Abstract
The mechanism of phosphate release from lake sediments in aerobic condition was investigated from the view point of solubilization of Fe (III) through formation of complex with dissolved organic matter. If the formation of Fe (III) -hydroxide which adsorbs phosphate was prevented by complexation of Fe (III), the release of phosphate into water will be possible even in aerobic condition.
In this study the complexing capacity of natural waters was measured by the copper (II) solubilization method. The method gave high recovery for strongly complexing ligand such as EDTA and NTA and low recovery for weakly complexing ligand such as glycollic acid and aspartic acid.
The measured complexing capacities of water ranged from 0.54 to 3.15 μM in Lake Teganuma and from 0.58 to 14.16 μM in the inflowing rivers. The seasonal change of the complexing capacity was exactly similar to those of s-Fe and PO4-P.
The measured concentrations of s-Fe in water were much higher than estimated from the solubility of Fe (III) -hydroxide and almost equal to the levels of complexing capacity of water. It suggests that s-Fe is dissolved through complex formation with organic ligands.
