BIO IOKLJU3.2

Energy Flow and Matter Cycling in Ecosystems

• Energy in ecosystems flows directionally:

  • Enters as sunlight or inorganic molecules for chemoautotrophs.

  • Leaves as heat during energy transformationUUUs between trophic levels.

• Matter in ecosystems is conserved and rUUUUUUUUUUUUUUecycled, rather than flowing continuously.

Key Elements in Organic Molecules

• The six most common elements associated with organic molecules include:

  • Carbon (C)

  • Nitrogen (N)

  • Hydrogen (H)

  • Oxygen (O)

  • Phosphorus (P)

  • Sulfur (S)

• These elements can exist in various chemical forms and can remain in the atmosphere, on land, in water, or beneath Earth's surface for long periods.

• Geologic Processes Impacting Element Cycling:

  • Weathering

  • Erosion

  • Water drainage

  • Subduction of continental plates

Biogeochemical Cycles

• Recycling inorganic matter between living organisms and their nonliving environment is termed biogeochemical cycles.

• Organisms utilize the six key elements in various critical biological functions:

  • Hydrogen and oxygen in water and organic molecules, essential for life.

  • Carbon as the backbone of all organic molecules.

  • Nitrogen as a component of nucleic acids and proteins.

  • Phosphorus for nucleic acids and phospholipids in biological membranes.

  • Sulfur for maintaining the three-dimensional shape of proteins.

• The cycling of these elements is interconnected, for instance:

  • Water movement is essential for leaching sulfur and phosphorus into aquatic ecosystems.

The Water Cycle

• The hydrosphere is defined by the movement and storage of water on Earth—including:

  • Liquid water on the surface (rivers, lakes, oceans).

  • Groundwater beneath the surface.

  • Ice (polar ice caps and glaciers).

  • Water vapor in the atmosphere.

• Human Water Composition:

  • Approximately 60% of the human body is water.

  • Human cells contain more than 70% water.

• Global Water Distribution:

  • Of Earth's total water, 97.5% is salt water.

  • Of the remaining 2.5% freshwater:

  • Over 99% is groundwater or ice.

  • Less than 1% of freshwater is accessible in lakes and rivers.

• Many organisms depend on this limited freshwater supply, and its scarcity can negatively impact ecosystems.

Human Technologies to Increase Water Availability

• Technologies developed include:

  • Digging wells to harvest groundwater.

  • Storing rainwater.

  • Desalination of seawater for drinking purposes.

Water Cycle Processes

• The main processes in the water cycle include:

  • Evaporation: Liquid water transitions to water vapor.

  • Sublimation: Ice transforms directly to water vapor.

  • Condensation: Water vapor cools and condenses into droplets to form clouds.

  • Precipitation: Water returns to the surface as rain, snow, hail, etc.

  • Subsurface water flow: Movement of water beneath the surface.

  • Surface runoff and snowmelt: Movement of water across the land surface.

  • Streamflow: Water moving through streams to larger bodies of water.

• The Sun’s energy drives the water cycle by warming bodies of water, facilitating evaporation and sublimation, and thus adding water vapor to the atmosphere.

• Transpiration:

  • Water absorbed by plant roots evaporates through stomata in leaves, contributing to total water returned to the atmosphere (collectively referred to as evapotranspiration).

Groundwater

• Groundwater exists in soil pores, sand, gravel, and rock fissures.

• Many streams rely on this groundwater for flow, rather than direct rainwater replenishment.

• Groundwater reservoirs, or aquifers, are vital for drinking and irrigation but can be depleted faster than they are replenished.

The Carbon Cycle

• Significance of Carbon:

  • Carbon is the second most abundant element in organisms by mass.

  • Essential for all organic molecules, including CO₂.

  • Carbon compounds contain energy and can be fossilized into fossil fuels.

• Impact of Fossil Fuels:

  • Usage has increased since the Industrial Revolution, drastically raising atmospheric carbon dioxide levels.

  • This increase is linked to climate change and is a global environmental concern.

Carbon Cycle Subcycles

• The carbon cycle consists of two interconnected subcycles:

  • Rapid Carbon Exchange: Occurs among living organisms.

  • Long-term Cycling: Involves geologic processes.

Carbon Exchange Processes

• In the atmosphere, carbon dioxide ($CO_2$) exists in gaseous form and dissolved in water.

• Photosynthesis:

  • Converts $CO_2$ into organic compounds.

• Respiration:

  • Breaks down organic compounds, returning $CO_2$ to the atmosphere.

• Organic carbon storages occur when living matter is buried or fossilized over time.

• Human emissions and volcanic activity release stored carbon back into circulation.

Biological Carbon Cycle

• Autotrophs capture atmospheric $CO_2$ to form high-energy organic compounds using solar energy.

• Carbon is transferred through the food web when consumers ingest producers.

• Organic molecules are broken down during respiration, releasing $CO_2$ back into the atmosphere.

• Example: The carbon from a cow is derived from the plants it consumes, demonstrating how carbon connects organisms through ecological processes.

Carbon Reservoirs

• Carbon is stored in various forms, termed carbon reservoirs:

  • Atmosphere ($CO_2$)

  • Bodies of Water (mostly oceans)

  • Ocean Sediments

  • Soil

  • Rocks (including fossil fuels)

  • Earth’s interior

• Geologic processes, such as subduction, can sequester carbon into the Earth as $CO_2$ is released during volcanic eruptions.

The Nitrogen Cycle

• Nitrogen Incorporation:

  • Most organisms cannot utilize atmospheric nitrogen ($N_2$, comprising approx. 78% of the atmosphere).

  • Nitrogen enters living systems through bacteria that perform nitrogen fixation, converting $N<em>2$ into ammonia ($NH</em>3$) and ultimately into ammonium ($NH<em>4^+$), nitrites ($NO</em>2^-$), and nitrates ($NO_3^-$).

• Importance for Ecosystems:

  • Organic nitrogen is crucial for processes such as primary production.

Nitrogen Cycle Processes

• Bacterial actions recycle nitrogen from organic waste back into nitrogen gas ($N_2$) through denitrification.

• Human Impact on Nitrogen Cycle:

  • Fossil fuel combustion releases nitrogen oxides.

  • Artificial fertilizers contribute to nutrient runoff, resulting in issues like acid rain and eutrophication:

  • Acid Rain: Formed when nitrogen oxides convert to nitric acid ($HNO_3$), affecting ecosystems and infrastructure.

  • Eutrophication: Nutrient runoff stimulates algae blooms, depleting oxygen and harming aquatic life.

The Phosphorus Cycle

• Significance in Biology:

  • Phosphorus is a major component of nucleic acids, phospholipids, and calcium phosphate in bones.

  • Phosphorus occurs as phosphate ions ($PO_4^{3-}$).

  • Often a limiting nutrient for freshwater ecosystems.

Phosphorus Movement

• Phosphates move from oceans to land through various natural processes, often taking thousands of years to cycle between ecosystems.

• Weathering of phosphate-containing rock releases phosphates into ecosystems through leaching, while ocean sediments also provide phosphorus needed for life.

• Human activities, such as fertilizer runoff, contribute to excessive phosphorus in water bodies, leading to issues like algal blooms.

Consequences of Phosphorus Runoff

• Excess phosphorus and nitrogen can lead to:

  • Algal overgrowth

  • Oxygen depletion in aquatic environments

  • Mass deaths of aquatic organisms (dead zones)

The Sulfur Cycle

• Role of Sulfur:

  • Critical for protein formation, especially through the amino acid cysteine.

Sulfur Sources and Processes

• Atmospheric sulfur ($SO_2$) enters through:

  • Organic decomposition

  • Volcanic eruptions and geothermal activity

  • Fossil fuel combustion by humans

• Sulfur is deposited on land through:

  • Precipitation

  • Atmospheric fallout

  • Rock weathering

• Decomposition releases sulfates back into the ecosystems after living organisms die.

Human Impact on the Sulfur Cycle

• Activities such as burning fossil fuels, particularly coal, increase hydrogen sulfide in the atmosphere.

• Acid rain results from sulfur dioxide interacting with rain, causing harm to ecosystems and man-made structures by reducing pH levels.

• The phenomenon of acid rain has led to significant environmental damage, including the erosion of historical monuments.