The impacts of oil on the marine environment
Oil spills can have very wide-ranging impacts on the marine environment and human activities – reducing the scope for recreational activities and tourism at sea or along the coast, harming fish farms and sea fisheries, and limiting the use of sea water in industrial processes. Oil spills also have many serious impacts on ecosystems.
Even if an accident happened out in the open sea, oil slicks could easily drift onto the shores of the Gulf of Finland within a day of any accident involving a spillage. A major oil spill could pollute very many stretches of shoreline all around the Gulf to varying degrees. This means that pollution control measures must begin immediately after any accident occurs. Cleaning up oil that has drifted onto shores is extremely difficult, laborious, and ten times as expensive as cleaning up oil slicks at sea.
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The rugged shores of the island of Nauvo.
Photo: Seppo Knuuttila,
SYKE
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The sensitive waters of the Gulf of Finland
The Gulf of Finland and the Archipelago Sea are particularly sensitive to pollution. The concentrations of hazardous substances are persistently high in the Gulf and in the Baltic Sea as a whole for the following reasons:
- the low volumes of water
- the slow rate of exchange of water with the open seas
- low temperatures and winter ice slow the evaporation or decomposition of pollutants
- stratification of the water into layers with different temperatures and salinities restricts the dispersal of pollutants through the sea
Oil pollution prevention is further hampered by the intricate shape of the coastline with its many islands and narrow channels, as well as by darkness and cold and icy conditions in the winter.
The consequences of an accident vary greatly according to the season. Oil spills in the winter or spring are the most destructive. Spills in the spring particularly affect the functioning of entire ecosystems and natural habitats by disrupting the breeding season. Oil is harmful to all living things
Due to the unique nature of the Baltic, its marine ecosystems contain fewer species and more limited food chains than those in the open oceans. This makes them highly sensitive to changes in the natural environment.
Hydrocarbons from oil spills may be absorbed by marine organisms in their food, or directly into their bodies in the form of fat-soluble compounds. The toxic compounds in oil may have unpredictable effects, as the concentrations of some chemicals can accumulate in organisms higher up marine food chains.
Oil spills can limit the amounts of light absorbed by planktonic algae, killing off their cells. The declining quantities of microalgae reduce the amount of food available for zooplankton and other sea creatures. These changes are then reflected further up the food chain, in fish stocks. The effects of oil pollution on plankton are not long term, however, as these organisms can regenerate rapidly when conditions improve.
Oil also contains ring-structured poly-aromatic hydrocarbon (PAH) compounds, some of which are highly toxic, and these chemicals may sink into the sediments on the seabed. If an oil slick sinks during its decomposition, the benthic organisms on the sea floor may be poisoned. Benthic animal communities may take five years or more to recover from such contamination.
Oil also affects marine plants, as it can easily pass through the cell walls and pores of marine algae and plants along shores. If the vegetation along the shoreline is harmed, this may lead to the disappearance of vital habitats for many other species.
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The isopod crustacean Mesidotea entomon is commonly found
on the Baltic seabed.
Photo: Paula Väänänen,
SYKE.
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Oil can harm the scales, tissues and brains of fish, while also disturbing the food chains that fish depend on. Adult fish can avoid oil slicks, but fish populations in polluted spawning waters still decline. Eggs contaminated with oil become infertile. It may take years for spawning grounds to recover from such pollution, so the effects on fish stocks can be long term. Many commercially important fish species, including the Baltic herring, spawn in May.
Oil is a particularly serious hazard when it accumulates on animals’ respiratory organs, leading to the risk of suffocation. Chronic exposure to oil may also cause mutations in cells and tissues that may later become cancerous growths. Oil and seabirds
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Photo: Markku Mikkola-Roos,
SYKE
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Oil spills often result in very serious consequences for marine wildlife. The sensitive ecosystems of islands and shores suffer wherever oil drifts ashore, and marine animals like seabirds and seals become stained with oil from the sea. The situation can be particularly serious if an oil spill occurs during birds’ spring or autumn migration, when large numbers of water birds gather in flocks to feed and rest.
The dangers facing oiled seabirds include their loss of the ability to fly, stress, hypothermia, fluid loss, starvation, and the decomposition of their red blood cells. Their eyes and skin may additionally become irritated or infected, while oil can also induce liver and kidney disorders.
It is vital for water birds to keep their plumage and the fatty layer of their skin in good condition, to provide insulation. Birds regularly preen their plumage with their beaks, but this behaviour can easily spread oil contamination to previously unsoiled parts of their bodies, and into their respiratory and digestive organs.
The speed at which marine and coastal ecosystems can recover from an oil spill may vary from weeks to years, depending on factors including the openness of the shores, the vegetation type, and prevailing wave and current conditions.
Research into the long-term impacts of oil spills is often hindered by the shortage of background information, especially since it can be difficult to separate these impacts from other environmental factors that naturally regulate marine ecosystems and the populations of marine species. Impacts depend on the type of oil spilt
The consequences of an oil spill at sea vary considerably according to the type of oil spilt. Oil tankers may carry crude oil, light fuel oil or heavy fuel oil. Large ships are themselves fuelled by heavy fuel oil, and almost all vessels at sea contain varying quantities of oils of lighter grades. Crude oil spreads rapidly
The composition and properties of crude oil vary considerably. Crude oil is refined to produce lighter petrochemicals such as petrol and diesel fuels, leaving heavy fuel oil as a residual distillate.
When spilt into the sea, crude oil spreads rapidly over the surface, and its lighter constituent chemicals immediately begin to evaporate. Crude oil is described as a persistent oil, since after its lighter constituents have evaporated the remaining oil does not significantly evaporate or disperse through the sea water. Since crude oil contains the constituent petrochemicals of both light and heavy fuel oils, its impacts on the marine environment include the effects of both these oil grades.
Crude oil often forms an emulsion, consisting of tiny droplets of oil mixed in with the seawater. The volume of such an emulsified oil slick can be as much as four times greater than that of the original oil spill.
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Booms can also be used in the winter to limit the spread of oil spills.
Photo: Oil pollution control vessel Halli
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Heavy fuel oil is slow to decompose
Heavy fuel oils are residual products of the refining of lighter petrochemicals from crude oil. They are widely used as fuels in power plants and ships. In ships, such fuels are also known as "bunker oil". Heavy fuel oil is black; and since it is very viscose in cold conditions, but runny when warm, it is usually warmed for transportation and storage.
Heavy fuel oil spilt into the sea congeals and does not evaporate. Its characteristics vary considerably. Some varieties are denser than water, meaning that they float beneath the surface, and are more difficult to observe. The wind will not directly affect any such spills, which tend to drift according to the prevailing water currents.
Collecting oil from underwater is a difficult task, since booms can only contain the spread of oil relatively near the surface. A lot of the other equipment on oil pollution control vessels can similarly only be used to collect oil near the surface. Heavy fuel oil often forms congealed slicks of oil extending beneath the surface for tens of centimetres. Such sticky and inflexible slicks of heavy fuel oil are very difficult to clean up. One reason for this is that the pipes in the recovery equipment must be heated to ensure the congealed oil does not block them.
Heavy fuel oil is very persistent in the marine environment, and some of its constituent petrochemicals will not decompose at all. On the land, heavy fuel oil and other dense petrochemicals do not percolate into the ground. Light petrochemicals evaporate
Lighter petrochemicals such as petrol, diesel, and light fuel oils are used for heating, to fuel motors, and as lubricants.
Spills of lighter petrochemicals in the sea evaporate at varying rates according to the oil grade and factors such as the wind, wave and temperature conditions. They will often evaporate from the surface of the sea within 24 hours, or even within just a few hours of the spill.
Light petrochemicals nevertheless have the most serious toxic effects on marine life.
On the land, if light petrochemicals are spilt in areas with permeable soils, they will rapidly percolate into the ground.
Background information:
For more information
- Limnologist Mr Seppo Knuuttila, Finnish Environment Institute,
tel. +358 40 760 9232
E-mail addresses: firstname.surname@ymparisto.fi
Oil pollution prevention:
- Senior Engineer Mr Kalervo Jolma,
tel. +358 400 444 686
E-mail address: firstname.surname@ymparisto.fi
Effects of oil spills on birds:
- Senior Adviser Mr Timo Asanti, Finnish Environment Institute,
tel. +358 40 740 1597
E-mail address: firstname.surname@ymparisto.fi
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