Leaching phosphates from rock

[asylumdown]

So I recently completed 2.5 months worth of lab work for my masters. I was doing soil analysis stuff and one of the tests I was *going* to do (I ended up not doing it because it all took 10 times longer than I thought it would) was to test my soil samples for 'plant available' phosphorous, i.e. the phosphate component of the soil that could theoretically become available for biological activity.

Now, I'm by no means an expert on this stuff, but I had to do a tremendous amount of research in to this to figure out what 'plant available' phosphorous actually was, and how you'd go about testing for it. Turns out, 'labile' (the stuff that can enter biological cycles) phosphorous is an INCREDIBLY complex topic, and there's not actually a single way to completely measure it because what is 'plant available' is as much a function of time and chemical process in otherwise inert parent material as it is a measure of the water soluble phosphate that you can detect moment to moment.

Anyway, asides from the interesting implications that has for people who have seemingly mysterious algae problems when all their nutrient parameters test undetectable, the most commonly used testing protocol got me thinking:

If you're an analytical soil scientist who's interested in doing a quick and dirty test of the amount of phosphate that is 'plant available' in a soil sample at any one moment, the way you'd go about doing it would be to do an aqueous extraction of phosphate, filter the extracting solution, and then test the solution for the amount of dissolved phosphate using either spectrophotometry, or more direct measurements of ions.

The interesting bit, is that the extracting solution a soil scientist would use to get this 'plant available' phosphorous out of the soil is a simple bicarbonate solution.

The logic comes from a paper published by Olsen et al. in 1958, who proposed (this next bit is quoted from the Natural Resources Conservation Service at http://soils.usda.gov/technical/methods/): "... introduced 0.5 M (molar) sodium bicarbonate (NaHCO3) solution at a pH of 8.5 to extract P from calcareous, alkaline, and neutral soils. This extractant decreases calcium in solution (through precipitation of calcium carbonate), and this decrease enhances the dissolution of Ca-phosphates. Moreover, this extracting solution removes dissolved and adsorbed P on calcium carbonate and Fe-oxide surfaces."

When I read that for the first time it was like a lightbulb went off. I thought "wow, if you were using Marco rock, or any other form of 'dead' base rock for your cycle, or you were using rock that you'd just bleached or treated with muriatic acid, you could really enhance the health of your system by leaching phosphates from them using a week long baking soda bath!"

so my questions are thus:

1. Will this principle work with calcareous rock?

2. Is this something that everyone already knows about and it's commonly used and recommended but because I live under a rock I've just never heard about it?

[IanWR]

And THIS is what makes canreef such a cool resource! I don't know enought to even answer #2 ( I haven't heard of it, but it seems like I know about 5% of common knowledge). Is there any reason there would be any harm from a soak in bicarb solution?

Sorry for you that you seem to have spent a bunch of time that won't directly come out in your project, but I have enjoyed your posts regarding phosphates. Maybe you have enought to write an article for a reef publication?

Thanks for your work!

- Ian

[michika]

Originally Posted by asylumdown

so my questions are thus:

1. Will this principle work with calcareous rock?

2. Is this something that everyone already knows about and it's commonly used and recommended but because I live under a rock I've just never heard about it?

That would be a no on number 2 for me.

I wonder if this has an applicability for better solutions to exporting or ridding our systems of the dreaded algae with no measurables.

[Delphinus]

I feel an experiment coming on!! Haha. Game on.

[asylumdown]

Well the reason it's so interesting from a soils point of view is that the phosphorous that is 'available' to plants is not necessarily the free, highly soluble phosphate trapped within the soil. The concentration of those species are almost always vanishingly small to undetectable in non-agricultural soils because they're taken up so readily by plants. But that's just one tiny component of the phosphorous load in a soil, with phosphates being bound to organic molecules, calcareous material, and generally just being otherwise trapped in other complex inorganic compounds. There's never really a moment where you could measure the 'true' available phosphorous, because through a series of incredibly complex and (even still to this day) poorly understood chemical processes, phosphorous is always in transit through various phases in the soil, so to measure 'plant available' phosphorous you need to also get a picture of how it's moving in that particular soil and add a time function to your measurement.

Now this is all in soils, but in an aquatic environment, there's going to be just as many interesting relationships between available phosphorous and the phosphorous bound to various parent materials. I've been scouring the academic journals trying to suss out whether or not things like microbial mats (i.e. cyanobacteria) in aquatic environments are able to liberate nutrients directly from a substrate or if they're limited to taking in only what's already dissolved in the water column, and so far I'd have to call it inconclusive. It's certainly the case on land in which complex symbiotic relationships between roots, fungus, and bacteria chemically weather parent material, but most of the aquatic research I've seen has focused only on the relationship between the water column and the algae. Considering the complexity of cyanobacteria mat communities and the highly structured micro gradients of oxygen and pH within them, it's hard to believe they wouldn't have some effect on the parent materials they sit on top of. Though, interestingly, I think I have figured out why biopellets are so closely linked to cyanobacteria, and why cyanobacteria seems to thrive in low nutrient tanks if anyone ever cares to know (surprise, the solution is NOT to further reduce nutrients in the water).

In any case, the less phosphate that's in a rock, the less phosphate that can leach out over time.

When I'm back in Calgary I'll see if the lab at school is willing to give me a few powder pillows from our low range phosphate test kits and try something with spare marco rock that I have in my garage. It should be pretty easy to test:

1. Place one batch of marco rock in pure DI water for 48 hours
2. place another batch of marco rock in 0.5 molar bicarbonate solution for 48 hours
3. and just for kicks, put another batch of marco rock in freshly mixed salt water for 48 hours.

Carry a 'blank' of each solution through the whole procedure and measure the initial and final phosphate concentrations.

It shouldn't take me very long.

[michika]

I like where this is going.

[hillegom]

me too

[titus]

Hello

This is cool stuff. Am interested in your findings.


Titus

[syncro]

Originally Posted by asylumdown

I think I have figured out why biopellets are so closely linked to cyanobacteria, and why cyanobacteria seems to thrive in low nutrient tanks if anyone ever cares to know (surprise, the solution is NOT to further reduce nutrients in the water).

I'm interested!

I have wondered if phosphates were leaching from my sand or rock. To test, I left sand, rock and nothing (control) in small containers with DI water for a week. Measured 0 phosphates with a seachem test kit. But still have cyano. Dosing nitrates seems to help green algae outcompete cyano where nitrates are always 0 (it also helps bacterial blooms!).

[Reef Pilot]

Use MB7 to out compete cyano. Works very well in conjunction with bio pellets or other carbon dosing. And makes your water crystal clear.

Use Foz Down to leach out phosphates from your live rock and sand. But be careful, because if you lower your phosphates too rapidly, your corals may not like it. Once your phosphates are close to zero, you can maintain with GFO. I did that with a tank early last summer, and it worked very well.