Origin and transport of 238U and 226Ra in riverine, estuarine and marine sediments of the Krka River, Croatia

Spatial distribution Of U-238 and Ra-226 activities in sediment columns along the Krka River and estuary, were studied using gamma spectrometry. Markedly different U-231 and Ra-226 activities between riverine, estuarine and marine sediments were observed. Distribution of these radionuclides, as well as their anthropogenic and natural origin, was evaluated by activity measurements, taking into account sedimentation rates estimated by Cs-137 distribution in sediment columns. Naturally present U-238 and Ra-226 activities were highest in riverine and lowest in marine sediments. U-238 and Ra-226 activities in historic riverine sediments revealed anthropogenic influence from town of Knin, which diminished for 15-20% in 1990s due to warfare that caused stop of industrial, agricultural and transport activities. Drainage of the flysch material naturally elevates U-238 and Ra-226 activities in the vicinity of its inflow in the upper part of estuary. U-238 and Ra-226 from the phosphate ore discharge in the port of Sibenik did not spread further in estuary, which was also confirmed by U-238 and Ra-226 activities detected in Mytilus sp. mussels' tissue. (C) 2009 Elsevier Ltd. All rights reserved.