BEST IELTS General Reading Test 498

Table of Contents

IELTS GENERAL READING TEST 498 – PASSAGE – 3

IELTS GENERAL READING TEST – 498

READING PASSAGE – 3

Oceanic Dead Zones

Dead zones are areas of water bodies where aquatic life cannot survive because of low oxygen levels. They begin to form when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilise blooms of algae. The major nutrient sources are fertilisers, sewage, and the burning of fossil fuels. When these algae die and sink to the bottom of the sea, they provide a rich food source for bacteria, which in the act of decomposition consume dissolved oxygen from the surrounding waters. This decomposition also breaks them down to nutrients again, continuing the cycle.

If stratification of the water column prevents the mixing or dissolution of atmospheric oxygen into these waters, the deleted areas will remain oxygen poor. Shallow waters are much less likely to stratify compared to deep waters, and are thus less liable to develop hypoxia. First, shallow waters tend to be well-mixed by winds and tides, and second, waters that are shallow and clear enough to allow light to reach the bottom can support primary oxygen producers such as phytoplankton, algae, and seagrasses that release oxygen during photosynthesis.

IELTS General Reading Test

The darkness of deeper water prevents phytoplankton from producing the required oxygen. As the situation worsens, more and more oxygen is used up until all organisms die, and a dead zone is formed.

Dead zones are primarily a problem for bays, lakes and coastal waters, since they receive excess nutrients from upstream sources. About half of the hypoxic zones around the world are seasonal, as oxygen depletion occurs in spring and summer following the increase in phytoplankton that results from nutrient enrichment. These hypoxic zones usually last from a few weeks to several months; however, in some locations, about 8 per cent of worldwide hypoxic conditions occur continuously throughout the year. The size of these hypoxic zones can vary significantly from year to year.

IELTS General Reading Test

As human populations increase and the land suffers further degradation, requiring more and more fertiliser, dead zones will become more commonplace. For example, every year now, near where the Mississippi River goes into the sea, large dead zones form of 22,000 square kilometres. These areas are totally devoid of fish and other life except for anoxic bacteria. Farming using excessive nitrogen fertilisers in the river’s catchment area is blamed for this and a plan has been formulated to reduce dead zones by 30 per cent over the next 3 years.

When some types of algae blooms are large and produce chemicals, or toxins, the event is called a harmful algal bloom. Harmful algal blooms can occur in lakes, reservoirs, rivers, ponds, bays and coastal waters, and the toxins they produce can be harmful to human health and aquatic life. Harmful algal blooms are mainly the result of a type of algae called cyanobacteria, also known as blue-green algae. These harmful algal blooms release toxins that contaminate drinking water, causing illnesses for animals and humans.

IELTS General Reading Test

After being consumed by small fish and shellfish, these toxins move up the food chain and can hurt bigger animals like sea lions, turtles, dolphins, birds, manatees, and fish. Even if algal blooms are not toxic, they can hurt aquatic life by obstructing the sunlight and clogging fish gills.

Algal blooms and dead zones also have less obvious effects. Economists have examined the effects of nutrient overenrichment on both market goods, primarily commercial fisheries, and nonmarket industries, primarily recreational. Although many aquatic ecosystems have yet to be properly studied in this regard, there is plenty of research that shows how much impact dead zones have had on these two economic spheres.

IELTS General Reading Test

For example, it’s been recently shown that there would be considerable benefits in terms of the economy to reducing nitrogen loading and hypoxic conditions in the Baltic Sea, which is an area that has long suffered dead zones caused by these problems. It has been suggested that reducing dead zone areas in the Baltic could be valued at about 10 billion dollars.

A more fundamental effect of hypoxia is the loss of energy from the ocean. By precluding or stunting the growth of bottom-dwellers such as clams and worms, hypoxia robs their predators of an important source of nutrition. For example, scientists estimate that Chesapeake Bay in the United States loses about 10,000 metric tons of energy to hypoxia each year, 5 per cent of the Bay’s total production of food energy. The Baltic Sea has lost 30 per cent of its food energy – a condition that has contributed to the significant decline in its fisheries’ yields.

IELTS General Reading Test

Dead zones are a key stressor of marine ecosystems and rank with over-fishing, habitat loss, and harmful algal blooms as global environmental problems. They take a toll on the economy, hurting industries and sectors that depend on clean water. In addition, federal, state and local governments spend billions of dollars per year to combat nutrient pollution or prevent its effects. In order to improve the situation, a variety of action is required, including regulatory programs, the education of the various areas of society that are in any way involved and the provision of support, including financial commitments, to ensure that the programs and education takes place effectively and successfully.

Questions 28-30

Label the diagram below. Write NO MORE THAN ONE WORD from the text for each answer.

IELTS General Reading Test

Questions 31-40

Write NO MORE THAN TWO WORDS for each answer.

Oceanic Dead Zones

– Many oceanic areas suffer from dead zones; they can be permanent or (31)…………………. . The size varies.

– With more (32)…………………. of agricultural land, there will be more dead zones like the ones at the mouth of the Mississippi River. Nitrogen pollution from the (33)…………………. Of the river has created very large dead zones.

– Harmful algal blooms can pollute drinking water and can make animals sick. As the toxins are absorbed into this water and the (34)…………………. , larger animal and humans can be affected. In the sea, the blooms can block both the sun and (35)………………….

IELTS General Reading Test

– Dead zones also affect market and nonmarket goods, in the business and (36)………………….sectors. (37)…………………. already illustrates the effects and the (38)…………………. of improving the economic situation in various areas.

– (39)…………………. is also taken from the oceans by dead zones by removing food. The Chesapeake Bay and Baltic Sea have been studied in this regard.

– Dead zones have various negative effects and a lot of money is spent on controlling them.

– New laws, (40)…………………. of important stakeholders and resources are required to make a positive difference.

IELTS General Reading Test

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