Variability of 137Cs inventory at a reference site in west-central Iran

137Cs technique has been widely used for the evaluation rates and patterns of soil erosion and deposition. This technique requires an accurate estimate of the values of 137Cs inventory at the reference site. This study was conducted to evaluate the variability of the inventory of 137Cs regarding to the sampling program including sample size, distance and sampling method at a reference site located in vicinity of Fereydan district in Isfahan province, west-central Iran. Two 3 × 8 grids were established comprising large grid (35 m length and 8 m width), and small grid (24 m length and 6 m width). At each grid intersection two soil samples were collected from 0 to 15 cm and 15-30 cm depths, totally 96 soil samples from 48 sampling points. Coefficients of variation for 137Cs inventory in the soil samples was relatively low (CV = 15%), and the sampling distance and methods used did not significantly affect the 137Cs inventories across the studied reference site. To obtain a satisfactory estimate of the mean 137Cs activity in the reference sites, particularly those located in the semiarid regions, it is recommended to collect at least four samples along in a grid pattern 3 m apart.