Eutrophication
is caused by excess nutrients, such as nitrogen and phosphorus, being washed into the sea from farmland and with sewage, causing the overproduction of algae. When the algae die, the bacteria that decompose their remains use much of the oxygen dissolved in the water, leading to the death of other organisms, including fish.
Another important land-based source is emission in the atmosphere from industry or transport. Once emitted many chemical compounds (copper, nickel, mercury, cadmium, lead zinc and synthetic organic compounds) stay in the air for weeks or more and this is the major route by which they reach the Ocean, travelling with the winds. All these pollutants are then redistributed around the world by marine currents.
Pollution at sea
However, marine activities such as mining operations, shipping, fishing, cruise liners and direct spilling either from inland facilities or from sea vessels, also introduce large quantities of these toxic substances, into the Ocean. Oil spills are largely confined to navigation corridors where they pollute beaches and harm fish, shellfish and bird population.
Types of pollution
Pollutants include oil, fertilizers (nitrogen and phosphorus), sewage, toxic chemicals (heavy metals, toxic contaminants like pesticides and other Persistent Organic Pollutants), nuclear waste, gas like carbon dioxide, plastic and other trash. In shipping, oil pollution arising from incidence of ship grounding and collision has been a major international concern. In recent years, this concern has also included other hazardous and noxious substances, ballast water discharge and antifouling paints.
Impacts
Pollution of the Ocean particularly in coastal waters occurs due to land- and sea-based activities. It results in physical and ecological changes and/or damages such as habitat loss, altered sediment flows and atmospheric changes.
The continuous and chronic aggression due to pollutants can have various effects on marine species: reproductive dysfunction, cancer, immune depression or alteration of the endocrine system, among others. Pollutions have impact on humans by causing health problems (linked to bathing or consumption of sea food), economics losses (living resources inappropriate for consumption, decreasing benefits linked to tourism, increasing of the costs linked to health problems, coastal management, social problems…).
Solutions and management
Integrated plan and coastal management at an international level must be put in place to control run-off, develop water treatment, limit atmospheric pollution, collect and recycle sewage. As for sea born pollution, legislation on maritime transport and navigation, control of offshore industry and legislation and control even in international waters must be reinforced.
