Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife. Aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal regions.
The health of an aquatic ecosystem is degraded when the ecosystem’s ability to absorb a stress has been exceeded. A stress on an aquatic ecosystem can be a result of physical, chemical of biological alterations of the environment. Physical alterations include changes in water temperature, water flow and light availability. Chemical alterations include changes in the loading rates of biostimulatory nutrients, oxygen consuming materials, and toxins. Biological alterations include the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems.
Abiotic Characteristics of Aquatic Ecosystems
An ecosystem is composed of biotic communities and abiotic environmental factors, which form a self-regulating and self-sustaining unit. Abiotic environmental factors of aquatic ecosystems include temperature, salinity, and flow.
The amount of dissolved oxygen in a water body is frequently the key substance in determining the extent and kinds of organic life in the water body. Fish need dissolved oxygen to survive. Conversely, oxygen is fatal to many kinds of anaerobic bacteria.
The salinity of the water body is also a determining factor in the kinds of species found in the waterbody. Organisms in marine ecosystems tolerate salinity, while many freshwater organisms are intolerant of salt. Freshwater used for irrigation purposes often absorb levels of salt that are harmful to freshwater organisms.
Biota of Aquatic Ecosystems
The organisms (also called biota) found in aquatic ecosystems are either autotrophic or heterotrophic.
Autotrophic Organisms
Autotrophic organisms are producers that generate organic compounds from Inorganic material. Algae use solar energy to generate biomass from carbon dioxide and are the most important autotrophic organisms in aquatic environments. Chemosynthetic bacteria are found in benthic marine ecosystems. These organisms are able to feed on hydrogen sulphide in water that comes from volcanic vents. Great concentrations of animals that feed on this bacteria are found around volcanic vents. For example, there are giant tube worms (Riftia pachyptila) 1,5 min length and clams (Calyptogena magnifica) 30 cm long.
Heterotrophic Organisms
Heterotrophic organisms consume autotrophic organisms and use the organic compounds in their bodies as energy sources and as raw materials to create their own biomass. Euryhaline organisms are salt tolerant and can survive in marine ecosystems, while stenohaline or salt intolerant species can only live in freshwater environments.
Exercises
A.Comprehension
I. Answer these questions.
1. What does the term «aquatic ecosystem» mean?
2. What types of aquatic ecosystems do you know? Characterize briefly each one, pointing the difference between them out.
3. What percentage ofthe Earth’s surface does each of the ecosystems cover?
4. Name the zones of marine ecosystems and classes oforganisms found these.
5. Do marine ecosystems have any environmental problems? Prove your statement.
6. What types can freshwater ecosystems be divided into?
7. What have you learned about lentic ecosystems and the process of eutrophication?
8. What determines the major zones in river ecosystems?
9. What does the proximity of water and soil of wetlands lead to?
10. How can you characterize wetlands?
11. How important are wetlans?
12. Why is pond ecosystem a specific type of freshwater ecosystems?
13. What functions do aquatic ecosystems perform?
14. How do physical, chemical of biological alterations of the environment influence health of an aquatic ecosystem?
15. What do you know about (a) autotrophic organisms and (b) heterotrophic organisms?
II. Match the beginning of each sentence from the left column with the rest part of it in the right column.
| 1. Aquatic ecosystems | a) contain 41 % of the world’s known fish species. |
| 2. Lotic ecosystems | b) generate 32 % of the world’s net primary production. |
| 3. Marine ecosystems | c) contain slow-moving water, including pools, ponds, and lakes. |
| 4. Pond ecosystems | d) contain rapidly-moving water, for example streams and rivers. |
| 5. Wetlands | e) are the most productive natural ecosystems because of the proximity of water and soil. |
| 6. Freshwater ecosystems | f) may haw a scale of organisms from small bacteria to big creatures like water snakes, beetles, water bugs, and turtles. |
| 7. Lentic ecosystems | g) recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife. |
III. Write a summary of the text, using the words from Vocabulary Exercises.
B.Vocabulary
IV. Transcribe the following words:
aquatic marine chlorine reservoir estuaries saturated anaerobic
V. Give Russian equivalents of the following words and word combinations:
| freshwater continental shelf marsh exploitation littoral velocity vascular plants hydrogen sulphide | primary production salinity saturated soil pelagic riparian canopy attenuate | dissolved compounds benthic unsustainable wetland sediments proximity raw materials |
VI. Find in the text English equivalents of the following words and expressions. Translate the sentences which contain them.
1) морской; 2) производство сырых материалов; 3) пресноводный; 4) хлор; 5) обитающий на дне (бентический); 6) прилив и отлив (на море, океане); 7) коралловые рифы; 8) сода; 9) нерациональное использование морских ресурсов; 10) чрезмерный промысел (перелов); 11) отдаленный от берега; 12) прибрежный; 13) органические отложения; 14) область водосбора; 15) растворенный кислород; 16) растительный покров; 17) сосудистое растение; 18) болото, трясина; 19) осока; 20) солёность; 21) эвригалинный (выносящий различную солёность); 22) скорость, быстрота; 23) зарастание водоема.
С. Reading and Discussion
VII. Read the text carefully, without a dictionary. While reading, pay special attention to the words that you don’t know: look carefully at the context and see if you can get the idea of what they mean. After reading define each region of the aquatic biome. Mention the points of difference between the texts «Aquatic ecosystem» and «The aquatic biome». Summarize the text.
The Aquatic Biome
Water is the common link among the five biomes and it makes up the largest part of the biosphere, covering nearly 75 % of the Earth’s surface. Aquatic regions house numerous species of plants and animals, both large and small. In fact, this is where life began billions of years ago when amino acids first started to come together. Without water, most life forms would be unable to sustain themselves and the Earth would be a barren, desert-like place. Although water temperatures can vary widely, aquatic areas tend to be more humid and the air temperature on the cooler side.
The aquatic biome can be broken down into two basic regions, freshwater (i.e, ponds and rivers) and marine (i.e., oceans and estuaries).
Freshwater Regions
Freshwater is defined as having a low salt concentration — usually less than 1 %. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean). There are different types of freshwater regions: ponds and lakes, streams and rivers, and wetlands. The following sections describe the characteristics of these three freshwater zones.
Ponds and Lakes
These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciation. Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different «zones» which are usually determined by depth and distance from the shoreline.
The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sin’s heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this /one. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks.
The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well-lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Plankton are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone.
Plankton have short life spans — when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration.
Temperature varies in ponds and lakes seasonally. During the summer, the temperature can range from 4 °C near the bottom to 22 "C at the top. During the winter, the temperature at the bottom can be 4 °C while the top is 0 °C (ice). In between the two layers, there is a narrow zone called the thermocline where the ' temperature of the water changes rapidly. During the spring and fall seasons, there is a mixing of the top and bottom layers, usually due to winds, which results in a uniform water temperature of around 4 °C. This mixing also circulates oxygen throughout the lake. Of course, there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.
Streams and Rivers
These are bodies of flowing water moving in one direction. Streams and rivers can be found everywhere — they get their starts at headwaters, which may be springs, snowmelt or even lakes, and then travel all the way to their mouths, usually another water channel or the ocean. The characteristics of a river or stream change during the journey from the source to the mouth. The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found there. Towards the middle part of the stream/river, the width increases, as does species diversity - numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that require less oxygen, such as catfish and carp, can be found.
Wetlands
Wetlands are areas of standing water that support aquatic plants. Marshes, swamps, and bogs are all considered wetlands. Plant species adapted to the very moist and humid conditions are called hydrophytes. These include pond lilies, cattails, sedges, tamarack, and black spruce. March flora also includes such species as cypress and gum. Wetlands have the highest species diversity of all ecosystems. Many species of amphibians, reptiles, birds (such as ducks and waders), and furbearers can be found in the wetlands. Wetlands are not considered freshwater ecosystems as there are some, such as salt marshes, that have high salt concentrations — these support different species of animals, such as shrimp, shellfish, and various grasses.
Visit our gallery of wetlands images, which illustrate the amazing diversity of wetland ecosystems.
Marine Regions
Marine regions cover about three-fourths of the Earth’s surface and include oceans, coral reefs, and estuaries. Marine algae supply much of the world’s oxygen supply and take in a huge amount of atmospheric carbon dioxide. The evaporation of the seawater provides rainwater for tin- land.
Oceans
The largest of all the ecosystems, oceans are very large bodies of water that dominate the Earth’s surface. Like ponds and lakes, the ocean regions are separated into separate zones: intertidal, pelagic, abyssal, and benthic. All four zones have a great diversity of species. Some say that the ocean contains the richest diversity of species even though it contains fewer species than there are on land.
The intertidal zone is where the ocean meets the land — sometimes it is submerged and at other times exposed, as waves and tides come in and out. Because of this, the communities are constantly changing. On rocky coasts, the zone is stratified vertically. Where only the highest tides reach, there are only a few species of algae and mollusks. In those areas usually submerged during high tide, there is a more diverse array of algae and small animals, such as herbivorous snails, crabs, sea stars, and small fishes. At the bottom of the intertidal zone, which is only exposed during the lowest tides, many invertebrates, fishes, and seaweed can be found. The intertidal zone on sandier shores is not as stratified as in the rocky areas. Waves keep mud and sand constantly moving, thus very few algae and plants can establish themselves — the fauna includes worms, clams, predatory crustaceans, crabs, and shorebirds.
The pelagic zone includes those waters further from the land, basically the open ocean. The pelagic zone is generally cold though it is hard to give a general temperature range since, just like ponds and lakes, there is thermal stratification with a constant mixing of warm and cold ocean currents. The flora in the pelagic zone includes surface seaweeds. The fauna includes many species of fish and some mammals, such as whales and dolphins. Many feed on the abundant plankton.
The benthic zone is the area below the pelagic zone, but does not include t he very deepest parts of the ocean (see abyssal zone below). The bottom of the zone consists of sand, slit, and/or dead organisms. Here temperature decreases as depth increases toward the abyssal zone, since light cannot penetrate through the deeper water. Flora are represented primarily by seaweed while the fauna, since it is very nutrient-rich, include all sorts of bacteria, fungi, sponges, sea anemones, worms, sea stars, and fishes.
The deep ocean is the abyssal zone. The water in this region is very cold (around 3° C), highly pressured, high in oxygen content, but low in nutritional content. The abyssal zone supports many species of invertebrates and fishes. Mid-ocean ridges (spreading zones between tectonic plates), often with hydrothermal vents, are found in the abyssal zones along the ocean floors. Chemosynthetic bacteria thrive near these vents because of the large amounts of hydrogen sulfide and other minerals they emit. These bacteria are thus the start of the food web as they are eaten by invertebrates and fishes.
Coral Reels
Coral reefs are widely distributed in warm shallow waters. They can be found as barriers along continents (e.g., the Great Barrier Reef off Australia), fringing islands, and atolls. Naturally, the dominant organisms in coral reefs are corals. Corals are interesting since they consist of both algae (zooanthellae) and tissues of animal polyp. Since reef waters tend to be nutritionally poor, corals obtain nutrients through the algae via photosynthesis and also by extending tentacles to obtain plankton from the water. Besides corals, the fauna includes several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars.
Estuaries
Estuaries are areas where freshwater streams or rivers merge with the ocean. This mixing of waters with such different salt concentrations creates a very interesting and unique ecosystem. Microflora like algae, and macroflora, such as seaweeds, marsh grasses, and mangrove trees (only in the tropics), can be found here. Estuaries support a diverse fauna, including a variety of worms, oysters, crabs, and waterfowl.
VIII. Speak on the basic components of an aquatic ecosystem by referring to the picture and the information given below.
Экосистема — это комплекс всех организмов и неживых элементов, в результате взаимодействия которых потоком энергии в дам ном месте создается стабильная структура и круговорот веществ.
Основные компоненты водной экосистемы (рисунок):
1) поступающая энергия от Солнца;
2) климат и физические факторы;
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3) неорганические вещества;
4) органические соединения;
5) производители органических соединений, или продуценты (от лат. producentis— создающий) — укорененные растения и мельчайшие водоросли (фитопланктон, от грея, phyton —растение, plankton— блуждающий);
6) потребители первичные, или консументы первичные (от лат. consume— потребляю), питающиеся растениями — зоопланктон (животный планктон), моллюски, личинки, головастики;
7) потребители вторичные, или консументы вторичные — хищные насекомые и рыбы;
8) детрит (от лат. deferere — изнашиваться) — продукты распада и разложения организмов;
9) разрушители, деструкторы, редуценты (от лат. reducentis — возвращающий), детритофаги (от греч. phagos — пожиратель), сапротрофы (от греч. sapros —гнилой и trophe — питание)—донные бактерии и грибы, личинки, моллюски, черви.
producer; plankton; molluscum; larva (личинка); frog larva; detritus; decay product (продукт распада); reducer; detritus consumer; saprotroph
IX. Translate the text without a dictionary.
Rivers, lakes, wetlands, and estuaries are an important part of the globalecosystem. Rivers connect the land surface and atmosphere to the ocean, delivering about 40,000 km3 of water per year from land to ocean. Water en route to the oceans forms wetlands, lakes, and eventually coastal estuaries. Together these surface waters represent about 5—10 % of the global terrestrial surface area. The aquatic ecosystems that have developed in these surface waters provide habitat for diverse flora and fauna species (much of which is endemic to very small regions), transport nitrogen, carbon, phosphorus, sediments and numerous other elements, and support diverse biogeochemical activity. Together the aquatic ecosystems provide services, both to humans and the natural system, far beyond their limited boundaries.
Fresh water is vital to human life and economic well-being. Humans currently use more than 50 % of the available global runoff. Societies extract vast quantities of water from rivers, lakes and wetlands to supply the requirements of power generation, flood control, irrigation, and urban, industrial, and agricultural uses. Traditionally, this human use of water has been at the expense of equally vital benefits of water in sustaining healthy aquatic ecosystems. For example, at present 30 % of the world’s population does not have access to clean water, as a result of poor water management, and under current trends of global change and population growth two thirds of the population may be subject to moderate to high water stress.
There is growing recognition, however, that the many economically valuable commodities and services to society provided by functionally intact and biologically complex aquatic ecosystems have not been included in evaluation of the importance of aquatic ecosystems. These services include flood control, transportation, recreation, purification of human, industrial, and agricultural wastes, habitat for plants and animals, and production of fish and other foods and marketable goods.
Runoff – сток; sustain – поддерживать; commodity – товар; intact – нетронутый
X. Talking points:
1. Marine ecosystems.
2. Freshwater ecosystems.
3. The biota and biome of aquatic ecosystems.
4. Functions of aquatic ecosystems.
Unit 1.
Nature Protection
Computers project that between now and the year of 2030 we are going to have an increase of the average temperature between 1,5-4,5 degrees C. Sea levels would rise by several metres, flooding coastal areas and ruining vast tracts of farmland. Huge areas would be infertile and become uninhabitable. Water contamination could lead to shortages of safe drinking water. It locks like the end of civilization on the Earth. For hundreds of thousands of years the hurrran race has thriven in Earth's environment. But now, at the end of the 20th century, we are at a crucial turning point. We have upset nature's sensitive equilibrium releasing harmful substances into the air, polluting rivers and oceals with industrial waste and tearing up the countryside to accommodate our rubbish. These are the consequences of the development of civilization. We are to stop it by joint efforts of all the people of the world. The range of environmental problems is wide. But the matters of people's great concern nowadays are atmosphere and climate changes, depletion of the ozone layer, freshwater resources o"Lurr. and coastal areas, deforestation and deserti-fication, biological diversity, biotechnology, health and'chemical safety, United Nations Environment Programme (UNEP) concentrates its activities on these issues.
Acid Rains
One of the most alarming forms of air pollution is acid. rain. It results from the release into the atmosphere of sulphur and nitrogen oxides that react with water droplets and return to earth in the form of acid rain,'mist or snow. Acid rain is killing forests in Canada, the USA, and central and'northern Europe. (Nearly every species' of free is affected). It has acidified lakes and streams and they can’t support fish, wildlife, plants orinsect.
