14:30 〜 14:45
[HQR04-09] プランクトンに対するDNAメタバーコーディングを用いた古環境復元：宍道湖における研究例
キーワード：環境DNA、堆積物古代DNA、原生生物、堆積物コア、人新世
The DNA metabarcoding (DNA-MB) is a powerful and practical method to thoroughly clarify the composition of organisms contained in environmental samples. This approach is widely used not only in biological surveys but also in earth science studies. The DNA-MB targeted on the plankton community demands wide knowledge on diverse taxa. This analysis also needs correct reference DNA sequences, which are occasionally not enough to identify the detected taxa. Partly because of these reasons, the DNA-MB focused on plankton community has scarcely been conducted in the field of sedimentary sciences. Such analysis, however, could be effective to elucidate the paleo-environment because plankton contain the primary producers. Furthermore, they possess large biomass and respond sensitively to environmental changes.
As a case study, we will present a sedimentary study targeted on plankton community in Lake Shinji, Japan. Lake Shinji is a low salinity lake (the PSU is ca. 5 in the highest layer), but it was a semi-closed bay filled with sea water before 2000 years ago. Previous studies clarified that the concentration of sulfur, which indicates the inflow of sea water, decreased in a certain period during the past 2000 years. It is therefore hypothesized that in this period, the semi-closed bay became an almost freshwater lake. Yet, this hypothesis was not supposed by enough biological evidences.
Given this situation, a sedimentary core of ca. 4 m was sampled in July 2021 from the center of the lake, and the DNA-MB focused on plankton was conducted for the sedimentary samples taken from every 4 cm. Marine plankton were mainly detected in the samples lower than ca. 2.5 m in depth, and the plankton composition was largely different among the samples upper and lower than ca. 2.5 m. This core depth corresponded to the timing of the sulfur decrease, and the age was estimated at A.D. 1250–90. Judging from these results, the desalinization of the lake and the drastic change of ecosystem stared presumably around A.D. 1250–90.
As a case study, we will present a sedimentary study targeted on plankton community in Lake Shinji, Japan. Lake Shinji is a low salinity lake (the PSU is ca. 5 in the highest layer), but it was a semi-closed bay filled with sea water before 2000 years ago. Previous studies clarified that the concentration of sulfur, which indicates the inflow of sea water, decreased in a certain period during the past 2000 years. It is therefore hypothesized that in this period, the semi-closed bay became an almost freshwater lake. Yet, this hypothesis was not supposed by enough biological evidences.
Given this situation, a sedimentary core of ca. 4 m was sampled in July 2021 from the center of the lake, and the DNA-MB focused on plankton was conducted for the sedimentary samples taken from every 4 cm. Marine plankton were mainly detected in the samples lower than ca. 2.5 m in depth, and the plankton composition was largely different among the samples upper and lower than ca. 2.5 m. This core depth corresponded to the timing of the sulfur decrease, and the age was estimated at A.D. 1250–90. Judging from these results, the desalinization of the lake and the drastic change of ecosystem stared presumably around A.D. 1250–90.