AP Enviro: Nitrogen Cycle

Nitrogen is important because its a building block of proteins and nucleic acids making it one of the limiting nutrients (once it gets used up, plant growth stops)

nitrogen cycle - movement of nitrogen around the biosphere among reservoir sources and sinks 

The largest sink of nitrogen is in the atmosphere (78%). Here, it is biologically unusable

• The process of nitrogen fixation allows us to convert nitrogen gas into forms that plants and algae can use 

  • Happens through nitrogen fixing bacteria found in the root nodules of legumes; or through lightning, which helps break the bonds and convert the ions 

• Once plants and algae convert it into ions such as ammonia, nitrite (most usable), and then into nitrate, they have finished nitrification

  • Nitrogen fixation: ammonia → nitrite 

  • Nitrification: nitrite → nitrate 

Once nitrogen is turned into usable ions , it is then assimilated into animal tissues and when herbivores feed on plants. The herbivores then release any nitrogen not assimilated as waste products 

Eventually, organisms die and fungal and bacterial organisms break down the organic matter to convert it back into ammonium, known as ammonification or mineralization

The final step is to return nitrogen gas into the atmosphere through multiple steps: through anaerobic conditions by bacteria through the process of denitrification 

Leaching is the process of nitrogen making it into the soil, becoming dissolved in the water and coming into a water source. Runoff from farms can also put nitrogen into bodies of water. → causes excess plant growth 

• Human usage of fertilizer leads to a lot of run off, taken into waterways (through leaching), where the dissolved molecules run into the soil/make their way into the lakes/streams causing eutrophication 

• Burning fossil fuels can put nitrogen oxides into the atmosphere (NO_x is one of the compounds responsible for acid rain)