Cycles in an Ecosystem

Name______Period____

Cycles in an Ecosystem

Chapter 6.2

Earth

Earth is a ______system.

It is like a large ______.

There is a set amount of ______, ______, ______, and other ______.

This means that there will never be ______or ______.

The three major cycles are:

1)  ______

2)  ______

3)  ______

Water Cycle

Water plays many different roles on the Earth. Some is at the poles in ice caps, and some is in the snow and glaciers at the tops of high mountains. Some is in lakes and streams, and some is underground. Some is vapor in the atmosphere. But most of the water on Earth is in the oceans.

Water is always on the move! The Sun’s energy causes water to evaporate from oceans and lakes into the atmosphere. Plants and animals also release water vapor into the atmosphere as they breathe. When the atmosphere cools, water vapor condenses; making clouds that might produce rain or snow. Water has been recycled in its different forms as ice, liquid, or vapor –for more than 3.5 billion years.

Vocab:

·  Evaporation

·  Condensation

·  Precipitation

·  Run-off

·  Percolation

·  Absorption

·  Transpiration

Water Cycle Diagram

Draw a diagram of the water cycle that includes the following parts:

Evaporation, Condensation, Precipitation, Run-Off, Transpiration, Percolation, Absorption

Carbon Cycle

All living things are made of carbon. Carbon is also a part of the ocean, air, and even rocks. Because the Earth is a dynamic place, carbon does not stay still. It is on the move!

In the atmosphere, carbon is attached to some oxygen in a gas called carbon dioxide.

Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon like coal and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters the atmosphere as carbon dioxide.

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world.

Vocab:

·  Carbon

·  Photosynthesis

·  Respiration

·  Decomposition

·  Fossil Fuels

·  Emissions

Carbon Cycle Diagram

Draw a diagram of the carbon cycle that includes the following parts:

CO2, Photosynthesis, Respiration, Decomposition, Fossils, Fossil Fuels, Emissions

Nitrogen Cycle

Take a deep breath. Most of what you just inhaled is nitrogen. In fact, 80% of the air in our atmosphere is made of nitrogen. Your body does not use the nitrogen that you inhale with each breath. But, like all living things, your body needs nitrogen. Your body gets the nitrogen it needs to grow from food.

Nitrogen is used by lifeforms to carry out many of the functions of life. This element is especially important to plant life. Yet, nitrogen in its gaseous form is almost entirely unusable to lifeforms. It must first be converted or ‘fixed’ into a more usable form. The process of converting nitrogen is called fixation.

There are specialized bacteria whose function it is to fix nitrogen, converting it, so that it can be used by plants. There are still other bacteria that do the reverse. That is, they return nitrogen to its gaseous form through a process called denitrification.

After nitrogen is fixed, it can be absorbed and used by plants, and subsequently by animals.

The process of nitrogen being fixed, used by plants and animals, and later returned to the atmosphere is referred to as the nitrogen cycle.

Vocab:

·  Nitrogen

·  Nitrate

·  Proteins

·  Nitrogen Fixation

·  Denitrification

Nitrogen Cycle Diagram

Label the following parts of the nitrogen cycle in the boxes above:

·  Plants use nitrates to make proteins

·  Nitrogen enters the soil

·  Animals eat plants

·  Decomposers release nitrogen into the air

·  Free atmospheric nitrogen

·  Bacteria change nitrogen into nitrates

Industrialization and the Carbon Cycle

1.  What was the average global temperature in 1900? ______°C

2.  What was the average global temperature in 2000? ______°C

3.  How much did the average global temperature increase between 1900 and 2000? ______°C

4.  Based on the graph, what do you predict the average global temperature to be in 2020? ______°C

1.  What is the story that this graph tells?

2.  Based on the graph above, describe the relationship between temperature and CO2 in the atmosphere.

3.  What are two main reasons why the atmospheric CO2 concentration is rising? (hint: Page 167 in your textbook)

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4.  What do you think society should do about this issue?

Nitrogen Fertilizer … A Blessing or Disaster?

By Eric Sideman, PH.D.

Since humans began to cultivate food, nitrogen has been the most common limit to crop yields. Modern agriculture has answered this limit with synthetic production of nitrogen fertilizers, which has greatly increased global food production and has supported an astonishing growth in the world’s population. However, the environmental problems are just being realized and are not yet being seriously dealt with.

Nitrogen, being a part of DNA, proteins and chlorophyll, is crucial for all life. Nitrogen cycles through living organisms, through the soil and water, and eventually returns to its largest reservoir, the atmosphere. It is the most common component of the atmosphere, making up almost 80%, yet, it is unavailable to plants or animals because of its peculiar chemistry. It exists in the atmosphere in a very stable form (N2) and enters the cycle through living systems only by the initial fixation by bacteria (either free living or symbiotic with such higher plants as legumes). The N2 nitrogen is converted by the bacteria to chemical forms that plants can absorb. The ecosystem is balanced by the stability of nitrogen in the atmosphere that naturally allows only a puny fraction of the reservoir to be fixed at any one time.

Humans have disrupted the natural cycling of nitrogen by burning fossil fuels, growing legumes, and by using nitrogen rich fertilizers. The chief culprit identified by recent studies reported in Scientific American is the industrial fixation of nitrogen gas to make fertilizer. More than half of the nitrogen fertilizer made before 1990 was used during the 1980s.

Traditional farmers provided nitrogen to their crops by enriching their fields with crop residues, animal wastes and human wastes, and by raising legume crops to be plowed into the soil (green manures). A real breakthrough in nitrogen fertilization occurred in the past century with the development of ammonia synthesis. Under high heat and pressure, which of course uses a lot of energy, nitrogen gas and hydrogen gas can be combined to produce ammonia gas. Modern nitrogen fertilizers, such as ammonium nitrate, anhydrous ammonia and urea, are made using ammonia gas. The first ammonia factory was built in Germany in 1913. More recent technical developments allowed cheaper production of ammonia, and the fertilizer industry zoomed ahead.

The ready availability of ammonia and of the nitrogen fertilizers derived from it has effectively eliminated a fundamental restriction on food production. During the 20th century, humanity has almost quadrupled its numbers, and this sudden growth is supported by the food production made possible by nitrogen fertilizer. The fertilizer industry fixes about 80 million tons of nitrogen per year. This will have to increase to support the global population as it zooms to 10 billion during the next century.

Obviously this vast fixation of atmospheric nitrogen leads to a change in the nitrogen cycle, with much more nitrogen pulled out of the atmospheric reservoir. Nitrates from extensive fertilizer use end up in the soil and contaminate ground water through leaching and runoff. Problems range from local health issues such as blue baby disease to global changes. Fertilizer nitrogen that escapes to surface water promotes algal growth and subsequent eutrophication. Nitrous oxide is released into the air. In the low atmosphere nitrous oxide promotes the greenhouse effect, much more so than carbon dioxide does. It also contributes to smog. In the upper atmosphere, reactions of nitrous oxide with excited oxygen contribute to destruction of ozone in the stratosphere.

The Scientific American articles point out that these disturbances receive surprisingly little attention. Carbon dioxide emissions are being reduced and research is supported to continue reduction. A transition away from the use of fossil fuels must eventually happen anyway, because these resources are finite. But there is no way to grow crops without nitrogen, and to grow crops at today’s expected yields per acre to feed the world’s exploding population from a shrinking farm land base takes highly concentrated nitrogen fertilizers. The EPA recognizes the damage caused by nitrous oxides from combustion and has introduced regulations to limit emissions. Cooperative Extension has “Best Management Practices” that reduce fertilizer use and nitrogen leaching and runoff; but not all farmers follow these and no controls exist on the amounts of fertilizers a farmer can use.

An early stabilization of the global population is the best solution to the problems raised by excessive nitrogen fixation. Organic methods of crop production, including crop rotation, using legume green manures, soil conservation, and the recycling of all organic wastes, are management techniques that are needed to reduce the damage that has been done. In land-rich nations these practices can produce enough food to feed today’s population. In land-poor areas nitrogen fertilizers are necessary to maximize production – which leads to devastating environmental disruptions. This is a very strong argument for preserving farm land. Let’s control our population, save our farmland, and farm organically.

Article Discussion Questions:

1)  What is the major benefit of the use of modern nitrogen fertilizers?

2)  What are some negative effects of nitrogen fertilizer use?

3)  What is one solution suggested in the article?

4)  What do you think society should do about this issue?

Cycles Review

Water Cycle

atmosphere / precipitation / vapor / condenses
water cycle / runs / soaks / evaporates

1.  Water moves between Earth and the ______.

2.  This movement of water is called the ______.

3.  Heat from the sun causes water on Earth to change from liquid to a ______as it ______, rising from Earth’s oceans, lakes, and rivers.

4.  Eventually, this water ______, or forms drops and falls to Earth as ______.

5.  Much of the rain that falls ______into the ground.

6.  The rest either ______along the ground or evaporates and begins the process again.

Carbon Cycle

oxygen / greenhouse / decayed / fossil fuels
volcanoes / photosynthesis / respiration / ocean

1.  Plants use CO2 in the process of______to make sugars and______.

2.  Animals use oxygen in the process of ______and make more CO2.

3.  The ______is the main regulator of CO2 in the atmosphere because CO2 dissolves easily in it.

4.  In the past, huge deposits of carbon were stored as dead plants and animals ______.

5.  Today, these deposits are burned as ______, which release lots of CO2 into the air.

6.  Another natural source for CO2 is ______.

7.  Too much CO2 in the atmosphere may be responsible for the ______effect.

Nitrogen Cycle

atmosphere / waste / proteins / denitrification
nitrates / nitrogen-fixation / plants / animals

1.  Animals and plants cannot directly use all the nitrogen found in our ______.

2.  Specialized bacteria “fix” nitrogen so other organisms can benefit through a process called ______.

3.  The process turns nitrogen into ______that other complex organisms can use to make their ______.

4.  Other bacteria in the soil can break down the ammonia into the gaseous form of nitrogen, which is not available for use by plants or animals. This reverse process is called______.

5.  In another part of the cycle, animals eat ______containing nitrogen, which is again returned to the soil by animal ______or decaying plants and ______.