Re: Phoshates/water chemistry

>   6. I disagree with the statement from Dr. Dave about "the
> chief benefits of the substrate being its anaerobic state and
> not its Cation Exchange Capacity CEC".  If this were true
> plants (terestrial) would grow very well in all types of soil. 
> The cec of silt, clay, sand and organic matter are all different.
> The best soils have a certian mix of these 4 things. The best
> mix grows the most in the way of crop production.  The sand
> soil cannot "hold" (low to no cec) the nutrients long enought
> for the plant to up take them.  Ask someone from Flordia. 
> Paul L.   "May the force be with you".  
You are thinking like an aggie here, Paul. Please dont relate the 
requirements of terrestrial plants to those of submerged aquatic plants. 
For one thing, aquatic plants can absorb nutrients from two vastly 
different environments ... the substrate and the water column. They have 
adapted to these conditions ... the aerobic water column generally supplies 
the cations Ca, Mg and K while the anaerobic sediment supplies NH4, PO4 
and ferrous iron (among other things). This is ideal since in many 
natural systems the cations are fairly stable in the water while the 
supplies of ammonia, phosphate and iron are much higher in the sediment.
Another interesting benifit of an anaerobic sediment is the fact that 
some aquatic plant roots are inhibited in the presence of oxygen. Elodea, 
for instance, cannot produce root hairs in an oxygenated environment.
I also never advocated using a sand substrate. A "good loam soil" was 
advocated as the best medium for growing rooted aquatic plants more than 
90 years ago by a man named Raymond Pond.

Dr. dave