ENVI 201 Lecture Notes - Lecture 7: Nitrogen Fixation, Nitrogen Cycle, Phosphorus Cycle

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Nutrient Cycle within and among Ecosystems
Nutrient cycles
Hydrologic
Carbon
Nitrogen
Phosphorus
Sulfur
Nutrients may remain in a reservoir for a period of time
Water cycle
Waters unique properties
Properties of water due to hydrogen bonds between water molecules
Carbon Cycle
Circulates through the biosphere
Based on co2
Producers remove co2 from the atmosphere
Consumers use co2
Some carbon takes a long time to recycle
Humans altering carbon cycle by burning fossil fuels
Excess carbon dioxide in the atmosphere has contributed to global warming
Nitrogen Cycle
Nitrogen is recycled through the earth’s systems by different types of bacteria
The nitrogen cycle converts nitrogen into compounds that are useful nutrients for plants
and animals
Nitrogen fixation
Lightning
Bacteria and cyanobacteria
Combine gaseous nitrogen w hydrogen to make ammonia and
ammonium ions
Nitrification
Soil bacteria change ammonia and ammonium ions into nitrate ions
Denitrification
Nitrate ions back to nitrogen gas
Human influence:
Humans are adding nitrogen from the atmosphere faster than it can be removed
Humans are removing nitrogen from the soil faster than it can be replaced
We destroy forests, grasslands, and wetlands, releasing large amounts of
nitrogen into the atmosphere
We pollute aquatic ecosystems with agricultural runoff
We remove nitrogen from topsoil from land-clearing and harvesting processes
Nitrous oxide that comes from livestock, wastes, and fertilizers can warm
atmosphere and deplete the ozone later
Burning fossil fuels adds nitric oxide to the atmosphere
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