A little deeper look at the Nitrogen Cycle

[SeanB]

I don't know if anyone is interested, but here is an excerpt from an article I wrote about starting a reef tank. Most of it has to do with setting up a larger tank, but the same basic principles apply.

Here is a portion explaining the nitrogen cycle:

 

...As mentioned earlier, decaying fish produce ammonia. In fact living fish produce ammonia as a product of respiration. It is also produced as fish waste and uneaten food decompose (Dissolved Organic Compounds - DOC’s.) If allowed to exist in any significant amount, ammonia will wreak havoc on your tanks inhabitants and can cause fish and coral death. This is where the bacteria enter the picture. The bacteria, which use ammonia in their own metabolic process, are called nitrosomonas. Nitrosomonas thrive in a highly oxygenated environment and consume ammonia in a process called aerobic nitrification. As these bacteria multiply, they use up the ammonia and produce nitrites as a by-product. Unfortunately Nitrites are also toxic to the marine environment. Luckily this isn’t the end of the cycle and there are bacteria which also consume nitrites. These bacteria thrive in low oxygen environments and are called nitrobacteria. They consume nitrites in a process called anaerobic (or anoxic) denitrification. The nitrobacteria convert the nitrite into nitrates. Nitrates are the end of the line in this process. The nitrates are LESS harmful to aquatic life than ammonia or nitrites, but still should not be allowed in any significant quantity. Nitrates are removed via frequent, small water changes – usually 10-20% per week. Some people choose to make larger, less frequent water changes. There are some other options for reducing nitrates, but that is a topic for another day....

[onthefly]

Not Bad SeanB....

 

A couple corrections/clarifications....

 

1) Every biochem text I've ever read states the simple products of respiration are CO2 and Water.....just wondering where the NH3 comes from?

 

2) The convertion of NO2 -> NO3 by the Genus Nitrobacter is an aerobic process. The process of denitrification N03-> N2 and O2 is an anaerobic process.

 

Where was the article published?

[SeanB]

Thanks. It was just for a website for The Marine Aquarium and Reef Society of Houston; not officially "publised."

 

#1. Do a search for "ammonia fish respiration." Ammonia is excreted through the fish's gills as they breath. It's kind of like they urinate through their gills.

 

#2. Denitricifcation is anoxic, but you are correct it is not done by nitrobacters. Thanks for catching that.

[lgreen]

So is ammonia an actuall product of respiration or are the gills just an excretion pathway?

 

very interesting, never heard of that before.

[SeanB]

Excretion pathway.

[lgreen]

"In fact living fish produce ammonia as a product of respiration."

 

well then statement sounds a little weird.

[lhooq]

http://www.newton.dep.anl.gov/askasci/bio9...99/bio99326.htm

 

Originally posted by onthefly

Not Bad SeanB....

 

A couple corrections/clarifications....

 

1) Every biochem text I've ever read states the simple products of respiration are CO2 and Water.....just wondering where the NH3 comes from?

 

2) The convertion of NO2 -> NO3 by the Genus Nitrobacter is an aerobic process.  The process of denitrification N03-> N2 and O2 is an anaerobic process.

 

Where was the article published?

[Reef_Mad_Man]

The gill's are part of the two part amonia excretion process with fish. thier excriment is the other.

[SeanB]

Originally posted by lhooq

http://www.newton.dep.anl.gov/askasci/bio9...99/bio99326.htm

 

Thanks for the link. I thought I had it right, but I didn't want to make any other statements I couldn't back up.

[MrAnderson]

Originally posted by SeanB

They consume nitrites in a process called anaerobic (or anoxic) denitrification. The nitrobacteria convert the nitrite into nitrates. Nitrates are the end of the line in this process.

 

The conversion of ammonia to nitrite, and nitrite to nitrate, is called nitrification, not denitrification.

 

Nitrate is not the end of the line for the nitrogen cycle.

 

The final step is denitrification, the conversion of nitrate to free nitrogen and nitrous oxide by anaerobic bacteria.

[SeanB]

I'm glad I posted this thread, since I seem to be the one getting the most out of it! I had to go back and do some more reading. Obviously I had a missconception about this process. The following states it much more simply - and accurately. Thanks Mr. Anderson.

I just hope you all can appreciate someone who can admit when he's wrong.

 

From WetWebMedia (Bob Fenner)

Denitrification is just what it appears to be; a reverse of the biological processes we've gone over called nitrification, with nitrate being converted back to nitrite, ammonia and finally nitrogen gas. This feat is accomplished by other bacteria species that thrive in the absence of oxygen (hence anaerobic). Some anaerobic denitrification does occur in every system; but not enough to offset the forward accumulation of nitrate. There are filter module products that portend to promote these microbes and their beneficial activities. Like dating, I urge you to be careful in their selection and use. Many (dates and denitrators) are "high-maintenance" units requiring daily fooling-with. All have the potential defect of other anaerobic production toxifying your system. Finally, in my opinion, they're just not worth the hassle, cost and possible chemical downside; compared with water changes, chemical filtrants, and other biological intervention (i.e. photosynthesis).

[onthefly]

Hey Sean - bah! We're all wrong most of the time

 

From Lhooq link: "The other toxic end product of metabolism in general is ammonia, which comes from the breakdown of amino acid, which contain nitrogen. This is handled in different ways by different animals." Even though this is referring to overall metabolism, not respiration, I'm really intrigued by the last sentence and that does lend some backbone to Seans statment. I can remember in all my biochem courses, but I think I remember seeing a pathway for this.

 

Much like in the kidneys where wastes are concentrated to a certain level then shunted to the bladder, I wonder if elevated levels of NH3 in fishes blood allows for a diffusion through the gills into the NH3-less environment? Follows the simple rule of diffusion.

[onthefly]

From "practical reefkeeping magazine" (a UK online rag):

Gills also get rid of wastes. Most fishkeepers know that fish excrete ammonia into the water, but few realise that the bulk of this ammonia (over 75% in some fish) is actually excreted from the gills, and not from urine or solid wastes as you might think.

 

And if you like me (hard to convince and skeptical of online info):

J Exp Biol. 2002 Sep;205(Pt 18 ):2765-75. Related Articles, Links

 

Active ammonia excretion across the gills of the green shore crab Carcinus maenas: participation of Na(+)/K(+)-ATPase, V-type H(+)-ATPase and functional microtubules.

 

Weihrauch D, Ziegler A, Siebers D, Towle DW.

 

Lake Forest College, IL 60045, USA. Weihrauchblues@gmx.net

 

Although aquatic animals are generally believed to export nitrogenous waste by diffusion of NH(3) or NH(4)(+) across external epithelia, evidence for active ammonia excretion has been found in a number of species. In the euryhaline green shore crab Carcinus maenas, active excretion of ammonia across isolated gills is reduced by inhibitors of the Na(+)/K(+)-ATPase and vacuolar-type H(+)-ATPase. In addition, a functional dynamic microtubule network is necessary, since application of colchicine, taxol or thiabendazole leads to almost complete blockage of active and gradient-driven ammonia excretion. Actin filaments seem not to play a role in the excretory process. The NH(4)(+)-dependent short-circuit current and the conductance of the isolated cuticle were reduced in a dose-dependent manner by amiloride, a non-specific inhibitor of the Na(+)/H(+) exchanger and Na(+) channels. Combined with an analysis of gill morphology, the strong intracellular but weak apical abundance of V-type H(+)-ATPase and the fact that ammonia flux rates are equal under buffered and unbuffered experimental conditions, our observations suggest a hypothetical model of transepithelial ammonia movement that features active uptake across the basolateral membrane, sequestration in acidified vesicles, vesicle transport via microtubules and exocytosis at the apical membrane.

 

PMID: 12177142 [PubMed - indexed for MEDLINE]

 

Good job Dude!!! This paper suggests an active system for this and not simple diffusion.

[lgreen]

cool stuff.

 

didn't know that.

[Undertheradar]

He he he...and the biochemists come together again! how you guys been doing since our look at denitricication last time? Did any of you talk with Randy Holmes-Farley?

 

http://www.nano-reef.com/forums/showthread...5148#post595148

 

As you can see Sean, we have been busy beating the Nitrogen cycle to death already...lol.

[SeanB]

Ha ha. I have opinions on bio-balls too.

 

Here's a thought that rattles around in my head. Bacteria can only reproduce to the extent that they have a food source. So, if your bio-balls are "nitrate factories" then you still have excess ammonia to deal with - yes?

[MrAnderson]

Right!

 

You can't get nitrate unless you have ammonia to begin with.

 

When everything in the cycle is balanced, you have metabolically equal populations of bacteria for all steps of the NC. Excess nitrate impilies 2 things: not enough denitrifiers to convert the nitrate to N2 and N2O; and further up the cycle, excessive ammonia (as far as the capacity of downstream NC metabolism is concerned).

[lgreen]

Originally posted by SeanB

Ha ha.  I have opinions on bio-balls too.  

 

Here's a thought that rattles around in my head.  Bacteria can only reproduce to the extent that they have a food source.  So, if your bio-balls are "nitrate factories" then you still have excess ammonia to deal with - yes?

 

No

 

Consider the life cycle of a bacterium. A colony can multiply like 10x in a matter of minutes if food becomes available.

 

Plus there is always hungry bacteria waiting to eat ammonia.

 

Now if there is something that causes an ammonia spike you might be in trouble

[onthefly]

Well it is all related to carrying capacity. Is there enough food for the bugs to thrive? E. coli (a fast grower) has a doubling time of 30min at 98F. If there is a shortage of nutrients (e.g nutrient depletion)...for a short time, there will be a slight elevation in the population, but it will rapidly drop off to a level that can (as MrA stated) be at equilibrium.

 

Granted that, if experienced a NH3 spike, the equilibrium can shift quite rapidly and within 24hrs you can have alot more bacteria on your hands.

 

I'm still waiting for "bjn" to reply to my last post in the bioball thread.

[SeanB]

So, a normal supply of bio-balls are too effective in colonizing bacteria for converting ammonia to nitrite to nitrate. In other words, the average dsb/lr tank doesn not provide enough anoxic space for denitrification to keep up with the bio-balls and therefore the equation is not balanced. If it were balanced, water changes would only be necessary to replenish mineral content.

 

Did I get that right?

[lgreen]

sounds pretty good.

 

yep, so then we are left with nitrate. What the heck to do with freakin nitrate.

[Diatome]

I fee dit to my oysters, clams and such. I keep nitrate a little elevated in one of my tanks for my bi-valve hitchikers. No way am I getting rid of my jewel boxes.

[onthefly]

The problem I have with Bioballs, is those colonizing bacteria would normally be in your LR and LS.....and perform the same job. Now, you have them in an external source that could potential be removed from the system (say you decide to clean out your sump or change methods). In this case, you now have the exact same bioload, but you're missing a huge part of your biological filtration...that could lead to some serious issues.

[Diatome]

That's the problem I have with them. In an exteranl area, they don't even have to be cleaned. One power failure and they go dry and boom, they are useless and your tank suffers.

[SeanB]

Originally posted by lgreen

sounds pretty good.

 

yep, so then we are left with nitrate.  What the heck to do with freakin nitrate.

 

Macro Algae : That reminds me, I need to add chaeto to my supply list.