[MIS10-P25] Diatom Assemblages in Lacustrine Sediments of Lake Tazawa, Akita Prefecture, Northern Japan
Keywords:Lake Tazawa, Diatom assemblage, Acidification
In TZW15-1 core, Cyclostephanos tazawaensis and Discostella spp. were abundant in whole the core. These species are freshwater planktonic species and indicates the lake has been a freshwater lake in the past 7000 years. Discostella spp. increased in 500-4000 years ago, however the detail of the environmental change was not cleared. Changes of diatom assemblages was not found at the top of the core, implying that the top of core is missing.
Surface core includes water condition changes since 1940. Diatom assemblage at the bottom of the core was similar to TZW15-1 core, indicating water environments before the lake acidification. At 17 cm core depth, Eunotia spp., Surirella spp. and total sulfur (wt%) increased by inlet of acidic water in 1940. Eunotia exigua is abundant in Tamagawa River, so its occurrence in the surface core samples indicates that part of Eunotia spp. was carried through water tunnel. Decrease of total sulfur at 8 cm core depth should correspond to the construction of neutralization plant, however diatom assemblages of pre-acidification have not yet recovered.