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Re: Nutrient limitation

A few points;

Any nutrient can be used as a limiting nutrient, however;
It is difficult to have an algal free N limited tank because blue-green 
algae can fix N2.
It is relatively difficult to have an algal free Fe limited tank because it 
is a micronutrient and therefore small amounts can produce large algal 
IMHO, the easiest to use as a limiting nutrient is phosphorus. It is used 
in relatively large amounts by plants and can easily be omitted from 
water-based plant fertilizers. Having said that, its important to 
understand that macrophytes can in no way outcompete algae for P. Algal 
uptake kinetics are such that they can drive the P levels far lower than 
macrophytes can... after discussing this with Sears and Conlin and 
thinking about it for a few months I came to the conclusion that the 
algae become P limited because the TURNOVER rate of P in algae is much 
higher than in macrophytes. As the P becomes available (through algal 
senescence) the macrophytes 
sequester just a small amount but keep it much longer so that over time 
the algae eventually lose out. This is at present not supported by any 
research that I know of.
Diana's systems of course are sediment based and allow the removal of 
BOTH N and P from the water column... a strong argument for fertile 
substrates in my mind... of course you cant have non-rooted plants under 
these conditions.