Changes in the composition of phosphorus (P) compound groups in sediment and P in sediment pore water in a shallow eutrophic lake: a 31P NMR study

We observed phosphorus (P) compound groups in sediment in Lake Kasumigaura in winter (February and March) and summer (July and August) to identify how their composition differs between the seasons. The concentration of soluble unreactive P in sediment pore water (SUPpore) was significantly higher in winter than in summer, whereas the concentration of soluble reactive P (SRPpore) was significantly higher in summer than in winter. In summer, when the concentration of SRPpore was high, the concentration of orthophosphate was greatest (similar to 80 %) among the P compound groups. The concentration of orthophosphate diesters had a significant negative correlation with SUPpore concentration and was significantly lower in winter (high SUPpore concentration) than in summer. Such relative abundance of P compound groups in sediment could have resulted from adsorption of orthophosphate in summer and degradation of orthophosphate diesters in winter; these seasonal processes could contribute significantly to the changes in the concentrations of SRPpore and SUPpore, possibly influencing the P concentrations in the water column in Lake Kasumigaura.