Nitrogen and Phosphorus Cycles Lesson
Nitrogen Cycle
Ammonia: enters the system via animal excretions, decomposing organic matter, sewage, and agricultural fetilizers
Ammonia to Nitrite: Nitrosomal bacteria in the seawater convert ammonia to nitrite (NO2)
Nitrite to Nitrate: Nitrobacter bacteria in the seafloor sediments convert nitrite to nitrate (NO3).This is called nitrogen fixing where nitrites are converted to a usuable form that plants can use
Nitrate Uptake: seaweed and algae take in the nitrate as a nutrient for growth. Nitrate is a usable form of nitrogen for animals
Nitrogen Intake: Primary consumers (herbivores) eat the seaweed and algae and produce proteins for growth/development. The nitrogen from plants is the source of nitrogen for the rest of the food web. The nitrogen is converted to ammonia as a by-product of nitrogen metabolism
Phosphorus Cycle
Notice that Phosphate (PO4) enters the cycle in two ways: 1) decomposition where PO4 recycles through Earth's system 2) weathering where rocks are broken by wind, water, etc where the PO4 in rocks leaches out into the soil and water
How these elements are used in nature
Nitrogen is an essential component for organic materials (such as amino acids, chlorophyll, and nucleic acids such as DNA and RNA)
animals eat this plant tissue and create tissue. Nitrogen is passed up through the levels of the food web, from plant to primary consumer to apex predator
Phosphorus is an essential nutrient for all living things as it is involved in the formation of genetic material (RNA and DNA), usable energy molecules (ATP), and cell membranes (phospholipids)
for animals to use bioavailable phosphate, they must consume plants or animals that already contain it. Phosphate is passed up through the food web by plant to primary consumer to apex predator
Eutrophication
this is an excessive richness of nutrients in the seawater, which causes an overgrowth of plant life in the form of algae. This results in a loss of animal life in the area due to low oxygen levels (hypoxia) or lack of oxygen (anoxia) in the water
The algae use huge amounts of oxygen when the die (they only live for around 2 days) and decompose on the floor where decomposition uses the oxygen and in this state of eutrophication the level of oxygen within the water sharply decreases
the result of low oxygen is death of marine life or migration of marine animals away from the hypoxic area. These are called dead zones
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Negative impacts on the marine nitrogen and phosphorus cycle
Crop Fertilization
this fertilization runs off into the watershed when it rains
Livestock Farming
organic compounds from manure wash into the watershed and go into the ocean
Wastewater Runoff
Human sewage is high in nitrogen, ammonia, and phosphates which eventually runs into the watershed into the ocean
Mining and Construction
both involve the mechanical breakdown or weathering of rock where phosphates leach into the water and travel into the ocean