Normally ships are designed to carry heavy materials and bulky cargo. However, when they are empty, probably after offloading, they are filled with ballast water to stabilize them as they cross the ocean. They will discharge the ballast water on reaching the port where they are supposed to load up again. This discharged ballast water is obviously contaminated with oil and other wastes within the ballast tanks and therefore a source of water pollution. Discharges of ballast water by ships usually have harmful consequences to marine environment.
Another cause of oil pollution is the bilge water; basically this is seepage that normally collects in the hold of a ship and it is usually discharged regularly. Bilge water is obviously contaminated with the oil from tankers that seeps out of the cargo. These discharges are normally referred to as operational pollution as they are known to be part of operation of day to day of ships.
2. Solid waste disposal
The disposal of solids such as plastics at the sea is one of the major problems that cause environmental harm. This is because the materials are both persistent and buoyant. Debris is of different types; old nets and old nets that are used by fishing boats are frequently disposed to the sea and are made of plastics, dunnage which is used to pack break bulk freight and keep it from shifting is usually made of wood or plastic. These materials have over the past years accumulated and have been found to be as far as the poles at the ea bottom. Discarded plastics and wooden materials pose a great danger to both marine and the coastal region. Fishing nets that are discarded trap animals as they drift through the water and probably kill them. Band shaped materials can entangle marine animals and fish forming a girdle which becomes tight as the animals grows. Marine animals also ingest these materials which may kill them or reduce the value of nutrients in the food that they take. Dunnage which is made of wood can damage small boats if it is not grated or pulped, (US Department of Transportation, 1996)
3. Air pollution
Air pollution is not one of the major environmental impacts of shipping. However all commercial ships are normally powered by combustion engines and therefore they emit air pollutants. These may happen in two circumstances: one is when underway and the other is when docked. Our most concern is when docked as the emitted gases will have a direct impact to the immediate population than when it is underway.
18 to 30% of all nitrogen oxide and 9% of sulphur oxide pollution is considered to come from ships. By the year 2010 almost 40% of air pollution over land came from ships. One of the major impacts is that sulfur in the air creates what is called the acid rain which in turn damages buildings and crops. Again when inhaled, sulfur is known to cause respiratory problems and increase the danger of having a heart attack.
Shipping is known to cause more than 3.5% of all climate change emissions. Cruise ships generate air pollution by burning sulfur producing sulfur dioxide, (TRB, 1993)
4. Port and Channel Construction and Maintenance
The maintenance and construction of ports usually poses a number of environmental hazards and risks. One of them is the dredging in order to permit large ships and vessels to enter ports, or to preserve inland channels. Naturally the sediment which flows in the sea with rivers is at equilibrium with the sediments transported out of the sea maintaining an equilibrium depth. However, this is not deep enough to allow a safe passage for vessels and therefore harbors and navigational channels are dredged to make them deep. Nature will keep on changing these dredged channels and therefore the need of dredging from time to time to maintain them.
Scouring poses direct dangers to the areas where it is mostly done. This is because it establishes sediments into the neighboring water column which is then redeposited to the bottom. This on the other hand has short term effects to the benthic community and the pelagic fish. Increased turbidity due to suspended sediments reduce light penetration hence reducing the photosynthetic activities, (Pickering, 1994)
Dredging may also have long term effects which include water circulation patterns. Water circulation patterns decide how the fresh and salt water will be distributed and patterns of dissolved water. Salinity changes affect the feasibility of freshwater wetlands and tidal marshes bringing negative impacts on how marine life will be distributed. Also water circulation may change how the sediments will accumulate thereby affecting all ecosystems in the area.
5. Non-Indigenous Aquatic Species
While shipping from one region to another, it is possible to transport aquatic species. They are mostly transported through ballast water or they may attach themselves to the boat hulls or be carried together with the goods being transported. Some of them may not survive in their new environments and therefore do not pose any financial or ecological costs. However, some of them may flourish and might outdo the existing ones or bring imbalance of the existing ecosystem. A good example is the “zebra mussel Dreissena polymorpha” which was carried from Europe to North America through ballast water. These mussels have different impacts one of them being to clog water pipes in power plants causing costly repairs and change of technology to avoid future problems. They also brought a decline in numbers of phytoplankton, decrease in the number of those fish which have planktonic larval stages, increase in water clarity in the North American Great Lakes and causing a change of habitat for a dult fish, (Button & Kenneth, 1993).
Environmental care should be taken in order to save marine and the communities living at the coast. The ship owners, the exporting countries, the ship breakers or the local governments should take part in maintaining rules and regulations of shipping in order to reduce these environmental risks. When the damage is already done it cannot be replaced. There is immediate need to compare the reality on the ground, the ruling economic welfare of the shipping industries and the negotiations taking place worldwide, in order to change the shipping and environmental situation on the work area.