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Cyanobacteria fixing nitrogen

Subject: Re: Nutrient limitation
David W. Webb wrote:

>> I've found that cyanobacteria do contribute organic nitrogen to the system.
>> The process involves the cyanobacteria rapidly consuming nutrients until
>> they become nutrient limited in some way other than nitrogen.  At this
>> point, they begin to die off and decay, contributing their nutrients back
>> to the system.

Bjorn Straube wrote:

>But this is not nitrogen "Fixing", they are not pulling in nitrogen that
>comes from outside the system (what a horrible thought ;)).  They only
>give up nitrogen that was avalible within the aquarium to begin with,
>they just "got there first".

Yes it is.  At least some cyanobacteria are capable of fixing atmospheric
nitrogen.  This is what allows them to grow even in the absence of nitrogen
products in the water.

Karen Randall
Aquatic Gardeners Association