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Vol. 6 No. 2 - April 2000

Threat to Our Coastal Guards

By: Anjum Farooqui

Mangrove vegetation, a littoral forest cover has in store one of the critical potentials for various ecological, environmental and socio-economic resources, which has been used by coastal communities for thousands of years. This vegetation provides a buffer zone and acts as barrier against the sea furies, floods etc. thereby, averting soil erosion in the coastal zone and protecting the human habitation. The deltaic regimes world over have remained a matter of greater attraction, since the time the early inhabitants started settling along river banks. It is mainly because of their potential for irrigation, evergreen biomass blanket and also more often, enjoyable climate. It was only in seventies that our scientists discovered the potential repositories of hydrocarbon. Since then the botanists, ecologists, palaeobotanists, geologists and others have started studying the deltas in detail.

It is considered that the history of land surface and contemporary geomorphic as well as associated pedogenic processes together determine the pattern of mangrove growth. Climate regime affects the discharge of freshwater and sediments into the salinity regime of estuaries, lagoons and deltas where mangroves grow. The tidal exchange, exposure and inundation of land surface influence the environmental setting of mangrove growth. Similarly, fresh- water discharge which alter the salinity regime, play very important role in the formation of mangroves in the delta regions. The larger and main deltas of India are Ganges, Mahanadi, Godavari, Krishna and Cauvery. The Gulf of Kutch represents the deltaic environment to a smaller extent along the west coast of India. The total deltaic environment has been estimated to be 0.95 million km2 and 70 per cent of the total mangrove cover of India exists in the deltaic regions. The total area of mangroves from the deltas of India have been estimated to be 2,56,000 ha, of which 78 per cent occurs in Sunderbans alone.

The luxuriant growth of mangroves in Sunderbans could be attributed to heavy alluvial sedimentation and freshwater discharge in the deltaic regions. However, due to tectonic or change in the deltaic configuration from west to east, the Ganges has changed its course more and more towards eastern side. Therefore, fresh-water supply in the mangrove areas have been reduced causing great damage to the species which were freshwater loving. The composition and luxuriance of mangroves in the Mahanadi delta was similar to Sunderbans in the past. However, indiscriminate cutting, erosion, salt penetration and poor freshwater discharge have degraded the littoral forest. The total of 21,458 hectares of mangrove area has been estimated from the Mahanadi Delta which was the second largest formation of mangroves in India. Poor mangrove cover from the other south-eastern deltas are the consequences of various factors that perhaps prevailed in the past. Besides, human interference in the ecosystem, the changing physical factors in the region has also been one of the factors. Palynostratigraphical evidences from areas along the coastal belt represent the mangrove vegetation during early to late Holocene. Apparently, it appears to be a continuous belt during this time period which has been reduced to only pockets in the present day scenario.

The onset of the Holocene (10,000 yrs. BP or 11500 cal yrs.) witnessed the start of various environmnetal processes which have regularly/irregularly continued upto the present day and thus, climate, ecosystems and landforms have not remained static. Most of the palaeoworld evidences from these early periods have been drowned by Holocene high sea levels, so that it is only for the late Quaternary or Holocene that the adequate record of coastal occupational patterns are available.

The eustatic rise in sea level dominated during early Holocene for most of the world's coastlines, as northern ice caps finally melted away. It is from 9000-7000 yrs. BP that the coastlines world over and in India took on their familiar modern form, with the exception of coastal belt experiencing glacio-isostatic rebound. However, mid and late Holocene period was of relative sea level stability.

It is estimated that nearly 40 per cent of mangrove forest has been reduced during the last three decades. Human habitation and utilization of coastal wetland resources certainly extend well back into the Pleistocene. Although, the anthropogenic activity has affected the coastal vegetation, the various biophysical and physical factors also affect mangrove wetlands considerably.

Palaeovegetational records with reference to mangrove forest have great potential in assessing the past climate and sea level fluctuations. The evidences from Indian coastal belt show that the present shoreline was formed during early mid-Holocene. This span of time has experienced a number of cyclic changes in the climate and relative sea-level rise and fall. The natural hazards, physical and biophysical changes have brought about configurational change -in the deltaic landforms along the coastal region. This has perhaps led to drastic and abrupt changes in the ecology and thereby, the vegetational changes in some parts eg., Pulicat lake, Chilka lake and Kolleru lake, the three important coastal lakes on the eastern and south eastern areas. Since all these lakes drain the inland river/ streams water finally into the Bay of Bengal, it is likely that the saline water intrudes in during high tides. Therefore, sea level fluctuations and climatic pattern play a vital role in the ecological changes. As a result, the changes in the vegetational pattern are observed that serve as potential biological indicators of sea level and climatic fluctuations through the geological time period. Palaeovegetational record from pulicat lake at 4 m (a.m.s.l.) dated to about 7000 yrs. BP shows 75 per cent mangrove taxa in the area which is now 18 km inland from the present shoreline. Sediments above this sequence show evidences of dessication and finally the topographical changes in the area brought about a complete change in the vegetational pattern representing the Allogenic succession. At present, the area is represented by psamophytes and is devoid of any mangroves. However, number of aquatic weeds and shallow water cover in the area also provide congenial ecosystem for the migratory birds. Presently, Pulicat lake is conserved as a bird sanctuary. Similar, is the case with Kolleru and Chilka Lake, where the decline in mangrove species represented by degraded mangroves are evident. Vegetational reconstruction from coastal sediments deposited during Late Holocene in these areas show good biodiversity of mangroves. It is during last three or four decades that the mangroves have degraded fast. Presently, these areas have been developed for tourist attraction on the south eastern coastal regions of India. However, the good assemblage of about 47 mangrove species can be observed in pockets along the Indian coastal belt viz: Sunderban (West Bengal), Mahanadi, Brahmini and Baitarni delta (Orissa), Krishna and Godavari delta (Andhra Pradesh) and Pichavaram, Muttupet, Vedaranyam and some islands in the Cauvery delta (Tamil Nadu). Backwaters along the Kerala coast, Maharashtra and Gujrat are also represented by patches of mangroves which are being threatened in the present time period.

Above all, the biodiversity scenario of mangroves in India is very grim; numerous plant and animal species are either on the verge of extinction or are threatened or vulnerable. The cosequences of this alarming rate of extinction and displacement of mangrove species along the Indian Coastal belt has prompted a call to the scientific community to make comprehensive studies on the trends of biodiversity and recommend conservation strategies for management of the coastal vegetation.

Studies provide an estimate that during the last century the global sea level rose by 10-14 cm. A rise of 5 cm was attributed to thermal expansion of waters while the remaining 5-10 cm was due to the deglaciation. Based on the sea level records at Bombay, Cochin, Chennai and Visakhapatnam, a rise of 0.67 mm/yr. is noticed. Similar studies on a global scale suggest a rise of 1.0-1.5 mm/yr. The sea level rise in the next century is estimated to increase by a meter. What will happen if the sea level rises by a meter by the end of the next century? Bangladesh will be the most affected and could loose about 40 per cent of its territory and create some 28 million ecological refugees. Pakistan, Surinam, Senegal, Thailand, Mozambique and Maldives will also be affected. In India, the region most vulnerable to sea level rise is the low lying coral atolls of Lakshadweep archipelago. Because of low topographic slope, and more frequent .storms, the east coast is more vulnerable than the west coast. The stretch between 12 to 18'N along the west is the safest. The erosion tendency at the south west coast may further increase when the sea level rises. Global warming could enhance the storms and storm surges. Frequency of cyclones and severe cyclones in the Arabian sea and Bay of Bengal during the last 100 yrs. shows an increasing loss of property. The frequency of storms is 3 to 4 times more in the Bay of Bengal than in the Arabian sea. We are aware of the recent severe cyclones and the loss of lives and properties worth crores of rupees in Oct. 1996 in Andhra coast and Oct. 1999 in the Orissa coast in India.

Residential sectors, industries, defence and other organisations may have to be shifted. In low lying areas, several hectares of land will be lost. Most of the beaches and historical monuments near the coast may disappear due to severe erosion. Sea water intrudes into the estuaries and this may create a shortage of drinking water. This is an example to show that the sea level rise can affect the people who are living even far away from the coast.

With such a situation ahead, it is important that we conserve and protect our mangrove vegetation along the coastal belt and also create condusive ecological factors in areas where either the mangroves have degraded or vanished so as to provide a buffer zone between the sea and land.

Dr. (Mrs.) Anjum Farooqui is a scientist at the Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow

This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.

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