6. Natural Threats and Impacts to Mangroves Within the Coastal Fringing Forests of India

Mangrove forest acts as a buffer against the storm waves, tidal waves, tsunami waves, littoral currents and shoreline erosion of the coastal fringes in intertidal region. However, the natural impacts are strongly felt on the fringing forests of different physiographic settings on India’s East Coast and West Coast at present. The different physiographic settings for mangrove ecosystems in the eastern and western coasts of India include carbonate platforms of the coral fringed coasts, estuarine deltaic islands with swampy clay surface, clay dominated swale topography of inter-dune sand ridges of deltaic chenier coasts, various embayments and estuaries, and back waters.

Some events of cyclone landfalls, occurrences of seismic activities with tsunami event, increased hyper salinity, and impacts of current sea-level rise have produced a great damage to the mangrove forests of the intertidal region of the coast of India in the previous decades.

The entire work is carried out on the basis of the field observations, analysis of the physicochemical characters of mangrove substrates of different physiographic settings, time series analysis of wave and tide data and identification of mangrove zonations and areas of wetland changes using geospatial technology.

The present study reveals that some natural impacts are responsible for the loss of mangrove forests from different physiographic settings of India’s East Coast. Hypersalinity in the inner parts of the islands due to drainage loss and exposure to evaporation, and storms driven inundation and erosion by frequent landfall of cyclones are producing damages to the fringing forests of Sundarban deltaic islands. Storm drifted over wash sand fan lobes into the swales across beach ridge cheniers, sheet erosion of uncovered compact mangrove mud banks by tidal waves associated with lateral shifting of sediment filled tidal channels, and hyper salinity of higher marshes have produced significant damages to the mangrove forests of the barrier back tidal basin of beach ridge chenier coasts and estuary fringes of Subarnarekha delta. Finally, the upliftment and subsidence of carbonate platforms by seismicity, and tsunami incidences with storm induced log drift have generated natural impacts of the loss of mangrove forests in carbonate settings of Andaman group of islands. Mangroves of Gujarat and Maharashtra coasts are threatened due to shortages of river flows into the coastal zones, aridity of the inner parts and hyper salinity.

Conservation through environmental zoning and construction of artificial drainage ditches to restore the frequency of inundation, and afforestation in the existing tidal mud flats are immediately needed to restore the threatened mangrove wetlands from the natural impacts along the shoreline of the Bay of Bengal and some parts of the Arabian Sea.