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When most of us talk about sea pollution or marine pollution, we automatically think about oil tankers grounding such as the Exxon Valdez or oil and gas offshore disasters, for instance the recent one in the Gulf of Mexico.
However, there are many more sources of pollution, some natural, but mostly anthropogenic, both from land and sea sources.
This is an article in Marine Engineering, and in particular about the pollution of our seas. We begin with a look at the common sources of pollution then examine in more detail the consequences on marine life and shipping.
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Image: Flickr, Arnooo
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Common Sources of Marine and Sea Pollution
There are four main sources of sea pollution;
1. From sea sources
- Discharges from ships or oil installations
- Oil installation disasters
- Ships collisions or groundings
2. From natural sources under the sea
- Crude oil and natural gas are discharged naturally from undersea fissures that are natural springs of hydrocarbons. These hydrocarbons are held in sedimentary rocks that make their way to the ocean floor.
3. From land sources
- Run-off from the land both directly to the sea and by rivers.
- Discharge from industrial plants such as power plants, oil refineries, and chemical plants.
4. From the atmosphere
- The atmosphere is polluted by the escape of gasses from hydrocarbon discharges between oil installations and tankers, from gas stations when we fill our cars with petrol or diesel, and numerous other sources. These airborne hydrocarbon gasses are dissolved into our oceans.
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The Effects of Sea Pollution on the Marine Environment
When oil is discharged into the sea the sea surface slick is carried towards the shore by the waves, ending up on the shoreline. Here the seabirds and mammals get their fur and feathers coated with oil and this destroys their body heat insulation, leading to death. Oil ingestion can also cause long term illness, eventually leading to death and species extinction.
Many species of marine surface larvae are also decimated by oil floating on the sea surface, as the fish, birds and mammals feed on this they will have to migrate to other feeding grounds.
When oil disperses, it also sinks to the sea floor breaking up into smaller globules on the way down that fish ingest this and die. The oil then lies on the sea bed until absorbed by the silt/sand, only to re-emerge at a later date.
Finally reefs and corals, mangroves, and wetlands are particularly susceptible to oil pollution, due to the very nature of their construction and location, absorbing the oil and destroying the ecosystem.
Ships Ballast Discharge
When ships ballast their tanks with seawater, the seawater contains species local to that ecosystem. When the ship deballasts at a foreign port, it discharges these now alien species, often with disastrous consequences to the local ecosystem.
Land Based Pollutant Effects
Discharges from industry such as chemical plants, oil refineries, and numerous types of metal ore extraction sites can contain poison in the form of heavy metals- mainly mercury and lead.
These are ingested by the fish and gradually build up as smaller fish are eaten by the larger ones until, at the top end, sharks, tuna and swordfish will contain significant amounts of heavy metals. When these fish are consumed by us humans, we can develop serious medical conditions.
Many other chemicals that are discharged into the sea from industry cause marine pollution, leading to degradation in marine life, and again if they are consumed by humans can cause cancer and other serious medical conditions.
Run-off from land can contain fertilizers high in nitrogen and phosphates that promote eutrophication- excessive plant growth that reduces the supply of oxygen to the sea. This is more prevalent in estuaries where rivers have carried fertilizers into the sea; here it destroys the natural habitat, fish and shellfish along with recreational facilities.
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The Effects of Marine Pollution on Ships Business
All classes of ships such as cruise liners, oil tankers, and cargo vessels are bound by international laws regarding pollution.
This has necessitated either their fitting antipollution measures or staying out of many international ports' three mile limits.
The antipollution measures include the following components:
- Sewage and wastewater treatment plants
- Incineration plants with appropriate fume extraction
- Oily water separators
- Ballast water treatment
- Main and auxiliary engine fume extraction plants
- Oil tankers- new builds now required to be double hulled
These measures are expensive, and although necessary to prevent marine pollution and sea pollution, can be bad for business, requiring increase in charges for ship’s cargo and passengers. There is potential here for putting shipping companies out of business, or seriously curtailing their ports of commerce.