Nutrient Cycles

1. Nutrient Cycles Carbon, Nitrogen and Phosphorus cycles

2. Nutrients • Nutrients are chemicals that are required for plant and animal growth and other life processes • Nutrients are accumulated for short or long periods of time in Earth’s atmosphere, oceans and land masses • Scientists refer to these accumulations as STORES • Biotic and abiotic processes can cause nutrients to flow in and out of stores  this continuous flow of nutrients are called nutrient cycles

3. Nutrient Cycles • There are 5 chemical elements (nutrients) that limit the amount of life possible in an ecosystem: • Carbon • Hydrogen • Oxygen • Nitrogen • These four are cycled between living organisms and the atmosphere • Phosphorus • Enters the environment from sedimentary rock

4. Carbon Cycle • All living things contain billions of carbon atoms in their cells • Carbon is an essential component in the chemical reactions that sustain life, such as cellular respiration

5. Where Carbon is stored • Short term carbon stores include: • Vegetation on land • Plants in oceans • Land-based and marine animals • Decaying organic matter in soil • In the atmosphere as carbon dioxide (CO2) • In the top layers of the ocean in its dissolved form • Long term carbon stores include: • In the middle and deep layers of the ocean as dissolved CO2 • Coal deposits • Oil and gas deposits • Coal, oil and gas are fossil fuels that are formed from dead plants and animals • Marine sediments and sedimentary rock • This is the largest long-term carbon store

6. How Carbon is cycled • There are several ways in which carbon is cycled through ecosystems, including: • Photosynthesis • Cellular respiration • Decomposition • Ocean processes • Natural events • Volcanoes • Large-scale forest fires

7. Photosynthesis • Photosynthesis is a chemical reaction that converts solar energy into chemical energy During photosynthesis, carbon (in the form of CO2 in the atmosphere) enters through the plants and reacts with water in the presence of sunlight to produce carbohydrates and oxygen Energy + 6 CO2 + 6 H2O  C6H12O6 + 6 O2

8. Cellular Respiration • Cellular respiration is the process in which both plants and animals release CO2 back into the atmosphere by converting carbohydrates and oxygen into CO2 and water • During cellular respiration, energy is released within the cells of organisms and can be used for growth, repair and reproduction. • CO2 gas is released as a waste product • C6H12O6 + 6 O2 6CO2 + 6 H2O + energy

9. Decomposition • Decomposition is the breaking down of dead organic matter Decomposers, such as bacteria and fungi, convert organic molecules back into CO2, which is released into the atmosphere

10. Ocean Currents • CO2 dissolves in the cold ocean waters found at high latitudes • The cold water sinks and moves slowly in deep water currents towards the tropics • In the warm tropics, the water rises as it warms and mixes with the middle and top layers of the ocean • At the surface, some CO2 is released to the tropical atmosphere while the ocean currents move the warmed water back towards the polar areas

11. Natural Events • Some carbon dioxide is released from volcanoes • Some carbon dioxide is slowly released from decomposing trees • Some carbon dioxide is rapidly released during forest fires

12. Human Activities and Carbon • Human activities that impact the carbon cycle include: • Industry • Motorized transportation • Land clearing • Agriculture • Urban expansion • Since the Industrial Revolution (1850s) the amount of CO2 in the atmosphere has increased by 30% • It only increased ~ 3% during the previous 160,000 years!

13. Global Warming • Human activities that involve burning fossil fuels have reintroduced carbon into the cycle that was removed from it long ago • So much carbon is released so quickly that the natural carbon cycle can no longer move all of it into stores • CO2 that is stored in the atmosphere (because it has no where else to go) is a greenhouse gas, which contributes to global warming 

14. Nitrogen Cycle • Nitrogen is an important component of DNA and proteins, which are essential for the life processes that take place inside cells • Nitrogen is essential for muscle function in animals and for growth in plants

15. How Nitrogen is Stored • The largest store of nitrogen is in the atmosphere as nitrogen gas (N2) • Other major stores of nitrogen include oceans and organic matter in soil • Smaller stores include living organisms, lakes and marshes

16. How Nitrogen is Cycled • Most organisms cannot use nitrogen in the form of N2, so much of the nitrogen cycle involves processes that make nitrogen available to plants and animals • Some of these processes include: • Nitrogen fixation (when nitrogen gas (N2) is converted into compounds that contain either nitrate (NO3) or ammonium (NH4) • In the atmosphere • In the soil • In water bodies • Nitrification (when ammonium (NH4) is converted into nitrate (NO3) • Uptake

17. Nitrogen Fixation • Nitrogen fixation in the atmosphere occurs when lightning converts N2 into NO3 compounds • This NO3 then enters terrestrial and aquatic ecosystems through the rain • Nitrogen fixation in the soil occurs when nitrogen-fixing bacteria that lives in the root nodules of legumes and other plants converts N2 into NH4 • The plants supply the bacteria with food (sugars) and the bacteria supply the host with nitrogen needed for growth • Nitrogen fixation in water bodies occurs when certain species of cyanobacteria fix N2 into NH4 • Nitrogen-fixing cyanobacteria make these nitrogen compounds available to plants in the surface waters of oceans, wetlands and lakes

18. Nitrification and Uptake • Nitrification is when NH4 is converted into NO3 This occurs in two steps: • Certain species of nitrifying bacteria in the soil convert NH4 into NO2 (nitrite) • Different species of nitrifying bacteria in the soil then convert the NO2 into NO3 (nitrate) • Once nitrate is available it can enter plant roots and eventually be incorporated into plant proteins • When these plants are consumed by herbivores and omnivores, they incorporate nitrogen into the proteins in their tissues • Some types of decomposers can take the nitrogen trapped in the DNA of dead organisms and convert it back into NH4 to be re-nitrified

19. How Nitrogen is Returned • Nitrogen is returned to the atmosphere in a process called DENITRIFICATION • In a series of chemical reactions, denitrifying bacteria convert nitrate (NO3) back into nitrogen gas (N2) • Nitrogen is also returned to the atmosphere as ammonia (NH3) in volcanic ash, nitrogen oxide and nitrogen dioxide • NO3 and NH4that are not taken up by plants mix with rainwater and are washed from the soil into ground water and streams • This unused nitrogen may settle to ocean, lake or river bottoms in sediments • Eventually these sediments will form rock and the nitrogen will be trapped until centuries of weathering releases it back into the water

20. Human Activities and Nitrogen • Human activities have doubled the available nitrogen in the biosphere in the past 50 years • Millions of tonnes of nitrogen are added in the form of NO and NO2 as a result of fossil fuel combustion • Clearing forests and grasslands by burning also releases trapped nitrogen into the atmosphere • These compounds eventually return to terrestrial and aquatic ecosystems as acid rain (HNO3)  • Chemical fertilizers that fix N2 into nitrogen compounds that crops can use are used in agriculture • The excess nitrogen that is not used can escape back into the atmosphere or can be washed or leached from the soil and end up in water systems • This can can lead to algae blooms, which deprive other aquatic plants of sunlight and oxygen, causing death

21. Phosphorus Cycle • Phosphorus is essential for a variety of life processes in plants and animals • In plants, phosphorus contributes to root development, stem strength and seed production • In humans, a large amount of phosphorus is found in bones

22. How Phosphorus is Stored • Phosphorus is NOT stored in the atmosphere as a gas  it is trapped in phosphate (PO4, HPO4, and H2PO4) • This phosphate is found in phosphate rocks and in the sediments of ocean floors

23. Where Phosphorus comes from • Weathering (the process of breaking down rock into smaller fragments) releases phosphate into the soil • Chemical weathering is when a chemical reaction causes phosphate rocks to break down and release phosphate into the soil • Physical weather is when processes, such as wind, rain, and freezing, release particles of rock and phosphate into the soil

24. How Phosphorus is Cycled • On land, plants take up phosphate through their roots and animals obtain phosphate by eating the plants • Decomposers break down animal waste and dead organisms, returning the phosphorus to the soil to become available to the producers again • In aquatic ecosystems, phosphate enters as a result of erosion, leaching, and run-off • Water plants take up some dissolved phosphate and pass it through the aquatic food chain • Most phosphate in run-off settles on lake and ocean bottoms • This sediment will eventually form sedimentary rock, and the phosphorus will remain trapped for millions of years • Only when layers of rock become exposed will the phosphorus become available again when the cycle of weathering begins again

25. Human Activities and Phosphorus • Phosphate rock is mined primarily to make commercial fertilizers and detergents • On some islands, guano (bird droppings) is still being mined as a natural fertilizer • Commercial fertilizers, phosphate-containing detergents, animal waste from large-scale livestock farming, some industrial waste, and untreated human sewage all enter the waterways through run-off and leaching • This contributes additional phosphate to the phosphorus cycle • Too much phosphorus can negatively affect species that are sensitive to an overload of this nutrient • Clearing of forests by the slash-and-burn method releases the phosphates contained in the trees in the form of ash, which accumulates in the soil and leaches into run off and settles on ocean bottoms and eventually becomes locked up as sedimentary rock