g - Biogeochemical Cycles Group 7

7/28/2019 g - Biogeochemical Cycles Group 7

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BIOGEOCHEMICAL CYCLES


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Nutrient Cycles in Nature A biogeochemical cycle or nutrient cycle

is a pathway by which a chemical

element or molecule moves throughboth biotic (biosphere) and abiotic

(lithosphere, atmosphere, and

hydrosphere) compartments of Earth.


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It is

Bio because it involves the biota

Geo because it involves the earthsrocks, soil, water and air

Chemicalbecause it involves

chemical nutrients undergoing

changes as they go through the cycle


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Patterns and Components Populations, communities all interact with the

environment.

A key part of the interaction is the cycling of

nutrients through different populations and

trophic levels in an ecosystem; and thru this

the living and non-living world maintains

ecological balance.


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A nutrient cycle is composed of:

Exchange (cycling or available) pool, the fast-

moving part of the cycle which involves the

trophic levels; and Reservoirs (nutrient or unavailable pool),

where the element is accumulated or held for

a long period of time.


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Biogeochemical cycles always involve

equilibrium states :

A balance in the cycling of the element

between compartments.

However, overall balance may involvecompartments distributed on a global

scale.


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Types of Cycles There are two main types of cycles based on

the reservoir of the element.

Gaseous Cycle. This is when the element ismainly stored in the atmosphere or

hydrosphere, e.g. carbon and nitrogen cycles

Sedimentary Cycle. This is when the element

is stored in the lithosphere a sedimentaryrocks, e.g. phosphorus and sulfur cycles


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Systems All chemical elements in

an organism is part of thenutrient cycle.

Closed System. Allnutrients used by theorganism operate on aclosed system, therefore

these chemicals arerecycled instead of beinglost.


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Open System. The energy

of an ecosystem occurs onan open system; the sun

constantly gives the

energy in the form of light

while it is eventually used

and lost in the form of

heat through the trophic

levels of food chains and

webs.


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Water Cycle The water or hydrologic cycle is unique

because water exists in three phases solid,

liquid and gas during the cycles.

Water exists naturally at all temperatures

which occur on earth and can easily change

from form to another.


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Evaporation. Heat causes liquid water to

change to gas (water vapor) and rises to the

atmosphere.

Condensation. As water goes up it reaches a

point where temperature is low and form

droplets called clouds in a process called

condensation.


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Dew which forms earlymorning is condensation

of vapor coming incontact with coldsurfaces.

Fogs are low-lying clouds;occurs whencondensation is close tothe surface as in the caseof highlands.


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Saturation. As more watervapor fills in the

atmosphere, it reaches apoint where it could nolonger hold more vapor.

This is a state calledsaturation.

Humidity refers to theamount of moisture in theatmosphere.


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Precipitation. Droplets of watercondense around dust particles

(the condensation nuclei) untilthey are too large to withstandthe pull of gravity.

When too heavy, they fall to thesurface as precipitates like snow,hailstones or rain.


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Run-off. Precipitates reaching

the surface move down a

body of land as surface waterrun-off through specific paths

as channel flow or move

anywhere as overland flow.

Lakes , streams , ponds and

other forms of surface waterare manifestations of this part

of the water cycle.


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Percolation. Gravity and soil porosity move

some water molecules down to thegroundwater reservoir in a process called

percolation or infiltration.

Capillary action. Increased pressure may

move groundwater upward to become springs

and artesian wells.


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Surface and ground water all flow toward the

sea, which supplies 90 % of all water that thatstart the process of evaporation again.

When temperatures are too high, precipitatesmay evaporate and does not reach the

surface.


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Carbon Cycle In the carbon cycle, plants absorb carbon

dioxide from the atmosphere and use it,

together with water so photosynthesis could

take place.

Carbon molecules are assembled into sugar

and other organic molecules which all living

things need to survive.


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Photosynthesis. Carbon molecules become

part of molecules of carbohydrates and may

later be changed to other organic compounds.

The carbon becomes part of the energy

system for ecosystems, the carbohydrates,

lipids and hydrocarbons being forms of stored

energy.


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Respiration. Carbon molecules travel through

the food chains, with decomposers at any stepof the way.

Oxygen is taken in respiration to oxidizecarbohydrates to transfer energy in the form

of Adenosine triphosphate (ATP) and the

release of carbon dioxide back to the

environment.


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Decomposition. Carbon in animals stay in its

bones as carbonates until they undergo

decomposition after the death or via waste

matter in excretion.

Sedimentation. Bones and shells of calcium

carbonate may accumulate in the lithosphere

by sedimentation as sediments and fossils.


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Combustion. Incineration (combustion) or

burning is a form of rapid oxidation, whichreturns carbon dioxide back to the

atmosphere.

Fossil fuels, cloth, dead bodies, fuel return

carbon dioxide via burning.


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Oxygen Cycle The oxygen cycle involves three main

reservoirs - atmosphere, biosphere, and

lithosphere, with photosynthesis as the main

driving factor.

This explains that the cycles of oxygen and

carbon dioxide are closely linked.


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Photosynthesis.

Oxygen is released

during the light-dependent reactions

when water undergoes

photolysis.

Respiration. Oxygen is

removed from theatmosphere by

respiration; carbon

dioxide is released.


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Decomposition. Bacteria consume oxygen

from the environment as they work during theprocess of decomposition; carbon dioxide is

released.

Oxidation. The slow oxidation process of

rusting and the rapid oxidation process of

combustion remove oxygen from the

environment.


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Flux between Biosphere and Lithosphere.

Marine organisms create calcium carbonate

shells that is rich in oxygen; when they die

their shells are deposited and become

limestone rocks of the lithosphere.

Weathering process can free oxygen from the

lithosphere; plants also extract minerals from

rocks and release oxygen in the process aswell.


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Nitrogen Cycle The nitrogen cycle involves the earths

atmosphere which is about 78 % nitrogen.

Nitrogen is of no use by itself for most living

things and when animals breathe it, it goes

back out again; however, nitrogen is vital to

life when combined with other elements.


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Nitrogen Fixation. Gaseous nitrogen in the

atmosphere is incorporated into the nitrogen-containing compounds and thereby brought

into the soil and the exchange pool.

To a small extent, the abiotic processes of

lightning and flash photography can provide

energy for fixation to occur.


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Most fixation is done bythe biological activities ofnitrogen-fixing bacteria

(e.g. Rhizobium in the rootnodules of legumes) andcyanobacteria (blue-green

algae) of OrderNostocales.

90 % of nitrogen in the soilcomes from biologicalorigin; the rest comes fromchemical fertilizers.


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Ammonification. Soil

bacteria and fungidecomposing dead

matter utilize the

proteins and aminoacids as source of

food, releasing excess

nitrogen as ammonia(NH3) and ammonium

(NH4) in the soil.


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Nitrification. Ammonia orammonium is oxidized by

several species of nitrifyingbacteria in the soil.

One group convertammonia or ammoniuminto nitrite (NO2); in turnanother group converts

nitrites to nitrate (NO3) , aform that could be absorbedby plants


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Absorption and Assimilation. Absorbed

materials are utilized in cell metabolism.

One process converts nitrogen back to

ammonium; ammonium ions formed are

transferred to carbon-containing compoundsto produce amino acids and other nitrogenous

compounds.


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Denitrification. Denitrifying bacteria

especially in boggy, poorly aerated soil, reducethe nitrates to gaseous nitrogen, thus

returning it to the atmospheric reservoir.

Note that in almost every step of the cycle,

microorganisms are involved.


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Weathering and Erosion. Phosphates in rocks

gets exposed to the surface and gets carried

away by the erosive action of water.

Leaching. Phosphorus together with otherminerals get carried by flowing water from the

soil and gets transferred to soil and streams

on their way to the sea.


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Phosphorus in food chain. Phosphorus in thewater may get into the flesh of aquatic

invertebrates, then to small vertebrates, then

to other predators by ingestion.

Excretion and Decomposition. Phosphorus

within the living body can be released viaexcretion of waste; or when a dead body

undergoes decomposition.


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Guano (Quechua 'wanu', via Spanish) is thewaste (feces and urine) of cave dwelling

insectivorous bats, seabirds, and seals.

Guano manure is an effective fertilizer and

gunpowder ingredient due to its high levels ofphosphorus and nitrogen.

Soil that is deficient in organic matter can bemade more productive by addition of thismanure.


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Human Interference.Human interference in

the cycle occurs byoveruse or careless useof phosphorusfertilizers.

This results in increasedamounts of phosphorus

as pollutants in bodiesof water resulting ineutrophication.


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Chemosynthesis. Plants cannot use elemental

sulfur, so all living things depend upon

chemoautotrophic bacteria to oxidizeelemental sulfur to sulfates, which then could

become organic sulfur (as part of proteins)

that goes with the food chains and webs.

Excretion and Decomposition return sulfur

back to the lithosphere.


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Earth constantly receives energy

from the sun, it's chemical

composition is essentially fixed,

as additional matter is onlyoccasionally added by

meteorites.


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END of LESSON

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