Peat subsidence and its practical implications: a case study in Malaysia

Due to pressure for land, substantial areas of peat swamps in South-East Asia have been and presently are being reclaimed for agriculture or for other land use. As soon as peat swamps are drained, the irreversible process of subsidence starts, which can only be stopped by waterlogging the peat again. Long-term subsidence recordings for a project area in peninsular Malaysia were analyzed, resulting in the quantification of relationships between subsidence and time as well as between subsidence and water management. The average subsidence rate for the area was found to be 2 cm per year. Consequences of this average subsidence rate were evaluated in terms of the risk that acid sulphate soils, which often underlie the peat, might surface. The established relation between subsidence and groundwater level proved to give an adequate description of the observed parabolic shape of the ground levels between two drainage canals. Compared to subsidence rates for more temperate regions, the rates for Malaysia were high. The oxidation and shrinkage components of total subsidence were quantified and the contribution of subsidence to the emission of CO2 was estimated to be 27 tonnes per hectare per year. To alleviate the negative consequences of drainage of peat swamps, it is recommended to shift from a drainage system that focuses on discharge of excess water towards a system that combines drainage and water conservation, allowing the maintenance of constant high groundwater levels and thus reducing subsidence