A study on the discharge of base cation in mountainous catchments, considering the variation and component of cation adsorption pool in soil(Department of Sciences for Biospheric Coexistence)

博士学位論文要

Soil catena along a collapsed mountainous slope underlain by granitic rock in Hiroshima Prefecture

To clarify soil catena and its characteristics of mountainous slope in temperate region, physical and chemical analysis on soil were conducted for 6 soil profiles along granitic mountainous slope. The soil types were residual soil at upper slope and colluvial soil at lower slope. Soil contents of dissolved Na^+ and K^+ were high at upper slope and sischarge area, and exchangeable base cation contents

River Bed Form in a Granitic Mountainous Catchment : A Case of the Source Area in Kurose River, Hiroshima Prefecture

In order to clarify spatial variations in a river bed form in a granitic mountainous catchment, we surveyed topographically a steep river on a source area of Kurose River in which the debris flow occurred in 1999. Firstly, we found that the spatial variation in erosion-deposition process on the steep river. Both of the lower stream and upper one held much sediments with large gravels (φ>2m). On the other hand, the middle stream exposed mainly the bedrock. Secondary, we confirmed spatial distribution of river falls. The height of river fall on the upper stream rose with the increase of river gradient. On the contray, the frequency of falls was constant in spite of inclination

Effect of forestation of hinoki and larch on soil chemistry in mountainous water source area for water supply to Tokyo

Effects of forestry on soil properties, stream water chemistry and mass balance in watersheds had been confieremed by many previous studies. However, they have not clarified in detail variation processes of soil chemistry and soil physics after the hinoki and larch forestation. To clarify the variation processes, it is important to confirm the difference of soil chemistry and soil physics on the artifitial and natural forest. In this research, we conducted the soil physical and chemical investigations on seven slopes covered by hinoki (chamecyparis obtusa) and larch (Larix leptolepis) artificial and beech (Fagus crenata) natural forest in a highland area, the western side of Tokyo. The water repellency of A_0 horizon was stronger on the artificial forest slope than on the natural forest. In addition, the permeability was low on the artificial forest due to the strong water repellency. On the artificial forest, both of the exchangeable base cation content and soil pH were low and Al concentration was high, as compared with those on the natural forest. These results suggest that the soil acidification is progressed on the artificial forest. The decline of soil pH by the forestation was controlled by the increase of H^+ supply at the A_0 horizon due to the property of litter decomposition and the decrease of base cation supply at the A-horizon. In general, the cation supply rate such as weathering rate is controlled by the infiltration rate and temperature. These soil physical and chemical properties suggest that infitration rate at the A-horizon. declines after the forestation, weathering rate declines and consequently soil is acidified