Land use changes and soil redistribution estimation using 137Cs in the tropical Bera Lake catchment, Malaysia

The catchment of Bera Lake in Pahang State, Peninsular Malaysia has experienced severe land use changes since 1972 with some 340 km2 (out of a total area of ∼600 km2) having been converted to oil palm and rubber plantations and in some places, newly cleared for monoculture. The proportional model using the 137Cs radionuclide was recognized as being the most suitable conversion model for estimating soil redistribution in the catchment as the deforested land has been cultivated once in a medium-term range of 30–40 years. Thirty-five bulk core soil samples were taken to a depth of 25 cm in areas of different land use and known dates of tillage commencement in the catchment. Ten bulk core samples were also collected in the bottom sediments of wetlands and open waters to estimate accumulation rates in these sink areas. Individual land development districts with known elapsed times from start of tillage allowed determination of soil redistribution rates and preparation of a soil redistribution map. A mean soil erosion rate of 915 ± 345 t h−1 y−1 was determined in areas of cleared land, whereas rates of 117 ± 36, and 70 ± 35 t h−1 y−1, were determined in areas of developing, and developed, oil palm and rubber plantations, respectively. The overall accumulation rate of eroded soils within the wetlands and open waters was determined to be 1.025 cm y−1 since 1995. The Bera Lake catchment soil redistribution map is the first attempt in Malaysia to map soil redistribution using the 137Cs technique on a catchment scale. The soil redistribution map will provide good guidelines for future soil conservation practices and sustainable land use programs.