2019 Volume 40 Issue 1 Pages 45-56
This study investigated recent environmental changes in the catchment of Lake Onuma, Japan, based on a physical and geochemical analysis of sediment cores obtained in 2011. Fluctuations in the sediment density, mineral grain size, and C/N ratio of the sediment cores indicate that the sediment yield in the catchment increased between the 1950s and 1970s, with this increase attributed to the artificial land transformation during this period. Clear mineral grain size peaks correspond to heavy rainfall events that caused local flooding and landslides in the catchment. The C/N ratio and δ13C values of the sediment core are within both the planktonic material and river sediment ranges, which suggest that the lacustrine sediment is an almost constant mixture of these two sources. However, the δ15N values have increased in the core since the 1950s, which reflects recent and ongoing anthropogenic nitrogen inflow into the lake.
