To clarify the geochemical and environmental behaviors of the high manganese content of sediment point 5 in Lake Biwa reported previously by S. Nakashima, some samples of five sediment points (1-5) and two sediment core parts (4 cm depth at 2 cm intervals, L1-L3, and 6 cm depth at 2 cm intervals, H2-H4) were collected from the northern and sourthern parts of the lake. The organic matter, minerals and phosphorus species in the bottom sediment were analyzed by solid-state ^<13>C, ^<27>Al, ^<29>Si and ^<31>P NMR. The organic matter : At the sediment points (1, 2, 3) and sediment core parts (L1-L3), these samples appear to have a high amount of aromatic compounds. The aromatic compounds are relatively constant regardless of depth in the core parts (L1-L3, H2-H4). At point 5, non-aromatic compounds appear be present in high amounts. So, non-aromatic compounds seem to tend to concentrate in areas of high manganese content. The minerals : At sediment point 5, minerals mainly consist of (2 : 1) layer-clay mineral. The clay mineral holds together simply with heavy metals such as manganese. As a result, it seems that manganese is enriched in the sediment point. The phosphorus species : At points 3, 4 and H3, the organic phosphorus species is the major group. At point H4, an inorganic orthophosphate (PO_4^<3->) appears in high amount, but the remarkable enrichment of manganese at point 5 could not be assumed. In conclusion, we presumed that organic matter and minerals play an important role in the enrichment of manganese content at sediment point 5 of Lake Biwa.
