HR: 1340h
AN: H23D-1462    [Abstracts]
TI: Hydrochemical and hydrological dynamics of bedrock groundwaters in a weathered granite headwater
AU: * Katsuyama, M
EM: katuyama@kais.kyoto-u.ac.jp
AF: Research Institute for Humanity & Nature (RIHN), 335 Takashima-cho, Kamigyo-ku, Kyoto, 6020878 Japan
AU: Ohte, N
EM: nobu@bluemoon.kais.kyoto-u.ac.jp
AF: Graduate Schoolof Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 6068502 Japan
AU: Kosugi, K
EM: kos@kais.kyoto-u.ac.jp
AF: Graduate Schoolof Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 6068502 Japan
AU: Katsura, S
H23D-1462 AF: Graduate Schoolof Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 6068502 Japan
AU: Uenoyama, M
H23D-1462 AF: Graduate Schoolof Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 6068502 Japan
AB: The importance of the bedrock groundwater to the hydro- biogeochemistry in forested headwater catchments has been stated. However, there are few studies which directly measured the bedrock groundwater dynamics and their chemistry because of the difficulties to access to the bedrock groundwater. We directly collected their samples within 1m depths from the bedrock surface at the headwater subcatchment (0.086ha) within the Kiryu Experimental Watershed (KEW; 5.99ha) and measured their chemistry and the stable isotope ratio of water to evaluate the role of bedrock groundwater to the streamwater chemistry in a weathered granite catchment. Half of the total rainfall infiltrated into the bedrock at the hillslope plot (0.024ha). This bedrock groundwater was the dominant in the baseflow. The SiO2 concentrations in the bedrock groundwater were highest within the catchment, and those in the streamwater were similar to or lower than them. The NO3- concentrations in the streamwater were clearly lower than those in the groundwater above the bedrock, and therefore, the bedrock groundwater with low NO3- may be contributing to the streamwater. The NO3- concentrations in the bedrock groundwater decreased with the time and along the infiltration processes, though these were higher than those in the streamwater. These mean that there are some processes of which the NO3- concentrations decrease within the bedrock. The isotope data showed that the deeper bedrock groundwater had the longer mean residence time. Thus, the bedrock groundwater seems to be affected much by the biogeochemical reactions before it contributed to the stream. Considering the water budget, the contributions of the bedrock groundwater increased at the outlet of KEW, though the streamwater had similar SiO2 concentrations there. Therefore, the bedrock groundwater, contributing to the streamwater in the weathered granite headwaters, has uniform geochemistry within the catchment; in other word, the hydrologic pathways within the bedrock may be relatively shallow.
UR: http://www.bluemoon.kais.kyoto-u.ac.jp/kiryu-e/contents.html
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 1831 Groundwater quality
DE: 1839 Hydrologic scaling
DE: 1876 Water budgets
SC: Hydrology [H]
MN: Fall Meeting 2005