The article presents the results of the integrated study of radiocesium behavior in Lake Tapeliai using not only conventional data on radiocesium activity concentrations in lake water and sediments but also a complex data set on seasonal variations and vertical profiles of standard water variables. Radiocesium activity concentrations in lake water as well as the vertical structure of the water column considerably depend on the inflows of the colored waters from the swampy watershed of the lake enriched in radiocesium. The global fallouts are mainly responsible for radiocesium inventory in lake sediments, which reaches maximum in the upper part of the water column above the ~5.4-m depth. The maximum values of radiocesium inventories in lake sediments are consistent with the respective densities of its deposits in the nearest forest soils. The main process of sediment activation is the direct sorption of radiocesium onto the sediment surface. Sedimentation rates in the lake vary mainly in the range of 3.5–5 mm·a^–1. Lake bottom feeding sources located mainly on the southern terrace as well as their related near-bottom flows reduce respective sedimentation and radiocesium inventories in the sediments.

Article in Lithuanian