Nutrient Cycles

Learning Objectives

  • Understand movement of chemical components of life throughout the earth.

  • Describe cycling of water, carbon, nitrogen, and phosphorus.

  • Define processes in these nutrient cycles.

  • Explain how organisms acquire nutrients.

  • Compare and contrast movement of different nutrients through ecosystems.

Hydrologic Cycle (Water Cycle)

  • Key Components:

    • Evaporation: Conversion of liquid water to water vapor (not boiling).

    • Transpiration: Water vapor released from plant tissues.

    • Condensation: Water vapor converts back to liquid water.

    • Precipitation: Water falls from the atmosphere back to Earth.

    • Percolation: Water moves through rock and soil to recharge groundwater.

Carbon Cycle

  • Key Processes:

    • Photosynthesis: Plants take in CO2 from air/water and convert it into organic compounds.

    • Cellular Respiration: Organisms break down organic compounds, releasing CO2 back.

    • Consumption: Transfer of carbon as living organisms consume each other.

    • Decomposition: Breakdown of dead organic matter, releasing carbon into soil/water/atmosphere.

    • Weathering: Erosion frees trapped carbon from rocks/soil.

    • Ocean-Atmosphere CO2 Exchange: CO2 exchanges based on concentration; positive flux (ocean releasing CO2) and negative flux (ocean absorbing CO2).

    • Combustion: Burning fossil fuels and forest fires increases atmospheric CO2.

Nitrogen Cycle

  • Key Processes:

    • Nitrogen Fixation: Conversion of atmospheric N2 into ammonia (NH3) via bacteria or lightning.

    • Nitrification: Bacteria convert NH3 into nitrite (NO2-) and nitrate (NO3-).

    • Assimilation: Plants uptake nitrate from soil.

    • Consumption: Nitrogen moves through food chain as organisms are eaten.

    • Decomposition: Breakdown of organic matter to release nitrogen into ammonia (ammonification).

    • Denitrification: Converts NO3- back to N2, returning nitrogen to the atmosphere.

    • Excretion: Animals release excess nitrogen through urine.

Phosphorus Cycle

  • Key Components:

    • Assimilation: Uptake of phosphates (PO4^3-) by plants from soil.

    • Consumption: Transfer of phosphates as organisms consume each other.

    • Decomposition: Breakdown of organic matter releases phosphates into soil/water.

    • Weathering: Erosion frees up phosphorus trapped in rocks/soil.

Big Picture Questions

  • Why have the oceans shifted from a net positive flux to a net negative flux of CO2?

  • Why is CO2 more concerning for atmospheric studies than water vapor, despite its potency as a greenhouse gas?

  • Why do animals urinate while plants do not?

  • Why is carbon not considered in fertilizer labels, which focus on nitrogen, phosphorus, and potassium?

  • Why are floodplains often more productive than surrounding areas?

These notes outline the key nutrient cycles necessary for life on Earth, detailing the processes involved and posing critical questions that further explore the intricacies of these cycles. The understanding of these concepts is crucial for studying ecology and environmental science.