3.BIOGEOCHEMICAL CYCLES

Biogeochemical Cycles

• Definition: Biogeochemical cycles describe the movement of elements and compounds between living organisms and the environment.

• Types of Cycles:

  • Gaseous Cycles: Reservoirs are the air or oceans. Examples include nitrogen, oxygen, carbon, and water cycles.

  • Sedimentary Cycles: Reservoirs are found in Earth's crust. Examples include iron, calcium, phosphorus, and sulfur cycles.

• Characteristics of Cycles:

  • Gaseous cycles generally move more rapidly than sedimentary cycles.

  • Local accumulations of gases (e.g., CO2) are quickly balanced by natural processes (e.g., wind, plant uptake).

  • Significant disturbances like global warming can affect these cycles.

• Reservoirs and Exchange Pools:

  • Reservoirs: Where chemicals are stored in large quantities and for long durations (e.g., oceans for water).

  • Exchange Pools: Where chemicals are held temporarily (e.g., clouds for water).

  • Residence Time: The length of time a chemical resides in a reservoir or exchange pool.

Water Cycle

• Importance: Essential for all living organisms, water cycle is critical for maintaining life.

• Hydrosphere: Encompasses all forms of water on Earth (liquid, ice, vapor).

• Processes:

  • Evaporation: Transforming liquid water into vapor, requiring energy (600 calories per gram of water).

  • Transpiration: Release of water vapor from plants, part of evapotranspiration (sweating by organisms).

Oxygen Cycle

• Definition: Involves the transitions of oxygen atoms among different oxidation states through redox reactions across Earth's spheres.

• Key Components:

  • Elemental/diatomic oxygen (O2) is central to many biochemical cycles.

  • Sources include biological processes (photosynthesis) and geological events (lightning).

  • Nitrogen oxides (O3) are produced during lightning events.

Nitrogen Cycle

• Overview: Nitrogen (N2) comprises 79% of the atmosphere; it undergoes conversion through multiple forms, impacting soil and organisms.

• Key Processes:

  • Nitrogen Fixation: Conversion of atmospheric nitrogen into ammonia (NH3) via bacteria (e.g., Rhizobium).

    • Types of Nitrogen Fixation:

      1. Atmospheric fixation (via lightning)

      2. Industrial fixation (producing ammonia for fertilizers)

      3. Biological fixation (nutrient transformation through bacteria).

  • Nitrification: Ammonia is oxidized into nitrites (NO2-) and then into nitrates (NO3-) by soil bacteria (e.g., Nitrosomonas, Nitrobacter).

  • Assimilation: Plants absorb nitrogen compounds for growth and protein synthesis, entering the food web through herbivores.

  • Ammonification: Decomposition of organic matter releases nitrogen back into the soil as ammonium (NH4+).

  • Denitrification: Conversion of nitrates back to atmospheric nitrogen (N2) by denitrifying bacteria under oxygen-limited conditions.

Phosphorus Cycle

• Overview: Phosphorus moves through the lithosphere, hydrosphere, and biosphere, essential for life but slowly replenished.

• Key Functions:

  • Vital for DNA/RNA nucleotide formation and bone structure.

• Weathering: Phosphorus is released from rocks into soil and water through natural erosion processes.

• Absorption: Plants, fungi, and microorganisms take up phosphorus from the soil and water.

• Return to Environment: When organisms die, decomposition returns phosphorus back into the ecosystem, repeating the cycle.

Law of Conservation of Energy

• Energy is neither created nor destroyed, only transformed between different forms, playing a role in various biogeochemical cycles.

Sulfur Cycle

• Sources of Sulfur: Naturally released from volcanic eruptions and hot springs.

• Atmospheric Presence: Existed primarily as sulfur dioxide (SO2) or transformed into sulfuric acid in the atmosphere.

• Deposition: Returns to Earth through precipitation (acid rain) and enriches soil and water systems.

Biogeochemical Cycles

Definition:

Biogeochemical cycles encompass the intricate movement of essential elements and compounds between living organisms and their surrounding environment. These cycles play a crucial role in sustaining life by ensuring the availability of vital nutrients.

Types of Cycles:

Gaseous Cycles:

• Reservoirs: The primary storage for these gases is found in the atmosphere or oceans.

• Examples: Nitrogen, oxygen, carbon, and water cycles are categorized as gaseous cycles.

Sedimentary Cycles:

• Reservoirs: These cycles feature reservoirs located in the Earth's crust, such as rocks and minerals.

• Examples: Iron, calcium, phosphorus, and sulfur cycles exemplify sedimentary cycles.

Characteristics of Cycles:

• Gaseous cycles generally exhibit a more rapid movement compared to sedimentary cycles, due to the less complex interactions occurring in the atmosphere.

• Local accumulations of gases (e.g., carbon dioxide) are quickly balanced by natural processes, such as wind dispersion and plant uptake, effectively regulating greenhouse gas concentrations.

• Significant disturbances, such as global warming, can have profound effects on these cycles by altering temperature and precipitation patterns, thereby influencing biological activities.

Reservoirs and Exchange Pools:

• Reservoirs: These are large storage areas where chemicals exist in substantial quantities for extended periods (e.g., oceans serve as reservoirs for water).

• Exchange Pools: These are temporary holding areas for chemicals, where they may enter and exit rapidly (e.g., clouds represent exchange pools for water).

• Residence Time: This term refers to the duration a chemical remains in a reservoir or exchange pool, which can vary significantly among different elements and their cycles.

Water Cycle

Importance:

The water cycle is indispensable for all living organisms, as it regulates weather patterns and supports ecosystems. Furthermore, it helps in maintaining temperature and resource distribution across the planet.

Hydrosphere:

• The hydrosphere encompasses all forms of water on Earth, including liquid water, ice, and water vapor, and its interactions are vital for life.

Processes:

• Evaporation: This process transforms liquid water into vapor, requiring energy (about 600 calories per gram of water) to overcome molecular forces, playing a key role in climate regulation.

• Transpiration: Involves the release of water vapor from plants into the atmosphere, contributing to evapotranspiration, comparable to sweating in animals, which aids in cooling and nutrient transport.

Oxygen Cycle

Definition:

The oxygen cycle involves the transitions of oxygen atoms through various oxidation states via redox (reduction-oxidation) reactions, facilitating vital processes across Earth's ecosystems.

Key Components:

• Elemental/diatomic oxygen (O2) serves as a critical element in numerous biochemical cycles, crucial for cellular respiration in animals and photosynthesis in plants.

• Sources: Oxygen is primarily produced through biological processes such as photosynthesis, while geological events (e.g., lightning) also contribute by generating nitrogen oxides (NO3) and ozone (O3).

Nitrogen Cycle

Overview:

The nitrogen cycle is vital for converting atmospheric nitrogen (N2), which comprises 79% of the atmosphere, into biologically usable forms that nurture soil and organisms. This cycle includes multiple transformation processes.

Key Processes:

• Nitrogen Fixation: This process converts atmospheric nitrogen into ammonia (NH3) through specialized bacteria (e.g., Rhizobium), making nitrogen accessible to plants. It occurs via various mechanisms:

  • Atmospheric fixation (triggered by lightning)

  • Industrial fixation (production of ammonia for fertilizers)

  • Biological fixation (conversion by nitrogen-fixing bacteria).

• Nitrification: This involves the oxidation of ammonia into nitrites (NO2-) and subsequently into nitrates (NO3-) by soil bacteria (e.g., Nitrosomonas, Nitrobacter), facilitating plant uptake.

• Assimilation: Plants absorb nitrogen compounds (nitrates) for growth and protein synthesis, which allows nitrogen to enter the food web through herbivores.

• Ammonification: In this process, the decomposition of organic matter returns nitrogen to the soil as ammonium (NH4+), enriching the soil nutrient content.

• Denitrification: This process converts nitrates back to atmospheric nitrogen (N2) through denitrifying bacteria, particularly under oxygen-limited conditions, thus completing the cycle.

Phosphorus Cycle

Overview:

The phosphorus cycle illustrates the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Although essential for life, phosphorus is slowly replenished, making its cycle crucial for ecosystem health.

Key Functions:

• Phosphorus is vital for the formation of DNA/RNA nucleotides and contributes to bone structure in vertebrates, playing a significant role in energy transfer via ATP.

• Weathering: Phosphorus is released from rocks into soil and water through natural processes such as erosion, weathering, and leaching.

• Absorption: Plants, fungi, and microorganisms absorb phosphorus from soil and water, facilitating biological growth and energy transfer.

• Return to Environment: Upon the death and decomposition of organisms, phosphorus is cycled back into the ecosystem, allowing for continual nutrient availability.

Law of Conservation of Energy

The principle states that energy is neither created nor destroyed but transforms between various forms, playing a critical role across biogeochemical cycles, affecting processes like photosynthesis and respiration.

Sulfur Cycle

Sources of Sulfur:

Sulfur is naturally released into the environment through volcanic eruptions and hot springs, contributing significantly to global sulfur availability.

Atmospheric Presence:

In the atmosphere, sulfur primarily exists as sulfur dioxide (SO2), which can be transformed into sulfuric acid (H2SO4) through atmospheric reactions, leading to acid rain formation.

Deposition:

Sulfur compounds return to Earth via precipitation (acid rain), enriching soil and aquatic systems, ultimately influencing plant growth and ecosystem dynamics.