Hydrologic cycle in a mountainous catchment

In the Maekawa River catchment at the east slope of Mt. Norikura, the water balance and mass balance were examined for three years. The precipitation frequency is high from the rainy season to the autumn in the catchment. Then, the stream discharge increases temporarily in these seasons. The base flow discharge becomes biggest for the spring snowmelt season. The pH and electric conductivity of stream water increase gradually during the winter. The pH and electric conductivity of stream water decline rapidly with the beginning of the snowmelt runoff. When the discharge increases temporarily in the rainy season or at a typhoon event, the pH and electric conductivity of stream water decline temporarily. The Cl- concentration of stream water increases in the early stage of snowmelt season. In addition, the NO3- concentration of stream water increases when the rainfall increases discharge. The major ion concentration of stream water except Cl- and NO3- almost synchronizes with the change of electric conductivity. In the mass balance of the cation, the runoff rate from the catchment exceeds absolutely compared with the atmospheric deposition rate to the catchment. The reason is because there is extremely much elution of ions from rock and soil which are composed by the new volcanic structure. As for the Cl- ion, the runoff rate from the catchment balances with atmospheric deposition rate to the catchment. Also, the atmospheric deposition rate of NO3- ion is bigger with the biological consumption in the catchment than the runoff rate from the catchment.