4 interactions environments and organisms 环境学 环境生态.ppt

* Nitrogen Cycle * Phosphorus Cycle Human Impact on Nutrient Cycles Burning of fossil fuels releases large amounts of carbon dioxide into the atmosphere. Fossil fuel burning also increases the amount of nitrogen available to plants（nitric acid precipitation ）. Converting forests (long-term carbon storage) to agricultural land (short-term carbon storage) has increased the amount of carbon dioxide in the atmosphere. If too much nitrogen or phosphorus is applied as fertilizer, or if it is applied at the wrong time, much of the fertilizer is carried into aquatic ecosystems. The presence of these nutrients increases the growth rate of bacteria, algae, and aquatic plants.（eutrophication（富营养化）） * Issues and analysis * What’s your take? In the United States about $20 billion is spent each year on the care of lawns and gardens. A significant amount of this cost involves the use of fertilizer to stimulate the growth of grass. Fertilizer runoff from lawns is a significant water pollution problem. Although most lawns will grow without fertilizer, the quality of the lawn is often not as nice. It is often possible to substitute groundcovers or natural landscaping for lawns. Should people maintain grass lawns? Choose one side of the question and develop arguments that support your position. * Summary An organism’s environment can be divided into biotic (living) and abiotic (nonliving) components. The space an organism occupies is its habitat, and the role it plays is its niche. Organisms interact with one another in a variety of ways. Symbiotic relationships are those in which two species live in physical contact and at least one species derives benefit from the relationship. In an ecosystem, energy is trapped by producers and flows from producers through various trophic levels of consumers. The sequence of organisms through which energy flows is called a food chain. Multiple interconnecting food chains constitute a food web. The flow of atoms through an ecosystem involves all t