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To elucidate the historical changes in polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), coplanar polychlorinated biphenyl (co-PCB), and polycyclic aromatic hydrocarbon (PAH) inflows in Lake Suwa, their concentrations in the sediment core were analyzed in 5 cm interval. The maximum concentrations (depth cm) of PCDDs/DFs, co-PCBs, and PAHs were 25.2 ng/g dry (30-35 cm), 19.0 ng/g dry (30-35 cm), and 738, 795 ng/g dry (50-55 cm, 30-35 cm), respectively. Age and sedimentation rate of the sediment were estimated from the vertical changes in apparent density. Deposition rate of dioxins and PAHs were calculated from the concentration and sedimentation rate of the sediment. The results indicate that large amounts of dioxins and PAHs flowed into the lake in flood stage compared to normal stage. CapsuleLarge amounts of dioxins and PAHs flowed into a lake in flood events

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Abstract. The Shimanto Supergroup of geosynclinal facies which ranges from Cretaceous to early Tertiary in age, is widely distributed in the outermost zone of Southwest Japan. Coeval volcanic and plutonic rocks are extensively distributed in the Inner Zone. The coarse clastic rocks mainly of sandstone occupy about a half of the Shimanto Supergroup, and a stratigraphic change of sandstone and conglomerate composition is recognized in the supergroup. The amount of rock fragments, chiefly acidic to intermediate volcanic rocks, increases upward throughout the Cretaceous sequence. Additionally, acidic tuff layers are frequently intercalated in the Late Cretaceous sequence. Conglomerates in the Late Cretaceous are very dominated by acidic volcanic rock clasts. The geosynclinal sedimentation of the Cretaceous Shimanto Supergroup proceeded with the coeval volcanism which became more active in the Late Cretaceous. The clastic sediments were supplied mainly from the sites of the volcanism. The volcanism corresponds to the Cretaceous volcanic activity in the Inner Zone of Southwest Japan. The Cretaceous Shimanto Supergroup may represent a typical forearc sedimentation in an arc-trench system.

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