Introduction
Marine pollution is defined by the 1982 UN Convention on the Law of the Sea as: “the introduction by man, directly or indirectly, of substances or energy into the marine environment… which results or is likely to result in such deleterious effects as harm to living resources and marine life.”
Types of Marine Pollution -
Marine pollution or Ocean Pollution has become one of the greatest threats due to industrial discharge and agricultural activities. There are different types of marine pollution such as -
1. Plastic Marine Pollution - Plastic is the most common type of marine litter, comprising up to 80% of total waste in marine litter surveys. Most come from land-based sources, with marine-based activities such as shipping, cruise lines, and fishing accounting for the remainder. The plastic dumps are affecting the marine ecosystem.
2. Toxin Marine Pollution - Industrial discharges and agricultural run-off containing pesticides, fertilizers, and various toxic chemicals such as DDT, Furan, Radioactive waste, pesticides, PCB, Phenol etc. find their way to the ocean. These toxins cause dangerous effects on marine life.
3. Acidification Marine Pollution - Oceans have absorbed around 30% of anthropogenic carbon dioxide emissions since the Industrial Revolution. Absorbed carbon dioxide reacts with seawater, resulting in the formation of weak carbonic acid and reducing the ocean’s pH. This process is called ocean acidification. There has been an increase in acidity of 26% since the beginning of the industrial revolution. Acidification of oceans threatens marine life.
4. Eutrophication Marine Pollution - It is a process by which a body of water develops a high concentration of nutrients, such as nitrogen and phosphorous resulting in abundant plant growth. In marine waters, the limiting nutrient usually is nitrogen. Limiting Nutrient is one which limits plant growth. If a large amount of limiting nutrients is suddenly available, plant populations will increase rapidly. Fertilizers and human sewage are rich in both nitrogen and phosphorous. The nutrients cause an increase in the growth of aquatic plants and the production of photosynthetic blue-green bacteria and algae.
Algae proliferate forming surface mats on water called an ‘Algal bloom’.
Algal blooms reduce the light penetration to below the surface and greatly reduce photosynthesis. As the bacteria and algae die, their decomposition increases the Biochemical Oxygen Demand (BOD) of water. If the dissolved oxygen is sufficiently lowered then other organisms like fishes will also start dying.
Sources of marine Pollution -
Since the ocean forms 71% of the earth’s surface, most of the pollutants in the atmosphere fall on it. In recent decades, however, there has been a huge amount of direct marine pollution caused by human activities.
- Industrial discharges and agricultural run-off (about 70 trillion litres a year) containing pesticides, fertilizers, and various toxic chemicals find their way to the ocean.
- Treated and untreated human and other domestic waste (about 6 million tonnes a year) end up in the ocean with all their contaminants. In fact, sewage remains the largest source of contamination of the coastal and marine environment.
- The oil industry contributes to deadly pollution through leaks, spills, and cleaning of tankers.
- Nitrogen input into the ocean has been rapidly increasing due to agricultural runoff, atmospheric deposition, and loss of natural interceptors like coastal wetlands, coral reefs, and mangroves.
- The result is greater marine and coastal eutrophication. Blooms of toxic or otherwise undesirable phytoplankton are increasing in frequency, intensity, and geographic distribution. Such blooms or red tides greatly affect fisheries, aquaculture, and tourism.
- Persistent Organic Pollutants, which spread through the atmosphere, are found everywhere in the ocean. Persistent Organic pollutants cause reproductive, immunological, and neurological problems in marine organisms and possibly in humans.
- Another concern is the increasing amounts of non-biodegradable waste like plastic articles and nets that float in the ocean. Large numbers of birds, turtles, and mammals are killed by entanglement in or ingestion of such waste.
Human activities have changed sediment flows into coasts and the ocean. Areas like deltas that need sediments do not get enough, whereas coral reefs are smothered by them.
What does Plastic Waste Do to the Ocean?
Plastic is the most common type of marine litter, comprising up to 80% of total waste in marine litter surveys. Most come from land-based sources, with marine-based activities such as shipping, cruise lines, and fishing accounting for the remainder.
10 to 20 million tons of plastic find its way into the world’s oceans each year, costing approximately US$13 billion per year in environmental damage to marine ecosystems. This includes financial losses incurred by fisheries and tourism as well as time spent cleaning up beaches.
Over two-thirds of plastic litter ends up on the seabed with half of the remainder washed up on beaches and the other half floating on or under the surface.
Levels of litter in the ocean are increasing in spite of efforts to control the problem.
Industry bodies, businesses, governments, civil society, and international institutions are recognizing the magnitude of the issue and the need to tackle it. Many of them have joined UNEP’s Global Partnership on Marine Litter and the global plastic associations have signed a declaration to develop solutions to marine litter.
How Bad is Coastal Pollution?
With the inexorable movement of the world’s population towards the coastal areas, the pollution of the ocean nearer the shores has reached alarming proportions. Thousands of tonnes of sewage and industrial effluents are directly discharged into the ocean in many parts of the world.
A few years ago, shrimp aquaculture was taken up on a large scale on the Indian coast. This industry requires fresh water as well as seawater and uses heavy doses of antibiotics. Within a short time, the effluents from the shrimp farms polluted large areas. The local soil and groundwater were affected. Ultimately, diseases and court orders put a stop to coastal aquaculture, but the industry flourishes in inland areas.
It is no wonder that marine pollution finds its way into the fish that we catch. For example, major shrimp species harvested off Mumbai’s coastal waters have tested positive for lead and cadmium. The fish catch itself is declining in these waters, probably due to marine pollution.
Are Oil Spills Common?
Oil spills result from tanker accidents and blowouts at offshore drilling rigs. They occur quite often and the spill sizes vary greatly. Some notable oil spills are:
- 1989 spill from the Exxon Valdez that struck Bligh Reef, in Alaska: Leaked only 35,000 tonnes, but its environmental impact was huge.
- 1991 Gulf War oil spill: Iraqi armed forces opened valves at the Sea Island oil terminal and let out oil from tankers into the Gulf waters in order to stall the US Marines from advancing. The spilled oil (820,000 tonnes or more) destroyed the marine ecosystem and killed thousands of birds, causing billions of dollars in monetary losses.
- 2010 Deepwater Horizon spill in the Gulf of Mexico: Largest accident spill in history, probably leaked 650,000 tonnes of oil.
A substantial amount of oil is also discharged into the ocean by the normal drilling operations and the cleaning of tankers. Ol is also spilled when pipelines and storage tanks rupture or explode. Oil pollution of the ocean comes from the land too. Waste oil of all kinds from industries, automobile workshops, and homes ultimately reaches the ocean.
Environmental Effects of Oil Spills and Oil Leaks
Chemicals in oil kill many marine organisms and coral reefs. Other chemicals form a black layer on the surface that coats the feathers of birds and the fur of marine mammals. They die or drown unless rescued and treated. Heavier components sink to the bottom and kill organisms like crabs and mussels or make them unfit for human consumption. When the oil spill reaches the coast, it destroys fishing activities and tourism.
Can the environment be restored after an oil spill?
About 10-15% of an oil spill can be removed through mechanical and chemical means. The rest remains in the water. Many marine organisms recover in about three to ten years. Beaches covered with oil slicks may take several years before they become clean and usable again. It has been found that ocean processes in general can absorb oil spills and break down hydrocarbons.
International Initiatives to Control Marine Pollution
Since 1972, a number of international agreements and programmes have focused on controlling marine and coastal pollution:
- The 1972 London Dumping Convention: The purpose of this Convention is to control all sources of marine pollution and prevent pollution of the sea through regulation of dumping into the sea of waste materials. It prohibits all dumping, incineration of wastes at sea, and the export of wastes.
- The 1989 Basel Convention on the Control of Transboundary Movement of Hazardous Wastes and their Disposal: Until 1999, the Convention was principally devoted to setting up a framework for controlling the movement of hazardous wastes across international frontiers. It has now expanded its scope to include the active promotion and use of cleaner technologies and production methods and the prevention and monitoring of illegal traffic.
- Convention on the Prevention of Pollution from Ships: It is the main international convention covering the prevention of pollution of the marine environment by ships from operational or accidental causes.
- Global Programme of Action for the Protection of the Marine Environment from Land-based Activities: This programme was adopted in 1995 by over 100 countries. The aim is to control contaminants like sewage, persistent organic pollutants, radioactive substances, heavy metals, oils, nutrients, sediments, and litter that enter the ocean from land.
- The UNEP Regional Seas Programme: This programme has fostered regional cooperation on behalf of the marine and coastal environment. It has stimulated the creation of Action Plans for sound environmental management in each region. India, Bangladesh, Maldives, Pakistan, and Sri Lanka are partners in the South Asian Seas Programme.
Frequently Asked Questions (FAQs)
Question - What is the marine pollution?
Answer - Marine pollution -also called ocean pollution occurs when pollutants are discharged directly or indirectly into water bodies without removing harmful compounds. Marine pollution affects plants and organisms living in these bodies of water as well as human communities that use the polluted water.
Question - What are the sources of marine pollution?
Answer - There are some sources of marine pollution such as Sediments, Oxygen-demanding wastes, Infectious microorganisms, Inorganic nutrients, radioactive substances, Thermal pollution etc.
- Excessive amounts of soil particles are carried by flowing water when there is severe soil erosion. Sediments cloud the water and reduce photosynthesis, destroy the feeding grounds of fish, and disrupt aquatic food webs.
- Synthetic chemicals containing carbon from industrial effluents, and surface runoff. These chemicals cause many health problems for humans and harm fish and wildlife.
- Acids, salts, and heavy metals like lead and mercury from industrial effluents, surface runoff. They make water unfit for irrigation, and harm fish and other aquatic organisms.
- Wastes from nuclear power plants, and mining and refining uranium and other ores. Such substances cause polluted marine ecosystems.
Question - What is Thermal Pollution of water?
Answer - Thermal pollution is defined as a sudden increase or decrease in the temperature of any natural body of water, which is caused by human activity.
This normally occurs when a plant or facility takes in water from a natural resource and puts it back with an altered temperature. Most often, water is used as a coolant and hence the discharged water is at a higher temperature.
Thermal pollution also occurs due to other causes. Here are some examples:
- Deforestation, which exposes water bodies to direct sunlight.
- Run-off from hot surfaces such as roads falling into water bodies.
- Volcanoes and geothermal activity under the ocean trigger warm lava to raise water temperature.
Question - What is Biochemical Oxygen Demand (BOD)?
Answer - Dead organic matter like plant and animal waste in water streams gradually undergoes decomposition. Bacteria carrying out this decomposition will require oxygen as it is aerobic bacteria. Biochemical decomposition includes biological activity like respiration by bacteria and chemical processes like natural oxidation. The amount of oxygen required for the biochemical decomposition process in a water body is called Biochemical Oxygen Demand (BOD).
BOD is commonly used as an indicator of water quality. If the BOD level is higher than 3mg/L, the water is unfit for drinking.
Question - What is Harmful Algal Blooms (HABs)?
Answer - Harmful Algal Blooms are large colonies of algae and other photosynthetic organisms that proliferate uncontrollably in oceans, brackish water or freshwater water bodies. They affect oceans and other water bodies like ponds, rivers, streams, and even reservoirs. They are caused by various photosynthetic organisms, like toxic phytoplankton, cyanobacteria, microalgae, and benthic algae. These algal blooms may be blue-green, red, brown or yellow in colour. Hus, red tide is one type of HAB.
Question - What are the major impacts of Harmful Algal Blooms?
Answer - The major impacts of HABs are:
- Such blooms produce toxins that can kill mammals, fishes, birds and other organisms. Toxins of HABs can contaminate food webs and can also cause human illness or death in extreme cases.
- Some algae are non-toxic, but they consume all the dissolved oxygen in the water. Such regions with depleted oxygen levels are called Hypoxic zones which aren’t able to sustain life. Thus, dead zones in water may be created where aquatic life cannot survive.
- Algae may also smother corals and block the sunlight availability for the coral reef ecosystem thus affecting the health of the coral reef ecosystem.
- Some algae may discolour water and contaminate drinking water.
HABs can occur both due to natural and human-induced factors. Increased nutrient discharge, mainly phosphorous and nitrogen, from agricultural runoff and untreated sewage can be a major driver of HABs.