Why is benthos difficult to explore?

Is benthos a favorable environment to various species of bacteria?

Which organisms are most common in benthos?

Why was benthos thought to be a dead zone?

What represents a dominant group in the benthos worldwide?

 

 

TEXT B

Dead Zones in the Ocean.

VOCABULARY LIST TO TEXT B

suffocate v	[ˈsʌfəkeɪt]	задыхаться
eutrophication n	[ˌjuːtrəfɪˈkeɪʃ(ə)n]	эвтрофикация, загрязнение водоёмов водорослями
issue n	[ˈɪʃuː]	проблема
aquaria   n	[ə'kwe(ə)rɪə]	аквариум
contribute  v	[kənˈtrɪbjuːt]	способствовать
fertilizer n	[ˈfəːtɪlʌɪzə]	удобрение
phosphorus n	[ˈfɒsf(ə)rəs]	фосфор
stratification   n	[ˌstrætɪfɪˈkeɪʃən]	стратификация
legislator  n	[ˈlɛdʒɪsleɪtə]	законодатель
require v	[rɪˈkwʌɪə]	требовать
undertake v	[ʌndəˈteɪk]	предпринимать
manure n	[məˈnjʊə]	навоз, органическое удобрение
disaster n	[dɪˈzɑːstə]	бедствие, несчастье

 

Exercise 47. Read and translate the following words and word combinations from English into Russian.

The northern Gulf of Mexico, dead zone, reduced oxygen levels, decaying matter, spawn rates, Hypoxic regions, Lake Erie and the Chesapeake Bay, natural zones,

sea flowing, Bosporus strait, environmental issue, eutrophication, bloom, fertilizer, manure, industrial waste, stratification, bacteria consume oxygen, legislator, disaster.

Read the text and translate. Be ready to discuss.

A dead zone is a common name for a region of reduced oxygen levels (hypoxia) in water. Because animals and plants need dissolved oxygen to live, entering a dead zone causes them to suffocate and die. However, dead zones aren't truly "dead," because bacteria thrive on the decaying matter.

Dead zones are found in rivers, lakes, oceans, ponds, and even aquaria. They can form naturally, but they can also form as a result of human activity. Dead zones kill fish and crustaceans, which immediately impacts the fishing industry. Surviving fish suffer reproductive problems, with low egg counts and spawn rates. Animals and plants that can't move have no escape. Dead zones are an important environmental issue.

Where Dead Zones Are Located

Any body of water has the potential to become a dead zone. Hypoxic regions occur in both fresh and saltwater worldwide. Dead zones mainly occur in coastal regions near watersheds, particularly in high population areas.

The largest dead zone in the world is located in the lower portion of the Black Sea. This is a natural dead zone, formed when the water of the Black Sea mixes with the Mediterranean Sea flowing through the Bosporus strait.

The Baltic Sea hosts the largest man-made dead zone. The northern Gulf of Mexico is the second-largest, covering over 8700 square miles (around the size of New Jersey). Lake Erie and the Chesapeake Bay have large dead zones. Almost the entire East Coast and Gulf Coast of the United States have dead zones. A 2008 study found over 400 dead zones worldwide.

Types of Dead Zones

Scientists classify dead zones according to how long the hypoxia lasts:

Permanent dead zones occur in very deep water. Oxygen concentrations rarely exceed 2 milligrams per liter.

Temporary dead zones are hypoxic regions that last for hours or days.

Seasonal dead zones occur every year during the warm months.

Diel cycling hypoxia refers to dead zones that occur during warm months, but the water is only hypoxic at night.

Note that the classification system doesn't address whether dead zones form naturally or as a result of human activities. Where natural dead zones form, organisms can adapt to survive them, but human activities may form new zones or else expand natural zones, throwing coastal ecosystems out of balance.

What Causes Dead Zones

The underlying cause of any dead zone is eutrophication. Eutrophication is the enrichment of water with nitrogen, phosphorus, and other nutrients, causing algae to grow out of control or "bloom." Usually, the bloom itself is non-toxic, but an exception is a red tide, which produces natural toxins that can kill wildlife and harm humans.

 

Sometimes, eutrophication occurs naturally. Heavy rains can wash nutrients from the soil into the water, storms or heavy winds can dredge up nutrients from the bottom, turbulent water can stir up sediment, or seasonal temperature changes can invert water layers.

Water pollution is the primary human source of the nutrients that cause eutrophication and dead zones. Fertilizer, manure, industrial waste, and inadequately treated wastewater overload aquatic ecosystems. In addition, air pollution contributes to eutrophication. Nitrogen compounds from automobiles and factories are returned to water bodies through precipitation.

How Algae Reduces Oxygen

You may be wondering how algae, a photosynthetic organism that releases oxygen, somehow reduces oxygen to cause a dead zone. There are a few ways this happens:

Algae and plants only produce oxygen when there is light. They consume oxygen when it's dark. When the weather is clear and sunny, the oxygen production outperforms nighttime consumption. A string of cloudy days can reduce the ultraviolet levels enough to even the score or even tip the scales so more oxygen is used than produced.

During an algal bloom, algae grow until it consumes the available nutrients. Then it dies back, releases the nutrients as it decays, and blooms again. When algae die, microorganisms decompose it. The bacteria consume oxygen, quickly making water hypoxic. This occurs so rapidly sometimes even fish can't swim outside of a zone fast enough to escape death.

Algae causes stratification. Sunlight reaches the algal layer, but it can't penetrate the growth, so photosynthetic organisms below the algae die.