The spatial variability of Chernobyl-derived 137Cs inventories in a small agricultural drainage basin in central Russia

Little information currently exists regarding the small-scale spatial variability of Chernobyl radiocaesium fallout and associated inventories. This contribution reports the results of a study of the variability of Cs-137 inventories within the 2.18-km(2) Lapki balka catchment located near Tula in central Russia. The local area was characterized by Cs-137 inventories in excess of 200 kBq m(-2) immediately after the Chernobyl accident and pre-existing bomb-derived inventories can be ignored in view of their very low magnitude. Field sampling and measurements included both collection of soil cores for subsequent laboratory analysis and in situ field measurements using a CORAD portable detector. The results obtained show evidence of a systematic south-north increase in the reference inventory across the basin, which must be taken into account when interpreting subsequent radiocaesium redistribution within the basin. Random spatial variability of Cs-137 inventories of a similar magnitude to that reported for bomb-derived fallout was also documented. The extent of random spatial variability varied between different geomorphological units. Maximum variability, with coefficients of variation up to 20%,was associated with areas of sediment accumulation within the balka bottoms. Substantial variability (cv. typically ca, 15%) was found within flat cultivated areas and undisturbed areas both on the interfluves and on the balka sides, all of which could serve as reference sites. Minimum variability (cv. typically ca. 12%) was associated with the cultivated slopes with no evidence of sediment accumulation. (C) 1999 Elsevier Science Ltd. All rights reserved.