Phosphorus budgetary analysis of sediment-water interface in a short-term anoxic condition in shallow Lake Kasumigaura, Japan

To investigate the effective depth from the surface sediment, and phosphorus fractions related to phosphorus release under short-term anoxic conditions, varying lengths of sediment cores taken from Lake Kasumigaura, a large shallow polymictic lake in Japan, were incubated for a few weeks and then analyzed. Results showed few differences in total phosphorus (TP) amount per unit area in overlying waters irrespective of the core thickness, and sums of TP in both overlying water and 0- to 2-cm sediment layers were nearly equal before and after the experiment, indicating that phosphorus was released mainly from the 0- to 2-cm layer by dissolution. In contrast, phosphorus was decreased in pore water below a 2-cm depth, probably through sorption to sediment solids. The citrate-dithionite-bicarbonate total phosphorus (CBD-TP) and non-reactive phosphorus extracted by NaOH (NaOH-NRP) in sediment solids in the 0- to 2-cm layer decreased during the experiment. The decreases of CBD-TP were 10 times higher than those of NaOH-NRP, suggesting that the released phosphorus came mainly from the fraction bound to iron in Lake Kasumigaura.