Nitrogen Cycle

Forms of Nitrogen

• Ammonia: NH3+• Ammonium: NH4• Nitrite: NO2-• Nitrate: NO3-

• Gas: N2• Nitrogen Oxide: NO• Dinitrogen oxide: N2O

• Each spot on the cycle is a reservoir of nitrogen; a place where it is stored or available in some form– Atmosphere– Living organisms– Soils– Oceans

• 78% of the atmosphere is nitrogen– Gaseous nitrogen (N2) is not usable to living

things– Nitrogen fixation must take place

• Nitrogen fixation- processing of nitrogen into forms that are usable by living things– 1 of 4 methods

• Lightning• Bacteria• Industrial fixation: the Haber-Bosch processes

convert N2 into fertilizer• Combustion of fossil fuels

– Bacteria: have an enzyme that breaks down N2 into ammonia

Assimilation

• Plants absorb nitrogen through roots• Bacteria can also take up N• Animals get nitrogen from eating plants or

other animals– N is important for making amino acids and

proteins– Also important part of DNA and RNA

Ammonification

• Organisms die and are broken down by decomposers

• Bacteria convert the nitrates into ammonia

Nitrification• Ammonium absorbed by soil and then

changed by bacteria to nitrite and nitrate

• Nitrate can then either be used by plants or go through denitrification

Denitrification

• Turn nitrates back into nitrogen gas

• Completes the nitrogen cycle, putting N back into the atmosphere

Anaerobic Ammonium Oxidation

• Nitrite and Ammonium converted straight to N2

• Occurs mostly in oceans

Humans affect the Nitrogen Cycle

• N-rich fertilizers put N into water; can be toxic to babies

• Fertilizers, cattle and feedlots, and industrial sources also release dinitrogen oxide (N2O) into the air; contributes to global warming

Humans and the N-cycle

• Burning fossil fuels and forests releases Nitrogen oxide; contributes to smog and acid rain

• Wastewater treatment plants release ammonia, toxic to fish