Seasonal dynamics of biogeochemical proton and base cation fluxes in a white birch forest in Hokkaido, Japan

Biogeochemical proton and base cation fluxes in a 30-year old white birch f orest composed of Dystric Cambisols in northern Hokkaido, Japan were estima ted using data on atmospheric deposition (AD), throughfall (TF), stemflow ( SF), and discharge from soils (DS) and plant uptake (UP) from early June to November 1999. In the monitoring period, proton flux was 0.20kmol(c)ha(-1) for AD, 0.07 for TF+SF, and 0.03 for DS, indicating that atmospheric acid input was neutralized through plant and soil. Base cation flux was 1.29 for AD, 1.23 for TF+SF, and 0.99 for DS and plant base cation uptake was 2.14, indicating that the soil was the major source of base cation for plant. Ho wever, these seasonal fluxes showed various trends. Cumulative base cation flux in TF+SF showed constant increase trend during the whole period, which was similar to AD. Proton flux in AD jumped once just after a heavy rain o f 255mm for 8 days at the end of July. Trends for the proton and base catio n fluxes in TF plus SF were similar to that of AD. Although proton and base cation fluxes of DS were not found until middle July because of vegetation uptake and no flow, both fluxes increased suddenly after the heavy rain in July. After August the base cation and proton fluxes in the DS increased c ontinuously, due to the lack of plant uptake and intermittent rainfall. In this study, it is clear that plant activity and water flow are very importa nt driving force for seasonal dynamics of biogeochemical cycling.