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Frequently Asked Questions

Water Quality and Pollution

1. What is water pollution?

Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing that drinks or uses or lives (in) it. When humans drink polluted water it often has serious effects on their health. Water pollution can also make water unsuited for the desired use.

What are the major water pollutants?

There are several classes of water pollutants:

  • The first are disease-causing agents. These are bacteria, viruses, protozoa and parasitic worms that enter sewage systems and untreated waste.
  • A second category of water pollutants is oxygen-demanding wastes; wastes that can be decomposed by oxygen-requiring bacteria. When large populations of decomposing bacteria are converting these wastes it can deplete oxygen levels in the water. This causes other organisms in the water, such as fish, to die.
  • A third class of water pollutants is water-soluble inorganic pollutants, such as acids, salts and toxic metals. Large quantities of these compounds will make water unfit to drink and will cause the death of aquatic life. Another class of water pollutants are nutrients; they are water-soluble nitrates and phosphates that cause excessive growth of algae and other water plants, which deplete the water's oxygen supply. This kills fish and, when found in drinking water, can kill young children.
  • Water can also be polluted by a number of organic compounds such as oil, plastics and pesticides, which are harmful to humans and all plants and animals in the water.
  • A very dangerous category is suspended sediment, because it causes depletion in the water's light absorption and the particles spread dangerous compounds such as pesticides through the water.
  • Finally, water-soluble radioactive compounds can cause cancer, birth defects and genetic damage and are thus very dangerous water pollutants.


2. Where does water pollution come from?

Water pollution is usually caused by human activities. Different human sources add to the pollution of water. There are two sorts of sources, point and nonpoint sources. Point sources discharge pollutants at specific locations through pipelines or sewers into the surface water. Nonpoint sources are sources that cannot be traced to a single site of discharge.

Examples of point sources are: factories, sewage treatment plants, underground mines, oil wells, oil tankers and agriculture. Examples of nonpoint sources are: acid deposition from the air, traffic, pollutants that are spread through rivers and pollutants that enter the water through groundwater. Nonpoint pollution is hard to control because the perpetrators cannot be traced.


3. How do we detect water pollution?

Water pollution is detected in laboratories, where small samples of water are analysed for different contaminants. Living organisms such as fish can also be used for the detection of water pollution. Changes in their behaviour or growth show us, that the water they live in is polluted. Specific properties of these organisms can give information on the sort of pollution in their environment. Laboratories also use computer models to determine what dangers there can be in certain waters. They import the data they own on the water into the computer, and the computer then determines if the water has any impurities.


4. What is heat pollution, what causes it and what are the dangers?

In most manufacturing processes a lot of heat originates that must be released into the environment, because it is waste heat. The cheapest way to do this is to withdraw nearby surface water, pass it through the plant, and return the heated water to the body of surface water. The heat that is released in the water has negative effects on all life in the receiving surface water. This is the kind of pollution that is commonly known as heat pollution or thermal pollution.

The warmer water decreases the solubility of oxygen in the water and it also causes water organisms to breathe faster. Many water organisms will then die from oxygen shortages, or they become more susceptible to diseases.


5. What is eutrophication, what causes it and what are the dangers?

Eutrophication means natural nutrient enrichment of streams and lakes. The enrichment is often increased by human activities, such as agriculture (manure addition). Over time, lakes then become eutrophic due to an increase in nutrients.

Eutrophication is mainly caused by an increase in nitrate and phosphate levels and has a negative influence on water life. This is because, due to the enrichment, water plants such as algae will grow extensively. As a result the water will absorb less light and certain aerobic bacteria will become more active. These bacteria deplete oxygen levels even further, so that only anaerobic bacteria can be active. This makes life in the water impossible for fish and other organisms.


6. What is acid rain and how does it develop?

Typical rainwater has a pH of about 5 to 6. This means that it is naturally a neutral, slightly acidic liquid. During precipitation rainwater dissolves gasses such as carbon dioxide and oxygen. The industry now emits great amounts of acidifying gasses, such as sulphuric oxides and carbon monoxide. These gasses also dissolve in rainwater. This causes a change in pH of the precipitation – the pH of rain will fall to a value of or below 4. When a substance has a pH of below 6.5, it is acid. The lower the pH, the more acid the substance is. That is why rain with a lower pH, due to dissolved industrial emissions, is called acid rain.


7. Why does water sometimes smell like rotten eggs?

When water is enriched with nutrients, eventually anaerobic bacteria, which do not need oxygen to practice their functions, will become highly active. These bacteria produce certain gasses during their activities. One of these gases is hydrogen sulphide. This compounds smells like rotten eggs. When water smells like rotten eggs we can conclude that there is hydrogen present, due to a shortage of oxygen in the specific water.


8. What causes white deposit on showers and bathroom walls?

Water contains many compounds. A few of these compounds are calcium and carbonate. Carbonate works as a buffer in water and is thus a very important component.

When calcium reacts with carbonate a solid substance is formed, that is called lime. This lime is what causes the white deposit on showers and bathroom walls and is commonly known as lime deposit. It can be removed by using a specially suited cleaning agent.


9. What are the most common causes of water pollution?

  • Storm water drains.
  • Solid waste from urban settlements.
  • Burst or overloaded sewerage lines.
  • Mismanaged effluent from industries.
  • Acid mine drainage.

Domestic households, industrial and agricultural practices produce wastewater (sewerage) that can cause pollution of many lakes and rivers.

Sewerage is the term used for wastewater that often contains faeces, urine and laundry waste. Sewerage disposal is a major problem in developing countries as many people in these areas don’t have access to sanitary conditions and clean water. Untreated sewerage water in such areas can contaminate the environment and cause diseases such as diarrhoea. Sewerage in developed countries is carried away from the home quickly and hygienically through sewerage pipes. Sewerage is treated in water treatment plants and the waste is often disposed into the sea. Sewerage is mainly biodegradable and most of it is broken down in the environment. In developed countries, sewage often causes problems when people flush chemical and pharmaceutical substances down the toilet. When people are ill, sewerage often carries harmful viruses and bacteria into the environment causing health problems.

Oceans are polluted by oil on a daily basis from oil spills, routine shipping, run-offs and dumping.

  • Oil spills make up about 12% of the oil that enters the ocean. The rest come from shipping travel, drains and dumping.
  • An oil spill from a tanker is a severe problem because there is such a huge quantity of oil being spilt into one place.
  • Oil spills cause a very localised problem but can be catastrophic to local marine wildlife such as fish, birds and sea otters.
  • Oil cannot dissolve in water and forms a thick sludge in the water. This suffocates fish, gets caught in the feathers of marine birds stopping them from flying and blocks light from photosynthetic aquatic plants.

An increase in water temperature can result in the death of many aquatic organisms and disrupt many marine habitats. For example, a rise in water temperatures causes coral bleaching of reefs around the world. This is when the coral expels the microorganisms of which it is dependent on. This can result in great damage to coral reefs and subsequently, all the marine life that depends on it.

The rise in the Earth's water temperature is caused by global warming.

  • Global warming is a process where the average global temperature increases due to the greenhouse effect.
  • The burning of fossil fuel releases greenhouse gasses, such as carbon dioxide, into the atmosphere.
  • This causes heat from the sun to get ‘trapped’ in the Earths atmosphere and consequently the global temperature rises.

A tank or piping network that has at least 10 percent of its volume underground is known as an underground storage tank (UST). They often store substances such as petroleum, that are harmful to the surrounding environment should it become contaminated. Many UST’s constructed before 1980 are made from steel pipes that are directly exposed to the environment. Over time the steel corrodes and causes leakages, affecting surrounding soil and groundwater.

Nuclear waste is produced from industrial, medical and scientific processes that use radioactive material. Nuclear waste can have detrimental effects on marine habitats. Nuclear waste comes from a number of sources:

  • Operations conducted by nuclear power stations produce radioactive waste. Nuclear-fuel reprocessing plants in northern Europe are the biggest sources of man-made nuclear waste in the surrounding ocean. Radioactive traces from these plants have been found as far away as Greenland.
  • Mining and refining of uranium and thorium are also causes of marine nuclear waste.
  • Waste is also produced in the nuclear fuel cycle which is used in many industrial, medical and scientific processes.
  • Dumping of litter in the sea can cause huge problems. Litter items such as 6-pack ring packaging can get caught in marine animals and may result in death. Different items take different lengths of time to degrade in water:
    • Cardboard – Takes 2 weeks to degrade.
    • Newspaper – Takes 6 weeks to degrade.
    • Photodegradable packaging – Takes 6 weeks to degrade.
    • Foam – Takes 50 years to degrade.
    • Styrofoam – Takes 80 years to degrade.
    • Aluminium – Takes 200 years to degrade.
    • Plastic packaging – Takes 400 years to degrade.
    • Glass – It takes so long to degrade that we don’t know the exact time.
  • Atmospheric deposition is the pollution of water caused by air pollution:
    • In the atmosphere, water particles mix with carbon dioxide sulphur dioxide and nitrogen oxides, this forms a weak acid.
    • Air pollution means that water vapour absorbs more of these gases and becomes even more acidic.
    • When it rains the water is polluted with these gases, this is called acid rain.
    • When acid rain pollutes marine habitats such as rivers and lakes, aquatic life is harmed.

Industry is a huge source of water pollution, it produces pollutants that are extremely harmful to people and the environment:

  • Many industrial facilities use freshwater to carry away waste from the plant and into rivers, lakes and oceans.
  • Pollutants from industrial sources include:
    • Asbestos – This pollutant is a serious health hazard and carcinogenic. Asbestos fibres can be inhaled and cause illnesses such as asbestosis, mesothelioma, lung cancer, intestinal cancer and liver cancer.
    • Lead – This is a metallic element and can cause health and environmental problems. It is a non-biodegradable substance so is hard to clean up once the environment is contaminated. Lead is harmful to the health of many animals, including humans, as it can inhibit the action of bodily enzymes.
    • Mercury - This is a metallic element and can cause health and environmental problems. It is a non-biodegradable substance so is hard to clean up once the environment is contaminated. Mercury is also harmful to animal health as it can cause illness through mercury poisoning.
    • Nitrates – The increased use of fertilisers means that nitrates are more often being washed from the soil and into rivers and lakes. This can cause eutrophication, which can be very problematic to marine environments.
    • Phosphates - The increased use of fertilisers means that phosphates are more often being washed from the soil and into rivers and lakes. This can cause eutrophication, which can be very problematic to marine environments.
    • Sulphur – This is a non-metallic substance that is harmful for marine life.
    • Oils – Oil does not dissolve in water, instead it forms a thick layer on the water surface. This can stop marine plants receiving enough light for photosynthesis. It is also harmful for fish and marine birds.
    • Petrochemicals – This is formed from gas or petrol and can be toxic to marine life.


10. What can be used to test for water pollution?

It is usually a good idea to do some basic observation when looking to see if a water body is polluted. Things to look out for are highly turbid water, extensive algal growth, lots of dead fish, frogs or insects, foam and froth, oil slick or a bad smell. These things will tell you whether the water is polluted.

After completing the physical observation, it is a good idea to carry out a simple pH test. This can be used as an indicator test to identify whether any effluent may have entered the water from industry, factories, mining, etc. Effluent, depending on what is in it, will indicate an acidic or alkaline pH.

A neutral pH for summer rainfall areas in South Africa falls between 6,5 and 8, depending on certain factors like the rocks present in the area, for example, the pH in some parts of the North-West Province is slightly alkaline due to the presence of dolomite (metamorphosed limestone). In the winter rainfall areas of the Western Cape a neutral pH is about 5,5. This is due to the poor soils in the area. The vegetation usually consists of hard-leaved, fairly unpalatable trees and shrubs which contain elevated levels of tannins and carbolic acids. These chemicals act as protection against over-browsing from animals and insects, therefore allowing the plants to conserve precious water and nutrients in the poor soil conditions. When these plants die, the acids and tannins taint the water, turning it the colour of cold coffee and lowering the pH.

A further indicator test is to take the temperature of the water. A standard summer water temperature for water is between 19 degrees centigrade and 24 degrees centigrade, while a standard winter temperature is between 10 and 12 degrees centigrade. Any reading drastically out of these ranges could indicate the presence of effluent in the water.

Once these two indicator tests have been done, further tests, such as nitrates, phosphates, coliform bacteria, etc, to identify the nature and source of the pollution, can be done.

11. What are the alternative cleaning agents that can be used in the home?

Households have been using products with these harmful ingredients for years. It is only in recent years that we are becoming increasingly aware of the personal health and environmental impact that these products are causing. According to the US National Centre for Health Statistics one in three people suffer from allergies, sinusitis, asthma or bronchitis. Treatment for the conditions should include reducing synthetic chemicals in the household. So what are our alternatives? Well, it’s back to basics. Back to the products used by our mothers and grandmothers! They also cost significantly less.

  • Baking Soda - cleans, deodorizes, softens water, scours.
  • Soap - unscented soap in liquid form, flakes, powders or bars is biodegradable and will clean just about anything. Avoid using soaps which contain petroleum distillates.
  • Lemon - one of the strongest food-acids, effective against most household bacteria.
  • Borax - (sodium borate) cleans, deodorises, disinfects, softens water, cleans wallpaper, painted walls and floors. It is recommended that gloves are used when handling borax and that it is not left lying around. Store it in the same manner as a pesticide.
  • White Vinegar - cuts grease, removes mildew, odours, some stains and wax build-up.
  • Washing Soda or SAL Soda is sodium carbonate decahydrate, a mineral. Washing soda cuts grease, removes stains, softens water, cleans wall, tiles, sinks and tubs. Use care, as washing soda can irritate mucous membranes. Do not use on aluminum.
  • Cornstarch - can be used to clean windows, polish furniture, shampoo carpets and rugs.


12. How does urbanization and industrialization contribute to water pollution?

Industries and urban development produce waste that can affect the:

  • pH of water (whether it is acid, neutral or alkaline);
  • colour of water;
  • amount of nutrients (increase in nutrients can cause eutrophication);
  • temperature (increase or decrease in temperature can have an impact on temperature sensitive organisms living in the water);
  • amount minerals and salts (too much can cause health problems);
  • murkiness of water (can block fish gills; bottom dwelling plants cannot photosynthesize as the sun’s rays cannot reach them; increase in disease as bacteria and viruses use the soil particles as a method of transportation).

13. How does increased human population in urban areas affect water quality?

As more and more people move into cities and towns, a number of factors cause pollution:

  • the physical disturbance of land due to construction of houses, industries, roads, etc.;
  • chemical pollution from industries, mines, etc.;
  • inadequate sewage collection and treatment;
  • increase in fertilisers to grow more food. This results in an increase in nutrients (nitrates and phosphates) in the water which causes enhanced plant growth (algal blooms). When this plant material dies and decays the bacteria uses the oxygen in the water. This lowering of oxygen levels results in the death of other water life that needs oxygen to survive, eg. fish, etc. This process is called eutrophication;
  • litter, which causes disease and has a negative visual impact.

14. How does deforestation contribute to water pollution?

Clearing land for agriculture and urban growth often leads to water pollution. Forestry has negative impacts upon bio-diversity, as the existing vegetation (often grasslands) is destroyed. When soil is stripped of its protective vegetation it becomes prone to soil erosion. This leads to an increase in the murkiness of the water which can cause the following:

  • it can block the gills of fish;
  • bottom dwelling plants cannot photosynthesize as the sun’s rays cannot reach them; and
  • there is an increase in disease as bacteria and viruses use the soil particles as a method of transportation.

Pine, Black Wattle and Eucalyptus plantations use up vast amounts of our water resources, depriving indigenous vegetation of water. Many plantations in South Africa are situated in the temperate, medium to high altitude grasslands in Mpumalanga and Kwa-Zulu Natal. These areas act as the major catchments for many east flowing rivers such as the Letaba, Sabie, Crocodile, Pongola, Thukela, Umkomazi and Umzimkulu rivers, and are essential for agricultural, urban and ecological communities downstream. These rivers and their tributaries have become a lot drier in the past decades and some have even temporarily dried up in the winter seasons due to the impact of these plantations.

15. What is meant by the term ‘Water Ecology’?

Ecology is the study of the interactions between organisms and their environment. Various different species living in the same place, interacting amongst themselves and with their environment together form an ecosystem. Within an ecosystem there are several food webs. A food web is an overview of which species in an environment consume which species (plant, animal or both). A healthy ecosystem has a variety of organisms that play different roles in various food chains. If the ecosystem loses one of its members, it can be crippled. For instance, if owls in the forest food web would die out, rodents might start to multiply at an enormous speed, causing them to overrun the area and finish resources that other animals also use.

Ecologists are people that study the interactions between organisms and their environment within food webs or other ecological relationships. Fieldwork is an essential component of this study. Laboratory experiments are also applied, under field conditions. Most of the time ecologists are involved in studying the natural environment and communities, but some are involved in applied ecology, using ecological knowledge in ecosystems directed by humans, commonly known as agro-ecosystems.


16. What kind of saltwater life zones are there?

The largest saltwater life zones on earth are not very hard to find, as these are in the oceans. Oceans cover about 71% of the earth's surface and are very important for the preservation of all life on earth. Oceans play an important part in the hydrological cycle, because precipitation (rain) consists of evaporated oceanic water and in the regulation of the earth's climate. Oceans also participate in other matter cycles. Oceans are the living environment for about 250,000 species of marine plants and animals. Unfortunately, oceans are also dumps for human waste, because the (polluted) water of all inland water bodies eventually ends up in oceans.

Oceans can be divided up into the coastal zone and the open sea. Here we will give an explanation of the various types of life zones found in the coastal zone and in the open ocean, along with a schematic overview of all these life zones.

Coastal life zones:

The coastal zone makes up only 10% of the oceanic environment, but it contains 90% of all marine species. Coastal zones are the most nutrient-rich life zones of the oceans.

Coastal zones can be divided up into several different life zones. One life zone that can be found in a coastal zone is an estuary. Estuaries are enclosed areas of coastal water where seawater mixes with freshwater from inland streams and rivers.

Temperatures and salinity levels of estuaries always depend upon the size of the flow from saltwater oceans and freshwater rivers and streams.

Another life zone found in a coastal zone is a coastal wetland. Wetlands are land that is covered with salt water all or part of the year. Coastal wetlands are the life zones for a number of species and they are popular recreation points. They aid the maintenance of the coastal water quality by filtering and settling out pollutants and nutrients. Coastal wetlands are particularly important because they protect coastal land from flooding and from damage and erosion caused by storms. Examples of plant and animal species found commonly on coastal wetlands are grasses and shrimps.

Along tropical coasts with too much silt for coastal wetlands we may find swamps. These help protect the coastline from erosion and are the environment for over 2,000 species of fish, birds and plants.

In clear and warm coastal waters of tropics and subtropics, coral reefs may form. Coral reefs are the most biologically divers aquatic life zones. In coral reefs many species live and interact with one another in complex ecological relationships. An example of a large coral reef is the Great Barrier Reef in Australia.

Open ocean life zones:

The open sea contains only about 10% of all marine species. The open ocean is divided up into three life zones, the euphotic zone, the bathyal zone and the abyssal zone. The subdivision is based on the penetration of sunlight.

The euphotic zone is the upper oceanic zone, where producer species produce oxygen. Nutrient levels are low and dissolved oxygen levels are high. The euphotic zone makes up about 90% of the oceanic surface, whereas only about 10% of the world's fish species are found here. Sunlight penetration rates are high in this oceanic zone.

The bathyal zone is hardly lit and the abyssal zone is very dark. These zones are only found in the open sea and do not contain any producers, because of a lack of penetrating sunlight. In the abyssal zone the water is very cold and dissolved oxygen levels are very low. There are high nutrient levels that support many of the species found in the open water. Below the abyssal zone, on the bottom of the ocean, there are many species of decomposers, which break down the organic material of dead oceanic organisms into nutrients.

The open ocean has a very high productivity. This makes the above-mentioned life zones of great importance.


17. What kind of aquatic environments are there?

There are two kinds of aquatic environments, which can sustain life. These are saltwater life zones and freshwater life zones. The major types of organisms found in aquatic environments are determined by the salinity of the water. Salinity means the amounts of salts dissolved in a volume of water. That is why aquatic life zones are divided up between saltwater life zones and freshwater life zones.

An example of a saltwater or marine life zone is a coral reef. An example of a freshwater life zone is a lake.


18. What kind of freshwater life zones are there?

Freshwater life zones are found in waters with a dissolved salt concentration of less than 1%. Freshwaters are divided up into standing bodies of freshwater, such as lakes, ponds and inland wetlands and flowing bodies of freshwater, such as rivers and streams. Only 1% of the earth's surface is covered with freshwater. However, about 41% of all known fish species live in freshwater. Run-off from land provides the water with nutrients, such as nitrogen and phosphorus, because the freshwater zones are close to terrestrial (land) ecosystems.

Here we will give an explanation of the various types of life zones found in standing and flowing bodies of freshwater, along with a schematic overview of all these life zones.

Life zones in standing freshwater bodies

Lakes and ponds are large, natural bodies of standing water. They are fed mainly by rainfall and melting snow, and they consist of various different life zones.

The first life zone in freshwater lakes is called the littoral zone. The littoral zone is found near the shore where rooted plants grow. It is the most productive zone of a lake, because it gets abundant sunlight and it receives nutrients from land run-off. The littoral zone sustains floating plants, surfaced plants, submerged plants and phytoplankton. There are also large quantities of decomposers and some animal species, such as frogs, fish and insects.

Under the littoral life zone there is the limnetic life zone. This is the zone on the surface of the lake, extending to the depth where sunlight penetrates. Depending on the available nutrients it contains phyto- and zooplankton, and various fish species.

Under the limnetic life zone is the profundal life zone. The profundal life zone is the deep, dark water that cannot be reached by penetrating sunlight. In this zone we can only find fish that can survive in cooler, darker circumstances.

Finally, at the bottom of freshwater bodies there is another life zone called the benthic life zone, mainly inhabited by decomposers and insect larvae.

Life zones in flowing freshwater bodies

Flowing bodies of freshwater, such as rivers and streams, are watersheds for precipitation water. This water becomes land run-off and flows with the rivers and streams to the sea. The flow of surface water to the sea takes place in three different life zones. These life zones all have their own environmental conditions, which causes species diversity to vary between the three zones.
In the first life zone streams of clear, cold water rush over waterfalls and rapids. While the water falls down, it dissolves large amounts of oxygen from the air. In this life zone plant species like algae and mosses and fish species like trout are most common. Few plankton species are found in these streams and fishes are usually flat-bodied.

In the second life zone there are wider and deeper streams and fewer obstacles. The water is warmer and the oxygen content lower, so that this life zone supports more producer species, such as phytoplankton.

In the third zone streams flow into wider and deeper rivers, which stream through flat valleys. The water in this life zone has a lower oxygen content and higher temperatures than the water in the first two zones. The rivers and streams are slowly moving and contain producers, such as algae and cyanobacteria, as well as rooted aquatic plants. Because of land erosion the water is often muddy and filled with suspended solids.

Flowing freshwater bodies usually receive their nutrients from land run-off.


19. Which species live in the aquatic life zones and how do they interact? producers to built life-sustaining matter.

Both saltwater and freshwater life zones contain a wide variety of organisms, which all interact with one another in various food webs. A food web is a system in which certain organisms consume other organisms, plant or animal, to form a sustainable system in which species will be in balance and will not experience overpopulation.

The main kinds of organisms in aquatic ecosystems are free-floating, very small organisms called plankton, strongly swimming organisms called nekton, bottom-dwelling organisms called benthos and decomposers, such as bacteria.

Plankton is a kind of organism that sustains many species, because it is consumed. Phytoplankton is the most important kind of plankton, because phytoplankton consists of producers. This basically means it produces matter that will sustain the lives of other aquatic organisms, such as oxygen. Phytoplankton is also the most widely eaten kind of plankton. The other species of plankton are either half-producers (nanoplankton) or consumers (zooplankton).

Nekton is a group of larger, swimming consumers, which eat plankton or other consumers. Examples of nekton are such as fish and turtles.

Examples of benthos, the bottom-dwelling organisms, are oysters and lobsters.

Decomposers have one single task in an aquatic ecosystem; to break down (decompose) organic material.


20. Which are the limiting factors for aquatic life?

Aquatic environments have many advantages. Water has many properties and because of that it is a unique kind of environment to live in.
Water pressure provides physical support. Temperature fluctuations are very limited, which reduces the risk for aquatic animals to become overheated or to dry out. The required nutrients are readily available, because they are dissolved in water. When toxins enter the water they are quickly converted or dispersed.

These are all very positive effects of living under water. However, there are also factors that limit aquatic life. Factors that determine which life forms can be sustained in an aquatic life zone are:

  • Temperature
  • Access to sunlight
  • Dissolved oxygen concentrations
  • Availability of nutrients, such as nitrogen and phosphorus

The water temperature usually falls with water depth, because less sunlight will penetrate the water at a greater depth. Most aquatic organisms have a limited range of tolerance to temperature changes. This is all they need, because temperatures are not likely to undergo great changes beneath the water surface. However, when sudden temperature changes do occur it will have a significant effect on the performance and survival of aquatic organisms.

Sunlight can only penetrate the water up to a depth of about 30 metres below the surface. Producers need sunlight to produce oxygen and other required substances that will sustain consumers. Production can only occur in the zone where sunlight can penetrate. Suspended matter may interfere with the penetration of sunlight into water. This may decrease the size of the zone in which production takes place.

Oxygen enters the aquatic ecosystem from the atmosphere and on account of production by (phyto)plankton. Dissolved oxygen concentrations deriving from atmospheric oxygen are influenced by water temperatures. When dissolved oxygen levels fall below 3 ppm many consumers, such as fish and zooplankton, will die.

This makes dissolved oxygen and water temperature very important limiting factors in aquatic life zones. Oxygen levels, like temperatures, also decrease with depth.

Nutrient supplies are usually satisfactory in freshwater ecosystems. However, in open oceans nutrients are often in short supply. They are an important limiting factor for productivity in aquatic life zones. Phosphorus is the main limiting nutrient in freshwater life zones, whereas nitrogen is the main limiting nutrient in saltwater life zones.


21. What impact do humans have on aquatic life zones?

Human's desire to live near the coast has aided to the degradation of aquatic life zones. Today, around two-thirds of the worlds' population lives near coasts. People have been drying wetlands and other coastal areas, in order to gain land for urban development.

Most water bodies are now severely polluted, because we have been discharging wastewater in it for a very long time, before we realised this was very bad for the water quality. Coastal life zones are particularly sensitive to toxic contamination, because they are a dump for pesticides, heavy metals and other pollutants, which will soon accumulate to high levels. Run-off from sewage treatment plants and other water treatment systems is threatening all aquatic life zones nowadays and we are trying very hard to solve this problem.

A human activity that seriously threats life in aquatic life zones is fishing. People do not know where to stop, so over fishing has become a common problem in oceans, as well as in inland waters.

We are trying very hard to protect coral reefs right now, because we are responsible for the destruction of about 10% of the world's coral reefs. Coral reefs are the most widely developed ecosystems on earth with an enormous variety of plant and animal species. But protecting coral reefs is complex and expensive. Only half of the countries with coral reefs have the resources to protect them.

Wetlands and swamps are disappearing because people convert them to farmland, or use them for mining, forestry, oil and gas extraction and highways. Many wetlands have already been converted. Today nature organisations are trying to restore wetlands. However, replacing wetlands is expensive and it does not guarantee the restored wetlands to resemble the natural ones that were once there.


22. What effect does a dam have on the water ecology and quality of water in a river?

Damming of rivers can have an impact on water quality in the following ways:

  • Water flowing out of dams:
    • has reduced suspended material as a large amount settles to the bottom of dams;
    • is usually more erosive as there is not much suspended material to deposit;
    • is depleted of nutrients; and
    • is often more saline
    • with detrimental effects on downstream agriculture and fisheries.
  • Enhanced eutrophication may result due to the water spending a longer time in the dam.
  • There is also increased evaporation in dams, especially those with a large surface area, such as the Vaal Dam.

Damming of rivers can also have the following impacts upon water ecology:

  • habitat alteration – where once a fast-flowing, stony stream occurred, it has been replaced with slow moving, nutrient rich, often turbid dam water with a silty bed;
  • loss of bio-diversity – aquatic invertebrates prefer clear, well-oxygenated water that is moving to slow, turbid water with a high nutrient and silt load. Many species such as mayfly larvae, stonefly larvae, damselfly larvae, dragonfly larvae and cadisfly larvae (all indicators of good water quality) will be replaced by flatworms, leeches and fly larvae which can tolerate adverse water quality conditions.
  • breaking down of healthy food-webs – loss of bio-diversity usually means that most species in the affected eco-system will suffer and many will be replaced by hardier, more invasive species.

23. Why are Gauteng's rivers in such poor health?

There are three major river catchments in Gauteng, the Jukskei/Crocodile system (Edenvale and Roodepoort area), the Blesbokspruit/Suikerbosrand system (Benoni and Springs areas) and the Klip River system Boksburg, Germiston and Soweto areas). The Witwatersrand Ridge, which runs from the Edenvale area in the east to Krugerdorp in the north-west is a major watershed, dividing the Vaal River catchment from the Limpopo River catchment. The Jukskei/Crocodile system drains the area of Johannesburg north of the city and feeds the Limpopo catchment, while the Blesbokspruit and the Klip River systems drain the area south and east of the city and feed the Vaal River.

All of these rivers have their sources in heavy urbanised and industrialised areas of Gauteng and are thus heavily impacted by these activities. Serious issues facing these rivers include polluted run-off from storm water drains, effluent from industries and the increasing problem of sewerage spills and mismanaged waste water works. Existing waste water works are battling to deal with an ever increasing load from the massive development taking place in the province.

One of the most important issues facing our rivers in Gauteng is that of Acid Mine Drainage (see the following question). This is affecting mainly the Vaal River catchment i.e. the Blesbokspruit system in the Springs/Brakpan area and the Klip River system in the Boksburg, Germiston and Soweto areas. However, in the Krugersdorp/Randfontein area acid mine drainage is also affecting the north flowing streams that feed the Crocodile river. Acid mine drainage poses a serious threat to our water resources not only in Gauteng but all over the world. The Olifants catchment in Mpumalanga is severely impacted by coal mining on the eastern Highveld to an extent that crocodiles in the Loskop dam have been dying from the toxic effects of polluted water.


1. What is Acid Mine Drainage?

Acid Mine Drainage is the biggest environmental crisis in the world after the issue of global warming and climate change. It is a problem associated with mining and its subsequent effect on water quality.

Source (following information):

Definition of Acid Mine Drainage (AMD) - Low pH drainage water from certain mines usually caused by the oxidation of sulphides (e.g. iron pyrite) to sulphuric acid. Mine drainage can also contain high concentration of metal ions.

Sub-surface mining often progresses below the water table, so water must be constantly pumped out of the mine in order to prevent flooding. When a mine is abandoned, the pumping ceases, and water floods the mine. This introduction of water is the initial step in most acid rock drainage situations. Tailings piles (Mine Dumps or slimes dams) or ponds may also be a source of acid rock drainage.

After being exposed to air and water, oxidation of metal sulfides (often pyrite, which is iron-sulfide) within the surrounding rock and overburden generates acidity. Colonies of bacteria and archaea greatly accelerate the decomposition of metal ions, although the reactions also occur in an abiotic environment. These microbes, called extremophiles for their ability to survive in harsh conditions, occur naturally in the rock, but limited water and oxygen supplies usually keep their numbers low. Special extremophiles known as acidophiles especially favor the low pH levels of abandoned mines. In particular, Acidithiobacillus ferrooxidans is a key contributor to pyrite oxidation.

Metal mines may generate highly acidic discharges where the ore is a sulfide or is associated with pyrites. In these cases the predominant metal ion may not be iron but rather zinc, copper, or nickel. The most commonly-mined ore of copper, chalcopyrite, is itself a copper-iron-sulfide and occurs with a range of other sulfides. Thus, copper mines are often major culprits of ARD.

Acid mine drainage (AMD), or acid rock drainage (ARD), refers to the outflow of acidic water from (usually) abandoned metal mines or coal mines. However, other areas where the earth has been disturbed (e.g. construction sites, subdivisions, transportation corridors, etc.) may also contribute acid rock drainage to the environment. In many localities the liquid that drains from coal stocks, coal handling facilities, coal washeries, and even coal waste tips can be highly acidic, and in such cases it is treated as acid rock drainage. Acid rock drainage occurs naturally within some environments as part of the rock weathering process but is exacerbated by large-scale earth disturbances characteristic of mining and other large construction activities, usually within rocks containing an abundance of sulfide minerals.

The Effect of Heavy Metals

  • Heavy metals associated with mining and acid mine drainage include iron, zinc, manganese, nickel, copper, cadmium, cobalt and uranium.
  • As the pH of the affected water drops below 3, these metals are dissolved into the water and cause it to become toxic to all life. This can cause a river system to die off completely.

2. How does mining contribute to water pollution in South Africa?

Mining has caused major pollution problems all over the world:

Case Study 1: Robinson Dam, Randfontein
(Who’s to Blame, Nadine von Moltke)

Uranium is a heavy metal associated with the gold mining industry on the East, Central and West Rands in Gauteng. It is present in the sediment of many of the surrounding river systems as a result of mismanaged tailings.

Robinson Dam in Randfontein is part of the Wonderfontein catchment, a system which has been heavily polluted with heavy metals such as uranium.

An abandoned mineshaft in Randfontein has been decanting since 2002. The mine was forced to pump this water into the nearby Robinson Dam as an emergency measure and since then has been treating the decant with caustic soda before sending it to a water treatment works.

The result is that the water in the dam has a pH of about 2,2 and the uranium has been dissolved into the water, turning the dam into a toxic, highly radio-active site containing no life. Studies in the area have shown that uranium levels in the water are 40000 times greater than the normal background uranium levels in water.

Case Study 2: The Mpumalanga Lake District
Severe threat posed to Mpumalanga Lake District

Proposed opencast coal mining within the catchments of the Mpumalanga Lake District would threaten many unique and largely pristine wetlands, according to a paper by Prof Terence McCarthy & co. Concerns have been raised that, while the economic benefits of the mining are apparent, many of the environmental and social costs have not been taken into consideration.

The pans that make up what is known as the Mpumalanga Lake District are geomorphically unique in South Africa, being deeper, more permanently flooded and more densely clustered than pans elsewhere in the country. These pans are situated at the eastern extremity of South Africa's pan belt, and centre on the well-known Lake Chrissie. Although the biodiversity of the area has not been studied comprehensively, there is a very good chance of high endemism and biological uniqueness, given its geomorphology. Says Prof Terence McCarthy of the University of Witwatersrand, "There's no other place like it in the world, it's completely unique. Although this is where four big drainage basins meet, there's no outflow from here - which is why the lakes exist." Four major rivers fringe the system, the Komati, uMpuluzi, Usutu and Vaal, but the pans themselves, which are fed by both rainwater and groundwater, have no direct surface connection to the drainage network.

One of the oldest land surfaces in South Africa, the Mpumalanga Lake District offers a glimpse of Africa as it was 20 million years ago. The history of the pans is fascinating with one hypothesis suggesting that they were originally part of the drainage network of the ancestral uMpuluzi River. When its waters were captured by headward erosion of the Vaal River, sand dunes fragmented the then uMpuluzi river channel into what became the isolated pans of today.

Potential impacts of coal mining

Scientifically intriguing and biologically valuable as it is, the area is also considered economically important for the coal mining industry, and several opencast mines are proposed, leading to concern that groundwater could be severely polluted and the natural hydrological functioning of the pan systems destroyed.

Acid mine drainage, commonly associated with mining, could prove to be particularly devastating in this hydrologically sensitive area. The rocks associated with coal contain iron pyrite, which reacts with water and oxygen during and after mining to produce several undesirable chemicals, including sulphuric acid. The acidified water also leaches heavy metals such as manganese, copper and zinc and becomes aluminium-enriched. Further, the acid mine drainage can displace fresh groundwater in the surrounding area and result in acidic and saline soils, making conditions unsuitable
Once started, the process of pyrite oxidation could take centuries to complete.

Studies at backfilled opencast coal mines to the west of the Lakes District show that the mines filled with water five to ten years after closure, resulting in polluted water emerging onto the surface. "In the case of the Mpumalanga Lake District," says McCarthy, "any pollution entering the pans will be trapped there, accumulating over time and eventually destroying all aquatic life. The pans would become virtually sterile, toxic pools." There is at present no way to completely stop the production of acid mine drainage.

Opposition to coal mining

When a coal mining licence was issued for portions of the Lusthof farm in the area in June last year, it was potential impacts like these that led landowners and the Mpumalanga Lakes District Protection Group to obtain an interdict to prevent the mine starting operations. Not only are they concerned about irregularities in the issuing of the licence, but they are also convinced that coal mining is not the best long term land use option for the area.

Says Koos Pretorius of the MLDPG, "For every rand you make through coal mining you're going to lose three to four rands of income - if you consider the impact on the economy of the loss of water and potential jobs from alternative less destructive land use options. The impact won't be immediate, we'll see it in 10 or 15 years when they move out. But mining is not a sustainable option." While mining benefits are generally received by private individuals and companies, many costs are borne by society as a whole. These costs include not only loss of biodiversity and ecosystem services but also the costs of restoration or developing substitutes for the loss of ecosystem services such as water provision and purification or natural grasslands for grazing.

The group is currently taking the Minister of Minerals and Energy to court to gain access to information pertaining to the issuing of the licence that they believe has been withheld from them. They are also concerned that no cumulative or regional strategic environmental impact assessment has been conducted or is required for any of the current applications that they are concerned with.


This is only one of several similar disputes that are looming large and loud, with the country's demands for coal expected to directly affect 65 of 106 farms between Carolina, Ermelo, Chrissiesmeer and Lothair. In the area between Wonderfontein, Dullstroom and Nooitgedacht Dam, all farms are expected to be directly affected by prospecting or mining.

The Department of Minerals and Energy, regional and national, was unavailable to comment for a week prior to completion of this article.

All images courtesy Terence McCarthy & co.

Koos Pretorius / 083-9864400 /
Professor Terence McCarthy / 011-7176558 /
Conservation of the Mpumalanga Lakes District is authored by Professor Terence McCarthy, Professor Bruce Cairncross, Professor Jan-Marten Huizenga and Allan Batchelor.

Despite the effects of coal mining on the river catchments in Mpumalanga, coal mining continues to be on the increase in the province in response to the growing demand for electricity in this country. The following diagram shows current mines in Mpumalanga (orange), with the red blocks showing applications for new mines. This does not paint a positive picture for the catchments of the Vaal, Olifants, Pongola, Incomati, Mpuluzi and Crocodile rivers.

Mining activities in Mpumalanga