Japan Geoscience Union Meeting 2016

Presentation information


Symbol A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW16] Water and material transport and cycles in catchment ecosystems: from headwater to coastal area

Thu. May 26, 2016 3:30 PM - 4:45 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Seiko Yoshikawa(Narional Institute for Agro-Environmental Sciences), Masahiro Kobayashi(Forestry and Forest Products Research Institute), Noboru Okuda(Research Institute for Humanity and Nature), Shin-ichi Onodera(Graduate School of Integrated and Arts Sciences, Hiroshima University), Kazuhisa Chikita(Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University), Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido University), Shinji Nakaya(Department of Water Environment and Civil Engineering, Faculty of Engineering, Shinshu University), Mitsuyo Saito(Graduate School of Environmental and Life Science, Okayama University)

3:30 PM - 4:45 PM

[AHW16-P19] Last 10,000 years variation of biogeochemical process in enclosed bay of a western Japan

*Shin-ichi Onodera1, Guangzhe Jin1, Toru Takeuchi2, Mitsuyo Saito3, Koichi Kitaoka4, Kazuhiro Yamaguchi4 (1.Graduate School of Integrated and Arts Sciences, Hiroshima University, 2.Fujita Geology Ltd., 3.Okayama University, 4.Okayama University of Science)

Keywords:nutrient, enclosed bay, warming, last 10,000 years

Some enclosed seas have a eutrophication issue, most of causes is due to anthropogenic supplies such as agriculture or human waste. But it is necessary to consider the background value or geological stock of nutrient in coastal regions. We aimed to confirm the geological stock and supply variation of the phosphorus in an alluvial plain for 10,000 years. Our research area is located on Okayama Alluvial Plain, western Japan. We drilled and collected the boring core of 6m to 19m at 4 sites. The each core was carried out the dating at the 2 depths, using 14C and volcanic ash. The core at the site of the mountain foot has sandy sediment, whereas another three cores at the coastal side has thick Holocene clay layer. The high phosphorus contents were found at the Holocene clay deposited in around 6,000 to 8,000 years ago under the sea level rising. These periods had rapid warming trend after the Last Glacial period, the increase of rainfall was also suggested. The increase of rainfall would cause the increase of sediment yield. The organic matters in soil are accumulated more in a headwater areas under the cooler climate because of the low decomposition rate, as compared with warmer climate. Based on the results and general present aspects, such high phosphorus content in the sediment is suggested that the organic matters including the phosphorus accumulated in the Last Glacial Period were eroded in headwaters and supplied to the coastal regions with the enclosed sea during the period from around 6,000 to 8,000 years ago with the warming and humid trend. After that, the organic phosphorus had been gradually decomposed, mineralized and released to the groundwater and sea. Such type of background phosphorus would also control the eutrophication and ecosystem environment in the enclosed sea.