a comparison of proportional and mass balance model to predict soil erosion and deposition rates using cs-137 technique in ardal district, charmahal and bakhtiari province

soil erosion and its associated land degradation represent major problems for development as well as for environmental resources protection. there is an urgent need to obtain reliable quantitative data on the extent and rates of soil erosion worldwide. the use of 137cs radionuclide for studying soil erosion and deposition is a valuable tool employed throughout the world. in the present study, use of 137cs technique as well as proportional, mbm1 and mbm2 models were employed to make measurements of soil loss in ardal district in charmahal and bakhtiari province. soil samples were collected from regular grid patterns of 20×20 m. all sample equally weighted 500 g and then 137cs activity measured through gamma spectroscopy by means of a high-resolution germanium detector. the local reference inventory was estimated at 2130 bqm-2 with the 137cs inventories of all soil cores collected from the catchment, ranging from 245 to 4744 bqm-2. the mean erosion rates for pm, mbm1 and mbm2 models were estimated 20.9, 29.8 and 20.1 t ha-1yr-1 respectively. the overall results indicated high soil erosion rates in the hilly regions of ardal district. the results of delivery ratio analysis indicated that a high proportion of soil particles are deposited subsequently after initial erosion, not moving to rivers. a comparison of the three studied models showed that mbm's have estimated soil erosion rate more than pm has. this difference is more pronounced where there are high erosion artes, whereas low differences observed in places of lower erosion rates.