For the purpose of estimating on fixation of CO2 in the forest ecosystem, CO2 concentration in soil gases has been observed in the field and changes in CO2 concentration were simulated by a numerical model. The results are as follows:
(1) The data of hydrological and soil-physical investigations on soils in red pine (Pinus densiflora) forest at CRIEPI Akagi Testing Center (in Gunma pref., Japan) are fed the SPAC (Soil-Plant-Atmosphere Continuum) model. Output on water content and soil temperature agree well with observed data.
(2) One dimensional non-steady diffusion model was newly proposed to simulate changes in CO2 concentration in a forest soil. Soil temperature and water content estimated by the SPAC model are fed as the input data. The model gives appropriate results that reproduced the seasonal changes in the measured CO2 concentration.
Lake Waku-ike, located in Nagano Prefecture in the central Japan, had been marked for its high vertical temperature gradient. The purpose of this study was to make clear the circulation mechanism of the lake. The vertical profiles of water temperature, electric conductance, dissolved oxygen (DO) and pH were measured at the center of the lake from June 2002 to November 2003. The concentrations of major chemical constituents, H2S, hydrogen and oxygen stable isotopic ratios were analyzed for the collected lake water at the depth of every 1 m. As the results, the maximum value of the vertical temperature gradient, 8.9℃/m, was found at the depth of 3 - 4 m on August 2003. The deeper lake water was anoxic in this period. The author divided the observation period into the circulation period (Nov. 2002 - Mar. 2003 and Nov. 2003) and the stratification period (June - Oct. 2002 and Apr. - Oct. 2003) based on the seasonal changes of the vertical profiles of the water temperature, DO, water quality and hydrogen and oxygen stable isotopic ratios. The water temperature and water quality were homogeneous in the whole depth during the circulation period. The lake water was classified into Ca-SO4 type in the circulation period. On the other hand, the lake water deeper than the high temperature gradient layer was classified into Ca-HCO3 type in the stratification period, although the shallower lake water belonged to Ca-SO4 type. Increases in the concentrations of H2S and HCO3- were observed in the deeper layer of the lake during the stratification period. These chemical features in the deeper layer suggested the reaction of the sulfate reduction that consumed organic matter and SO42- and alternatively generated HCO3- and H2S. Hydrogen and oxygen stable isotopic ratios of the deeper lake water during the stratification period decreased by about 10 ‰ and 1 ‰, respectively. Therefore, there was the possibility that the hydrogen and oxygen stable isotopic ratios of the groundwater flowing into the lake was much lower than the lake water.