Re: Sand, clay, soil substrates


I enjoyed your posting. In the course of my studies over the past 15 
years I have carried out several experiments on the growth of rooted aquatic 
plants. More importantly, I have read many, many studies on mineral 
nutrition in aquatic plants. It is abundantly clear from this research 
that the growth of rooted aquatic plants is vastly superior on a soil 
substrate than on sand or gravel. The reasons are only partly understood, 
but the main benefit is the anaerobic sediment. This solubilizes 
phosphorus and iron, and transforms nitrate to ammonia which is the 
preferred ion for plants. In fact, some aquatic plant roots are actually 
inhibited in the presence of oxygen. Aquatic plant are well adapted to 
anaerobic conditions; they have extensive air channels that allow oxygen 
to diffuse to the roots, some can respire anaerobically for extended 
periods and some even use the sediment as their main source of CO2.

As for the cold Steve, check the weather station, we havent been warmer 
than -20 C for over two weeks and our lows are generally around -35 to 
-38 C every night (of course its a damp cold in Vancouver). :-)

Dr. dave