What is marine pollution

The life of people and all living beings on earth originally came from the sea. Even today, the sea is an extremely important habitat for supplying people with food and energy. More than a billion people are directly dependent on the sea. The seashore is an important resort. The sea decides the world climate. Ebb and flood - the coming and going of the sea - already symbolized the emergence and decay of the living in the ancient cultures. But today's man has managed to put the marine ecosystem in a dangerous position in a relatively short time.

In the beginning there is the plankton

The food system in the sea is based on tiny microorganisms that float in the water without any drive of their own. These are referred to in their entirety as plankton. All life on earth originally developed from such microorganisms. The Phytoplankton in the sea consists mainly of algae. Like plants, it has the ability to convert mineral salts into organic compounds with the help of sunlight. The phytoplankton alone produce up to 80% of the atmospheric oxygen. It serves as a food source for the animal plankton. Small crabs, in turn, are the food source for smaller fish:

Ecological cycle in the sea (simplified)

The marine food system is normally in a state of equilibrium. If too many nutrients are supplied - for example through phosphates from fertilizers and detergents - this ecological balance is disturbed. This can lead, for example, to a mass multiplication of dangerous algae like the "killer algae" in the North Sea. Chrysochromulina polylepis happened impressively in the summer of 1988. This alga produced a toxin that blocked the permeability of the cell membranes in the fish's gills and caused mass extinction in the fish world. All living things in the marine food chain and especially the plankton at the beginning of the chain ingest insecticides. In the last link in the chain, these are enriched in a particularly high concentration. Toxins of all kinds can get into the human organism through fish food. The poisons can occur in high concentrations in predatory fish such as redfish or cod.

A significant proportion of the carbon dioxide released by humans dissolves in the oceans. This effect is known as Carbon dioxide sink. An ocean can also absorb heat. The sea can dampen global warming up to a certain degree. At the same time, however, the oceans become acidic due to the increase in carbon dioxide. The greatest threat to the oceans comes from the extinction of corals. A coral is a cnidarians that live in symbiosis with algae and build coral reefs. The alga supplies the coral with the products of photosynthesis, while the coral supplies the alga with amino acids. The corals are endangered by the sinking pH value in the water because the calcareous shell is attacked by the acid. If the water on a coral reef becomes too warm, the algae begin to produce toxins. The coral repels the algae, it dies due to a lack of oxygen, what remains is the white limestone shell. This effect can be recognized by "coral bleaching". The discharge of faeces also endangers the coral population. When the corals die, not only do the algae perish, but also all other inhabitants of the coral reef.

12 factors contributing to the destruction of the sea

1. Petroleum
2. Fertilizers
3. Sewage
4. Waste
5. Heavy metals
6. Dilute acid
7. Chlorinated hydrocarbons, insecticides
8. Radioactive materials
9. Increase in temperature
10. Mass tourism
11. Hunt
12. Military

1. Petroleum

Several causes are important for the oil pollution of the world's oceans:
  • Industrial and municipal waste discharged into rivers and the sea,
  • Losses in the transport of oil and tanker accidents,
  • Oil drilling losses,
  • Pumping out ballast water from the ships' fuel tanks,
  • improper removal of residues when cleaning the tanks of the oil tankers,
  • Wars also produce massive amounts of oil waste.
The oil film floating on the water prevents the gas exchange between air and water. This hampers the breathing of marine plants and animals. Most endangered, however, are the fish and birds. A deposited oil film in the gills of the fish causes suffocation, a layer of oil placed on the plumage of the birds makes them unable to fly and destroys the insulating effect of the plumage. The naphthenes, olefins and aromatics contained in petroleum are very toxic and can cause cancer in humans if they eat fish that are contaminated with these toxins. The lumps of tar that appear on almost every beach are the product of a complicated process of breaking down the oil.
Oil pollution of the sea can only be countered with effective policies and legislation. Many oil tankers travel the oceans with up to 300,000 tons of crude oil. Unfortunately, there are also tankers that do not have the latest safety standards. Another problem is the disposal of disused oil rigs, which are sometimes simply blown up and sunk to the seabed. When rusting on the seabed, considerable amounts of oil residue can escape from the old pipes. Therefore, all oil rigs should be towed to a coast and dismantled there.

Ecological cycle in the sea (simplified)

2. Fertilizers

The fertilizers containing phosphate and nitrogen used in agriculture find their way into the rivers via the groundwater and then into the sea. Algae absorb these as nutrients. If there is an oversupply of nutrients, this can lead to a mass reproduction of a species of algae that is threatening to other marine organisms, and eutrophication occurs. The consequences are a decrease in the oxygen content and an increase in bacteria. Agriculture is one of the main reasons for this pollution, and thus indirectly also every single consumer. A reduction could be achieved, for example, through the responsible use of fertilizers or through biodynamic cultivation in the fields.

3. Sewage

Wastewater contains faeces, detergent and, in some places, chemical residues. Some of the wastewater caused worldwide ends up untreated in rivers and seas. If it is cleaned in sewage treatment plants, as in Europe, sewage sludge remains, which is often enriched with poisons. Not all sewage treatment plants have a chemical purification stage. This means that only about 90 percent of the wastewater is cleaned by biological treatment. With an assumed annual amount of wastewater of one billion cubic meters of wastewater, the remaining 10 percent still means 100 million cubic meters of wastewater, which flows into rivers and the sea with practically no treatment.

Wastewater and sewage sludge cause putrefaction and use up the oxygen content of a body of water. Together with eutrophication, this can lead to an acute lack of oxygen, from which many organisms perish. Dangerous pathogens get into the sea with the sewage, so that there is a risk of microbiological contamination with germs, especially near the coast.

4. Waste

Many millions of tons of solid waste of all kinds end up in the oceans either intentionally or unintentionally each year. There are areas in the Pacific where garbage collects over an area of ​​thousands of square kilometers. Marine animals mistake floating plastic particles for food and perish miserably in the process. Every year, large amounts of civilization waste are washed up on the beaches of the North Sea. Particularly problematic is the dumping of dredged material contaminated with heavy metals such as chromium, mercury, nickel or lead, which today mainly arises when dredging fairways for shipping. The countries bordering the North Sea continue to sink millions of tons of dredged material into the North Sea every year.
5. Heavy metals

Heavy metal salts of the elements lead, mercury, cadmium, chromium and copper are carried into the sea with the rivers or through contaminated dredged material. Today's municipal and industrial sewage treatment plants in Europe remove almost all of the heavy metal salts from wastewater. The heavy metals are recovered through recycling. However, the contaminated sites that still lie dormant on the sea floor represent a problem. And heavy metal residues are not disposed of as effectively everywhere in the world as in Europe. Heavy metals accumulate in the organisms and cause chronic poisoning. For example, ulcers in fish can be traced back to mercury ingestion.

Mercury is a toxic heavy metal. The salts are also highly toxic.

6. Dilute acid 

During the production of the white pigment, titanium dioxide, the waste product is dilute acid. This essentially consists of 24% sulfuric acid and is contaminated with the toxic metals arsenic, lead, cadmium and chromium, among other things. In places where ships made of dilute acid were dumped, an accumulation of tumors was found in fish. The German waste acid dump in the North Sea has been prohibited by law since 1990. However, many countries in the world community do not have a ban on dumping dilute acid, so dumping abroad is possible at any time.

7. Chlorinated hydrocarbons, insecticides

The insecticides DDT, lindane or aldrin, the plasticizers PCB (polychlorinated biphenyls) and HCB (hexachlorobenzene) are representatives of these toxic, poorly degradable compounds that accumulate in all organisms via the food chain. Seals and sea birds have particularly high levels of chlorinated hydrocarbons.

Structural formula DDT

Chlorinated hydrocarbons such as DDT are suspected of causing cancer. Contact with lindane can damage male or female germ cells. The consequences are deformities in the birth of a child. The use of DDT as an insecticide is banned in Germany, but it is used with success in Africa to combat the malaria fly. Rivers and ocean currents transport the poison all over the world, so that in the meantime it can be detected even at the North Pole and in almost every breast milk.

Structural formula lindane

8. Radioactive materials

Nuclear explosions triggered for experimental purposes in the 20th century above or below water, as well as the nuclear disaster in Fukushima in 2011, scattered large amounts of radioactive material in the world's oceans. Substances such as cobalt 60, cesium 137 or plutonium 339 radiate for thousands of years and accumulate in almost all organisms via the food chain. With the increase in natural radioactivity, the likelihood of tumors and gene mutations in living things increases. A very dangerous time bomb are barrels sunk in the sea with radioactive waste from the nuclear industry. These have to be corrosion-resistant for thousands of years against the aggressive seawater. It has already happened that underwater currents drove individual, already sunk barrels to the coast.

The long-term effects of radioactivity on living ecosystems are still unclear, which is why nuclear weapons tests and nuclear power plants are an incalculable risk for land and sea. One effective measure is the worldwide ban on nuclear weapons tests, which unfortunately not all countries adhere to. Sticking to nuclear energy also seems hardly justifiable due to the numerous accidents and catastrophes.

9. Increase in temperature

A direct introduction of cooling water from a power plant into a body of water severely disturbs the thermal equilibrium in the water. An increase in the water temperature by 1 ° C can already wipe out a species of animal or plant. The temperature increase in the North Sea due to waste heat is very small, but can be more than 1 ° C in estuary areas. The warming of the oceans due to man-made climate change is particularly serious.

The mechanism of action in the event of a sudden increase in temperature in a body of water works like this: The solubility of oxygen in water is temperature-dependent. More oxygen can dissolve in cooler water than in warmer water. Warming means that the critical oxygen concentration, which is the minimum for the survival of the fish, is reached sooner, because when warming, oxygen escapes from the water. In addition, heating accelerates bacterial growth. The bacteria also consume oxygen during putrefaction processes. Therefore, a low heat input in a river or lake in connection with eutrophication can cause fish deaths. In the sea, some fish species solve the problem by simply looking for colder water in the north. However, some species of fish, such as salmon, have to swim up the rivers to spawn. Warming also means extreme stress for the corals. They are location-dependent and cannot simply swim away.

The maximum oxygen content in the water decreases as the temperature increases.

Some of the energy generated by global warming is absorbed by the oceans. The effect of the carbon dioxide sink decreases as a result of the warming, because less of the greenhouse gas dissolves in warm water than in cold water. A catastrophic, explosive course of global warming can occur if the warm water releases carbon dioxide again. The stored heat is also released again at certain intervals. If the ocean's “buffer function” for thermal energy collapses - for example by exceeding a critical mark - this leads to a complete destruction of the stable conditions in the atmosphere. This could lead to our planet becoming uninhabitable for humans within a few years.

Many fish in the Arctic Ocean migrate north to colder water, fleeing the warm water. In the North Sea, new species are increasingly appearing that are better adapted to the warmer water. These include, for example, the squids. They are the beneficiaries in the short term. The dissolving of the carbon dioxide in the water creates carbonic acid and acidification takes place. The carbonic acid attacks the calcareous shells of corals, mussels or crabs. You are the first to lose. The extinction of these living beings can trigger catastrophic chain reactions, at the end of which man becomes extinct.

10. Mass tourism

The problems caused by mass tourism can be cushioned by “soft” tourism. Extensive measures by the EU and its member states from 1990 onwards resulted in the North Sea's ecosystem being significantly relieved in certain areas. For example, the population of seabirds and gray seals on Heligoland has risen sharply again despite tourism. Certain animal species can live well alongside humans if they are used to and trust humans. However, a safe haven must always be guaranteed for more sensitive species. Disturbances by seals are no longer a problem in the North Sea, among other things because the trips to the seal banks are supervised by rangers. The biggest problem caused by tourism today is the pollution of the environment due to the negative ecological balance when traveling to the destination area.

11. Hunt

Fishing, whaling, seal and brent geese hunting have already decimated entire populations of these animal species and in some cases almost wiped them out. Humans are responsible for the fact that the whales, as the largest marine mammals, may no longer swim through the seas in the near future.In order to protect the last specimens of their species, a worldwide whaling ban and seal hunting ban must be enforced. In the EU there has been a ban on trading in and bringing in seal parts since 2009. Since 2015 there has not been a seal hunt in Norway either.

Brent geese on a dam near Husum.

12. Military

Pollution from exhaust fumes, oil and other waste, alarm from aircraft noise, from ships or from practice shooting are the consequences of the presence of the military in coastal areas. The production of armaments also pollutes the environment. In the 1991 Gulf War, floating oil caused the largest environmental disaster in a body of water to date. Political understanding and disarmament can help reduce pollution.

The future of the sea and of man

The interaction of these factors can lead to a catastrophe in the sea. It would be a mistake to believe that the immense amounts of water in the oceans simply “put away” everything. Mass extinction can occur, so that the food base for a billion people is destroyed. The destruction of phytoplankton and corals in the world's oceans would also mean the destruction of the most important oxygen producers. The loss of marine biodiversity combined with the collapse of elemental ecosystems in the oceans endangers the survival of all humanity. The global “ground zero” lies with the coral banks. For this reason there is a need for immediate action. The measures taken so far are nowhere near sufficient. All living things arose from the sea, it is the most important ecosystem.

The knutt is a snipe that has become rare in the Wadden Sea.

(Thomas Seilnacht's original text from 1990 was revised in 2020 and supplemented with current figures)

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