The Sundarban forest lies in the vast delta on the Bay of Bengal formed by the confluence of the Ganges, Brahmaputra and Meghna rivers across southern Bangladesh. Sundarbans features two ecoregions -'Sundarbans freshwater swamp forests' and 'Sundarbans mangroves'. The seasonally flooded Sundarbans freshwater swamp forests lie inland from the mangrove forests on the coastal fringe. The forest covers approximately 10,000 km2 of which about 6,000 km2 are in Bangladesh. The Indian part of Sundarbans is estimated to be about 4,110 km2, of which about 1,700 km2 is occupied by water bodies in the forms of rivers and creeks of width varying from a few metres to several kilometres. The Sundarban along the Bay of Bengal has evolved over the millennia through natural deposition of upstream sediments accompanied by intertidal segregation. The physiography is dominated by deltaic formations that include numerous drainage lines associated with surface and subaqueous levees, splays and tidal flats.
Major abiotic components:
Soil
The Sundarban deltaic alluvium is formed out of the silt brought from the Himalayas. The soil is mainly of fine silty clay in northernmost part. Peaty deposits are found in the middle and the swamp area. Sandy clay with sand dunes are seen towards the sea face. The upper layer of the soil is grey to greyish black in colour. The soil of the mangrove delta is less in oxygen content. Humus content is generally high in the mangroves.
Climate
Despite its close proximity to the Tropic of Cancer, the extreme climate does not prevail here because of its location nearer to the sea as well as due to tidal flushing of rivers and creeks inside. The mean maximum temperature is 30 degree Celsius (June- July) and mean minimum temperature is 20 degree Celsius ( December- January) which are soothing to people. The average rainfall of the area is about 180 cm. Humidity ranges normally 70-80% in the region.
Hydrology
Due to heavy rain and variable tidal influx, the estuaries of the region have become dynamic. A rhythmic cyclical pattern is noticed in the hydrology of the rivers. Temperature, salinity, pH and turbidity vary according to the horizontal zonation of a river from the sea and freshwater flow due to rain.
