Peat is a mixture of fragmented organic material formed in wetlands under appropriate climatic and topographic conditions and it is derived from vegetation that has been chemically changed and fossilized. Peat is partially or totally decomposed remains of dead plants which have accumulated under water for tens to thousands of year. Decomposition or humification involves the loss of organic matter either in gas or in solution, the disappearance of physical structure and the change in chemical state. Peat is generally found in thick layers in limited areas, has low shear strength and high compressive deformation which often results in difficulties when construction work is undertaken on the deposit. Peat represents the extreme form of soft soil. It is an organic soil which consists more than 75% of organic matters. However, the cutoff value of the percentage of organic matter necessary to classify a superficial deposit or soil as peat varies throughout the world, usually depending on the purpose of classification. This cutoff value also serves to differentiate peat from superficial deposits or soils with lesser amounts of organic content. The terms peat and organic soils, used for describing soils with an organic content, were once synonymous but term organic soils is presently used for superficial deposits or soils that contain organic matter.
Figure 1 Location of Peat Soil in Malaysia
PEAT SOIL SUBSIDENCE
Draining of peatland lowers water table causing subsidence
Rate of subsidence 20 – 50 cm per year over a period of 5 years after drainage & thereafter 5 cm per year. Oxidation & acidity:
Peatland water is acidic & once drained, peatwater causes severe damage to flora & fauna habitats in adjacent areas. Compaction or shrinkage of peat soils may cause groundwater containing fertilizer or pesticide residues to flow from agricultural area to adjacent water catchment area.