Properties of sediment phosphorus in seven wetlands of the Swan Coastal Plain, South-Western Australia

Seven wetlands from two dune systems on the Swan Coastal Plain, Western Aus tralia were studied for sediment properties associated with phosphorus rete ntion and potential remobilization. Sediments from the Spearwood Dunes had higher contents of silt, clay, and organic material. Sediment total phospho rus was positively correlated with water content, organic matter and silt c ontent but inversely related to the amount of coarse materials. Part of the organic matter was refractory humic substances, and the molecular weight o f humic acids ranged from less than 10,000 to over 600,000. Significant por tions of sediment total P (5-73%) were bound to humic substances. The fract ion of "loosely-bound phosphorus" (NH,CI-P) accounted for less than 10% of total-P. NaOH-extractable P was high; some humic substances were extracted with NaOH. Correlations between phosphorus forms and other components sugge st an affinity between 'fine particles' of similar hydrologic density durin g sediment transport and reworking, and this involves most humic-P in these wetlands.