17:15 〜 18:45
[BPT02-P05] Indicator properties of diatom assemblages in sediment core for eutrophic estuary
キーワード：珪藻、湖底堆積物、人為的環境改変、マルチプロキシー解析、水圏環境、汽水域
Diatoms are indicators of various aquatic environments, but their validity to eutrophic state remains unclear in individual taxa. We investigated the multiproxy records in the sediment from Lake Nakaumi, an estuarine lake in Japan. In this study, we infer the relationship between temporal variations of diatom assemblage with the environmental changes focusing on natural and anthropogenic factors.
Using the age model inferred from 137Cs, 210Pb, and 14C dating, the core sediment is estimated to have been deposited for the past 600 years in 0-183 cm core depth, and the sedimentation rates range between 0.24 and 0.38 cm/yr.
Most of the diatom taxa in cores are estuarine-littoral diatoms. This suggests that diatoms comprise fewer allotopic [bb1] taxa from the surrounding environment and are well represented by the aquatic environment in the lake. The vertical trend of diatom concentration is consistent with the CNS trend, except for the uppermost 15 cm, where organic matter is under the process of diagenesis. This suggests that the diatom production has been controlled by nutrient conditions in Lake Nakaumi.
The diatom concentration decreased in the 1600s and rapidly rose in the early 1900s. They result from the dilution effect of nutrient supply after the change of the inflow-liver channel and the impact of a drastic shift in the aquatic environment caused by anthropogenic loads of nutrients and the intense stagnation because of the construction of the port area, respectively. The trends of the six dominant species, such as Skeletonema costatum and Neodelphineis pelagica, in the 1900s correspond to diatom concentrations, but the timing of the peaks varies. It is considered to be the variations in their ecology to nutrient states, suggesting that they can be the effective indicator of the past eutrophic conditions of the aquatic environment.
Using the age model inferred from 137Cs, 210Pb, and 14C dating, the core sediment is estimated to have been deposited for the past 600 years in 0-183 cm core depth, and the sedimentation rates range between 0.24 and 0.38 cm/yr.
Most of the diatom taxa in cores are estuarine-littoral diatoms. This suggests that diatoms comprise fewer allotopic [bb1] taxa from the surrounding environment and are well represented by the aquatic environment in the lake. The vertical trend of diatom concentration is consistent with the CNS trend, except for the uppermost 15 cm, where organic matter is under the process of diagenesis. This suggests that the diatom production has been controlled by nutrient conditions in Lake Nakaumi.
The diatom concentration decreased in the 1600s and rapidly rose in the early 1900s. They result from the dilution effect of nutrient supply after the change of the inflow-liver channel and the impact of a drastic shift in the aquatic environment caused by anthropogenic loads of nutrients and the intense stagnation because of the construction of the port area, respectively. The trends of the six dominant species, such as Skeletonema costatum and Neodelphineis pelagica, in the 1900s correspond to diatom concentrations, but the timing of the peaks varies. It is considered to be the variations in their ecology to nutrient states, suggesting that they can be the effective indicator of the past eutrophic conditions of the aquatic environment.