Our Seas

This is new series about our seas, their use, their conservation, their state of health. You are invited to send any information you may have to the Webmaster for inclusion on this page.

Marine Pollution

Oil spills, toxic wastes and plastics are familiar marine pollutants. However, human interaction with the ocean results in other, often more serious threats.

Sources of marine pollution

Pipelines: Over 1000's of licensed pipelines discharge effluent along the coasts of all the continents.: One third discharge domestic sewage, half discharge industrial wastes, and the remainder discharge mixed effluent. These pipelines operate via various permits systems and of course there are also large numbers of unregistered pipelines.The licensing departments are supposed to monitor and control both the effluent and environmental effects. Pipelines usually discharge below the low water mark

Stormwater: Urban runoff, or stormwater, is more difficult to control. Stormwater drains collect and channel the water from all non-porous surfaces, such as pavements and tarred roads, within a catchment. Stormwater flow depends on rainfall, and the first flows following a dry spell often contain high levels of pollutants, such as heavy metals (particularly lead), oil residues, nutrients (nitrogen and phosphorus), and pathogenic (disease-causing) micro-organisms, such
as viruses, bacteria and protozoa, from faecal material. The latter is a problem particularly with water coming from informal settlements lacking adequate sanitation.

Rivers: Rivers carry to the sea, water containing contaminants such as nutrients, and pesticides from agricultural runoff, faecal pollution; and , industrial discharges. Soil erosion can cause increased water turbidity and siltation of estuaries.

At sea: Pollution sources at sea include accidental and deliberate discharges of oil, liquid petroleum gas, operational dumping of garbage (particularly plastics), and controlled dumping. Unlike many countries in Europe and the USA, South Africa does not dump industrial wastes or sewage sludges. Its dumping is limited to dredge spoils (mostly routine harbour dredging and unserviceable equipment. Dredge spoils are often rich in heavy metals /e.g. lead, copper, zinc, mercury, and cadmium, and are dumped at designated sites. The cargo of a ship involved in an accident may also be a pollution threat.

Effects of marine pollution

Sewage effluent, or organically rich industrial effluent such as that from fish processing plants, presents a number of problems:

i) Decomposition of organic matter causes a drop in dissolved oxygen, particularly in calm weather and sheltered bays. This can cause the death of marine plants and animals, and may lead to changes in biodiversity.
ii) Effluent, rich in nitrogen and phosphorus, results in eutrophication (overfertilisation), which may cause algal blooms. These blooms can discolour the water, clog fish gills, or even be toxic, eg red tides. Microbial breakdown of dead algae can cause oxygen deficiencies.
iii) Pathogenic microorganisms cause gastric, or ear, nose, and throat infections, hepatitis, or even cholera and typhoid. Filterfeeding animals (e.g. mussels, clams, oysters) concentrate pathogens in their gut so eating shellfish from polluted waters is a health risk.

Oil spills smother plants and animals, preventing respiration. In seabirds and mammals it can cause a breakdown in their thermal insulation. Chemical toxicity can cause behavioral changes, physiological damage, or impair reproduction. Oil pollution is an eyesore, and cleanup and subsequent disposal of oily wastes is difficult.

Pesticides. such as DDT, and . other persistent chemicals e.g. PCBs, accumulate in the fatty tissue of animals. These chemicals can cause reproductive failure in marine mammals and birds.

Ships often paint their hulls with anti-fouling substances, e.g. tributyl-tin (TBT), to prevent growth of marine organisms. These substances leach into water and, in high traffic areas such as harbours and marinas, can affect animal life. This has contributed to a call for a world-wide ban on the use of TBT. In the mean time, alternatives are being considered.

Plastics kill many marine animals. Turtles, for example, often swallow floating plastic bags, mistaking them for jelly-fish. Animals are often strangled when they become entangled with plastic debris.

The South African situation:

Bays: South Africa has approximately 3000 km of coastline, much of it high energy with strong winds and waves which disperse pollutants. Many large coastal towns are situated on bays, e.g. those at. Saldanha Bay, Table Bay, False Bay, Mossel Bay, Algoa Bay and Richards Bay. These areas receive large amounts of pollution which is not dispersed and mixed with the greater ocean as a result of the protection offered by the bay. Eutrophication in South Africa used to be limited to inland waters, e.g., Hartebeespoort Dam, but there are now indications that it may be starting to occur in some coastal bays. Increased numbers of people cause increased pollution. This is compounded by the fact that stormwater from urban areas runs off hardened surfaces rather than filtering through porous ground, thus increasing the volume of contaminated water reaching the sea. Destruction of wetlands, which filter and slow water flow, intensifies this problem .

Shipping and Oil: South Africa lies on one of the world's busiest shipping routes. Rough seas, an aging world tanker fleet, human error, and deliberate discharge, make oil pollution a real threat around our coasts. South Africa has developed contingency plans allowing equipment and manpower to be mobilised at short notice to protect beaches, estuaries, bird colonies and other sensitive areas in the event of a major spill. The Kuswag fleet of two antipollution vessels, and a patrol aircraft, plus an unsympathetic approach to illegal oil discharges at sea, has contributed to a decline in the number of oil slicks off our coast.

This page updated 30th December 2006