Interrelations between iron extractability and phosphate sorption in reflooded air-dried sediments

To understand the effects of drying on phosphorus sorption properties of wetland sediment, the acid ammonium oxalate and citrate-dithionite-bicarbonate (CDB) extractions were applied to sediments from seven shallow lakes near Perth, Western Australia. Air-drying generally led to a marked increase in oxalate- and CDB-extractable Fe, but not in extractable-Al which varied less than 2%. Air-drying also induced changes in equilibrium concentration, labile potential and sorption capacity of phosphorus in reflooded sediments. These were accompanied by changes in pH, turbidity, E-440 and soluble Fe3+ in the water. The Fe Ox/Fe CDB ratios of wet and air-dried sediments suggested an increase in iron crystallinity upon drying, correlated with the decrease in P-sorption capacity (R-2= 0.72, p < 0.05).