Biogeochemical Cycles

Biogeochemical Cycles

• Ecosystems vary
• Net primary productivity
• Efficiency of energy flow
• These affect the distribution and abundance of organisms
• Biogeochemical cycles
• Describe the path of essential chemicals through the ecosystem
• Living (biotic)
• Non-Living (abiotic)
• Together these form the closed system of Earth

Carbon Cycle

Carbon

• Essential building block of life
• Exists in many minerals

Carbon Reservoirs

• Most carbon is stored in reservoirs Examples: Fossil fuels, sediment, dissolved in ocean, stored in plant and animals

Atmospheric Carbon

• Most available form for life
• Found as CO2 gas
• Removed from atmosphere by photosynthesis

Organic Carbon

• Terrestrial
• Plants remove CO2 from atmosphere
• Consumers eat plants to obtain carbon
• Release CO2 back into atmosphere through respiration (breathing)
• Decomposers break down complex carbon molecules and release back into cycle
• Aquatic Carbon
• Removed from atmosphere through photosynthesis
• Runs into water from terrestrial system

Nitrogen Cycle

Atmospheric Nitrogen

• N2 makes up 75% of Earth's atmosphere
• N2 is not usable by most organisms
• Must be "fixed" to use
• Nitrogen Fixation: process of converting N2 into usable organic compounds
• Performed by specific bacteria
• Combines N2 with hydrogen to create ammonia

Organic Nitrogen

• Nitrogen Assimilation: Plants take in nitrogen from the soil
• Consumers then eat the plants to acquire nitrogen
• Animal waste and decomposition contains nitrogen which is released back into the soil
• Oceans cycle nitrogen in a similar way

Phosphorous Cycle

• Slowest biogeochemical cycle
• Phosphorus never enters the atmosphere
• Always exists as a solid
• Most common form in nature is the phosphate ion (PO4) 3-
• Terrestrial phosphate is found in minerals, but is inaccessible
• Weathering of rocks eventually releases phosphorus into the soil
• Phosphorus is water soluble
• Over time phosphorus can leach into the oceans, depleting the terrestrial system