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Chemical Flux to the Coast of Bangladesh – a Review

Dilip K Datta*
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Subrota K Saha
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Md Sayadur Rahaman
Fisheries and Marine Resource Technology Discipline, Khulna University, Khulna, Bangladesh

Abstract/ Executive Summary:

This paper deals with the state of chemical flux to the coast of Bangladesh from ex-situ-, in-situ- point and non-point sources of geogenic and anthropogenic origin. Except for ex-situ chemical flux, no in-situ chemical flux to the coast of Bangladesh has been studied. The major elemental dissolved flux contributed by the Ganges-Brahmaputra-Meghna (GBM) river system to the coast of Bangladesh accounts for about ~5% (152 × 106 t.yr-1) of the annual global dissolved chemical flux to the oceans by rivers. This river system also contributes ~115 × 103 t.yr-1 of dissolved fluoride and ~105 × 103 t.yr-1 of dissolved phosphate to the coast of Bangladesh. The GBM river system is also one of the highest sediment dispersal systems in the world and transports about 1060 million tons of sediments to the coast of Bangladesh each year. Studies showed that DDT in zooplankton, fish and bottom sediments from the Bay of Bengal also occurs in the range of 4.0 to 5.9 ppb, 0.3 to 8.6ppb and 0.032 to 720 ppb respectively. Since the coastal ecosystems are sensitive to chemical changes in the aquatic environment, estimation of chemical flux to the coast of Bangladesh is important.

Keywords: Coast, Chemical load, Ex-situ chemical load to coast, In-situ chemical load to coast, Bangladesh.

Location: Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Start Date:

End Date:

Program Area: Chemical Analysis

Commodity: Water quality, Water pollution

Objectives:

This paper deals with the state of chemical contribution to coastal Bangladesh from ex-situ and in-situ point and non-point sources of geogenic and anthropogenic origin.

Methodology:

The ex-situ contributions The primary routes for ex-situ elemental contribution to coastal Bangladesh are the surface runoff (the river flux), the groundwater flux and the flux from atmospheric precipitation. There is no flux study for individual rivers except for the Ganges-Brahmaputra-Meghna (GBM) system in Bangladesh. The GBM river system is responsible for the major contribution to the coast. The river system contributes to the coast about ~5% (152 × 10⁶ t.yr^-1) of the annual global dissolved chemical flux to the oceans by rivers9. This chemical flux includes only the major elements and does not include the yearly flux of dissolved fluoride (~115 × 10³ t.yr^-1)10 and dissolved phosphate (~105 × 10³ t.yr^-1) 11 to the coast of Bangladesh. The Ganges and Brahmaputra are notable for their high Uranium concentration12, and a considerable amount of dissolved uranium, thorium and radium may reach coastal Bangladesh via the GBM river system. It is to be noted here that the GBM river system contributes about 4.5% (~1330 km³.yr^-1) of the total annual global freshwater flux to the oceans, ranked fourth among world rivers in annual discharge to the seas14. The GBM river system is one of the highest sediment dispersal systems in the world and transports about 1060 million tons of sediments to the coast of Bangladesh each year. The chemistry of suspended sediments and bottom sediments of the GBM river system is available; however, there is no estimate regarding particulate elemental flux to the coast of Bangladesh via the GBM river system. The particulate chemistry signifies the appreciable presence of inorganic nitrogen in the sediments (ca. ~0.01 mg.g^-1). A significant amount of elemental flux to coastal Bangladesh also takes place through groundwater transport. Dowling et al. estimated the submarine flux of some selected elements such as Ca, Ba, Sr, Mn, Ni, Zn, As, Ag, Pb and U to the coast of Bangladesh and observed that As (40.7%) and Mn (29.4%) are the two major elements constituting the bulk of trace metal flux. They also observed that Sr and Ba flux to the Bangladesh coast are 3.3% and 1.2% respectively of their global flux to the world oceans and suggested that groundwater discharge into the coastal oceans are a significant source of trace metals and may influence the global isotopic balance.

Source of Information: Indian Journal of Marine Sciences Vol. 37(2), June 2008, pp. 214-219

Article Link (Online Journal):

Funding Source:

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Achievement/Findings:

An estimate of the chemical load to coastal Bangladesh is important primarily because of the vulnerable ecosystems but of global resource value such as the Sundarbans – the mangrove forest, the St. Martins Island and the Meghna estuarine system are located along the coast. These ecosystems are very sensitive to chemical changes in the water column and any perturbation may cause a drastic reduction of resources in these ecosystems. Moreover, the Bangladesh coast is connected by deep-sea channels to the Indian Ocean and any change in the chemistry of the coast would have an influence on the entire tropical oceans. Under such circumstances estimation of chemical flux to the coast of Bangladesh is important.

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