which also contain oxygen.

With stagnant pools of water, there may be so much dead and rotting material (because there is no flow to stir that material up and carry it away)that oxygen consumption from rotting tissue out-paces what the remaining plants and algae can replenish.....the result is deoxygenation of the water.

Something else to consider is that this is a normal thing in most lakes. If you go the the bottom, there is generally lower oxygen content. This is because:

1) All the rotting material sinks to the bottom and decomposes
2) There is less light at the bottom for photosynthetic processes, and
3) There is limited agitation to stir in more oxygen

 

[Randy Holmes-Farley]

Erm, how about buoyancy? Oxygen is less dense than water, so it rises to the surface unless mixed.

For any individual molecule dissolved in water, no matter how dense or light it may be, there is no difference in the levels attained at the top of the water column or at the bottom based on density alone. The random movements from brownian motion and other processes are enough to keep molecules well dispersed in water.

 

[Randy Holmes-Farley]

What takes O2 out of solution? Is there non-biological processes (may be just surface phenonenon) that causes the O2 to leave the solution and becomes unavailable?

As Bill mentioned, there are some nonbiological processes.

O2 will slowly react with many organic molecules, taking O2 from solution. Over a long enough period, this could remove all O2 from sterile water, assuming there was enough organic matter present. But this process is fairly slow for most organic molecules.

O2 also reacts with some inorganic molecules, reducing O2. generally, there are not high concentrations of these, but iodide, ferrous ion (Fe++), Mn++, sulfide, nitrite, and ammonia all can react with O2 over time. Oxidation of metals (rusting) also reduces O2.

 

[Mattik]

Just a reference or two for my earlier post:

http://www.lakemerrittinstitute.org/info_projects2.html

" What Causes Low Oxygen?
Oxygen is used up by respiration (breathing) and by chemical reactions. In Lake Merritt oxygen is used up by the respiration of plants and animals, and especially by biological and chemical reactions in the mud at the bottom where leaves and other organic matter are decomposed. Because of this, oxygen levels at the bottom of Lake Merritt are lower that at the surface. "

Apparently the brownian motion isn't quite strong enough to equally distribute oxygen throughout a water column. If you are talking about distilled water (or small volumes of water), then I agree with Randy's theory that normal processes would cause the oxygen levels to be pretty uniform. However, in a living environment , there are concentrations of biological / chemical processes that create variance in O2 levels throughout the water column.