Restoration of paleo-water level of Lake Biwa during Holocene

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We investigated depositional process and environmental history of inner lakes around Lake Biwa, by using of five boring cores.The results are follows. 1) There are two types of inner lakes. One is the closed inner lake which bates behind the mountains, so sediment supply is not enough. The other type is open inner lake which locates in the delta, enough sediment are supplied intermittently. 2) Closed inner lake deposits consist of continuous humic soil and peat, containing Kikai-Akahoya tephra (c.a. 7.3ka). This means stable marshy or shallow water environments had been continued during late Holocene in the closed lagoon. The open inner lake deposits consist of alteration of sand and mud and gravels, containing thin humic layers. Such deposits indicate frequent environmental changes in the fluvial plain and delta. 3) Inorganic sediments are concluded in the uppermost part of some closed inner lake deposits which dated historical age. This suggests that human activities such as reclamation on the lowland surrounding the inner lake affected product of inorganic sediments. 4) In comparison with two closed inner lake deposits in the western side and eastern side of Lake Biwa, Minami-numa located western side and Sone-numa located eastern side, the same datum horizons are systematically deeper at the Minami-numa core than at the Sone-numa core, while both two deposits consist of peat containing rootlets of true grasses under c.a.4ka horizon. This means active faults near the western side of Lake Biwa acted before c.a.4ka, and western side of Lake Biwa subsided