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

Little information currently exists regarding the small-scale spatial varia bility of Chernobyl radiocaesium fallout and associated inventories. This c ontribution reports the results of a study of the variability of Cs-137 inv entories within the 2.18-km(2) Lapki balka catchment located near Tula in c entral Russia. The local area was characterized by Cs-137 inventories in ex cess of 200 kBq m(-2) immediately after the Chernobyl accident and pre-exis ting bomb-derived inventories can be ignored in view of their very low magn itude. Field sampling and measurements included both collection of soil cor es for subsequent laboratory analysis and in situ field measurements using a CORAD portable detector. The results obtained show evidence of a systemat ic south-north increase in the reference inventory across the basin, which must be taken into account when interpreting subsequent radiocaesium redist ribution 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 differe nt geomorphological units. Maximum variability, with coefficients of variat ion up to 20%,was associated with areas of sediment accumulation within the balka bottoms. Substantial variability (cv. typically ca, 15%) was found w ithin flat cultivated areas and undisturbed areas both on the interfluves a nd on the balka sides, all of which could serve as reference sites. Minimum variability (cv. typically ca. 12%) was associated with the cultivated slo pes with no evidence of sediment accumulation. (C) 1999 Elsevier Science Lt d. All rights reserved.