All consist of biotic (living) and abiotic (nonliving) OBJECTIVES components. Interactions occurring between the biotic and abiotic parts of an are essential to make it function as one unit or system. As we Compare the movement of learned in Section 1.6, solar energy is an important abiotic component of energy and the movement of nearly every ecosystem. matter in an ecosystem. Once the solar energy is converted to chemical energy, it may be used for essential life processes. Much of it is lost as heat. Energy passes Compare the movement of through an ecosystem in much the same way that cars travel on a one-way matter in natural ecosystems and street. It travels in only one direction—from sun to producer to . human-made ecosystems. The process of must constantly replace the energy that is Create models or illustrations lost from the ecosystem. showing the relationships Unlike energy, matter can be recycled within an ecod^stem. Matter between the biotic and abiotic may be defined as anything that takes up space and h/sjnass. Matter components of the refers to all of the chemicals that make up the earth, the air and the biogeochemical cycles. in an ecosystem. The chemicals cannot be created or destroyed, but they can be changed from one form to another. Recycles Imagine an aquarium, that doesn't require someone to feed the fish. In a closed ecosystem, matter is never gained nor lost. Working for NASA, Dr. Joe Hanson developed a totally closed . Dr. Hanson carefully selected species of shrimp, algae and , and then he sealed them in glass containers. No one ever needs to feed the shrimp or change the water in the aquarium. With controlled light and temperature conditions, the sealed ecosystems continue to function without the loss or gain of any matter. The light provides the energy, and the microorganisms recycle the chemicals. Most human-made ecosystems are not closed ecosystems. They usually require huge inputs of matter and energy. Zoos are an excellent example of an unnatural ecosystem where matter is not recycled within the system. In natural ecosystems, some matter is gained or lost, but most matter is recycled. Although it is unusual, meteors and debris from outer space Ecosphere —A totally enclosed sometimes inject matter into an ecosystem. It is far more likely that matter ecosystem. entering an ecosystem was removed from another ecosystem by wind or water. Water sometimes removes large amounts of from an ecosystem and deposits it in an aquatic ecosystem. Wind picks up and carries small particles and gases great distances. Rain cleanses the air and deposits the matter in a distant ecosystem. Human activities sometimes disrupt the normal flow of matter and threaten the continued existence of an ecosystem. The biogeochemical cycles, the flow of chemicals between the environment and organisms in it, are essential to the survival of all ecosystems. As you study each cycle, give A zoo is not a closed ecosystem particular attention to the potential environmental impacts of technology. because it requires huge inputs of resources. The Carbon-

Plants use (CO2) from the atmosphere in the process of photosynthesis. Using light energy, plants combine carbon dioxide and water to form sugar. The sugar is both a source of energy and a building block for other compounds such as proteins, oils and starches. The compounds produced by plants contain carbon and are called organic compounds. Plants give off oxygen (O2) as a waste product. Although algae in the ocean produce most of the oxygen in our atmosphere, trees are also an important source. Plants, animals and microorganisms use oxygen in the process of respiration. In respiration, the compounds containing carbon—the organic compounds—are broken down, and carbon dioxide is released. When respiration occurs without enough oxygen, the organic chemicals are not completely broken down, and the organic compounds released often have offensive odors. The Carbon-Oxygen cycle is out of balance. There is more carbon dioxide being released into the atmosphere than is being removed from it. Smokestacks at coal-burning power Most of the carbon dioxide is produced during the process of burning— plants and industries release huge combustion. When compounds containing carbon (coal, oil, or wood) are amounts of carbon dioxide and water burned, the carbon is chemically combined with oxygen, and carbon vapor into the atmosphere. dioxide is released. In a short period of time, combustion releases carbon dioxide into the atmosphere. The use of carbon dioxide by plants during photosynthesis is a much slower process. As a result of the imbalance between these two processes, the level of carbon dioxide in the atmosphere is increasing. In Unit 2, pages 111, 119, and 124, we will examine the possible effects of the increasing levels of carbon dioxide. When organisms die, break down the carbon compounds in their bodies, and carbon dioxide is returned to the atmosphere. During (decay), other chemicals are also returned to the soil or released into the air. One of these chemicals is nitrogen.

380

Algae, such as this seaweed clinging to the rocks and microscopic algae (phytoplankton), produce most of the oxygen in the atmosphere.

310 1955 1965 1975 1985 1995 2005 YEAR The increasing level of carbon dioxide over time is due to the burning of fossil fuels. Carbon-Oxygen Cycle

Oxygen

Respiration Photosynthesis Combustion in most cells in green plants and algae burning of fuel

Algae, Fungi, Plants, Vehicles, Furnaces, Factories, Animals, Bacteria, Protists Volcanoes, Forest Fires, Power Plants

Carbon Dioxide

The Without plants and decomposers, the carbon—oxygen cycle would stop. Plants and decomposers are also important in the nitrogen cycle, but a UIUJUI certain group of bacteria is essential to this cycle—the nitrogen "fixers." For information on the Plants and animals need nitrogen to make protein. The air is about 78% global carbon cycle, visit nitrogen, but plants and animals cannot use nitrogen (N2) directly from the www.whrc.org/carbon/carbon.htm. atmosphere. Special bacteria, in the soil and water, must change or "fix" nitrogen gas (N2) into nitrogen fertilizers (nitrate ions (NOj) or ammonium ions (NH^)} that plants can use. These bacteria are called nitrogen fixers. Most nitrogen-fixing bacteria live in little houses, or nodules, on the roots of plants called legumes. Legumes are members of a large family of plants that includes peas, beans, alfalfa, clover, vetches, and locust trees. The plants provide food and cover for the bacteria, and the bacteria convert nitrogen gas into fertilizer for the plant. Animals get nitrogen from plants or from other plant-eating animals, in the form of protein. The nitrogen is recycled by special bacteria that break down the nitrogen compounds (proteins) in dead plants and animals, and in animal wastes. If plants do not use the nitrogen compounds as fertilizer, special forms of bacteria may recycle it. These bacteria convert the unused fertilizer into nitrogen gas and release it into the atmosphere. All natural ecosystems depend upon bacteria to keep the nitrogen cycle going. Lightning plays a small role in the nitrogen cycle. The huge amount of electrical energy, called lightning, combines nitrogen and oxygen in the atmosphere. Dissolved in the rain, the "fixed" nitrogen enters the soil Crown vetch has been planted along where bacteria convert it into nitrate fertilizer. But nature is no longer in highways to control erosion. It needs total control of the nitrogen cycle. Human activities are dramatically no fertilizer because bacteria on its increasing the nitrogen available to ecosystems. roots can "fix" nitrogen from the air. To grow crops that require large amounts of nitrogen, farmers add commercial fertilizers. Fertilizer manufacturers take nitrogen from the air Nitrogen Cycle

Nitrogen Gas Lightning Nitrogen Oxides

Blue-Green LegufrfeVwith Bacteria Nitrogen-Fixing Bacteria jRoots

Fertilizer

and hydrogen from natural gas and combine them in a high-pressure, high-temperature environment. Since this process is very expensive, farmers often plant legume crops to take advantage of their natural abilities to fix nitrogen. There is also a large demand for some legume crops such as soybeans. Another major source of nitrogen comes from burning fossil fuels. Bacteria in the nodules on the roots The atmosphere contains 78% nitrogen and nearly 21% oxygen. The high of soybeans and other legumes can temperatures created during combustion cause nitrogen and oxygen to "fix" or change nitrogen gas into combine creating nitrogen oxides (NOx). Motor vehicles, factories, power fertilizers. plants, forest fires, fireplaces and even grills are all sources of nitrogen oxides. The gases dissolve in the rain and are carried to an ecosystem somewhere downwind from where they were created. While their fertilizing effect may benefit some crops, there are some disadvantages. These are discussed in Unit 2, page 123. The Mineral Cycle Most of the minerals (such as calcium and phosphorus) in an ecosystem are stored in rocks. They are released from the rocks by the action of wind, water and changes in temperature. The process of physical and chemical forces releasing minerals from rocks is called weathering. Wind sometimes acts as a sand-blaster, breaking off small particles of the rock. Rocks are broken into smaller pieces when water freezes and thaws. Rocks are also broken by the action of the roots. Plant roots exert a great amount of force as they grow. This can be seen when walking along a sidewalk on a tree-lined street. The tree roots often cause sections of concrete to crack. The foundations of buildings and underground pipes are sometimes cracked by the growth of tree roots. This is physical weathering. At Mammoth Springs in Yellowstone Chemical weathering occurs when acidic rain dissolves minerals in National Park, hot water evaporates the rocks. Roots also produce chemicals that dissolve minerals in the leaving behind an impressive deposit rocks. The trees absorb some of the minerals. Others are carried away by of minerals. water moving through the soil. This process is known as leaching. b. Mineral Cycle Phosphate and Other Minerals are Released by: I) Weathering

To Ocean 2' Ac: dnfcf F int Roots

3) Mining

To City and Farm Ecosystems

Due to leaching and mining, the mineral cycle is a leaky cycle. Mining is the process of removing a natural substance from an ecosystem faster than it is replaced. Humans mine many ores for the minerals they contain—aluminum, zinc, lead, gold and phosphorus. You can think of What forces will cause weathering of others. We often remove these materials for use in our human-made the rocks shown in this picture? ecosystems. Some of the minerals will be recycled and used over and over again. Others will be discarded in a landfill. Mineral particles are also removed from an ecosystem by the action of wind and water. This process is called erosion. The mineral particles carried away by the flowing water may become a part of a sand bar in a large river or they may be deposited in the ocean. Whether they are removed from the cycle by leaching, mining or erosion, the minerals are no longer available to the ecosystem. UIUIIU The Hydrologic Cycle For information on the hydrologic cycle, visit "Hydro" means water. The hydrologic or water cycle describes the www.epa.gov/seahome/ movement and storage of water on planet earth. The total amount of water groundwater/src/cycle.htm and doesn't change. Its movement is influenced by the earth's surface. Winds utility.co.Dinellas.fl. us/hydro.html. transport water vapor in the atmosphere and influence climate. The sun provides the energy for the water cycle. Water re-enters the atmosphere by one of two processes—evaporation or transpiration. Water is lost from the soil and all surface water—rivers, lakes, streams and oceans—through the process of evaporation. Since the oceans cover more than 70% of the earth's surface, most water enters the atmosphere through the process of evaporation. Evaporation occurs Did when the sun's energy heats the water, changing it from its liquid state The average water molecule ; into its gaseous state known as water vapor. resides in the atmosphere for 10 Water taken up by the roots of plants travels to the leaves. Some of days where it may travel these water molecules move by the process of osmosis through the cell thousands of miles before membranes and into the microscopic spaces within the leaf. The water returning to the earth as vapor then diffuses out of the leaf through openings called stomata. This precipitation. loss of water vapor from the leaves of plants is called transpiration. During the growing season, as many as 500,000 gallons (2 million L] of water vapor may re-enter the atmosphere through transpiration from one acre (0.4 ha) of corn. As warm humid air rises, it loses energy. As the air cools, the water vapor collects on small particles in the atmosphere called condensation nuclei. The tiny droplets that form on the surface of these particles form clouds. This process of water vapor changing into its liquid form is called condensation. When the water droplets become too heavy to remain in the atmosphere they begin to fall. The temperature of the air determines the form of moisture—rain, snow, sleet or hail. All moisture falling from the atmosphere is collectively called precipitation. The tiny water droplets in these Some precipitation falling through a warmer mass of air will re- clouds are formed by the process of evaporate before it reaches the earth's surface. Since most of the earth's condensation. surface is covered by water, most precipitation falls into the oceans or into other bodies of water. If the precipitation falls on land, it may enter the soil or flow over the surface as runoff. The runoff flows into streams or lakes where the water may begin its journey back to the ocean. Along the way it may evaporate or be withdrawn for many uses. Did You Know Infiltration is the process of precipitation entering the ground. Plants Morning dew is formed when (f may take up water that enters the soil, or it may move or percolate the night air is cooled below a through the soil and rocks until it reaches a layer of impermeable rock or temperature called the "dew clay. This layer of water is called groundwater. The layer of permeable point." The water vapor in the air (porous) rock where the water is stored is an aquifer. Seepage occurs condenses into tiny droplets.The when groundwater flows naturally from the ground at a spring. More droplets form on the surface of often it is pumped from a well drilled into the aquifer. the soil, and on plant leaves and The amount of precipitation is an important factor in determining the stems. These droplets of type of ecosystem and the populations of organisms it can support. Unit condensed water vapor are called 4 investigates the role of water in much more detail. dew.They will remain on plant surfaces until the warmth of the sun evaporates them.You may want to check the newspaper's daily weather report for further Transpiration information.

^ Think About It

What happens when you take a iljifi It ration! Evaporation soda can from the refrigerator on a •Percolation,*P !•] hot summer day? Can you explain ^•k Runoff what actually happens when the can "sweats"? What process in the hydrologic cycle is occurring on the surface of the can? (Fed by Underground Springs) 1.7 QUESTIONS FOR STUDY AND DISCUSSION: 1. Define the following terms: ( VOCABULARY ) abiotic / erosion mining runoff aquifer " , evaporation nitrogen fixers seepage biogeochemical cycles V groundwater"^/ nodules «y' spring biotic infiltration v organic compounds ** stomata v combustion leaching %/ photosynthesis transpiration -^/ condensation legumes \/ precipitation water vapor condensation nuclei matter respiration weathering

2. Compare the flow of matter and energy through 10. Identify plants that are legumes and explain an ecosystem. how they are important to the nitrogen cycle. 11. In what way is lightning important to the Nature Recycles nitrogen cycle? 3. How did Dr. Hanson's ecosystems differ from 12. Why do farmers plant legume crops? most human-made and natural ecosystems? 4. Compare the recycling of matter in natural The Mineral Cycle ecosystems and in human-made ecosystems. 13. How are minerals removed from rocks? 14. Identify three processes that create "leaks" in The Carbon-Oxygen Cycle the mineral cycle. 5. What process uses carbon dioxide and produces oxygen? The Hydrologic Cycle 6. What kind of produces most of the 15. Identify the two processes that return water to world's oxygen supply? the atmosphere. Most water enters the 7. What two processes produce carbon dioxide? atmosphere by which of these processes? What process produces most of the carbon 16. What is the process in which water vapor dioxide in the atmosphere? collects to form tiny droplets? 8. By what process do decomposers return carbon 17. What is the term that describes all forms of dioxide to the atmosphere? moisture leaving the atmosphere? 18. What term describes the layer of porous rock The Nitrogen Cycle which is filled with water? What two processes 9. What kinds of organisms are essential for the are necessary to maintain water in this layer. nitrogen cycle? ^) Target Reading Skill Sequencing Refer to 3. a. Reviewing Why do organisms need nitrogen? your cycle diagram about the water cycle as you b. Sequencing Outline the major steps in the answer Question 1. nitrogen cycle. c. Predicting What might happen in a Reviewing Key Concepts if all the nitrogen-fixing bacteria died? 1. a. Defining Name and define the three major processes that occur during the water cycle. b. Making Generalizations Defend this Writing in Science statement: The sun is the driving force behind the water cycle. Comic Strip Choose one of the cycles 2. a. Reviewing Which two substances are discussed in this section. Then draw a comic linked in one recycling process? strip with five panels that depicts the b. Comparing and Contrasting What role important events in the cycle. Remember that the last panel must end with the same event do producers play in the carbon and that begins the first panel. oxygen cycles? What role do consumers play in these cycles? c. Developing Hypotheses How might the death of all the producers in a community affect the carbon and oxygen cycles? 1. Describe the two processes of the carbon cycle. CRITICAL THINKING 5. Making Comparisons Write a short paragraph 2. Describe how the burning of fossil fuels affects the that describes the importance of bacteria in the car- carbon cycle. bon, nitrogen, and phosphorus cycles. What role do 3. Explain how the excessive use of fertilizer affects the bacteria play in each cycle? nitrogen cycle and the . 6. Applying Ideas What is one way that a person can 4. Explain why the phosphorus cycle occurs more slowly help to reduce the level of carbon dioxide in the than both the carbon cycle and the nitrogen cycle. atmosphere? Can you think of more than one way? Lesson Review

1. Explain the sequence of events in the 4. Will Earth ever run out of water? cycle that moves carbon from the soil, Explain your answer. through living organisms, and then 5. Describe the role of plants in the water directly back into soil. cycle. Describe the role of the sun. 2. Summarize the ways in which human 6. Explain why nitrogen is important to activity is affecting the carbon cycle. living things. 3. Explain the importance of carbon for 7. Why is nitrogen fixation a necessary part living organisms. of the nitrogen cycle? Salve Nutrient Cycling in an Ecosystem

The soil in each ecosystem contains nutrients. STAGE 1 These nutrients—nitrogen, phosphorus, potassium—are taken up by plants, make their way through the ecosystem , and then return to the soil after the death and decay of plants and animals. Of course, not every bit of these nutrients enters plants. When it rains, for example, some nutrients leave the ecosystem as runoff. The graphs at right show the amount — Time — of nitrate that a forest ecosystem loses as a result of runoff at various stages in its history. STAGE 2 At each stage, the forest is in a different condition. Use the graphs and your knowledge of ecosystems, nutrient cycles, and human activities in forests to answer the questions below.

Questions 1. Infer which graph shows the loss of nitrate in a forest ecosystem in which many trees •Time- are being cut down. Explain your answer. STAGE 3 2. Infer which graph shows a forest ecosystem that was heavily logged several years before but in which the plant community is growing back. Explain your answer. 3. Infer which graph shows nitrate loss in an intact, stable forest ecosystem. Explain your answer. 4. Describe how the graph that shows • Time • nutrient loss in a stable forest ecosystem could be different if the area experienced Figure 6.15 Forests lose different amounts of drought for a long period. nitrate as a result of runoff at various stages in their history.