Nitrate- cannot get it to fall

[BeanAnimal]

In supply and consumption certain nutrient ratios matter but not in water concentrations (standing stock of nutrients).

If we take the example of the Redfield ratio N:P 16:1 and you have for example a culture of plankton algae, it makes sense if the supply is also in the ratio 16:1 to create a steady state if you want to run a chemostat culture.

You may run a reef tank similar to a chemostat by creating a steady state of supply and consumption. Then the nutrient concentrations in your reef tank remain constant and, if you want, at low concentrations without getting limiting. Ratios of consumption in reef tanks will differ from the Redfield ratio.

Agreed. Matching supply to consumption prevents either nutrient from becoming limiting or accumulating to a harmful level. I think that somewhat goes to what @Lasse is driving at with regard to knowing that consumption"ratio" for a given system and desired state. He can then regulate his input or export to "chase" his balance by automation instead of manual correction.

 

[JonasRoman]

There are no "true" and "false" phosphates, just orthophosphate and so on, I have commented on this here already.

Po4 unbound in free in water is what photometry measure. Besides that we have P incorporated in organics and that is together with free po4 what icp oes P is measure. That mean icp oes wrongly assume all P is coming from free po4 meaning the calculated po4 from icp is always to various extent false high. Is this a problem? Yes, as sometimes the diff is 100%
I have showed that several times. Thats why more and more icp labs include a photmetric measure.
Take home message is you can't "calibrate" your home photometer with icp calculated.

 

[JonasRoman]

To that end, many people promoting “ratios” are using ppm instead of molar quantities, so the numbers they cite are not even the Redfield ratio or whatever other ratio they think they are promoting.

Ofcourse we (most of us at least) know its molar atoms. For the lazy guy you can take nitrate in ppm * 1.54 divide by po4 in ppm. That gives NP ratio in molar.

 

[Hans-Werner]

You now perfectly what I mean when I express in that way of pedagogical reason. Po4 unbound free in wayer is what photometry measure. Besides that we have P incorporated in organics and that is together with free po4 what icp oes P is measure. That mean icp oes wrongly assume all P is coming from free po4 meaning the calculated po4 from icp is always to various extent false high. Is this a problem? Yes,as sometimes the diff is 100% I have showed that several times.

Why is a higher total phosphate a problem? When I did photometer tests and digestion to get total phosphate I got sometimes 8 times higher total phosphate compared to orthophosphate.

I suspect that the problem is not the high total phosphate of ICP but the low orthophosphate of photometers. I also have stated this in the other thread. Coral can make use of total phosphate, not only of orthophosphate. Like many other organisms corals excrete alkaline phosphatase to make organic phosphates and polyphosphates available.

This is not pedagogical but the central question: Is total phosphate really less available to corals than orthophosphate? If not, "true" is give to the wrong parameter, the total phosphate should be "true" phosphate.

The fact that we have more experience with orthophosphate doesn't satisfy to declare it as "true".

 

[JonasRoman]

With phosphate this may be the case at low natural phosphate concentrations

What is the evidence for that ? Strictly its the zooxanthelle we are talking about. I do not think that dinoflagellates uptake of po4 stops when po4 reach 0.02. Still higher than on a natural reef. I am not sure its correct at all that nutrient uptake stops before it reaches zero for a specimen that is coming from natural conditions adapted to ultra low N and P situations. Where is your study that support this?

 

[JonasRoman]

photometer tests and digestion to get total phosphate I got sometimes 8 times higher total phosphate compared to orthophosphate.

If its a problem is up to user to decide. I just say its a false value you get from icp. We are not interested in total P including organics. We are only interested in free po4 in water=zooxanthelle food.

 

[JonasRoman]

suspect that the problem is not the high total phosphate of ICP but the low orthophosphate of photometers. I al

At least in my case this is not the ruth. My photometer measure ×- 0.005 and is always fine tuned versus Hach ref solution.

 

[JonasRoman]

This is not pedagogical but the central question: Is total phosphate really less available to corals than orthophosphate? If not, "true" is give to the wrong parameter, the total phosphate should be "true" phosphate.

Thats a completely different question as that gives totally new reference interval. So far we are talking about and understanding the free po4 as a zooxanthelle source.
It may be of interest to know total P aswell as ling as you understanding the difference. Most icp interpreter do not.

 

[JonasRoman]

phosphate is at the minimum uptake concentration at 0.2 µM/L

According to info when I search on his is that this is not correct. On the contrary I found some data that corals may thanks to active channels absorb down to almost zero independent of the intracellular concentration. A mechanism to manage the natural reef ultra low po4. So if this info is correct coral may absorb far lower than 0.02 ppm po4.

 

[Hans-Werner]

What is the evidence for that ? Strictly its the zooxanthelle we are talking about. I do not think that dinoflagellates uptake of po4 stops when po4 reach 0.02. Still higher than on a natural reef. I am not sure its correct at all that nutrient uptake stops before it reaches zero for a specimen that is coming from natural conditions adapted to ultra low N and P situations. Where is your study that support this?

See for example Sorokin, "Coral Reef Ecology", who did tracer experiments to measure uptake and release.

Zooxanthellae is just a part of the symbiont.

I just say its a false value you get from icp.

In no case it is "false", it is just another fraction or parameter. You can't compare and equate different fractions or parameters.

 

[JonasRoman]

no case it is "false", it is just another fraction or parameter. You can't compare and equate different fractions or parameters.

I think you know exactly what I mean. This turns to be a language issue. I have explained my best.

 

[JonasRoman]

See for example Sorokin, "Coral Reef Ecology", who did tracer experiments to measure uptake and release.

Its divergence in the info then. I found some good articles about the sodium-po4 channel making coral absorb po4 "if they need" far below your stated 0.02 ppm.

 

[Hans-Werner]

Its divergence in the info then. I found some good articles about the sodium-po4 channel making coral absorb po4 "if they need" far below your stated 0.02 ppm.

See also here and here. However I still highly recommend the Sorokin book, and I think the tracer method is very good and conclusive.

Michaelis-Menten kinetics and nutrient uptake is a central point in algal culture and ecological physiology of algae, since you asked for the zooxanthellae. I have read about all this 30 years ago and it is one of my main interests since then. I have prepared and given lectures for symposiums about nutrients.

 

[JonasRoman]

Welcome to the club where we have used a lot of last decades in try to learn and read about this fascinating field. I do not doubt your skills.

I hope you can understand that its natural to question the statement that a zooxanthelle can't absorb po4 when its below 0.02 especially thanks to active transports. The article I found was about how the zoo could absorb po4 in ultralow conditions as long as sodium existed as it was a sodium dependent channel.
Anyway. I will search for your links when time. Thanks for good links