[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.