Detailed Notes on Nitrogen and Phosphorous Cycles

Nitrogen Cycle

  • N₂ Fixation:

    • Conversion of nitrogen gas (N₂) to ammonia (NH₄⁺) by nitrogen-fixing bacteria.
    • These bacteria are found on plant roots and in the soil.
    • Cyanobacteria and phytoplankton also contribute to nitrogen fixation.

  • Nitrification:

    • Conversion of ammonia (NH₄⁺) to nitrites (NO₂) and nitrates (NO₃⁻) by nitrifying bacteria in the soil.
    • Nitrates (NO₃⁻) can then be used by plants.

  • Denitrification:

    • Conversion of nitrites (NO₂) and nitrates (NO₃⁻) back into nitrogen gas (N₂) by denitrifying bacteria.
    • Nitrogen gas (N₂) diffuses back into the atmosphere.

  • Biotic Components:

    • Nitrogen-fixing bacteria in nodules and soil.
    • Plants take up nitrates (NO₃⁻).
    • Dead organisms and animal waste.
    • Decomposers break down organic matter.
    • Nitrifying bacteria convert ammonia to nitrites and nitrates.
    • Denitrifying bacteria convert nitrites and nitrates back to nitrogen gas.

  • Human Activities & Runoff:

    • Runoff from human activities affects the nitrogen cycle.

Excess Nitrogen & Algae Blooms

  • Fertilizers Impact:

    • Excess nitrogen from fertilizers causes algae blooms.

  • Decomposition & Oxygen Depletion:

    • When algae die, they are decomposed by bacteria.
    • This decomposition process consumes oxygen, potentially leading to oxygen depletion in the water.

  • Harmful Effects:

    • Oxygen depletion can kill fish and other aquatic life.

Acid Rain

  • Sources of Acidic Gases:

    • Burning coal and other fossil fuels releases sulfur dioxide (SO₂), nitrogen oxides (NO₂), and carbon dioxide (CO₂).

  • Formation of Acid Rain:

    • These gases combine with atmospheric water droplets to form acids.

  • Environmental Impact:

    • Acid rain destroys plants, pollutes water sources and soil, and erodes buildings.

Phosphorous Cycle

  • Biotic Cycle:

    • Phosphorus is cycled from the soil to producers (plants).
    • It then moves from producers to consumers (organisms).
    • When organisms die, decomposers return phosphorus to the soil.

  • Components:

    • Mineable rock contains phosphorus.
    • Sewage treatment plants can be a source of phosphorus.
    • Fertilizers contain phosphorus.
    • Phosphate is found in soil and in solution.
    • Plant and animal wastes are part of the cycle.
    • Detritus (dead organic matter) contributes to the cycle.