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BIOGEOCHEMICAL

CYCLES (NUTRIENTCYCLES) - Continuation

Davis, M. L. and Masten, S.J. (2004). Principles of

Environmental Engineering and Science. NY:McGraw Hill (Chapter 4)

Mines, R.O. and Lackey, L.W. (2009). Introduction toEnvironmental Engineering. NJ: Pearson Education.

http://www.starsandseas.com/SAS%20Ecology/SAS%20

chemcycles/ecolcycle.htm


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SULFUR CYCLE

In nature, the primary inorganic form of sulfuris sulfate ion found in natural waters

Elemental sulfur and combined forms of sulfursuch as pyrite FeS2 are found in geologic

deposits Plants are dependent upon bacteria, in this

case chemoautotrophic bacteria, whichoxidizes elemental sulfur to sulfates, as in thefollowing formula

2S + H2O + 3O2 ---> 2H2SO4


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In sanitary sewer systems and wastewater

treatment facilities, sulfate is reduced under

anaerobic conditions to sulfides and

hydrogen sulfide gas (H2S).

In the presence of oxygen, sulfur bacteria

(Thiobacillus) oxidize hydrogen sulfide

converting it to sulfuric acid. H2S + 2O2 H2SO4 (Oxidation)


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Once in the form of sulfate (2H2SO4), plants can

then incorporate the sulfur into proteins.

Sulfate is taken up by plants and microorganisms

for the production of cell tissues. Animals consumeplants and microorganisms for production of cell

tissues.

Upon death, sulfur is released to the environmentthrough degradation of proteins contained in the

plant and animal tissues


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Sulfates and organic matter undergo under

degradation under aerobic or anaerobic

conditions (microbially mediated or in the

presence of Desulfovibrio) to form H2S. Theprocess is reduction.


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Proteins are not only made from carbon and

nitrogen, but many important proteins also

contain sulfur.

Sulfur is also an important component ofcoenzyme A, which is used to produce

energy in cellular respiration.

So the availability of sulfur is essential tomaintaining life.


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PHOSPHORUS CYCLE Organic compounds containing phosphorus

are found in all living organisms (no gaseouscomponent)

Inorganic phosphorus occurs naturally in soils

and rocks as calcium phosphate and calcium

hydroxyapatite

Wastewater discharges from industrial and

municipal wastewater treatment plants and

agricultural runoff from fertilizers are majorcontributors of phosphorus release to

environment


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The keystone of getting phosphorus into

trophic systems are plants.

Plants absorb phosphorous from water and

soil into their tissues, tying them to organicmolecules.

Once taken up by plants, phosphorus is

available for animals when they consume theplants.


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When plants and animals die, bacteria

decomposes their bodies, releasing some of

the phosphorus back into the soil.

Once in the soil, phosphorous can be moved100s to 1,000s of miles from were they were

released by riding through streams and

rivers. So the water cycle plays a key role of moving

phosphorus from ecosystem to ecosystem.


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Phosphorous in unpolluted waters is importedthrough dust in precipitation or via weathering ofrocks.

Phosphorus is normally present in watersheds in

extremely small amounts as inorganicorthophosphate, suspended as organic colloids,absorbed onto particulate organic and inorganicsediments

In polluted waters, the major source of phosphorus

is from human activities The decomposition of algae releases phosphorus

which is transferred to sediments and toundecomposed organic matter


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In some cases, phosphorous will travel to a

lake, and settle on the bottom.

There, it may turn into sedimentary rocks,

limestone, to be released millions of yearslater.

So sedimentary rocks store or conserve

much of the phosphorus for future eons.


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http://www.starsandseas.com/SAS%20Ecology/SAS%20chemcycles/cycle_phosphorus.htm


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Additional Notes


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CARBON CYCLE Photosynthesis - plants take up CO2and convert it

into organic matter Organic compounds in fossil fuels also come from

photosynthesis (plants)

CO2 is released from fossil fuels by combustion

process Terrestrial (plants and geologic formation)

reservoir of carbon

Ocean- the major carbon sink (reservoir), contains

dissolved CO2, carbonate and bicarbonate ions Cycling of carbon involves release of CO2by animal

respiration, fires, diffusion from oceans, weatheringof rocks, and precipitation of carbonate minerals


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NITROGEN CYCLE

Proteins, nucleic acids, and other organic

chemicals contain nitrogen, so nitrogen is a

very important atom in biological organisms.

Nitrogen makes up 79% of Earth's

atmosphere, but most organisms can not use

nitrogen gas (N2).


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N2 enters the trophic system through a

process called nitrogen fixation. Bacteria

found on the roots of some plants can fix N2

to organic molecules, making proteins. Again,animals get their nitrogen by eating plants


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Animals releases nitrogen in their urine.

Fish releases NH3, but NH3 when concentrated, is

poisonous to living organisms. So organisms must

dilute NH3 with a lot of water. Living in water, fish have no problem with this

requirements, but terrestrial animals have problems.

Animals convert NH3 into urine, or another chemical

that is not as poisonous as NH3. The process ofNH3 release is called ammonification.


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Because NH3 is poisonous, most of the NH3

which is released is untouchable. But soil

bacteria have the ability to assimilate NH3

into proteins. These bacteria effectively eatsthe NH3, and make proteins from it. This

process is called assimilation.


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Some soil bacteria do not convert NH3 intoproteins, but they make nitrate NO3- instead.This process is called nitrification.

Some plants can use NO3-, consumingnitrate and making proteins. Some soilbacteria, however, takes NO3-, and convertsit into N2, returning nitrogen gas back into the

atmosphere. This last process is calleddenitrification, because it breaks nitrateapart.


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Human Influences on the Ecosystem

Ecosystems change naturally but humanactivity can speed up natural processes byseveral magnitudes in terms of time

Examples: Large scale agricultural operations (for food

supply) can result in the release of pesticides,fertilizers and carbon dioxide and other

greenhouse gases to the environment Dam construction for hydroelectric power (a clean,

renewable energy source) can have detrimentaleffects on river ecosystems


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Human activity can also change ecosystems

through destruction of species , where the loss of

habitat can threaten the existence of individual

species (forests)

Localized destruction of the milkweed plant deprives the

butterfly of its nesting environment

Excessive hunting causes the extinction of

species e.g., the manatee whose habitat is the

Everglades is threatened by poaching, also the

rhinoceros is threatened by poaching for its horns


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Introduction of nonnative (exotic) species into the

ecosystems can threaten species e.g., the

introduction of rabbits into Norfolk island resulted

in the loss of 13 species of vascular plants

The release of toxic chemicals can threaten

wildlife e.g., DDT which threatened the existence

of the American bald eagle; DDT uptake fromcontaminated prey results in failure to reproduce

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