The Wildlife Trust's North Sea Wildlife Project

Pollution

Pollution can be harmful to marine wildlife both directly and indirectly through affecting a habitat that species uses. Pollution can also enter a marine ecosystem through various routes, not just directly through the ocean but through our river-ways also.

River Pollution

Can take many forms, including agricultural run off, littering, industrial waste and sewage. 

• The addition of sewage or farm waste and the run off from fertilisers used within fields has the same effect, this is the development of algal blooms which occur due to the addition of nutrients (nitrates) within the water column.  These block out the light, causing aquatic plants to die.  When the algae dies, the oxygen found within the water becomes depleted as it is used up by bacteria. This effectively suffocates most other organisms within the water, a process known as eutrophication.  Only a few organisms can survive in water with a high biological oxygen demand (much of the oxygen that dissolved in the water is quickly used up), such as blood worms. This can affect marine wildlife using rivers to spawn.
• Water from power stations is often fed back into rivers.  This water is clean, but it is much warmer as it has been used to cool steam used to drive the generators.  This alters the amount of oxygen dissolved in the water and can cause the death of species within rivers.
• Industrial waste, such as cyanide, zinc, lead and copper may enter rivers.  This is reasonably rare due to restrictions and penalties companies face, but it can have lasting and devastating effects.  These substances are very poisonous and can kill wildlife in large areas of rivers.  They may also accumulate in the food chain and kill the animals at the top such as mammals and birds. 
• Oil pollution is also more rare but serious.  On a slow moving river, oil makes a rainbow sheen on the surface.  It stops oxygen from dissolving in the water, reducing the species that are able to live and breed within it.

Major indicators for polluted rivers are blood worms and tubifex worms.  These are both animals that survive in water where there is not much oxygen available.  To catch them, sweep a net around at the bottom of a stream or river and empty it into a tray to identify the species.

Pollution that enters rivers may also enter the sea.  An example of this is the Santoz chemical accident in 1982, when a fire at an organic chemical company in Switzerland caused huge levels of pollutants and poisonous chemicals to enter into the river Rhine.  These traveled the length of the river and entered the North Sea.  Many aquatic animals were killed, and several were wiped out from the length of the river, including the Salmon which is a good indicator of pollution.  The species returned in 1997, three years ahead of estimate. 

Any chemicals are dumped in rivers, and any litter, can easily affect the oceans.  Fertiliser run-off can also cause a similar effect, causing algal blooms that will alter the balance of nutrients and oxygen in the water and having knock-on effects on the ecosystem. 

Recreational Pollution

It is very easy for people to pollute rivers and seas without being aware of what they are doing.  Many recreational activities can cause pollute, including boating.  Chemicals used to paint boats, wash boats or even to fuel boats (oil) can get into the water and can cause damage to the ecosystem directly to marine wildlife or to the habitats they inhibit.

Litter

Pollution through litter is also often common, particularly from recreational use.  Many people do not consider this as impacting on marine wildlife as well as freshwater, however a river is rarely a static system transporting anything on or within it eventually out to sea.

Litter washed down to the sea can cause big problems, the least of them being that they wash up on beaches and look unpleasant.  Floating litter can be mistaken as food by many different animals, including turtles, who often mistake plastic bags for jellyfish.  Many animals are killed by ingesting or getting tangled up in litter.    

Plastic waste rarely ever fully biodegrades, staying within the environment for a long time.  In the sea plastic is worn down by a combination of wave action, salt and sun, producing tiny grains of plastic dust which can’t be removed, these particles can prove deadly to delicate filter feeding marine life living within or on sandy seabeds.