Recent Eutrophication and Environmental Changes in the Catchment Inferred from Geochemical Properties of Lake Onuma Sediments in Japan

Abstract

This study investigated the continuous record of eutrophication in Lake Onuma based on the geochemical properties of two lake sediment cores obtained from the deepest part of the lake in 2011. Based on a tuff layer deposited during the eruption of Mt. Komagatake, and on the correlation between fluctuations in • 13 C and • 15 N values, two sediment cores, ON11-2-2 and ON11-6, were dated to the 1920s and 1890s, respectively. The • 13 C value and C/N ratio for the lake sediments show values within the ranges for planktonic material and river sediment, suggesting

Organic carbon accumulation and productivity over the past 130 years in Lake Kawaguchi (central Japan) reconstructed using organic geochemical proxies

“…210 Pb, 137 Cs, and 134 Cs concentrations The chronology of the KAW14-1A, KAW14-4B and KAW14-7A cores was constructed based on 210 Pb (Krishnaswamy et al 1971) and 137 Cs dating (Ritchie and McHenry 1990). The powdered sediment samples were packed into a 20-mL plastic vessel and stored for 1 month in a plastic bag to establish a radioactive equilibrium between 222 Rn and 214 Pb (Ochiai et al 2015). The radioactivities of 210 Pb (46.5 keV), 214 Pb (352 keV), 134 Cs (604.7 keV) and 137 Cs (661.6 keV) were determined for every 1-cm slice by gamma-ray spectrometry using Ge detectors at the Low Level Radioactivity Laboratory (GEM-FX5825-HJ, EG&G ORTEC) and Ogoya underground laboratory (EGMP60-30-R, CANBERRA EURISYS; EGM3800-30-R, EURISYS MESURES), Kanazawa University (Hamajima and Komura 2004 D r a i n a g e t u n n e l t o M i y a g a w a R i v e r Drainage tunnel from Lake Sai Fig.…”