Application of Cs-137 techniques to problems of sediment redistribution in Sungai Lui representative basin, Selangor, Malaysia (Part 1)

Since the beginning of the nuclear age, Cesium-137 has become a part of the world's ecosystems. Cs-137 is carried from the atmosphere to the ground by rainfall. On reaching the earth's surface, 137Cs becomes strongly adsorbed to soil profiles and is concentrated predominantly in the surface layer, particularly in clayey soils. Systematic measurements of Cs-137 levels will therefore permit estimates to be made of the cumulative effects of soil redistribution over the past 25 years. Sediment movement in river catchments and coastal areas is a very old problem in Malaysia. In view of rapid development of urban and agricultural areas in Malaysia it was realised tha soil loss problems are particularly serious. The Sungai Lui catchment was chosen to be the investigational site. Geologically, the area comprises of granite and granitic schist. The area is mostly covered by forest (approx. 83%) and rubber (13%), padi (2%) and others (2%). The climate is considered to be typical of Peninsular Malaysia (equatorial) characterised by uniform temperature, high humidity and high rainfall. The area is mainly drained by the Lui River. Soil samples were collected from the catchment area at 4 sampling points in April 1981. The results of analyses of Cs-137 in soil samples from Sungai Lui catchment area ranged from 1.3 to 6.8 M Bq g-1 of sample and they could still be detected even up to 20 cm depth. A general pattern of Cs-137 distribution was observed in the soil profile at each site. The highest activity being in the top 3 cm layer and then decreasing up to about 6 cm. The activity increases again up to about 9 cm layer. From there onwards, it decreases. Based on these results, the estimated rate of sediment accumulation in the area was found to be about 0.47 cm/year. Since the samples were only collected from the depositional sites, further sampling especially from erosional site should therefore be carried out in order to obtain more complete data