All ecosystems consist of biotic (living) and abiotic (nonliving) OBJECTIVES components. Interactions occurring between the biotic and abiotic parts of an ecosystem 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 consumer. human-made ecosystems. The process of photosynthesis 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. organisms in an ecosystem. The chemicals cannot be created or destroyed, but they can be changed from one form to another. Nature 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 aquatic ecosystem. Dr. Hanson carefully selected species of shrimp, algae and microorganisms, 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 soil 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-Oxygen Cycle Plants use carbon dioxide (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, decomposers break down the carbon compounds in their bodies, and carbon dioxide is returned to the atmosphere. During decomposition (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 Nitrogen Cycle 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.