The use of Oxygen-18 as a natural tracer of soil moisture and estimation of recharge in different types of soils is presented and discussed. The 8 values of 18O in summer and winter precipitation in southern Sweden differ by about 6-8‰ SMOW, giving the soil moisture a distinct isotopic profile. For instance, meltwater having low δ18O labels the upper soil horizon with isotopically light water and pushes down the isotopically heavy old moisture contributed by the preceding summer precipitation. The soil moisture thus exhibits a cyclic pattern having low and high 18O contents. The temporal displacements of soil moisture layers depleted or enriched in 18O have been used to calculate seasonal and annual recharge in esker and moraine formations. In Uppsala region the annual recharge varies from 230-300 mm. These estimates are reliable since 18O depleted soil moisture layers contributed by two years consecutive meltperiods have been observed in the soil profile.

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