Exercise 11. Read and translate the following words and word combinations from Russian into English

Полярный сегмент земли, пресноводные беспозвоночные, живущий в воде, фитопланктон, наличие света, довольно устойчивая температура, быть сбитым с толку, мигрирующие виды, широкий ассортимент растений, драгоценный ресурс, живое существо, плывущие облака, зоопланктон, зимородок, родник, утки, насекомые.

Exercise 9. Define the term and remember it's explanations.

Wetland, polar cap, freshwater ecosystem, lake, pond.

Exercise 12.Look through the text and find information about:

- freshwater ecosystemsare a subset of Earth's aquatic ecosystems;

- every living thing on Earth needs water to survive;

- fresh water starts out as water vapor;

- aquifers are filled with groundwater;

- scientists who study freshwater ecosystems are called limnologists;

- freshwater ecosystems naturally share resources between habitats;

- lakes and ponds can exchange nutrients in a seasonal cycle;

- the ecosystem varies too far outside of the norm;

- the diversity of a freshwater ecosystem.

Exercise 13. Test yourself by answering these questions and summarize given information.

1. What does the term “ aquatic ecosystem” mean?

2. How can Aquatic ecosystems be divided?

3. What are the types of freshwater ecosystems?

4. What percentage of the Earth's surface do freshwater ecosystems cover?

5. Why are freshwater ecosystems considered to be a precious resource?

6. How do you understand the formation of fresh water?

Who studies freshwater ecosystems?

What does the diversity of freshwater ecosystem depend on?

What forms the bottom layer of freshwater food chains?

What kind of amphibians can live on land and water?

Part 2

VOCABULARY LIST TO TEXT A part 2

lotic adj	[ˈləʊtɪk]	проточный
stream n	[striːm]	ручей
dragonfly n	[ˈdraɡ(ə)nflʌɪ]	стрекоза
snowmelt n	[ˈsnəʊmɛlt]	таяние снегов
trout n	[traʊt]	форель
muddy adj	[ˈmʌdi]	непрозрачный; мутный
murky adj	[ˈməːki]	тёмный, мрачный
detritus n	[dɪˈtrʌɪtəs]	детрит
precipitation n	[prɪˌsɪpɪˈteɪʃ(ə)n]	осадки
sharp adj	[ʃɑːp]	острый
lentic adj	[ˈlɛntɪk]	непроточный
ameba n	[əˈmiːbə]	амеба
thermocline n	[ˈθəːmə(ʊ)klʌɪn]	слой температурного скачка
benthos n	[ˈbɛnθɒs]	бентос
cattail n	[kəˈteɪl]	рогоз
reed n	[riːd]	тростник

Exercise 14. Read and translate the following words and word combinations from English into Russian.

Littoral zone, bottom sediments, single-celled organisms, riparian zone, freshwater environments, cattails grow, lotic organisms, flattened bodies, to swept away, to be murky with sediment, saturated soil, lower oxygen level, burrowing worms, food sources, anaerobic microorganisms, detritus, single-celled organisms like ameba, dragonflies, littoral zone, thermocline, bottom sediments, cattails, rushes, muddy, lower oxygen level, flattened body, precipitation, epilimnion, murky, silt.

Read the text and translate. Be ready to discuss.

Rivers and streams are lotic, or flowing, freshwater environments. Their water flows in one direction and they begin at a source—which could be a spring, lake, or snowmelt—and travel to their mouths, which may be the sea or another river. The water at the source is generally cooler, clearer, and has a higher oxygen content than at the mouth. Freshwater fish such as trout are often found near the source. There tends to be more biodiversity in the middle of a river or stream, while the water near the mouth is often murky with sediment that decreases the amount of light and the diversity of the ecosystem. Fish requiring less oxygen, like carp, are found near the mouth of a river. Lotic organisms tend to be small, with flattened bodies, so they are not swept away. Fallen leaves, insects, and other detritus are important food sources. Rivers and streams carry precipitation to oceans, so there are streams in most localities. There is no sharp boundary between water and land with a stream. There is saturated soil both laterally and vertically beyond the banks of a stream, known as the riparian zone.

Lakes, ponds, and reservoirs are lentic, or layered, systems with generally still water varying in size between a few square feet to thousands of square miles. The surface layer is populated by plankton, protists (single-celled organisms like ameba), and insects. Beneath the surface is the epilimnion, which is relatively warm and sometimes mixed by the wind. The penetration of sunlight through the layer depends upon how much silt is suspended in the water. The layer just above the bottom,known as the hypolimnion, is cold and unmixed. The interface between these two layers, which marks a sudden fall in temperature, is called the thermocline. The bottom layer of a lake, the benthos, is occupied by burrowing worms and snails, with the ecosystem varying depending upon whether the bottom is rocky, muddy, or sandy. Levels of both oxygen and light decline with-depth. Anaerobic microorganisms, which can live without oxygen, often live in the bottom layers of a lake. A blue lake is lower in productivity than a green lake, but when productivity is too high, algal blooms may result with lower oxygen levels. The littoral layer, near the edge of a lake, generally has a large ecosystem with organisms that can use both land and water, such as dragonflies, frogs, ducks, and turtles. Plants such as rushes, reeds, and cattails grow rooted in the bottom sediments of the littoral zone.

Exercise 48. Define the term and remember it's explanations.

Hypolimnion, epilimnion, reed, thermocline, benthos.

Exercise 14. Read and translate the following words and word combinations from Russian into English.

Прибрежная зона океана, донные отложения, одноклеточные организмы, прибрежные зоны, пресноводная среда, рогоз, организм проточных водоёмов, мутный осадок, насыщенная почва, низкий уровень кислорода, источник питания, анаэробные микроорганизмы, пресноводная среда, тростник, стрекозы, выпадение осадков, поверхностный слов.

Exercise 15. Make up collocations using words from both columns.