Greg,
That is exactly right. Aquakler works by oxidizing the sediment. Mr. Martin is exactly correct. The soluble Fe2+ is easily oxidized to Fe3+ by oxygen in a wide pH range. Fe3+ has a great affinity to form insoluble complexes with ligands such as mono and polyphosphates. If these complexes are subjected to anoxic conditions, Fe3+ is reduced to the soluble Fe2+ and the phosphates are released in solution.
Moreover the soluble Mn2+ oxidizes only under alkaline conditions (pH >8) to the higher valence states. Oxidation of Mn2+ under alkaline conditions is catalyzed by Fe. Oxidation of Mn2+ is enhanced by H2O2 leading to a Mn3+ polymer with O. In the presence of Fe, Fe-O-Mn complexes can also form. Acidification of this complex quickly releases Fe back in solution.
Effects of Anoxic Conditions:
Other oxidants become more important
Sulfate reduction (SO42-) forming H2S then FeS�
Denitrification (NO3-) releasing NH3 which accumulates
Fe reduction (FeOx) forming Fe2+ releasing P
Mn reduction (MnO2) forming Mn2+ releasing P
Also to answer your question on depth, because a body of water has exchange of oxygen with the atmosphere may mean that the water column itself is aerobic, but 2mm into the sub-aqueous content pH will drop as will the oxygen levels. The exchange of porewater from the sediment into the water column can carry Phos.
I hope this helps....
