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Effects of roots, sinking vermiculite

As a newcomer to APD, I have been enjoying the various discussions.  
I have just been getting back into the aquarium hobby after several 
years out of it, and there have been a few changes!

Steve Pushak wrote
>I don't believe I said that the transpiration stream of submerged
>aquatics is responsible for aeration of the substrate. I have said at
>other times that the aerenchyma of stems and roots DOES provide oxygen
>in the substrate and that in some circumstances, plant roots could grow so
>densely over time that the reduction of iron would be greatly diminished.

A number of years ago, I was doing some post-grad research involving 
the rooted aquatic Lagarosiphon major (a significant aquatic weed in 
this country).  At one time I grew some plants of this in transparent 
plastic containers (disposable tumblers I think) and the zone of 
richly red-brown oxidised iron surrounding each root was very 
striking, especially against the blackish reduced sediments in which 
the plants were rooted.

This oxidised  zone was about 2 to three times as wide as the root, 
as I remember, so a dense root mass would have just the effect that 
Steve mentions.

On another theme, I read of the use of vermiculite as a medium for 
aquatic plants, and tried the recommended method of waterlogging it - 
repeated squeezing and kneading.  This seemed to be getting me 
nowhere, so I used lake sediment (there is a lake at the bottom of my 
garden) instead.  However, I subsequently tried placing a bowl full 
of very wet vermiculite in the microwave oven.  After a few minutes 
heating it came to the boil, the vermiculite expanded somewhat then 
started falling to the bottom of the water column.  Some still 
floated, and a second microwave treatment fixed that. 

Readers may care to try this approach.  Assuming that NZ vermiculite is 
the same as that elsewhere, it may save some trouble.  A week later, the 
vermiculite is still submerged, and I was able to remove the fines by 
washing it as if it was gravel, by using a gentle flow of water 
upwards through it.

Nick Miller
Rotorua, New Zealand