3.2 Energy flow and nutrient cycling in ecosystems

Ecosystems are all about energy flow and nutrient cycling. These processes keep life going, with plants capturing sunlight and nutrients moving through food webs. It's like a giant recycling system where everything's connected.

Understanding these cycles helps us see how ecosystems work and how we affect them. From carbon in the air to nitrogen in the soil, these cycles show how life and the environment are linked. It's crucial for grasping the bigger picture of biodiversity and ecosystem health.

Energy flow through ecosystems

Thermodynamics and energy transfer

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• Energy flow in ecosystems follows the laws of thermodynamics (energy transfers and transforms but never creates or destroys)
• Solar radiation serves as the primary energy source for most ecosystems
  • Autotrophs capture solar energy through photosynthesis
  • Autotrophs convert solar energy into chemical energy
• Energy transfer between trophic levels operates at ~10% efficiency
  • Heat loss and metabolic processes account for the 90% energy loss
• Ecological pyramids visually represent decreasing energy at higher trophic levels
  • Types include energy pyramids, biomass pyramids, and numbers pyramids
• Net primary productivity (NPP) quantifies available energy for transfer to higher trophic levels
  • NPP accounts for energy remaining after producer respiration

Food chains and food webs

• Food chains model simple linear energy flow in ecosystems
• Food webs illustrate complex interconnections between species in ecosystems
• Both food chains and food webs demonstrate energy transfer between organisms
• Examples of food chains:
  • Grass → Grasshopper → Frog → Snake → Hawk
  • Phytoplankton → Zooplankton → Small fish → Large fish → Seabird

Producers, Consumers, and Decomposers

Primary producers (Autotrophs)

• Organisms capable of synthesizing their own food from inorganic compounds
• Primarily use photosynthesis or chemosynthesis for energy production
• Examples of primary producers:
  • Terrestrial plants (trees, grasses, shrubs)
  • Algae and phytoplankton in aquatic ecosystems
  • Chemosynthetic bacteria in deep-sea hydrothermal vents

Consumers (Heterotrophs)

• Rely on other organisms for energy
• Classified based on position in food chain:
  • Primary consumers (herbivores) eat producers
  • Secondary consumers (carnivores) eat primary consumers
  • Tertiary consumers (top predators) eat secondary consumers
• Examples of consumers:
  • Primary consumers (rabbits, deer, zooplankton)
  • Secondary consumers (foxes, owls, small fish)
  • Tertiary consumers (wolves, sharks, eagles)

Decomposers and their ecological role

• Primarily bacteria and fungi break down dead organic matter and waste products
• Release nutrients back into ecosystem for reuse by producers
• Crucial for nutrient cycling and energy flow in ecosystems
• Examples of decomposers:
  • Soil bacteria (Bacillus, Clostridium)
  • Fungi (mushrooms, molds)
  • Detritivores (earthworms, millipedes)

Ecosystem balance and keystone species

• Interconnected roles of producers, consumers, and decomposers form the basis of energy flow
• Nutrient cycling in ecosystems depends on the balance between these groups
• Keystone species have disproportionate impact on ecosystem structure and function
  • Can be producers, consumers, or decomposers
  • Examples (sea otters in kelp forests, beavers in riparian ecosystems)
• Ecosystem stability and resilience rely on maintaining balance between these groups

Nutrient cycling in ecosystems

Carbon cycle

• Describes carbon movement through atmosphere, biosphere, hydrosphere, and geosphere
• Key processes involved:
  • Photosynthesis removes carbon dioxide from atmosphere
  • Respiration releases carbon dioxide back into atmosphere
  • Decomposition of organic matter releases carbon
  • Ocean absorption and release of carbon dioxide
  • Fossil fuel formation and combustion
• Human activities significantly alter the carbon cycle (deforestation, fossil fuel burning)

Nitrogen cycle

• Involves exchange of nitrogen between atmosphere, soil, and living organisms
• Key processes mediated by microorganisms:
  • Nitrogen fixation converts atmospheric nitrogen to biologically available forms
  • Nitrification converts ammonium to nitrate
  • Denitrification returns nitrogen to the atmosphere
  • Ammonification converts organic nitrogen to ammonium
• Examples of nitrogen-fixing organisms (Rhizobium bacteria, cyanobacteria)

Phosphorus and water cycles

• Phosphorus cycle primarily sedimentary
  • Main reservoir in rock and soil minerals
  • Processes include weathering, plant uptake, and aquatic sediment deposition
• Water cycle (hydrologic cycle) crucial for nutrient distribution
  • Involves evaporation, transpiration, precipitation, and runoff
  • Dissolves and transports nutrients throughout ecosystems

Human impacts on ecosystems

Land use changes and agricultural practices

• Deforestation alters primary productivity and disrupts energy flow patterns
• Agricultural practices lead to nutrient imbalances and water pollution
  • Fertilizer use causes eutrophication in water bodies
  • Pesticides affect non-target species and disrupt food webs
• Examples of impacts:
  • Amazon rainforest deforestation for agriculture and ranching
  • Gulf of Mexico "dead zone" caused by agricultural runoff

Overfishing and hunting

• Cause trophic cascades, altering ecosystem structure and function
• Examples of impacts:
  • Collapse of Atlantic cod fishery off Newfoundland
  • Removal of wolves from Yellowstone National Park (later reintroduced)

Urbanization and climate change

• Urbanization increases energy consumption and waste production
  • Alters local and global biogeochemical cycles
• Climate change affects energy flow and nutrient cycling through:
  • Changes in temperature and precipitation patterns
  • Increased frequency of extreme weather events
  • Shifts in species distributions and phenology

Conservation and mitigation efforts

• Reforestation and sustainable agriculture aim to restore ecosystem balance
• Development of renewable energy sources reduces disruption of natural cycles
  • Examples (solar, wind, geothermal energy)
• Circular economy practices promote efficient resource use and waste reduction
• Conservation efforts focus on protecting keystone species and critical habitats
  • Examples (marine protected areas, wildlife corridors)