Distribution pattern and source of ¹³⁷Cs in the sediment cores from the Liao River Estuary

¹³⁷Cs activities are measured for the 17 sediment cores collected from the coastal zones of the Liao River in order to disclose the distribution patterns and geochemical behaviors of ¹³⁷Cs. It is found that ¹³⁷Cs activity concentrations in the surface sediments vary in a significant spatial range from 1.03±1.01 to 15.68±1.13 mBq/g around an average of 6.727±0.251 mBq/g(1σ) attributing to the changes in vegetation types. Highest ¹³⁷Cs activity concentration (15.686±1.131 mBq/g) is observed in the sediment core of Z-9 where reeds predominate natural vegetation and human activity is rare. The vertical distribution pattern of ¹³⁷Cs activity concentrations falls into three categories, one-peak curve, two-peak curve and irregular curve. For the two-peak curves of ¹³⁷Cs activity concentration, there is a sub-peak of ¹³⁷Cs activity concentration in the sediment profiles except the maximum of ¹³⁷Cs. As to the irregular curves of ¹³⁷Cs (LH-15, LH-18), the ¹³⁷Cs activity concentrations decreases from the sub-layer to the bottom and part of the surface sediment was missing, or for another possibility bottom sediment was putting on the surface layer by anthropogenic activities Sedimentation rates are calculated with the initial ¹³⁷Cs appearance value (1954) up to the maximum value (1963) of the sediment cores. The average value of sedimentation rates (0.48 to 1.63 cm/a) deduced from ¹³⁷Cs maximum value seem to be lower than the rates (0.51 to 1.77 cm/a) calculated from ¹³⁷Cs initial appearance. The ¹³⁷Cs inventories vary from 980±46 to 6094±92 Bq/m², with an average of 2278±42 Bq/m². Furthermore, the average ¹³⁷Cs inventories of the study are higher than the global fallout flux 1310 Bq/m² (¹³⁷Cs activity was decay corrected to 2015). This result clearly indicates that the ¹³⁷Cs atmospheric precipitation is the main source of ¹³⁷Cs in the region of Liao River Estuary.