GEF

Unit 4   |  The Global Ecosystem 95 Humans influence the nitrogen cycle in several ways. The use of nitrogen fertilizer on crops and gardens adds nitrogen to the soil (lithosphere), and enters water systems through rain and runoff, impacting the hydrosphere. Although nitrogen fertilizer increases agricultural yields, it also pollutes lakes and streams by promoting explosive growth of phytoplankton. In turn, the phytoplankton blooms cause eutrophication : decreased oxygen levels that kill off aquatic organisms. Agriculture and industrial processes increase levels of atmospheric nitrous oxide (N2 O ) and other nitrogen compounds, contributing to air pollution, acid rain , climate change , and ozone depletion . Less than 1% of the world water supply is fresh drinkable water. EUTROPHICATION The process in which a body of water becomes excessively enriched with nutrients, resulting in growth of aquatic life and depleting the oxygen availability for other organisms. ACID RAIN Unusually acidic rain water that is caused by air pol- lution, primarily sulfur dioxide emissions from coal-fired power plants. Acid rain harms soil and ecosystem health. CLIMATE CHANGE A long-term alteration in the Earth’s weather patterns and temperature, currently caused by human emissions of greenhouse gases. OZONE DEPLETION Damage to the ozone layer of the atmosphere, causing increased levels of ultra- violet radiation to reach the Earth’s surface.