Discuss how humans impact each of the following cycles, providing specific examples of each.The nitrogen cycle, the phosphorus cycle, and the carbon cycle.

Expert Answers
trophyhunter1 eNotes educator| Certified Educator

The nitrogen cycle is impacted by humans whenever fertilizer is applied to farmland to help crops grow. This adds nitrates to the soil. If soil erodes, the nitrates are transported and deposited in the nearest body of water. This can cause algae to overgrow in a process called eutrophication. The lake will run out of oxygen as the algae die off and bacteria begin their decomposition.Sessile organisms are greatly affected. Later, it can result in fish kills and smelly water. The phosphorus cycle occurs between the land and the sea. The atmosphere is not involved in this cycle at all. Phosphorus usually weathers from rocks and is incorporated into plants, which are in turn eaten by herbivores which are consumed by carnivores. In urine and feces, phosphorus is excreted and when organisms decompose, phosphorus is returned to the ecosystem. When humans add additional phosphates to the environment, just as with nitrogen, eutrophication can occur in fresh water ecosystems. By adding manure to farmlands, this can add phosphates to the environment. The carbon cycle is influenced by humans because they have been adding more carbon to the atmosphere since the industrial revolution due to the combustion of fossil fuels. When coal, oil and gas are burned, carbon dixoide is added to the atmosphere as well as carbon monoxide. Plants need carbon dioxide for photosynthesis, but due to air pollution which kills plants, and clearing land by cutting down forests, there is excess carbon dioxide in the atmosphere because the plants cannot keep up. It has been shown that carbon dioxide in the atmosphere leads to global warming due to the greenhouse effect. Sunlight can enter the earth's atmosphere but the heat energy becomes trapped near the surface, leading to higher temperatures. This in turn, can melt the polar ice caps and may lead to flooding when the sea level rises. It can change the earth's climate and possibly spread dangerous disease-carrying organisms like mosquitoes, which thrive in higher temperatures.

Access hundreds of thousands of answers with a free trial.

Start Free Trial
Ask a Question