ASSESSMENT OF DEPTH-DISTRIBUTED FALLOUT RADIONUCLIDE (FRNS) AND SOIL EROSION/DEPOSITION IN THE HILLSLOPE DISTRICT (KHAGRACHARI) IN BANGLADESH

This experiment was carried out on a hillside at the Hill Research Centre in the Khagrachari (238.509'E, 09200.059'N) district to ascertain the erosion rate and depth distribution of a single fallout radionuclide (FRN) ( 137 Cs, 210 Pb, 210 Pbex, and 226 Ra) in 2020.Five locations, the summit, upper slope, middle slope, lower slope, and bottom, were used to gather the soil samples.A possible reference location was found 200 m away from the study area, with an elevation of 382 feet above mean sea level.The average value for 137 Cs in the local reference inventory was 946.4 Bq m -2 .The distribution of FRN ( 137 Cs, 210 Pb, 210 Pbex, and 226 Ra) tended to decrease as the soil depth increased.Compared with the reference inventory, the total inventory of the FRN at various sites revealed a similar trend from the summit to higher slope positions, indicating that these positions experienced soil erosion.The reference inventory was 144.5%, 108.1%, and 28.8% lower than the inventory for the bottom position (2314 Bq m -2 ), lower slope position (1969.5Bq m -2 ), and medium slope position (1218.8Bq m -2 ), respectively.The soil eroded from the summit and upper slope positions by 24.93 and 6.33 t ha -1 yr -1 , respectively, and was deposited at the middle slope position (10.21t ha -1 yr -1 ), lower slope position (38.34 t ha -1 yr -1 ), and bottom position (51.26 t ha -1 yr -1 ).These estimated erosion/deposition rates were derived from mass balance Model II.The sediment delivery ratio was -219%, the gross erosion rate was 5.2 t ha -1 yr -1 , and the net erosion rate was 11.4 t ha -1 yr -1 .The entire inventory was 23.4% and 63.6% smaller than the reference inventory for the upper slope position (725.4Bq m -2 ) and the summit (344.5 Bq m -2 ), respectively.The inventories were 28.8%, 108.1%, and 144.5% greater than the reference inventory for the intermediate slope position (1218.8Bq m -2 ), lower slope position (1969.5Bq m -2 ), and bottom position (2314 Bq m -2 ), respectively, indicating that this site experienced soil sedimentation.