The increasing salinity and pollution have also threatened the health of the forest.
This is evident fromthe top-dying of sundari (Heritiera fomes) trees. In addition to changes caused by the construction ofthe Farraka Barrage, the landscapes around the Sundarbans have further been altered by massiveshrimp cultivating operations and the vegetation is vanishing due to high salinity and chemicalfertilizer used in the shrimp farms. The southwestern part of Bangladesh is now a productive shrimpcultivation zone. Shrimp farming requires that landscapes are modified, resulting in threats toecosystems in the coastal region. There are fifty thousand fishermen and local stakeholders that enterthe Sundarbans for fishing and the collection of natural resources on a daily basis.In addition to these developments, construction, urbanization and tourism activities inside the forestare also helping to change the mangrove landscapes in Sundarbans areas.The Sundarbans mangrove ecosystems are delicate, dynamic and complex and their principalparameters are the environment, the flora, the fauna and human interference (Choudhury, 1984). Theforest land is highly influenced by tidal interactions because of the presence of these water bodies.
The forest receives freshwater and sediment from a number of distributaries of the Ganges. It hostsone of the richest natural genepools for forest flora and fauna species in the world, including theBengal tiger (Huq, Karim, Assaduzzaman and Mahtab, 1999). Each one of the following elements ofthe ecosystem, namely climate, salinity, fresh water, siltation, erosion, substrate and nutrients havefirst order reaction on flora and fauna. The upper regions of the Sundarbans are primarily influencedby the upstream stress conditions. To some extent, the decomposing litter and detritua do affect theparticular tension zone. The factors in the cycles of transported materials include daily tides, run-off,rainfall, decomposition, mineral intake, and activities of the fauna in general, fish and wildlife inInt. J.
Ecol. Econ. Stat.; Vol. 13, No. W09, Winter 2009 73particular. A survey of water and soil salinity was conducted at eight sites in the Sundarbans in April2003.The survey samples were collected from 8 different sites in the Sundarbans region includingMunchiganj, Mirgang, Koramjal, Rupsha River, Kasiabad, Mongla Port, Nilkamal, and SibsaPaikgacha location.
These findings have shown that in general water and soil salinity in theSundarbans increases from north toward the southwest depending on salinity levels of inundatingwater. Similarly water salinity increased rapidly and varied from east to west and north to south. Theincreasing rate is gradually higher in the dry season (February to June).The results indicate that until February, water salinity levels were less than 20 ECwdS/m and a highest density of over 50 ECw dS/m was found in Mirgang, Munchiganj and Nilkamalpoints, which are situated in the North West and south middle of the study area. The soil sampleswere also collected from the same eight sites and soil salinity levels show trends similar to thewater data .
The highest soil salinity levels measured were ECs 41.2 dS/m at Nilkamal, ECs 40 dS/m at Mirgangand third highest rate of soil salinity is ECs 24 dS/m at Munchiganj point in the northwesternSundarbans . The increasing salinity levels are major threats for both biotic and abiotic factorsof mangrove wetland ecosystems in the region. In the Sundarbans mangrove ecosystems, there areflora that adapt to water-logged areas, breathing by means of outgrowths of roots around the tree.
The best environment for mangroves to flourish is that, there should be adequate fresh water, on theother hand, all types of mangrove vegetation, trees, shrubs, small plants and chippers are verysensitive to saline water. Some species flourish in a highly saline environment, while others prefer aless saline one. The present study focuses on water salinity modelling for up to 13 rivers in theSundarbans. After completion of this study, it would be possible to assess the salinity and to estimatethe future negative impacts in the coastal areas. The Fourier polynomial models using a time seriesapproach would be an important tool for making policies and developing an adequate managementplan for the ecosystems protection in the Sundarbans region.