Human activity can have many negative effects on Yellowstone’s ecosystem. The presence of humans in the park has caused many animals to become vulnerable to disease. Human interaction with the ecosystem has rapidly spread disease to Yellowstone’s wildlife, which has proven to have adverse effects on populations. Also, humans tend to leave trash in poor areas. Littering is a problem in Yellowstone because it can be ingested by the wildlife and also pollute the park. Trash is not a part of the park ecosystem and should be disposed of properly. In addition, the use of vehicles in the park can affect air quality. While a car’s engine is running, several different types of gasses are emitted that can have poor effects on the environment. Carbon dioxide, nitrogen oxides, sulfur oxide, solid particles, and other volatile substances are produced by vehicles and go into the air. These emissions can affect the health of wildlife as well as create smog.Humans can also upset the nitrogen cycle (discussed on the biogeochemical cycle page) through activities such as the burning of fossil fuels, the use of artificial fertilizers, and sewage dumping.[6]