Spatial Distribution of ¹³⁷Cs in Suface Soil under Different Land Uses in Chao Phraya Watershed: Potential Used as Sediment source Tracing

Sediment fingerprinting techniques involves the discrimination of sediment sources based on differences in source material properties and quantification of the relative contributions from these sources to sediment delivered downstream to the river catchments. Results of the previous study indicated that fallout radionuclides (FRNs); ¹³⁷Cs and excess ²¹⁰Pb (²¹⁰Pbex) are the most suitable radionuclides to be used as sediments sources tracers. This study investigated the spatial distribution of ¹³⁷Cs in soil under different land uses in Chao Phraya watershed, the most significant watershed in Thailand. Emphasis was placed on discriminating among potential sediment sources include the cultivated (upland crops), pasture field, uncultivated (swamp, forest, and grass field), and channel erosion (stream and river bank). One hundred and twenty four soil samples were collected from all sources and determining for ¹³⁷Cs. The ¹³⁷Cs mass activities in pasture areas varied from the limit of detection (LLD) to 1.22±0.05 with the average of 0.64±0.14 Bq kg^-1. In cultivated areas the ¹³⁷Cs mass activities varied from LLD to 1.41±0.04 with the average of 0.38±0.04 Bq kg^-1.The ¹³⁷Cs mass activities were higher in uncultivated areas varied from 0.12± 0.03 to 1.73 ±0.05 with the average of 0.76±0.15 Bq kg^-1. The ¹³⁷Cs mass activities in channel bank varied from LLD to 1.16±0.04 with the average of 0.39±0.05 Bq kg^-1.GIS and geospatial interpolations revealed pattern in the spatial concentrations of ¹³⁷Cs and indicated important differences in its distributions showing the differences behavior of ¹³⁷Cs in different land uses.