Influence on environmental parameters on the fractionation of oxygen isotopes in the local ecosystem

Sudden changes in the δ18O values of subsequent precipitations can be used as a tool to study the water movement in the ecosystem, especially in the soil. Oxygen isotopes were observed during a whole season. The water vapour in the air is in close equilibrium with the actual precipitations. The δ18O values of leaf water reflect the actual weather conditions, while the values of twigs and stalks correspond to the actual δ18O values of precipitation. An intense precipitation in summer had penetrated down to the 40 cm layer, a distance which is typical for the water movement during the whole growth period. Starting in the warm season, the soil has a constant δ18O value, corresponding to the mean of the local precipitation. During summer, evapotranspiration leads to an enrichment, especially in the upper layers. Starting in November, however, the soil water pool is refilled and can supply the local groundwater. (author). 7 refs, 7 figs