Effects of acid irrigation and liming on the migration of radiocesium in a forest soil as observed by field measurements.

The effect of normal irrigation, acid irrigation, and liming on the vertical migration of radiocesium from Chernobyl and global fallout was investigated by determining the activity of 134Cs and 137Cs in the upper horizons (LOfl, Of2, Oh, Aeh, Alh, Al) of six experimental plots of a forest soil (spruce stand) as a function of time. For the Of2 and Oh horizons (but not for the LOfl horizon) of the control plots during our period of observation (600 days from 30 April 1986), we found a significant increase in the mean residence half-time (τ) of Chernobyl-derived cesium from ~ 70 to 500 days, indicating that Cs is sorbed more strongly with time. The different types of soil management showed an effect only in the Of2 horizon. Irrigation, especially when acid, prevents the increase of τ with time. Liming reduces the rate of migration of Cs significantly, even if the plots are irrigated with normal or acid water. Cesium-137 from global fallout was present mainly in the Oh and Aeh horizons, but was less mobile than Chernobyl-derived Cs by one order of magnitude