Abstract
Abstract
Forest floor humus is a long-term reservoir of radiocaesium, but its behaviour decades after the Chernobyl accident remains incompletely understood. In 2020, 283 humus samples from Czech coniferous forests were analysed for 137Cs, 40K, and 210Pb activities, element contents and site characteristics. 137Cs activity ranged from 6.26 to 931 Bq kg−1, with a geometric mean (GM) of 90.5 Bq kg−1. At 157 corresponding monitoring locations, GM 137Cs activity decreased from 342 Bq kg−1 in 1995 to 195 Bq kg−1 in 2005 and 99 Bq kg−1 in 2020. Effective half-lives increased from 12.3 to 15.4 years, while environmental half-lives increased from 20.8 to 31.5 years, indicating a slowing of 137Cs removal or redistribution. Present-day variability was associated mainly with post-Chernobyl deposition and modified by 40K, 210Pb, Pb, acidity, and humus type.