Sorption of Inorganic Phosphate by Lake Sediments

Abstract

AbstractTwenty‐five sediments from nine soft‐water and five hard‐water Wisconsin lakes sorbed between 20 and 100% of the inorganic P added at a level of 830 µg P/g oven‐dried sediment and between 14 and 99% of that added at a level of 6,700 µg P/g oven‐dried sediment. Noncalcareous sediments usually sorbed more added P than calcareous sediments. P sorption fended to be inversely related to the CaCO3 content of the calcareous sediments. Treatment with oxalate destroyed or virtually eliminated the ability of noncalcareous sediments to sorb added P and greatly reduced that of the calcareous sediments. Oxalate extracted widely varying amounts of Fe (3 to 131 mmoles/100 g) and Al (6 to 26 mmoles/100 g) from the noncalcareous sediments; an appreciable proportion of the total Fe in the noncalcareous sediments was oxalate‐extractable. One noncalcareous sediment, high in oxalate‐extractable Fe, sorbed over 80% of inorganic P added at a level of 16,700 µg P/g oven‐dried sediment. With one exception, two treatments with citrate‐dithionite‐bicarbonate or one oxalate extraction had similar effects on the P‐sorption capacity and released comparable amounts of Fe, suggesting that the extractable Fe is derived from an amorphous iron oxide complex. The proportion of added P sorbed was closely related to the amount of oxalate Fe and to the levels of native total inorganic P in the sediments. It is postulated that a gel complex of hydrated Fe oxide which contains small amounts of Al2O3, Si(OH)4, and organic matter, is the major P‐sorbing component of sediments.