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RE: Kitty Litter & CEC
James wrote at length and I quote just a bit for context:
> Might we be either carrying the importance of CEC a bit too far, or might we
> be ignoring the environmental constraints of small glass boxes full of
> "stagnant" water (stagnant as compared to natural conditions)?
Yes, CEC is not the only factor which affects how well a substrate can
provide or retain nutrients of various kinds. I think there are 4
factors or categories:
1) nutrients held in organic forms, yet to be released by decomposition.
Peat contains some nutrients but it is very slow to decompose. The
easily decomposable compounds from plant remains are leached out leaving
the lignin and cellulose (peat) which are resistant to decay. TThis
category (organic forms) also includes everything living or dead in the
aquarium which is lying around waiting to be decomposed eventually. Fish
poop holds lots of nutrients in it but gives it up relatively quickly
(measured in days and weeks). A lot of these materials don't ever get
into the substrate; they just decay in the filter or floating around in
the water or lying on the surface. As such their nutrients are either
absorbed through the plant leaves or are inducted into the substrate and
roots by the plant transpiration stream.
2) nutrients in solution in the inter-stitial spaces between substrate
particles, not attached to anything but with nutrient gradients caused
by slow diffusion such as inside clay and silt mixtures or inside
material designed to occlude the nutrients such as plastic coatings or
whatever it is that Jobe's sticks are made out of. Clay balls can hold
inside them high concentrations of nutrients that are not attached to
any CEC sites. Only the low permeability of the clay prevents the
nutrients from diffusing more rapidly. If you made fired clay granules,
you could also have certain kinds of minerals inside the fired ceramic
matrix. Some chemicals would vaporize or react with oxygen when heated
such as nitrogen, sulphur and carbon. I think phosphorus would stay in a
fired clay material; anybody know?
3) nutrients attached to CEC sites. This includes the CEC which develops
as a result of detritus in an ordinary gravel substrate!
4) nutrients held in insoluble crystal forms such as silicates and
oxides (the plethora of clay/rock minerals) which are only released very
slowly by dissolving, surface chemical reactions and very slow diffusion
from inside crystals (geological chemical reactions over hundreds of
years). These would typically be trace minerals but aluminum (not a
nutrient) is a mineral in this category.
4a) nutrients in insoluble crystal forms that require reduction
reactions in order to dissolve (Fe compounds, Mn compounds, P compounds)
These include ferric oxides, ferric hydroxides, FeS, and complex iron
containing mineral structures like vermiculite et al.
The kinds of nutrients held in each of these categories is different.
The trace minerals are held by the last two categories mainly but are
also released from organic compounds during decay.
Steve Pushak Vancouver, BC, CANADA
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!