The Sundarban, one of the UNESCO World Heritage Sites, home to the Bengal tiger, the Ridley turtle, the Ganges dolphin and several migratory birds apart from various rare species of crocodiles is the life line of Bangladesh, has already experienced a number of oil tanker accidents but being in small scale has failed to draw any public concerned or attention.
But On Tuesday, 9 December, 2014 an oil tanker carrying more than 350,000 liters (77,000 gallons) of bunker oil sank on the Sela River, a sanctuary for aquatic life flowing through the Sundarban, after being hit by a cargo vessel. The seepage had spread over a 60-kilometre-long (37-mile-long) area of the Sundarbans. Following that, it has been reported the movements of dolphins, crocodiles, etc. in the region has already seen a drastic fall, especially in Sela and Pushur Rivers.
Ecologist Dr. Shahriar Hossain, Secretary General of Environment and Social Development Organization-ESDO said “The oil spill in Bangladesh is ultimately affecting the inhabitants, fish stock, mangrove trees, fishermen, and the people living in the region who are paying the price for this catastrophe”. He informed that, as a coastal mangrove forest, the vegetation in the Sundarban gets inundated twice a day by high tides. Now that there is oil, as water recedes with low tide, the oil will remain on the vegetation and the forest topsoil. The mangrove ecosystem of Sundarban is primarily made up of four kinds of salt-water trees: Sundari, Kewra, Goran, Poshur and Golpata.
These trees reproduce from the windfall seeds that fall on the ground. Dr. Shahriar said, as oil settles on the forest topsoil, these seeds will die and in the long run, the regeneration of the Sundarban will be badly affected. That in turn will put the deer and different types of primates in trouble who depend on these trees for living. The Sela River is known as a sanctuary for sweet-water Irawaddy and brackish-water Ganges dolphins. So, these marine creatures will be the first in the line of victims of the oil spill.
“The oil spill took place in the largest aquatic protected area declared by the Bangladesh government and home of marine, aquatic species, that indicate long-term environmental consequences,” said the Syed Marghub Murshed, Former Secretary Govt. of Bangladesh and ESDO chairperson. He urged the government, coastguard, and navy to take immediate steps to remove and suck up the oil immediately”.
Forest officials are also trying to put some fishing nets on the mouth of the canals so that oil cannot enter into those. At least 20 canals connected with the Sela River have already been polluted, said by the divisional forest officer, east zone of the Sundarbans.
Ms. Siddika Sultana, Executive Director of ESDO highlighted on the slog in the amount of emission of carbon di oxide in air. She said this will cause destruction to the bio-diversity, ecology, water management, flora and fauna of the Sundarban and the coastal areas. So, there is no substitute to shielding the Sundarbans from any of these damages.
ESDO urge for collective steps to protect Sundarban ecosystem and Biodiversity,
Steps can be taken
Considering the characteristics of Sundarbans ecosystems, a number of cleanup and treatment techniques have been proposed and tested to deal with oil contamination in coastal wetlands. The feasibility of these methods also depends on various factors, such as the type and amount of spilled oil, season of the year, and environmental conditions of the spill site.
• Booming and sorbents
– Use of booms to contain and control the movement of floating oil at the edge of the wetland and removal of the oil by adsorption onto oleophilic materials placed in the intertidal zone. This method can be an effective strategy to prevent floating oil from reaching sensitive habitats with minimal physical disturbance if traffic of the cleanup crew is strictly controlled.
• Low pressure flushing
Oil is flushed with ambient-seawater at pressures less than 200 kpa or 50 psi to the water edge for removal. This technique can be used selectively for quick removal of localized heavy oiling with minimal damage to wetland vegetation.
• Cutting vegetation
Cutting vegetation may be a useful cleanup technique to remove oils that form a thick coating on the vegetation and to prevent oiling of sensitive wildlife. However, the feasibility of this method depends strongly on the season in which the spill occurs. In general, winter cutting of dead standing vegetation has little effect on subsequence growth of wetland.
Stripping of surface sediments can cause severe environmental impacts and may only be considered in the case of extremely oiled wetlands where the oil in the sediments is likely to kill the vegetation and prevent plant regrowth.
Dispersants are chemicals that promote the dispersion of floating oil from the water surface into the water column. Fields studies have shown that application of dispersants in near shore waters can significantly reduce the retention of oil within the intertidal zone and, therefore, the impacts to wetland plants.
Cleaners are chemicals that help to wash oil from contaminated surfaces. These formulations have been used with low-pressure flushing operations to facilitate oil removal from wetland vegetation. Studies have shown that the application of cleaners can prevent mortality of salt marshes and mangroves.
• In-situ burning
In-situ burning involves controlled burning of the oil and oiled vegetation at the contaminated site. This technique is capable of rapidly removing large amounts of oil with limited equipment and personnel. In fact, fall burning of marshes has been a commonly used management strategy for controlling wetland overgrowth in many areas.
• Bioremediation of Oil Spills in Salt Marshes
Bioremediation is an emerging technology that involves the addition of materials (e.g. nutrients or other growth-limiting substrates) to contaminated environments to accelerate the natural biodegradation processes. This technology has been recognized as one of the least intrusive methods and has been shown to be an effective tool for the treatment of oil spills in medium and low-energy marine shorelines.