Characteristic diurnal fluctuations in soil water content in peatland were detected by time domain reflectometry (TDR) technique in Sarobetsu Mire, Hokkaido, Japan. The water content measurements were conducted in clear day from 3 to 7 August 1995 at a sphagnum peatland (Site M) and at a transition peatland which has been invaded by Sasa Palmata (Site S). At both sites, the volumetric water content increased by 1 or 2% from about 12:00 to about 0:00, and then decreased until about 12:00 the next day. These characteristic diurnal fluctuations occurred not only in the unsaturated zone but also in the saturated zone. These fluctuations cannot be explained either by the time variation of groundwater level or that of ground-surface height or soil temperature.

In contrast, the weight of the lysimeter decreased from about 6:00 to 18:00, and remained constant until about 6:00 of the next day. The volumetric water content by the TDR in the lysimeter, however, showed same tendency of the characteristic diurnal fluctuations in the volumetric water content. This indicates that the characteristic diurnal fluctuations of the soil water content cannot be explained only by net water balance in the lysimeter.

Hydrogen and oxygen isotopic ratios of precipitations, river waters and groundwaters were analyzed to obtain the fundamental data for studying the process of groundwater flowing into Lake Biwa. Monthly precipitations were collected from March 1994 to August 1995 and water samples of river and groundwaters were also taken in March and August 1995 in the eastern area of the Hiei mountains. The isotopic ratios of precipitations show seasonal variations having a sawtoothed shape with a minimum in July and a maximum in November. The weighted means of δD and δ¹⁸O values for precipitation are -52.6‰ and -8.6‰ near the summit, and -50.4‰, -7.7‰ at the low land. Alutitude isotopic effect per 100m elevation is -0.4‰ for δD and -0.2‰ for δ¹⁸O. The meteoric water lines are expressed as δD=8δ¹⁸O+16 near the summit and as δD=8δ¹⁸O+18 at the low land.

Hydrogen and oxygen isotopic ratios in river and groundwater samples show no remarkable changes with time. Altitudinal effect for river and groundwater as well as that of precipitation having a slight difference between the mountain area (-0.1‰/100m for δ¹⁸O) and the low land area ( -0.3‰/100m).