This study has examined geochemical and physical processes that have led to the enrichment of 137Cs in sediments of the Lena River estuary. Geochemical and physical factors examined in this investigation include mineralogy, sediment chemistry, particle transport mechanisms, and sea-ice related processes.

This investigation revealed that the average 137Cs inventory and surface sediment concentration values (843 Bq m-2 and 11.2 Bq/kg) are higher in the Lena River estuary than in the adjacent marine environment (462 Bq m-2 and 6.0 Bq/kg). Results also indicated that 137Cs concentrations in lacustrine sediments are elevated compared to the estuarine and marine sediments of the Lena River-Laptev Sea system. Average 137Cs inventory and surface sediment values determined for the lake sediments are 884 Bq m-2 and 125 Bq/kg, respectively. These elevated 137Cs concentrations indicate that the Lena River drainage basin serves as an additional source of 137Cs to the estuarine environment.

Results of this study also revealed that mineralogy and sediment chemistry have influenced the distribution of 137Cs in these estuarine and lacustrine environments. Analytical results indicate that estuarine sediments with the highest concentrations of fine-grain illite-rich particles possess the highest concentrations of 137Cs, as the result of the ability of illite to retain large quantities of 137Cs upon introduction to saline environments. In contrast, analytical results indicate that in the lacustrine sediments, the distribution of 137Cs appears to be influenced by the smectite content instead of illite, due to the high adsorption capacity of smectite in freshwater environments.

A fraction of 137Cs appears to have been remobilized in the lacustrine and estuarine sediments, as a result of cation competition reactions occurring under reducing conditions. Under such conditions, the majority of 137Cs in the estuarine sediments that contain relatively high concentrations of illite experience little remobilization, due to the ability of illite to selectively retain this radionuclide.

Results indicate that sediment transport processes play important roles in redistributing 137Cs-laden sediment particles in the Lena River-Laptev Sea system. 137Cs and 210Pb(excess) data indicate that sea-ice related processes and turbulent Lena River discharge have resulted in the irregular deposition and/or removal of 137Cs-laden particles in this Arctic environment.

Based on the 137Cs profiles determined for the lacustrine sediments, it appears as though these sediments were deposited and buried at fairly constant rates. Each of the 137Cs profiles determined for the lake sediments indicate two periods of maximum 137Cs input. Sedimentation rate calculations indicate that these events occurred in 1986 and in 1963, as the result of the Chernobyl accident and the year of maximum global atmospheric 137Cs release. The 137Cs that was deposited as a result of these two events has been buried, thereby prohibiting further transport of this material to the adjacent estuarine environment.

Lastly, there is a pattern of eastward decreasing 137Cs concentration throughout the Russian Arctic. Surface sediments decrease from a maximum value of 23 Bq/kg in the northeast Kara Sea to intermediate values of 7.1 Bq/kg and 4.2 Bq/kg in the Laptev and East Siberian Seas, respectively. This eastward decreasing 137Cs distribution pattern is likely the result of water mass transport of this radionuclide.