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Peaty soil in india Animation | Marshy soil | दलदली मृदा | by Ravi Yadav (MNNIT Alumni)
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Peat soil, known as one of the most problematic soils in the fields of civil and environmental engineering, is formed by the accumulation and decomposition of organic materials (derived from plant remains) under the waterlogged environment where there is lack of oxygen (O’Kelly, 2015). Basically, the soil with an organic content greater than 20% is defined as organic soil, yet the peat soils are defined to have organic content above 75% (Huat et al., 2014; O’Kelly, 2017). The plant remains in peat can be found at various degree of decomposition (ranging from undecomposed to highly decomposed stages); therefore the peat soil often exhibits a dark brown to black color and spongy consistency with a distinctive odor. Based on the degree of decomposition and fiber content, the peat can be categorized into three types: (1) fibrous peat, (2) hemic or semifibrous peat, and (3) sapric or amorphous peat (Zulkifley et al., 2014). The degree of decomposition of fibrous peat is low, hence the plant structure can easily be recognized (fiber content over 67%). Hemic peat exhibits a moderate degree of decomposition, in which the fiber content can be in a range from 33% to 67%. Sapric peat, on the other hand, is highly humified, and the plant structure is no more visible (fiber content less than 33%).
The peat deposits are found to be distributed in many countries all over the world, occupying nearly 5%-8% of land surface of the Earth (Mesri and Ajlouni, 2007). A recent study on peatland mapping has reported that the total area of the peatland is 4.23 million km2 (Xu et al., 2018), and the major distributions are summarized in Table 4.1. A high distribution of peatlands can particularly be seen in the northern hemisphere (including Canada, Russia, and Finland). In Japan the peat deposits are mainly found on Hokkaido island (the northernmost of Japan’s four main islands), yet a minor distribution exists in other islands as well. In Hokkaido, around 2000 km2 is occupied by peat deposits, which has been reported to be approximately 6% of the flat land in Hokkaido (Noto, 1991).