A 7,400-year formation
The Muthurajawela peat bog began forming around 7,400 years ago during the Holocene epoch. Situated in a coastal depression between the Negombo Lagoon and the Kelani River, the area was once a shallow bay. Over millennia, sea-level fluctuations and the growth of mangrove forests created a unique environment. The dense root systems of the mangroves trapped sediment and plant debris carried by inland waterways. In the waterlogged, low-oxygen conditions, this organic matter decomposed very slowly, gradually building up thick layers of peat.
This process of "paludification," or bog formation, has resulted in a peat deposit that covers 3,068 hectares (7,580 acres). Borehole data shows the peat layer thickens towards the coast, reaching depths of over 8 meters in some areas. The peat itself is classified as fibric and hemic, meaning it contains a high proportion of recognizable plant fibers. Chemical analysis reveals a composition rich in silicon, aluminum, and iron, confirming its coastal, sediment-trapping origin. The average rate of peat accumulation over its long history has been about 0.6 millimeters per year.
A vault of carbon and biodiversity
Muthurajawela is the largest saline coastal peat bog in Sri Lanka and is a significant carbon sink. Peatlands are among the most effective ecosystems for carbon sequestration. Studies of the Muthurajawela peat show an average carbon content of 42.8%. The partially decomposed plant matter holds vast amounts of carbon that would otherwise be released into the atmosphere as carbon dioxide. The entire wetland complex, including the Negombo Lagoon, provides critical ecosystem services, from filtering water to protecting the coastline from erosion.
The marsh is a designated sanctuary and supports an immense variety of life. Surveys have documented 192 species of plants and 209 species of vertebrate fauna. The animal life includes 22 mammal species, 102 bird species, 31 reptile species, 14 amphibian species, and 40 species of fish. Among these are 17 endemic species and 26 nationally threatened species. The diverse vegetation is organized into seven distinct communities, including mangrove swamp, reed swamp, shrubland, and grasslands, each providing a different habitat. Fauna includes the Fishing Cat (Prionailurus viverrinus), the Water Monitor (Varanus salvator), and many herons, egrets, and kingfishers.