Nutrient CyclesCarbon, Nitrogen and Phosphorus cycles

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

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

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

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

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

Photosynthesis• Photosynthesis is a chemical reaction that converts solar

energy into chemical energy

During photosynthesis, carbon (in the form of CO2 in the atmosphere) entersthrough the plants and reacts with water in the presence of sunlight to produce carbohydrates and oxygen

Energy + 6 CO2 + 6 H2O C6H12O6 + 6 O2

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 6 CO2 + 6 H2O + energy

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

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

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

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!

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

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

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

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

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

Nitrification and Uptake• Nitrification is when NH4 is converted into NO3

This occurs in two steps:1. Certain species of nitrifying bacteria in the soil convert NH4 into

NO2 (nitrite)2. 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

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 NH4 that 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

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

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

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

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

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

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