Carbon dioxide concentration in soil air was observed using gas detection device under coniferous (Red pine, ERC site) and deciduous (Oak, KEB site) forests from late May, 1993 to early December, 1994. Soil temperature and soil water content were also measured to discuss the relationships between carbon dioxide concentration in soil air and these environmental factors.
Results and conclusion of the study are summarized as follows:
1) Carbon dioxide concentration in soil air was always higher than in the atmosphere and ranged from 0.1% at the minimum to 0.75-0.85% at the maximum.
2) Carbon dioxide concentration in soil air increased from spring to summer and decreased from autumn to winter. In the summer of 1994, however, increase of carbon dioxide concentration was inhibited or even decreased because of an extremely low suction condition of soil. This seasonal change of the concentration reflects a similar seasonal change of carbon dioxide production in the soil which is mainly controlled by soil temperature and soil water content.
3) Carbon dioxide concentration in soil air was relatively low in shallow depth and increased with depths. In the summer of 1993, a peak of carbon dioxide concentration was observed at the depths of 50-70cm at KEB site. These concentration profiles are not consistent with general profiles of carbon dioxide production, that indicates the importance of a process of carbon dioxide transport.
4) Carbon dioxide concentration in soil air increased exponentially with soil temperature of the same depth. In a very dry condition (pF >2.4) at ERC site, however, this correlation reduced and carbon dioxide concentrations became lower than in a normal moisture condition. Carbon dioxide concentration in soil air was estimated using the relationship and soil temperature data. The estimated value agreed well with the observed value except when the soil was under extremely wet or dry condition.
Water qualities of spring and groundwater were investigated in the foot of Mt.Fuji. The pH values of the waters at the eastern region of the mountain were more than 8 and those of other regions were mostly neutral. The electric conductivities of the spring water at the side of the mountain were relatively low, under 100μS/cm, while those of other regions mostly ranged from 100 to 200μS/cm. The value becomes higher with the distance from the top of the mountain, it is considered to reflect the residence time of groundwater. Furthermore, some of the groundwater were above 200μS/cm to be influenced by human activities. The type of water quality was dominated by Ca-HCO3 type, and it tended to change to Na・Ca-HCO3 type with the flow or the residence time. As the results of the principal component analysis, the groundwater quality showed the distribution in the direction of the first principal component with the increase of the total amount of ions. It is considered that this direction indicates that of the evolution of the groundwater quality.
本会では, 本誌第26巻1号より「講座」を開設し, 第1回目のテーマとして「蒸発散」を取り上げた.5人の執筆者による講座「蒸発散」は, 現時点における最新の研究動向を踏まえ, 広範な角度から蒸発散についての基礎的な内容を伝えることができたものと思われる.第一線の研究者によるかなり高度な内容にもかかわらず, 好評のうちに第1回目のテーマを終了することができた.
本巻より始まる第2回目のテ-マは「降雨浸透」である.降雨浸透も古くて新しいテ-マであるが, 本講座では土壌の保水性や透水性といった水文土壌物理特性, クラストやマクロポアなどの土壌の間隙特性, 斜面の成層性や不均一性などの場の条件との関連において, 林地, 畑地, 都市, 傾斜地のそれぞれにおける降雨浸透過程についての基礎知識をとりまとめることを意図している.執筆者の皆様には最新の研究成果を取り入れていただき, 本講座によって降雨浸透現象についてのより一層の理解が増すことを願っている.