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Re: quartz/iron

---------- Forwarded message ----------
From: Paul Sears <psears at nrn1_NRCan.gc.ca>
Subject: Re: quartz/iron
To: Aquatic-Plants at actwin_com
Date: Wed, 11 Mar 1998 08:42:25 -0500 (EST)

> From: "A. Inniss" <andrewi at u_washington.edu>
> Subject: Caridina japonica/quartz binds Fe?
> 	On a different note, all this talk about substrates has reminded
> me to ask a question that's been bothering me for a while:  A long while
> back, I remember skimming through the Baensch Marine Atlas I, and
> somewhere in it, they have a chart on suitable versus unsuitable
> substrates.  They list quartz as unsuitable, because it binds iron. I'm
> wondering what our resident chemists have to say about this claim.  It
> would seem relevant to choosing our substrates.

	The surface of quartz might provide sites where iron could be
bound, but if you are using quartz gravel, the total surface area of
the gravel wouldn't be sufficient to bind a heck of a lot of iron, because
it would go on at most one atom thick.

	Even if iron were held on the quartz, the plants could probably 
use it.  We have seen lots of assertions here that cation exchange capacity
is important for substrates, and that is what would bind the iron.  If you
want high CEC, you need a more porous structure, like clays, rather than a 
pretty well packed one, like quartz.

Paul Sears        Ottawa, Canada