# [Wet Thumb Forum]-The nitrogen phosphorus ratio



## Robert Hudson (Feb 5, 2004)

A fellow emailed me this document, and thought I would share it with you folks

http://www.aquabotanic.com/nitrogenphosratio.htm

Robert
King admin
www.aquabotanic.com


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## Robert Hudson (Feb 5, 2004)

A fellow emailed me this document, and thought I would share it with you folks

http://www.aquabotanic.com/nitrogenphosratio.htm

Robert
King admin
www.aquabotanic.com


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## m.lemay (Jan 9, 2005)

Maybe somebody can decode that document and tell me what it means for us "wet thumbs". I thought there might be a "conclusion" at the end discussing the relevance of the information but I read the article twice and really got nothing from it. Not that the info's not there, maybe.









75 gal,pressurized CO2 with controller, 3WPG PC lighting,gravel/flourite 50/50 substrate, Filstar XP3, GH=7,KH=5,PH=6.9,NO3=10ppm, PO4=1-2ppm,K=20ppm+/-, FE=.1ppm


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## wetmanNY (Feb 1, 2003)

Well, sticking my neck out to get us started here, it seems that new experiments have confirmed findings, both in natural lakes and in lab aquaria, that changes in the _ratio_ of nitrogen to phosphorus control the make-up of the algal/cyanobacterial/diatom community. (The _absolute_ concentrations of nutrients do control the absolute biomass of photosynthesizers taken all together, nevertheless-- i.e, lots of nutrients do produce lots of photosynthesizers.)

High ratios-- by molecular weight-- of N to P favor green algae, while low N ratios favor cyanobacteria in the mix. That is, high ratios of N to P were unfavorable for cyanobacteria. And high ratios of Si to P favor diatoms, whereas lower ratios favor green algae.

Two possible aquarium conclusions:

If N levels remain the same, reducing PO4-rich flake feed over a period of several weeks may help reduce the relative abundance of cyanobacteria vis-a-vis green algae. Phosphate-containing buffers may encourage cyanobacteria. Conversely, N-enrichment, through fertilizing-- or even through added fish-- could reduce the presence of cyanobacteria in the algal mix.

As PO4 levels build in a newly maturing aquarium and diatoms scavenge available silica, Si ratios drop, a change unfavorable to diatoms vis-a-vis green algae (confirming many aquarists' observations).

There may be members of this board who still feel that field studies aren't generally relevant to lab studies and that neither are relevant to aquarium practice.

[This message was edited by wetmanNY on Thu February 13 2003 at 08:08 AM.]


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## Roger Miller (Jun 19, 2004)

The article is moderately interesting, but hard to read. I'm not sure if it's very useful.

The researchers and the sources they site were studying phytoplankton -- green water -- not the attached algae that are more common nuisances in aquariums. You might be able to extend the findings to cover attached algae, but that would be like using a study on grasses and applying it to trees.

The researches did not study changes that controlled the occurance of significant algae communities. They studied changes in the proportion of different organisms within an algae community. I suppose that if you have a green water problem and you want to change the species that makes the water green, then this study is useful. Certainly the report says nothing about the relative dominance of algae and higher plants, and that is what concerns most gardeners.

The researchers were studying conditions in which nutrient competition was thought to control algal growth. Most aquaria are probably not nutrient-limited. That is especially true of "high-tech" tanks where aquarists dose all nutrients to excess. In particular, the authors point out that cyanophytes out-compete green algae at low N ratios because the cyanophytes can fix atmospheric nitrogen. The common nuisance cyanobacteria in our aquaria are not nitrogen-fixers. Our resident cyanophytes would not profit from a low N ratio.

I'm not going to say that the study is irrelevant to aquaria. I'm sure that out there somewhere there is an aquarium with a problem and an aquarist who could use this information to help solve the problem. I'm also pretty sure that aquarium isn't mine.


Roger Miller


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## wetmanNY (Feb 1, 2003)

I do agree with Roger Miller that the article is about as opaque as green water! However, what the authors are comparing are cellular metabolic requirements, specifically of Chlorococcales vis-a-vis diatoms (Bacillariophyta) and cyanobacteria. Though many Chlorococcales are indeed part of the "green water" or phytoplankton, not all of this Order-- all with a similiar cellular metabolism-- are solitary or free-floating. Some of them form the periphyton that might trouble members of this forum. The University of Winnipeg offers a quick key to the Chlorococcales at http://www.uwinnipeg.ca/~simmons/ysesp/lb4pg10.htm .

_"You might be able to extend the findings to cover attached algae, but that would be like using a study on grasses and applying it to trees."_ I don't see the point of this, since Roger Miller is perfectly aware that monocots such as grasses run a C4 photosynthesis and neither he nor any of us would compare them to trees running a more common C3 photosynthesis. But a free-floating green alga is running the same basic metabolism as a plant-encrusting green alga, is it not?

The reason to confine the study to flask-grown Chlorococcales phytoplankton is that the products can be accurately measured, whereas attached algae (with the same basic metabolism) cannot.

The question of whether _"nutrient competition was thought to control algal growth"_ is often a concern in this forum, but it was not an immediate concern in any of the published studies. There it was instead the _ratio_ of nutrients, not the limitation of any one that were seen to control the makeup of the mixed algal/cyanobacterial/diatom population.

Were the two possible aquarium conclusions I drew just too rash, do y'all think?

Like Roger Miller, I'm ordinarily unaffected by diatoms or cyanobacteria in my own aquaria. But I wouldn't dismiss the article on that basis alone.


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## Guest (Feb 14, 2003)

It's not of much use to aquatic plant growing.

Phytoplankton is not an issue. N ratios are not particularly important to plant tanks(they can be 10:1 20:1, 5:1 etc and still no effect on either plants or algae) and the levels of N and P initially are _very_ rich.
We don't add NH4 to our tanks generally except from fish waste etc.

Chemosat experiments are notoriouly difficult in the lab, ponds, it's not clear if these were maintained at these N ratios or how from the article. A lot of issues were not discussed in the article. 

The article is NOT well suited for planted tanks nor as a general article on plants and algae. I don't think folks will come away with anything of use. 

It does talk about a genus that is the same as Green dust algae but no N ratio control was really found with that species.

Regards, 
Tom Barr


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## imported_aspen (Feb 20, 2003)

roger, after reading your descriptions of what causes and deters algae from reproducing in a fish tank, i might conclude that long periods of heavy o2 in solution, may be the missing link in this whole discussion, rather than specific chemical mixes of your water. is this more correct, than chasing down chemical causes for heavy algae growth?

i see it to be, that a longer photoperiod, say 14 hours, with a light fish load may be the answer we are all looking for. this will oxidise the algae, and make it a cleaner system. many people who do not monitor P N or iron, other than adding trace element mix when the plants seem to be a little iron deficient can grow nice clean tanks, even when it is found that N and P levels are quite high. the discussion of chemical mixes, may be useful in getting the plants to photosynthesise heavily, raising the o2 levels to harfmful levels for the algae. any thoughts?

rick


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## Roger Miller (Jun 19, 2004)

Rick,

I'll keep an open mind about oxygen suppressing algae growth. I've seen some arguments that it may be true.

But...

The idea of keeping lights on for long photoperiods flies in the face of long-standing advice. I remember Karen Randall long ago telling us that submersed plants are adapted to short photoperiods; that periods longer than 8 hours or so do far more good for the algae then for the plants. I know that some of my plants fold their leaves near the end of a day, which tends to give creedance to that idea.

Further, I've seen algae happily bubbling away near the end of a day. In eutrophic ponds algae alone can push oxygen concentrations far higher than atmospheric saturation. It seems like if oxygen were responsible for very much growth suppression that algae would never be able to generate such high oxygen levels.


Roger Miller


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## Wheeler (Feb 8, 2004)

Sorry to get in on this so late, but your example of eutrophic blooms intrigued me, Roger. 

I was always under the assumption that blooms like these were constantly killing themselves off and then the survivors would "feed" off the conditions of the die off; ie: low O2 and high DOC, N/P, etc.

It's a vicious circle, no? This could be useful if I've got my facts straight.

I can say for sure that plants growing at breakneck speed (and therefore high O2) isn't going to deter every algae, though. It *may* be a piece of the puzzle, but it isn't the whole solution....Not IME, anyway.

Can someone tell me, again, why H2O2 will kill algaes?

Best wishes,
John Wheeler


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## wetmanNY (Feb 1, 2003)

Oxygen is more effective against cyanobacteria, perhaps because they have no protection against free radicals, than it is against algae. I'm sure we are all making this distinction, but I wanted to state it explicitly..


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## Guest (Feb 27, 2003)

How much O2 though does harm to algae but not higher plants?

Most algae don't possess peroxisomes. I just got into a discussion about this at a biochemical level.

Some algae do have peroxisomes, eg Chara, Colechaete(green spot) but only a very few green algae.

But the others must have some form of protection agaist photorespiration.

Most algae use HCO3 but will nab the CO2 also.
When supplied with lots of CO2(5%), some algae photorespire but don't normally unless dosed with high CO2.
Chlamydomonas is one such beast.

I'm curious about if there is a catalase active region somewhere in algae. They would need this to deal with the nasty free radicals produced by high rates of Photosynthesis. There's some interesting cell wall development characteristics algae have that are not present in plants. 

I'll figure some of this out hopefully in about 1-2 months. O2 tank is coming.

Regards, 
Tom Barr


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