Analysis of Water Parameters Causing Top-Dying in Mangrove Forest Trees in the Sundarbans in Bangladesh

Abstract

Sundarbans is the largest, biologically richest, and most extensive mangrove forest in the world and representing 2.5 percent of the world’s natural mangrove forest (Saha, 1991), the Sundarban natural mangrove forest is still the largest natural single tract of mangrove forest and habitats in the world (Christensen, 1984; Seidensticker and Hai, 1983; Hussain and Karim, 1994) with 10, 029 km2 area. The total area of the part of Sundarban in Bangladesh is now about 6,017 km2 (Imam, 1982; Christensen, 1984; Chaffey et al., 1985), which arose due to the eastward shift of the Ganges (Blasco, 1977; Naskar 1999; and Bakshi, 1954; Thom, 1982). Heritiera fomes (Sundri) is the predominant tree species, supporting about 65% of the total merchantable timber (Chaffey et al., 1985, and Siddiqi, 2001). A unknown and serious-killer disease (top dying) of H. fomes in Sundarbans is affecting millions of the trees. An inventory by Chaffey et al., (1985) revealed that there were about 45.2 million top dying trees in the Sundarbans of which 20 million had more than 50% of their crown affected by top dying. The loss of H. fomes will have a major impact on the Sundarbans mangrove ecosystem, which leads to economic losses. Despite various hypotheses as to the causes of this top-dying, the underlying causes are still not well understood. The present work has explored some of the possible factors involved, focussing particularly on the relationship between the amount of top-dying in different places and the concentrations of a number of chemical elements present in the water, in order to test the hypothesis that chemical pollution might be responsible. Other factors such as the pH, salinity and nutrient status were also assessed. Nine plots were selected for sampling of water, and vegetation in order to categorise different areas in terms of their intensity of top-dying. 63 soil samples and 9 water samples were tested, mainly by ICPMS, to investigate certain parameters of the soil and water, such as Sn, Exchangeable K, Soil pH, Pb, Zn, Ni, soil pH, CEC, soil nutrients, soil moisture content, and elemental concentrations of 32 other elements. Most of the elements studied had no significant correlation with the top dying of Heritiera fomes. However, the present results have showed that some possible parameters in water in Sundarbans such as Salinity of water, water pH, Water EC, water nutrients could not be directly linked with top-dying of Heritiera fomes (Sundri) in Sundarbans.