ENVS 1100 Lecture Notes - Lecture 6: Nitrogen Fixation, Denitrification, Nitrification
3 May 2018
School
Department
Course
Professor
Biogeochemical Cycles
September 25, 2014
Nitrogen
• N2 makes up 78% of our atmosphere
• 6th most abundant element on Earth
• Essential ingredient in proteins, DNA and RNA
• Essential for plant growth
The nitrogen cycle is a continuous series of natural processes by which nitrogen
passes from the air to the soil, to organisms and then returns back to the air or soil
through decomposition or denitrification.
• Steps: decomposition, nitrification, denitrification
Nitrogen fixation is the conversion of atmospheric nitrogen into a biologically
usable form, carried out by bacteria found in soil or via lightning.
• N2 (from atmosphere) + hydrogen = NH3 (ammonia)
• N2 is not available to organisms
• NH4+ is water soluble and can be taken up by plants
Human influences on the nitrogen cycle:
• Excess inputs of nitrogen to water systems from use of fertilizers
• Haber-Bosch process – doubled natural rate of nitrogen fixation on earth
• Increased growth of legumes
• Acidified surface water and soils
• Burn fossil fuels and wood
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Document Summary
Nitrogen: n2 makes up 78% of our atmosphere, 6th most abundant element on earth, essential ingredient in proteins, dna and rna, essential for plant growth. Human influences on the nitrogen cycle: excess inputs of nitrogen to water systems from use of fertilizers, haber-bosch process doubled natural rate of nitrogen fixation on earth. Increased growth of legumes: acidified surface water and soils, burn fossil fuels and wood. Overall: nitrogen is often a limiting factor in primary production, humans have greatly increased the flux of nitrogen from the atmosphere to the biosphere/geosphere/hydrosphere which is greatly impacting terrestrial and aquatic ecosystems. Increasing primary producers in an aquatic system can lead to low oxygen levels in the system. Reservoirs: sedimentary rock, atmosphere, consumers, producers, ocean. Fluxes: photosynthesis (gpp) and respiration, burning of fossil fuels, ocean-atmosphere exchange, volcanic activity and hydrothermal emissions, net deforestation (reduced uptake by plants, forest fires ecosystem. If carbon dioxide increases in the atmosphere, it will also increase in the ocean.
