Global cycling lecture

Global cycling lecture - 1 Global Geochemical Cycling Earth...

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Unformatted text preview: 1 Global Geochemical Cycling Earth has but a thin atmosphere 50% of the atmosphere by mass is below an altitude of 5.6 km. 90% of the atmosphere by mass is below an altitude of 16 km. The common cruising altitude of commercial airliners is about 10 km. 99.99997% of the atmosphere by mass is below 100 km (almost all of it). The highest plane flights reach an altitude of ca 110 km. Mean radius of earth = 6,371.0 km Atmosphere thickness is 100/6371 = 0.016 of earth’s radius. Huge surface area, small atmospheric volume. Modest rates of pollution can foul the atmosphere. The same biological molecule is responsible for all biological nitrogen fixation. All nitrogenase on earth is in bacteria. No more than a few kilograms exist, in probably not more than 20 “species” of bacteria. About 20 bacterial genes in synthesis and control. Nitrogen fixation is such a complicated process that the fixation of one molecule of N 2 takes 1.2 seconds. Most chemical reactions take nanoseconds. 2 Much Nitrogen Fixation is Symbiotic and Mutualistic. On land 1. Rhizobium bacteria in roots of legume host plants. 2. Anabaena, a Cyanobacterium , in pores of water fern fronds. In the sea, rivers, and lakes. Cyanobacteria All natural biological nitrogen fixation is by means of nitrogenase, an enzyme in bacteria. Some N is fixed by lightening, in volcanoes, and forest fires. About 62% of global N fixation today is by means of the Haber Bosch process—Industrial Fixation for Fertilizer for agriculture. Reminder: Rhizobia bacteria in nodules on legume roots-- peas plants, soy beans Crop rotation--corn with soy beans Application of ecology in ag. Cyanobacteria. Nitrogen fixing bacteria in the sea and fresh water Salt ponds--southern San Francisco Bay Fixed N is used in explosives and agriculture. It was very expensive before… Mining fertilizer 2 Much Nitrogen Fixation is Symbiotic and Mutualistic. On land 1. Rhizobium bacteria in roots of legume host plants. 2. Anabaena, a Cyanobacterium , in pores of water fern fronds. In the sea, rivers, and lakes. Cyanobacteria All natural biological nitrogen fixation is by means of nitrogenase, an enzyme in bacteria. Some N is fixed by lightening, in volcanoes, and forest fires. About 62% of global N fixation today is by means of the Haber Bosch process—Industrial Fixation for Fertilizer for agriculture....
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This note was uploaded on 07/29/2010 for the course BIS 2B taught by Professor Strong during the Summer '08 term at UC Davis.

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Global cycling lecture - 1 Global Geochemical Cycling Earth...

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