The invention of the wheel added speed to human development. It brought comfort and convenience of transport of goods and people. One invention led to another and today Petroleum has become an essential fuel for growth. Despite the information about the perils of hydrocarbon gases released by burning of fuel and increase of green house effect, routine life remains paralyzed without petrol.
The hydrocarbon gases add to the green house effect in the atmosphere, which in turn adds to the rise in temperatures. It is kind of suffocating. Fortunately we are not marine organisms. The suffocation felt by them, as a petrol tanker grounds or pipe-line carrying crude begins to leak or leakage from any other source cuts their oxygen supply off by a thick film of oil on the surface. They are just choked to death. Apart from being a vital part of the eco-system, the marine fauna is an important part of the human food chain too. While the sea surface remains covered with an oil slick, the helplessness experienced by the fauna (and of course flora too) must be similar to that of our faces being covered with a plastic bag and both hands tied behind!
The demand of oil and gas is growing faster by the day and as such a large chunk has to be imported. Most of the petroleum products including oil are produced in the West Asian countries and transported to the rest of the world via Indian Ocean; therefore, the Indian coasts (especially west coast) are exposed to the hazard. As per a publication of National Institute of Oceanography (NIO), Goa, between 1982 and 2005 there have been 70 cases of Oil spills along the Indian coast between Gujarat and Vishakhapatnam. Most of the spills were of crude, fuel or heavy oil, though there were sporadic incidents of Petrol, K Oil and even lube oil spills. Barring one incident of leakage in the pipeline of ONGC between Jawahar Dweep and Trombay; the rest have been spills from the ships.
The data available from the NIO covers only the spills from the ships. However, their report says that only 10% of the global incidents of oil spills take place when an oil tanker breaks close to the shore and often the remaining oil slicks are either due to leakages or used mud from the off shore drilling operations slips out of control.
The world's demand for petroleum products has been estimated to go up from 84 million barrels per day in 2005 to 116 million barrels per day say S. Sivadas, A. Gregory and B. Ingole of N I O in the August issue of Current Science. Due to an increase in the maritime trade, especially the west coast of India has become more vulnerable to oil-spills say the researchers. In case of an oil spill, the bottom dwelling organisms or the benthic community are the worst affected.
It was on 30 May 2006, a Panamanian Ship MV Ocean Seraya carrying some 650 tonnes of fuel oil and 40 tonnes of diesel ran aground over the rocks off Karwar coast. As the ship broke, an oil slick was formed on the surface of the sea and it spread fast. By 2nd June it had reached Polem beach on Goa-Karnataka border. Monsoon winds soon carried it as far as Palolem and Canacona, 20 km on the south Goa coast.
It was this slick that prompted Sivadas et al to study the impact on the bottom dwelling marine organisms or the benthic community, specially the community living between the high and the low tides. They followed a systematic method of statistical analyses to establish the diversity and density of larger fauna. In addition with the help of various chemical analytical techniques they also correlated the relationship between the fauna and the sediments-the residences of the organisms! A large variety of bottom dwelling biota was found to be present in the area studied by them. Chemically, petroleum hydrocarbon content (PHC) values were high in the sediments closes to the Spill site, i.e. Polem. Here lies the catch. The spill may not affect the biota immediately, but PHC laced sediments continue to poison the benthic community for years to come.
Marine organisms like lobsters, crabs, shrimps, krill, and barnacles, belong to the group of aquatic insects, the crustaceans. Majority of them are marine and an important part of the human and other marine organism's food chain. Incidentally they are hyper-sensitive to oil spills. As the hydrocarbon content of the sediments is continuously released over a period of years, these are the organisms that suffer the maximum set-back. In case the population of PHC sensitive species is more, the long term impact of pollution is more.
After a ship MV Sea Transporter was grounded off the Goa coast, some scientists carried out the impact of spill on the smaller bottom dwelling (meiobenthos) organisms of the intertidal zone. The impact on this community of organisms including foraminifera etc was so powerful that they were wiped out. The meiobenthos incidentally form a part of the food chain for macrobenthos. Whether sea or land one organism is food for the other; that is why an ecological balance is important. Hydrocarbon, no doubt is important for our growth and development but the marine fauna is often essential for our survival.
A good feature in case of MV Sea Transporter spill was that a strong wave action on the beach and manual cleaning operations launched by the local administration helped to reduce the impact of PHC considerably. The meiobenthos recovered early.
Grounding of vessels, accidents etc are normal reasons of oil spills. In addition during routine operations like loading, discharging and bunkering at oil terminals spills occur quite often. In case of a spill the lighter fraction gets evaporated over a period of time while the heavier part settles down and forms tarballs. Wind and the current drive these balls to the beaches and they get deposited there. Their frequency is more during the monsoon. Usually these balls last for 33 to 58 days in the sea. However, their fate is not known on the beaches. It is estimated that each year about 40 tonnes of tarballs are deposited along the beaches. Tarballs and PHCs are a prolonged source of marine pollution.
Globally the picture has improved. Despite increased consumption of hydrocarbons the accidental oil spills have shown a decrease. Most of spills are from the tankers. In contrast to the global scenario the number of tanker spills/accidents has increased along the Indian coast. Of the total spills 70% were reported from the west coast of India say Sivadas and his co-workers. Unfortunately the majority of spills occurred during the SW monsoon period. Based on historical data it has been found that during monsoon shore surface currents develop an easterly shoreward component. This makes the west coast more vulnerable to any oil spill during the monsoon because then waves carry it straight to the coast. Monsoon also coincides with the spawning of majority of marine organisms and a spill ensures that the spawns never hatch.
Oil spill is bad for the marine environment. For the beaches of Goa it is worse because apart from the marine fauna, the tarballs and oil pollution spoils the fun for nearly two million tourists who visit Goa each year. Tourism is one of the major employment generators in Goa. Oil spills spell doom for the eco-system and spoil the ambience of the beaches for which Goa is famous.
Transporting hydrocarbon products is okay, but it is time that the government introduces a strict control about the safety measures so that Spills due to negligence are avoided.