SEGH Articles

# Depositional and ecological environments of the Bay of Bengal coast of northeast India

01 May 2012
Dr. Asok Kumar Bhattacharya summarises his work at the University of Calcutta on the Sundarban wetlands in India, including work on coastal sedimentology, impact of anthropogenic pollution and coastal zone management.

Dr. Asok Kumar Bhattacharya is a professor in the department of Marine Science,Calcutta University, India. Over the past 43 years he has been actively researching in the fields of fluviatile and coastal sedimentology, bioturbation processes and products, geomorphic and ecological changes of coastal zone by natural and anthropogenic forcing, impact of heavy metal contamination and persistent organic pollutants (POPs) in the biotic and abiotic components of Indian Sundarban wetland, and coastal zone management. The study areas belong to the siliciclastic, tropical, meso-macrotidal, low-lying coastal plains of northeast India having moderate wave climate excepting periods of tropical cyclonic surges with a wave height of about 7m.

While working on beach processes and sedimentation, Dr. Bhattacharya discovered a ‘new record of current crescents lacking preservation of obstacles’ formed by some semi permanent globose marine algae Valonia sp. stranded on beach surface. He is also the first to name and describe the ‘backwash-and-swash- oriented current crescents’ from the beach surface useful as good indicators of beach slope (1:50 to 1:90), current direction and depositional environment.

Dr. Bhattacharya studied a large variety of surficial- and internal bioturbation structures produced primarily by polychaetes, bivalves and crabs, and indicated their importance in differentiating shore-parallel biozonation of intertidal flats.  He is the first to identify the sandy megarippled substrate preference for the carnivorous polychaete Diopatra cuprea which was well known for its preference for muddy substratum. His research has also determined  that some soft-bottom polychaetes can thrive better in most polluted substrates of Sundarban wetland and hence, well suited for undertaking biomonitoring programme towards its sustainable management.

Drs.Bhattacharya and Sarkar (see previous article Feb 2012 for Sundarban) published their research about the threat of ecological imbalance of this fragile coastal zone due to rapid depletion  of living resources like tiger prawn seeds (Panaeus monodon),and bulk of mollusks due to indiscriminate overexploitation for aquaculture farms and other areas of commercial benefits.

His research further highlighted the adverse impacts of constructions of embankments on the ecological balance of mangrove ecosystem of Sundarban wetland. It is revealed that such constructions abruptly truncate the mangrove forests occurring behind the intertidal flats to be replaced later by marsh vegetation.

Figure 1: Mining and transportation of sand from Digha beach for construction purposes

Dr. Bhattacharya’s research has addressed several issues relating to coastal inundation
and hazards faced by the poor coastal communities. Mining and transportation of beach sands (Fig.1), destruction of dune vegetation by trampling and grazing, leveling of dune tops  for constructions and open sea vistas (Fig.2) have been identified to be the major anthropogenic stresses responsible for degradation of this coast The effects of tourism and fishing by trawlers  often enhance the process of coastal degradation. Natural forcing from high waves generated by periodic cyclones often breaches the dune trains for several meters and pushes the shoreline further inland (Fig.3).

Figure 2: Levelling of dune tops for construction of fisherfolks’s makeshifts and avenue to open sea approach. Inundation of inland areas takes place through such avenues during high water stage causing lot of coastal pollution.

Figure 3:  Landward invasion of beach at Dadanpatrabar. The well exposed roots of coconut tree and other plant reveal a good amount of beach lowering.

His collaborative research with scientists of India and abroad on persistent organic pollutants (POPs) in sediment and biota of Sundarban wetland evaluated for the first time the ecotoxicological risks of this fragile ecosystem. The coastal environments of Sudarban are badly affected by multiple sources of contaminants, of which municipal sewage; effluents from agriculture, aquaculture, upland industries, deforestation, dredging and shipping traffics are the most important. POPs are hazardous because of their semivolatile nature, toxicity, persistence, long–range transport and bioaccumulation potential. Contaminations from the residues of five classes of POPs such as DDTS, HCHs , PAHs , PCBs and PBDEs in sediments and in selective biota were found to be of variable range in both vertical and lateral extensions of this wetland. The pollutant effects were assessed by use of different sediment quality guidelines. Sediment dispersal patterns, wave–tide climate, biotubational churning of sediments, atmospheric precipitation and distances from sources to sinks of pollutants were identified as the primary causes of such variability. In addition to researches on POPs, the distribution and possible source of several trace elements in sediment cores and their ecotoxicological effects have also been determined tracing their routes from sources to sinks.

Professor Asok Kumar Bhattacharya, Department of Marine Science, University of Calcutta. bhattacharyaasok747@gmail.com

References

Overexploitation of shellfishes in northeast coast of India-A.Bhattacharya and S.K.Sarkar. AMBIO, published by Springer on behalf of Royal Swedish Academy of Sciences,  32,(1), 70-75,2003

Breaching of coastal dunes : An issue  of management  of the  coast  to safeguard  the coastal communities  of West Bengal ,India- A. Bhattacharya, A. Bhattacharya  and S.K.Sarkar. Asian Journal of Environment and Disaster Management, Singapore, 1(2),23-35,2009. DOI:10.3850/S1793924009000182

Quantification and source identification of polycyclic aromatic hydrocarbons in core sediments from Sundarban mangrove wetland, India –C.Dominguez, S.K.Sarkar,A.Bhattacharya,M.Chatterjee,B.D.Bhattacharya,E.Jover,j.Albaiges,J.MBayona,Md.A.Alam and K. K. Satpathy. Archives of Environmental Contamination andToxicology, Springer, 59(1):49-61, 2010 http//www.springerlink.com/content/132803q28210256t/

Fluvial  geomorphology of the Kupa River  drainage basin, Croatia: A perspective of its application in river management and pollution studies- Stanislav Franciscovic-Bilinski,Asok kumar Bhattacharya, Halka Bilinski, Bhaskar Dev Bhattacharya, Avijit Mitra and Sansosh Kumar Sarkar. Zeitschrift fur Geomorphologie, E.Schweizerbart’sche Verlagbuchhandlung Publishers, 55(2), DOI:10.1127/0372-8854/2011/0056

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