4 - Energy Flow and Material Cycling through the Ecosystems

Earth Spheres

• Lithosphere: Solid Earth layer.

• Hydrosphere: All water found on, under, and over the Earth's surface.

• Atmosphere: Gases that surround the Earth.

• Biosphere: All life forms on Earth.

• Interaction of these four spheres is essential for understanding Earth System Science.

Energy Flow in the Ecosystem

• Energy Flow:

  • Fundamental ecological concept unifying studies of plants, animals, and microorganisms.

  • Based on trophic relationships among organisms; a driving force for ecosystem function.

Sources of Energy in Ecosystems

• The primary energy source for the biosphere is solar radiation.

• Plants, algae, and some bacteria utilize sunlight through photosynthesis.

Key Concepts in Energy Flow

Biomass

• Definition: The energy content or organic matter content of an organism, population, or ecosystem.

• Renewable organic material from plants and animals, can be converted to usable fuels.

Production vs. Productivity

• Production: Increase in biomass amount.

• Productivity: Increase in production per time period.

• Biomass and production measured in energy units (calories) or mass units (grams).

Trophic Levels in Ecosystems

• Organisms classified into three groups:

  • Producers: Autotrophic and photosynthetic organisms that grow using sunlight (e.g., plants, algae).

  • Consumers: Heterotrophic organisms that consume plants or animals for energy; they acquire organic matter after obtaining energy from producers.

  • Decomposers: Bacteria and fungi that break down dead organic matter to release nutrients back into the ecosystem.

Energy Transition Between Trophic Levels

• As energy flows between trophic levels, available energy decreases.

• Energy loss occurs in forms of waste and heat during respiration.

• Only about 10% efficiency is observed in energy transfer to the next trophic level, with the remaining 90% lost.

Biomagnification

• Describes the concentration of toxic substances as energy moves up the food chain.

• Example: Pollutants like PCBs are absorbed by phytoplankton and biomagnified through consumption by higher trophic levels (e.g., zooplankton, herring, salmon, and orca whales).

The Water Cycle

• Water is vital for life, with human bodies containing about 63% water.

• Exists in three phases: solid, liquid, and gas, with uneven distribution in biosphere.

Biogeochemical Cycles

Carbon Cycle

• Carbon: Primary element of life, undergoing rapid cycling through food chains.

• Involves exchanges of carbon between living organisms and CO2.

• Plants use CO2 through photosynthesis; oxygen is produced, completing this cycle.

Nitrogen Cycle

• Nitrogen: Essential for protein synthesis, but largely inert in atmospheric form (N2).

• Usable forms include ammonium and nitrates, which are absorbed by producers.

• Cycle includes fixation, nitrification, and denitrification processes to return nitrogen to the atmosphere.

Oxygen Cycle

• Oxygen is necessary for aerobic respiration; however, excess levels can be toxic.

• Oxygen cycle works oppositely to the carbon cycle, primarily through photosynthesis and respiration.

• Human actions, like deforestation and fossil fuel combustion, affect the oxygen cycle significantly.

Phosphorous Cycle

• Phosphorous (P): Key element for living organisms, often limiting in ecosystems.

• Cycle includes recycling through decomposition, but significant loss occurs in deep ocean deposits leading to scarcity.

• Human activity, such as fertilizer use, exacerbates natural losses causing eutrophication in aquatic systems.

Sulphur Cycle

• Sulphur (S): Integral to some amino acids; cycles mainly in aquatic environments and soils.

• Sulphur is absorbed by plants for protein production, and human-induced activities like fossil fuel combustion enrich the biosphere with sulphur compounds.