Stable isotope studies of precipitation and river water in the Lake Biwa basin, Japan

The delta(18)O and delta D in 17 river waters flowing into and out of Lake Biwa, the lake water itself and precipitation at 11 locations in the Lake Biwa basin were observed from October 1996 to September 1997, to evaluate the origin of river waters and the effect of irrigation water from the lake on the river waters flowing into Lake Biwa. The regional difference and altitude effect of the stable isotopes in precipitation and river water were found in the basin. The delta(18)O in the rivers which are located in the eastern and the southern areas in the basin is heavier than that of the other rivers, due to the effect of irrigation for the nearby paddy fields. Evaporation from Lake Biwa and the inflow rate into the lake estimated from the delta(18)O balance agree well with the results of previous studies which used water balance methods. The stable isotopes can enable us to evaluate not only water balance but also the origin of the water and the water flow system. Copyright (C) 2000 John Wiley & Sons, Ltd.