Biogeochemical Cycles

Biogeochemical Cycles

Definition

  • Biogeochemical Cycle: The complete path a chemical takes through Earth's four major reservoirs:

    • Atmosphere: Layer of gases surrounding Earth.

    • Lithosphere: Outer layer of Earth, approx. 100 km thick.

    • Hydrosphere: Water portion including freshwater, oceans, glaciers, groundwater, and atmospheric water.

    • Biosphere: Parts of the planet where life exists, sustaining life systems.

Basic Concepts

  • Bio: Involves life.

  • Geo: Includes atmosphere, hydrosphere, rocks, and soil.

  • Chemical: Involves cycling of chemicals.

Chemical Elements and Their Cycling

  1. Quick Cycling Elements: (e.g., O, N)

    • Regenerated easily for biological activity.

    • Present in a gas phase and easily dissolved in water.

  2. Slow Cycling Elements: (e.g., P)

    • Tied up in immobile forms, returned slowly through geological processes.

    • Lack significant concentrations in the atmosphere; relatively insoluble in water.

Life and Chemical Requirements

  • Chemicals in Life: 24 out of over 103 chemicals required for life.

  • Macronutrients: Required in large amounts (C, H, O, N, P, S).

  • Micronutrients: Required in small amounts (e.g., B, Cu, Mo).

  • Toxicity: Some elements toxic at low concentrations (e.g., Hg), while essential elements can be toxic at high concentrations (e.g., Cu).

Atomic Weight and Nutrient Evolution

  • Most nutrients have light atomic weights; iodine is the heaviest micronutrient.

  • Life evolution has altered biogeochemical cycles, impacting planet conditions.

  • Continuation of these processes is vital for maintaining life on Earth.

Geological Cycle

  • Geologic Cycle: Processes forming and changing Earth materials.

  • Encompasses:

    • Tectonic cycle

    • Rock cycle

    • Hydrologic cycle

Tectonic Cycle

  • Involves the creation/destruction of Earth’s lithosphere.

  • Plates move relative to each other at rates of 2-15 cm/year, driven by internal heat.

  • Impacts:

    • Change in continent position, size, and shape.

    • Alter ocean and atmospheric circulation patterns, causing environmental changes.

    • Form ecological islands leading to new species development.

Types of Plate Boundaries

  • Convergent Boundaries: Plates collide.

    • Oceanic crust is subducted beneath continental crust, leading to volcanism (e.g., Andes Mountains).

  • Divergent Boundaries: Plates separate, creating new lithosphere (e.g., Atlantic Ocean).

  • Transform Boundaries: Plates grind past each other without creating or destroying lithosphere (e.g., San Andreas Fault).

The Rock Cycle

  • Processes that create igneous, sedimentary, and metamorphic rocks.

  • Serves as a carbon sink (e.g., coal formation).

  • Elements like calcium can be incorporated (e.g., limestone).

The Hydrologic Cycle

  • Transfers water from oceans to atmosphere to land and back.

  • Components:

    • Evaporation, precipitation, transpiration, surface runoff, storage on land.

  • Driven by solar energy; water distribution:

    • Oceans: 97%, Glaciers/Ice caps: 2%, Groundwater: 0.8%, Lakes/Rivers: 0.01%, Atmosphere: 0.001%.

  • Environmental implications of uneven water distribution.

The Carbon Cycle

  • Atmospheric Carbon: Exists as CO2 and CH4.

  • Removed by photosynthesis and diffusion; introduced by respiration, wildfires, fossil fuel burning, and volcanic eruptions.

  • Hydrospheric Carbon: Exists as dissolved CO2; removed through photosynthesis and introduced via rivers/wind.

  • Biospheric Carbon: Plants uptake C via photosynthesis; decomposition returns CO2 to the atmosphere.

  • Lithospheric Carbon: Organic material compression forms coal; marine systems lead to oil and gas formation.

The Phosphorus Cycle

  • Atmospheric Phosphorus: Exists as small dust particles; no gaseous phase.

  • Hydrospheric Phosphorus: Forms insoluble compounds, transported to oceans through rivers; agricultural waste runoff can introduce phosphates, leading to eutrophication.

  • Biospheric Phosphorus: Taken up by plants; returned through bird guano.

  • Lithospheric Phosphorus: Exists as phosphates; combines with minerals; slow transfer compared to carbon or nitrogen.