Re: Nitrate/Ammonia

The available literature to date indicates that aquatic plants prefer 
ammonia to nitrate. The reason (perhaps) is that it takes energy to 
reduce nitrates to ammonia and so it is more efficient to use ammonia. 
Rooted aquatic plants also prefer to absorb nitrogen through their roots 
from the sediment ... not surprising considering that in a reducing 
environment the ammonia concentration will be many times greater than the 
nitrate concentration.