Humans and Environmental Change 1.06 Explain and evaluate some ways that humans affect ecosystems. • Habitat reduction due to development. • Pollutants. • Increased nutrients.

Habitat Reduction Humans affect natural habitats in many ways. * Land is cleared to make room for homes and businesses. * Natural habitats are converted into farmland so we can grow crops. When land is developed, many of the nonliving and living resources are removed from the area. The top layer of the soil in the area is removed, leaving little or no nutrients for plants to grow. The organisms living in this area may be left without food and shelter, and often die out.

Many organisms that survive habitat loss must find new areas in which to live. As a result, all of the organisms living in that area have much smaller habitat in which to live, and there is increased competition between the organisms for nonliving and living resources. One example of habitat reduction is deforestation. Deforestation is the clearing of forested land. Humans use trees for lumber, food, and products such as paper and rubber.

Pollution Humans use a lot of natural resources in order to live. Many of the machines and vehicles we use produce unwanted by-products. Chemicals are released from cars into the air and water, and we throw away wastes, which often end up in landfills. These by-products produce pollution. Pollution is an unwanted change in the environment. A substance that causes pollution is called a pollutant.

Pollutants are often put directly into the air, water, or soil Pollutants are often put directly into the air, water, or soil. Pollution affects all the living things that come in contact with it. In some areas, pollution has harmed the soil and water so much that it is hard for plants and animals to live there.

Increased Nutrients Nutrients flow through an ecosystem by natural cycles. Plants take up nutrients in the soil or water, and the nutrients cycle through many organisms as energy flows through a food chain. Eventually, as organisms die, nutrients are returned to the soil. Humans use fertilizers, which are nutrients for the soil, on farms, golf courses, and gardens. These fertilizers often run off into nearby water sources when it rains. The increase of nutrients can harm nearby ecosystems by causing too many organisms to grow. One type of plant may take over an area and, as a result, other plants die out. Then the organisms that eat the other plants will be affected because their food source has been lost.

The Carbon Cycle All living things are made up of carbon. The carbon cycle describes how carbon moves through the environment and living things. The carbon cycle begins with photosynthesis. During photosynthesis, plants use carbon dioxide from the air and energy from the sunlight to make their own food. The food that plants make is mainly sugars. Read pages B52 & B53 in your textbook.

The Nitrogen Cycle When you eat meat, fish, cereal, or vegetables, you are taking in the nutrients that your body needs to make proteins. Proteins are a part of your muscles and many cell structures. Among other things, proteins are rich in the element nitrogen. You need nitrogen to make parts of your body, such as muscles, nerves, skin, bones, blood, and digestive juices.

Since air is 78 percent nitrogen, you might think that you do not need to eat protein to get nitrogen. However, animals and plants cannot use the nitrogen that is in the air. Animals get nitrogen by eating proteins. Plants get nitrogen by absorbing it from the soil. Some plants even get nitrogen with the help of a special group of bacteria. The way nitrogen moves between the air, soil, plants, and animals is called the nitrogen cycle.

The Nitrogen Cycle

Composting You can help nature recycle plant material by composting. Gardeners use compost to make soil more fertile. A good mixture for compost is three parts dry leaves and plant material, one part fresh grass clippings, and one part food scraps. Earthworms, insects, fungi, and bacteria break down the leaves, grass, and food scraps into compost. The compost contains nitrogen, phosphorous, and potassium, which enrich the soil. As you’ll soon discover, like water, nitrogen and carbon have their own cycles in nature. Earth is a closed system. With the exception of energy, almost nothing gets out or gets in. It is recycled.

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