Nitrogen and Phosphorus Cycles

Nitrogen Cycle

• Nitrogen is essential for DNA and proteins

• It’s stored in oceans, lakes, marshes, soil, and largest store is in the atmosphere-but organisms can’t directly use this form

• Nitrogen must be converted firrst

• Nitrogen fixation: Processes that make nitrogen available to plants

Nitrogen Fixation

• Nitrogen makes up 78% of air but is unuseable

• Nitrogen fixing bacteria in soil converts N2 into forms plants can absorb

• Lightning also fixes nitrogen-provides energy to react with oxygen forming nitrogen compounds that enters through rain

Nitrification

• Occurs when certain nitrifying bacteria convert ammonium into nitrate

• Two stages

  • Ammonium (NH4+) to Nitrite (NO2-)

  • Nitrite (NO2-) to Nitrate (NO3-)

• Nitrates enter plant roots through the process of uptake

• Herbivores eat plants and use nitrogen

Nitrogen Cycling:

• Denitrification: Nitrates are converted back to nitrogen by denitrifying bacteria (released into atmosphere) (opposite of fixation)

• Extra ways nitrogen can leave the cycle

  • Volcanic eruptions release nitrogen back into atmosphere

  • Nitrogen also dissolves in water, enters waterways and washes into lakes and oceans and settle in sediments And trapped in rocks

Human Influences:

• Using fertilizer adds excess nitrates to soil, causing excess nitrogen to be washed away or leaches into waterways

  • Promotes huge growth in aquatic algae called algae blooms

  • Algae consume O and Co2, block sunlight, kill aquatic life and produce neurtoxins

• Burning fossil fuels releases gaseous nitrogen oxides

• Deforestation releases trapped nitrogen and increases acid precipitation

The Phosphorus Cycle:

• Phosphorous is a nutrient essential for the growth and development of organisms

• Cycled through interactions between living and non living things

• Has no atmospheric stage (stored in geosphere)

• Short term cycle: soil to plants to animals to decomposers back to soil

• Long term cycle: minerals wash into oceans, incorporated into limestone and sandstone over millions of years

Weathering:

• Two ways rocks naturally release phosphorus

  • Chemical weathering: acid rain breaks down rocks

  • Physical weathering: wind, water, freezing

• Phosphorus is absorbed by soil and plants and eaten by animals and animal waste is broken down by decomposers returning phosphorus to the soil and water

Human Impacts on the Phosphorus cycle

• Fertilizer use: leads to algal blooms

• Mining, household cleaners/detergents, produce excess phosphorus that leaches and runs off into different systems

Nutrient Cycles and Biodiversity:

• Changes to any three cycles (Carbon, Nitrogen, Phosphorus) can harm biodiversity

• Temperature and water levels change from global warming, drastically altering ecosystems

• Excess nitrogen allows certain plants to outcompete others, reducing species variety

• Earth’s spheres are interconnected meaning one change in one will greatly impact all the other