HR: 0800h
AN: H51B-0446    [Abstracts]
TI: Effects of Levee Construction on Hydro-chemical Conditions in the Kushiro Mire, Northern Japan
AU: * Yamada, H
EM: hiroyama@env.agr.hokudai.ac.jp
AF: Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, 060- 8589, Japan
AU: Kawaguchi, T
EM: teppei8@env.agr.hokudai.ac.jp
AF: Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, 060- 8589, Japan
AU: Nakamura, T
EM: t3nakamu@bioindustry.nodai.ac.jp
AF: Tokyo University of Agriculture, Yasaka 196, Abashiri, 099-2493, Japan
AU: Yabe, K
EM: k.yabe@scu.ac.jp
AF: Sapporo City University, Geijyutuno-mori, Minami-ku, Sapporo, 005-0864, Japan
AB: In most cases, drastic changes in mire ecosystems have arisen from cumulative effects of nutrient loads and changes in the water balance of the catchment associated with various human activities. Such changes are serious issues in Japan, for example, in Kushiro Mire, the largest floodplain mire in the country. A rapid transition from a sedge/reed-dominant fen to an alder forest has occurred, especially in mire areas where levees have been constructed for flood management. Although hydro-chemical conditions are suspected to have occurred because of the levee, few attempts have been made to clarify the levee effects on conditions. This study clarifies the levee effects on hydro-chemical conditions. Mire areas around levees showing vegetation changes were investigated. The levee effects were examined through comparison of areas inside and outside of the levee. Three transects (almost 1.5 km long) were set to intersect the levee, and observation wells were set at 50 m intervals in each transect. Groundwater tables and chemical compositions were measured during 2005–2007. Furthermore, the vertical hydraulic gradient (VHG) was measured using a new method with a digital manometer. Although groundwater tables were generally higher near the end of transect inside the levee area, the dry season water tables became lower and fluctuations gradually increased with proximity to the levee. These effects were caused by a drainage ditch that was dug to protect the levee. However, no significant differences were found between conditions inside and outside of the levee. The groundwater chemistry indicated that nutrients such as NO3-, SO42-, K+, Mg2+ and Ca2+ concentrations were significantly higher near the levee because chemical fertilizers used for grass planted on the levee slope ran off into the mire. In the centers of the transects inside the levee, Na+ and Cl- were higher and upwelling of groundwater were identified using VHG distributions. Moreover, the Na+/Cl- ratio resembled that of seawater. These results indicate that seawater existing under the peat layer is upwelling. Although the reasons were not clarified, the upwelling might be an effect of the levee's existence because these were observed at each transect.
DE: 1813 Eco-hydrology
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1834 Human impacts
DE: 1890 Wetlands (0497)
SC: Hydrology [H]
MN: 2007 Fall Meeting