Abstract
There is a growing number of researches of 17O-excess, which is less sensitive to temperature, in order to develop 17O-excess as a new water tracer in hydrological and climate science. However, there is no data in paddy areas in Japan. In this study, 17O-excess values, its temporal variation and factors affecting that, and the relation with other isotopes in rainwater, surface water including paddy water and irrigation water, and groundwater are presented from the observation in paddy areas in Ibaraki, Japan. The results showed that the 17O-excess of rainwater is lower in summer, and relatively higher during autumn and winter. This temporal variation seems to arise from the following two; the water vapors, i.e., rainwater, formed on sea surface under different evaporative conditions, and re-evaporation of rain drops during precipitation particularly in summer season. The lower 17O-excess values resulting from kinetic fractionation during evaporation were observed in the terrestrial waters, especially paddy waters. The accumulation of further observation data is necessary to verify the validity of 17O-excess as a water tracer in hydrological cycle.
