4:00 PM - 4:15 PM
[AHW24-21] Relationship between transportation and palynofacies/palynomorph assemblage of suspended sediments in the rivers around Lake Shinji and Nakaumi Lagoon.
Keywords:palynofacies, palynomorph, biomacromolecule
The composition of sedimentary organic matter including amorphous organic matter, palynodebris, and palynomorph is called 'palynofacies' as an indicator of the depositional environment of sediment. The various types of rivers, including the Hii-kawa River and the Iinashi-gawa River, flow into Lake Shinji and Nakaumi Lagoon, forming one of the largest estuarine environments in Japan. Remains of green algae and cyanobacteria are deposited as allochthonous aquatic palynomorphs in the sediments of Nakaumi Lagoon and Lake Shinji. However, the formation and degradation processes of organic matter composed of resistant macromolecule during river transport, which are related to the character of the ecosystem in the hinterland and/or catchment area, are still unclear. In addition, there are few reports about palynomorph assemblage in suspended sediment compared with those in deposited sediments. In this study, we performed palynofacies/palynomorph analyses using the suspended sediments collected from the 16 rivers including the Hii-kawa River around Lake Shinji, the 9 rivers including the Iinashi-gawa River around Nakaumi Lagoon, and the Hino-kawa River flowing into Miho Bay (Japan Sea) to reveal the transportation process of sedimentary organic matter via the rivers.
Suspended sediments of collected 5L water samples in September 2021 were precipitated by a centrifuge. The obtained organic matter after acid (HCl, HF) treatment was observed by a microscope for palynofacies/palynomorph analyses. Pollen/spores of land plants, remains of chlorophyte algae (e.g., Pediastrum, Scenedesmus and Desmodesmus), remains/zygospores of zygnematophyte algae (e.g., Cosmarium and Zygnema), remains/akinetes of cyanobacteria, shells of testate amoebae and fungal spores/hyphae were observed as palynomorphs. Thecal plates of dinoflagellate and remains of euglenophyte algae were observed due to the particle sedimentary organic matter separated by this method including labile macromolecules like cellulose. Remains of Cosmarium were mainly observed in the samples of rivers that have large catchment areas such as the Hii-kawa, Iinashi-gawa and Hino-kawa Rivers, although remains of Staurastrum and Pediastrum are observed in the surface sediment samples from Lake Shinji and Nakaumi Lagoon. However, remains of Staurastrum and Pediastrum were observed from the samples collected from the Hii-kawa River after heavy rain in June 2021. From this result, the consideration of seasonality is necessary to discuss the bias of organic matter degradation/preservation during transportation via the river. The colors of AOM are pale brown in the samples, which suggests that these AOM are originated from phytoplankton like diatom living in rivers, rice fields and ponds/lakes formed by dams. On the other hand, blackening of AOM, which occurred by biodegradation of macromolecular during transportation, were proceeded in the samples of the Hii-kawa, Iinashi-gawa and Hino-kawa Rivers. In addition, palynodebris of plants are the main component in the sample having higher C/N values from the Tamayu-gawa and Kimachi-gawa Rivers flowing into the south coast of Lake Shinji. From these results, the palynofacies of river suspended sediment is related to the character of transportation of individual river, although the consideration of bias by chemical/biological degradation and physical destruction is necessary.
Suspended sediments of collected 5L water samples in September 2021 were precipitated by a centrifuge. The obtained organic matter after acid (HCl, HF) treatment was observed by a microscope for palynofacies/palynomorph analyses. Pollen/spores of land plants, remains of chlorophyte algae (e.g., Pediastrum, Scenedesmus and Desmodesmus), remains/zygospores of zygnematophyte algae (e.g., Cosmarium and Zygnema), remains/akinetes of cyanobacteria, shells of testate amoebae and fungal spores/hyphae were observed as palynomorphs. Thecal plates of dinoflagellate and remains of euglenophyte algae were observed due to the particle sedimentary organic matter separated by this method including labile macromolecules like cellulose. Remains of Cosmarium were mainly observed in the samples of rivers that have large catchment areas such as the Hii-kawa, Iinashi-gawa and Hino-kawa Rivers, although remains of Staurastrum and Pediastrum are observed in the surface sediment samples from Lake Shinji and Nakaumi Lagoon. However, remains of Staurastrum and Pediastrum were observed from the samples collected from the Hii-kawa River after heavy rain in June 2021. From this result, the consideration of seasonality is necessary to discuss the bias of organic matter degradation/preservation during transportation via the river. The colors of AOM are pale brown in the samples, which suggests that these AOM are originated from phytoplankton like diatom living in rivers, rice fields and ponds/lakes formed by dams. On the other hand, blackening of AOM, which occurred by biodegradation of macromolecular during transportation, were proceeded in the samples of the Hii-kawa, Iinashi-gawa and Hino-kawa Rivers. In addition, palynodebris of plants are the main component in the sample having higher C/N values from the Tamayu-gawa and Kimachi-gawa Rivers flowing into the south coast of Lake Shinji. From these results, the palynofacies of river suspended sediment is related to the character of transportation of individual river, although the consideration of bias by chemical/biological degradation and physical destruction is necessary.