Why is it a cycle?

[swbeginner]

I am not really a beginner, I am not a newb. I just used that name when I started...I regret it now ha

Anyway, I don't understand something. Instead of typing a bunch, I'll just pose a question.

Explain to me why it is called a cycle. Ammonification, nitrification, and denitrification result in the transfer of ammonia to nitrogen. Now, how is that a cycle? Does nitrogen fixation occur...and how?


In any case the point I want to make is that we tell beginners about the cycle and really it either isn't a cycle, or we don't explain all of what is happening.

 

[MeReefBeef]

its a cycle because there is an endless supply of things dying off in your tank, thats what the bacteria are feeding on....hence the ammonification and nitrification....

 

[swbeginner]

Cycles are circular. Nothing converts the nitrogen back to ammonia to make it a cycle: ie no nitrogen fixation.

We just add ammonia and the tank turns it to nitrogen or nitrates and macroalgaes and water changes removes it.

 

[xian]

Nitrification occurs in many ways.

The first is that nitrogen fixing bacteria absorb N2 directly form the atmosphere and through chemosynthesis turn it into some form that is available to plants or algae.

The second is absorption of nitrate, made by denitrifying bacteria, directly from the water, by plants and algae.

Plants an algae are then eaten by animal life which either exrete ammonia directly into the water or excrete urine which breaks down into CO2 and NH3

According to some recent research there may be many more pathways in this cycle that we were previously aware of.

I'll post the article if I can find it

 

[swbeginner]

Thanks! I know that in the ocean this cycle is complete, I was just thinking that nothing in my tanks personally eats the algae/plants that consumes nitrates or nitrogen...then again, snails and crabs do eat some of the algae...so I guess to an extent it is a complete cycle.

 

[WaterKeeper]

Wow, the answer needs a good typist (something I'm not).

Basically the term stems from FW tropical systems where a nearly sterile tank is set up. Devoid of bacteria it takes awhile for things to developed to a steady state. Any protein entering such a tank undergoes hydrolysis and the nitrogen in the protein becomes ammonia. Nitrifying bacteria are far slower growing than the hetrotrophs that convert protein to ammonia and it takes a week to 10 days before they can change the ammonia to nitrite, then nitrate. During that period the water is toxic to added fish.

That is FW but in a SW tank we add natural filtration in the form of LR and LS. This introduces all the bacteria that complete the nitrogen cycle in one swell swoop. The process of nitrate production is occurring on day one. Yet, often people add uncured LR to the tank. The rock has massive dieoff of materials during transport and it is more than the LR is able to assimilate. Ammonia spikes and it will take a couple of weeks for the nitrifying bacteria to catch up. Also large amount of other nutrients are released into the water and algae start to feed on that material. Even when ammonia is under control diatoms and and other algae thrive for weeks following the original set up of the tank. Curing the LR in curing vats rather than in the tank can shorten this part of the SW cycle.

A major player in the nitrogen fixation process is cyanobacteria. They are always present in the tank but thrive in areas with high exposure to atmospheric nitrogen and oxygen. That is the major reason I tell people to shun bio-wheels or wet/dry filters. Without major exposure to the atmosphere they do fix nitrogen but not at levels that cause problems in the reef tank.

 

[xian]

You, personally, are running middle man for the algae.

What do you feed your fish. If you are feeding them nori, the algae absorbed nitrate from somewhere else. If you are feeding mysis they ate algae that grew somewhere else, (or in their case pods that ate algae) Then when the fish add that to your system, you need to remove some of it (skimmer) or else you would overload the denitrifing capacity of your system.

Here is part of the article I was talking about. I can't get to the rest as it is a closed subscription

New twist on nitrogen cycling in oceanic oxygen minimum zones
Jonathan P. Zehr,1
+Author Affiliations

Department of Ocean Sciences, University of California, Santa Cruz, CA 95064
Large uncertainties in the future of Earth's climate have intensified research on the global biogeochemical cycles on land and in the sea. The ocean ecosystem is critical in the carbon balance between the atmosphere and deep ocean, but also plays a large role in chemical and nutrient fluxes that maintain oceanic productivity and greenhouse gas fluxes to and from the atmosphere. Particularly relevant to oceanâ€"œatmosphere gas fluxes and control of nitrogen (N) availability are the ocean regions called oxygen minimum zones (OMZs). A few years ago, we believed that we knew the major components of the N cycle and were only challenged by how to extrapolate these processes to global scales. A new perspective on N cycling was initiated with the finding that a relatively newly discovered microbial transformation, anaerobic ammonia oxidation (anammox) (1) occurred in oceanic OMZs (2, 3) and was the major pathway for formation of N2 in the Peruvian OMZ (4). This finding meant that previous notions of how, where, and when nitrogen was lost from the oceanic ecosystem had new uncertainties, not uncertainties of time and space, but of biological control of multiple competing biogeochemical pathways. In this issue of PNAS, Lam et al. (5) used a suite of approaches to tackle anammox in the Peruvian OMZ. They not only discovered how anammox requirements could be supported by other nitrogen transformations, but they added yet another nitrogen transformation to the oceanic nitrogen cycle mix: dissimilatory nitrate reduction to ammonia.