Biogeochemical Cycles Lecture Notes

Introduction to Biogeochemical Cycles

• Also known as nutrient cycles.
• Essential for the functioning of all life on Earth.
• They transform and recycle matter.
• Connect elements with living organisms and regulate flow between different spheres.

Importance of Nutrient Cycles

• Vital for ecosystem functioning.
• Transform nutrients between biotic (living) and abiotic (nonliving) systems.
  • Biotic systems: life in the biosphere.
  • Abiotic systems: atmosphere, hydrosphere, lithosphere, and cryosphere.

Energy Flow in Ecosystems

• Energy originates from the sun.
• Producers (plants): convert solar energy to usable nutrients via photosynthesis.
• Net primary production: energy remaining after plants use energy for respiration.
• Energy transfer occurs at each trophic level with energy loss as heat.
  • Ecological Pyramid: illustrates energy efficiency and productivity at each level.

Water Cycle

• Processes: evaporation, transpiration, evapotranspiration, sublimation.
• Condensation: forms clouds.
• Precipitation: releases water as rain or snow.
• Runoff: water moves into freshwater or oceans.
• Groundwater infiltration: starts cycle anew.

Carbon Cycle

• Photosynthesis: CO2 is absorbed by plants.
• Consumption: transfers carbon from plants to animals.
• Decomposition: returns carbon to soil when organisms die.
• Respiration and Combustion: releases CO2 back into the atmosphere.
• Oceans: absorb atmospheric carbon, dissolving it in water.

Nitrogen Cycle

• Nitrogen fixation: converts atmospheric nitrogen into usable forms.
• Nitrification: ammonia to nitrite/nitrate.
• Denitrification: returns nitrogen to the atmosphere.
• Assimilation: plant roots absorb nitrates/nitrites.
• Ammonification: decomposition converts organic nitrogen to ammonia.

Oxygen Cycle

• Produced by photosynthesis, used by respiration, combustion, oxidation, and decomposition.
• Respiration: animals use oxygen and exhale CO2.
• Decomposition: uses oxygen, releases CO2.
• Oxidation: metals rust, uses oxygen.
• Combustion: uses oxygen, produces CO2.

Phosphorus Cycle

• Weathering: releases phosphate ions from rocks.
• Uptake: plants absorb inorganic phosphate.
• Incorporation: organic phosphate forms in organisms.
• Decomposition: returns phosphate to the soil.
• Mineralization: bacteria convert organic matter into inorganic phosphorus.

Sulfur Cycle

• Essential for proteins and vitamins.
• Mineralization: organic sulfur to hydrogen sulfide.
• Oxidation: hydrogen sulfide to sulfate.
• Reduction: sulfate to sulfide in plants.
• Incorporation: sulfide into organic compounds.
• Immobilization: microorganisms fix sulfur compounds into inorganic forms.

Additional Resources

• Weekly podcasts available for deeper insights on nutrient cycles.