Particle size-related phosphate binding and P-release at the sediment-water interface in a shallow German lake

Phosphate binding and P-release in the sediment of the eutrophic shallow Lake Butzow are described based on sediment profiles, particle size fractions and incubation experiments. Total phosphorus was about 15% higher in the upper 0.5 cm layer than in the 0.5-1 cm layer. Phosphorus binding varied with sediment depth. Hot P. NaOH and P--> HCl were the dominant fractions in all sediment horizons down to 10 cm depth, with values ranging from 20 to 30%. The P--> H2O, P (--> BD), o-P (--> NaOH) and nr- P (--> NaOH) decreased with depth. The P (--> BD) contributed 21% to Tot-P in the horizon 0 - 0.5 cm and decreased by half in 1 - 2 cm. The greatest proportion of particles (35%) was found in the 100 - 200 mum fraction. This size fraction also accumulated most of the phosphate. Moreover, P-forms were differently distributed in the various particle sizes of the sediment. Sediment particles < 40 mu m can be resuspended by a wind velocity of 2 m s(-1), whereby 17% of the Tot-P from the topmost sediment were transported into the water column. The proportions of released labile phosphate, organic phosphate and hydrolysable phosphate were higher, with values of 24, 33 and 26%, respectively. Dissolved P was released under oxic and anoxic incubation, but anoxic release was higher. Comparison of the results shows that the P-release under anoxic conditions was equal to the P-release by resuspension, but under anoxic conditions the release of bioavailable P was higher.