AP BIOLOGY

Detailed explanation-1: -Human activities, such as making fertilizers and burning fossil fuels, have significantly altered the amount of fixed nitrogen in the Earth’s ecosystems. In fact, some predict that by 2030, the amount of nitrogen fixed by human activities will exceed that fixed by microbial processes (Vitousek 1997).

Detailed explanation-2: -Most of the human activities responsible for the increase in global nitrogen are local in scale, from the production and use of nitrogen fertilizers to the burning of fossil fuels in automobiles, power generation plants, and industries.

Detailed explanation-3: -Sources of nitrogen from human activities, such as electric power generation, industry, transportation and agriculture, can upset the natural balance of nitrogen in the environment. When fossil fuels are burned, they release nitrogen oxides into the atmosphere, which contribute to the formation of smog and acid rain.

Detailed explanation-4: -However, fertilizers are often overused, and that can cause problems. Nitrogen from fertilizers sinks into soils, often creating conditions that favor the growth of weeds rather than native plants. Nitrogen then washes into waterways, causing a surplus of nutrients, a situation called eutrophication.

Detailed explanation-5: -Human activities are substantially modifying the global carbon and nitrogen cycles. The global carbon cycle is being modified principally by the burning of fossil fuels, and also by deforestation; these activities are increasing the carbon dioxide concentration of the atmosphere and changing global climate.