Chapter 23Chapter 23Pathways of Elements in Pathways of Elements in

EcosystemsEcosystems

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No student presentations No student presentations todaytoday

BackgroundBackground

Cycling of elements and flux of energy in Cycling of elements and flux of energy in ecosystems are fundamentally different:ecosystems are fundamentally different: chemical elements are reused repeatedly (what is chemical elements are reused repeatedly (what is

that process?)that process?) energy flows through the system only once – energy flows through the system only once –

while chemical elements remain within the systemwhile chemical elements remain within the system

Many aspects of elemental cycling make sense Many aspects of elemental cycling make sense only when we understand that chemical only when we understand that chemical transformations and energy transformations go transformations and energy transformations go hand in hand.hand in hand.

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We know…We know…

Energy: lost as heatEnergy: lost as heat

Chemical elements: remain within the Chemical elements: remain within the biosphere – where they cycle continually biosphere – where they cycle continually between organisms and the physical between organisms and the physical environmentenvironment

Inorganic compounds: used by organisms to Inorganic compounds: used by organisms to synthesize organic compounds, then recycled synthesize organic compounds, then recycled over and over before being lost in sediments, over and over before being lost in sediments, streams, and groundwater or escaping to the streams, and groundwater or escaping to the atmosphere as gasesatmosphere as gases

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Energy transformation and Energy transformation and element cycling: linkedelement cycling: linked

Assimilatory processes:Assimilatory processes: incorporate inorganic forms of elements into incorporate inorganic forms of elements into

organic forms, requiring energyorganic forms, requiring energy example: photosynthesis (reduction of example: photosynthesis (reduction of

carbon)carbon)

Dissimilatory processes:Dissimilatory processes: transform organic forms of elements into transform organic forms of elements into

inorganic forms, releasing energyinorganic forms, releasing energy example: respiration (oxidation of carbon)example: respiration (oxidation of carbon)

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Energy transformations and Energy transformations and element cycling are linked.element cycling are linked.

Not all chemical transformations of elements in Not all chemical transformations of elements in ecosystems take place within living organisms. Many ecosystems take place within living organisms. Many reactions occur in the air, soil and water (weathering reactions occur in the air, soil and water (weathering of bedrock, for example, releases potassium, of bedrock, for example, releases potassium, phosphorus, and silicon)phosphorus, and silicon)

Organisms play important roles in cycling Organisms play important roles in cycling of elements when they carry out chemical of elements when they carry out chemical transformations:transformations:

most biological energy transformations are most biological energy transformations are associated with biochemical oxidation and associated with biochemical oxidation and reduction of C, O, N, and Sreduction of C, O, N, and S

these assimilatory and dissimilatory processes these assimilatory and dissimilatory processes are often linked, one providing energy for the are often linked, one providing energy for the otherother

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Coupled reactions are the basis of Coupled reactions are the basis of energy flow in ecosystems.energy flow in ecosystems.

A typical coupling of assimilatory/ A typical coupling of assimilatory/ dissimilatory reactions might involve:dissimilatory reactions might involve: oxidation (dissimilation) of carbon in oxidation (dissimilation) of carbon in

carbohydrate (energy-yielding), linked tocarbohydrate (energy-yielding), linked to reduction (assimilation) of nitrate-N to amino-reduction (assimilation) of nitrate-N to amino-

N (energy-requiring)N (energy-requiring)

Some processes may involve many steps.Some processes may involve many steps.

Energy is lost at each step (inefficiency).Energy is lost at each step (inefficiency).

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Energy-releasing / energy-Energy-releasing / energy-requiringrequiring

Energy flows through biochemical Energy flows through biochemical pathwayspathways

Ecosystems may be modeled as Ecosystems may be modeled as linked compartments.linked compartments.

An ecosystem may be viewed as a set of An ecosystem may be viewed as a set of compartments among which elements are compartments among which elements are cycled at various rates:cycled at various rates: photosynthesis moves carbon from an photosynthesis moves carbon from an

inorganic compartment (air or water) to an inorganic compartment (air or water) to an organic compartment (plant)organic compartment (plant)

respiration moves carbon from an organic respiration moves carbon from an organic compartment (organism) to an inorganic compartment (organism) to an inorganic compartment (air or water)compartment (air or water)

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Generalized compartment model of the cycling of elements Generalized compartment model of the cycling of elements within ecosystemswithin ecosystems

Elements move among Elements move among compartments at different rates.compartments at different rates.

Inorganic Inorganic carbon released through carbon released through respiration may be taken up quickly respiration may be taken up quickly through photosynthesis. The organic through photosynthesis. The organic carbon fixed may be respired again quickly carbon fixed may be respired again quickly by plants.by plants.

Organic Organic carbon stored in deposits of coal, carbon stored in deposits of coal, oil, or peat is not readily accessible and oil, or peat is not readily accessible and may remain in storage for millions of years.may remain in storage for millions of years.

Inorganic carbon may also be taken out of Inorganic carbon may also be taken out of circulation for millions of years by circulation for millions of years by precipitation as calcium carbonate in precipitation as calcium carbonate in aquatic systems.aquatic systems.

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A Physical Model for the A Physical Model for the Water CycleWater Cycle

The biosphere contains 1,400,000 The biosphere contains 1,400,000 teratons (TT, 10teratons (TT, 101212 metric tons) of water, metric tons) of water, 97% of which resides in the oceans.97% of which resides in the oceans.

Other water compartments include:Other water compartments include: ice caps and glaciers (29,000 TT)ice caps and glaciers (29,000 TT) underground aquifers (8,000 TT)underground aquifers (8,000 TT) lakes and rivers (100 TT)lakes and rivers (100 TT) soil moisture (100 TT)soil moisture (100 TT) water in atmosphere (13 TT)water in atmosphere (13 TT) water in living things (1 TT)water in living things (1 TT)

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Global water cycle; units Global water cycle; units in billion billion grams in billion billion grams (10^18)(10^18)

The water cycle is solar-The water cycle is solar-powered.powered.

The water cycle consumes one-fourth of the total The water cycle consumes one-fourth of the total solar energy striking the earth during a year:solar energy striking the earth during a year: precipitation over land exceeds evaporation by 40 precipitation over land exceeds evaporation by 40

teratons/yr; surplus returns to the ocean in riversteratons/yr; surplus returns to the ocean in rivers evaporation over the oceans exceeds precipitation by evaporation over the oceans exceeds precipitation by

40 teratons/yr; surplus is delivered by winds to the 40 teratons/yr; surplus is delivered by winds to the land massesland masses

Can calculate the energy that drives the Can calculate the energy that drives the global hydrologic cycleglobal hydrologic cycle Total weight of water evaporated (456 tt/year) * energy Total weight of water evaporated (456 tt/year) * energy

required to evaporate 1 g of water (2.24 kJ)required to evaporate 1 g of water (2.24 kJ) = ~10 to the 21= ~10 to the 21stst power kJ/yr = 32 billion megwatts power kJ/yr = 32 billion megwatts ¼ of the total energy of the sun’s radiation strking the ¼ of the total energy of the sun’s radiation strking the

earthearth

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Residence time?Residence time?

(remember?)(remember?)

Ecological efficiencies describe what Ecological efficiencies describe what proportion of the energy assimilated by proportion of the energy assimilated by plants eventually reaches each higher plants eventually reaches each higher trophic level of an ecosystemtrophic level of an ecosystem

Rate of transfer of energy between trophic Rate of transfer of energy between trophic levels = residence timeslevels = residence times Provides a second index to the energy Provides a second index to the energy

dynamics of an ecosystemdynamics of an ecosystem

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The water cycle is solar-The water cycle is solar-powered.powered.

The residence time of water varies by The residence time of water varies by compartment.compartment. Residence time of water = average time a water Residence time of water = average time a water

molecule will spend in that compartment; measure of molecule will spend in that compartment; measure of the average age of the water in that reservoirthe average age of the water in that reservoir

The atmosphere contains 2.5 cm of moisture at any The atmosphere contains 2.5 cm of moisture at any time; annual flux into and out of the atmosphere is time; annual flux into and out of the atmosphere is 65 cm/yr:65 cm/yr: residence time is compartment size/flux, or 2.5 cm / 65 residence time is compartment size/flux, or 2.5 cm / 65

cm/yr = 0.04 yr, about 2 weeks. (for water to condense and cm/yr = 0.04 yr, about 2 weeks. (for water to condense and fall as rain)fall as rain)

Soils, rivers, lakes and oceans have same flux rates Soils, rivers, lakes and oceans have same flux rates as atmosphere, but they contain about 100,000 as atmosphere, but they contain about 100,000 times as much water, yielding a mean residence times as much water, yielding a mean residence time of 2,800 yrtime of 2,800 yr..

Groundwater can spend 10,000 yrs beneath the Earth’s Groundwater can spend 10,000 yrs beneath the Earth’s surface; fossil water surface; fossil water

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Human activitiesHuman activities

Human activities that alter the water cycle include:Human activities that alter the water cycle include:

agriculture agriculture

industryindustry

alteration of the chemical composition of the alteration of the chemical composition of the atmosphereatmosphere

construction of damsconstruction of dams

deforestation and afforestationdeforestation and afforestation

removal of groundwater from wellsremoval of groundwater from wells

UrbanizationUrbanization

-- climate change -- -- climate change --

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The carbon cycle is linked to The carbon cycle is linked to global energy flux.global energy flux.

The carbon cycle is the focal point of The carbon cycle is the focal point of biological energy transformations.biological energy transformations.

Principal classes of carbon-cycling Principal classes of carbon-cycling processes:processes: assimilatory/dissimilatory processes assimilatory/dissimilatory processes

(mainly photosynthesis and respiration)(mainly photosynthesis and respiration) exchange of COexchange of CO22 between atmosphere and between atmosphere and

oceansoceans sedimentation of carbonatessedimentation of carbonates

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Global carbon cycle; Global carbon cycle; units in billions of units in billions of metric tons or gigatons metric tons or gigatons (GT) and GT/yr(GT) and GT/yr

First class of carbon cycling: First class of carbon cycling: Photosynthesis and RespirationPhotosynthesis and Respiration

Approximately 85 GT of carbon enter into Approximately 85 GT of carbon enter into balanced assimilatory/dissimilatory balanced assimilatory/dissimilatory transformations each year.transformations each year.

Total global carbon in organic matter is Total global carbon in organic matter is about 2,650 GT (living organisms plus about 2,650 GT (living organisms plus organic detritus and sediments).organic detritus and sediments).

Residence time for carbon in biological Residence time for carbon in biological molecules = 2,650 GT / 85 GT/yr = 31 years.molecules = 2,650 GT / 85 GT/yr = 31 years.

Figure 23.5 – good representationFigure 23.5 – good representation

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Second class of carbon cycling: Second class of carbon cycling: Ocean-Atmosphere ExchangeOcean-Atmosphere Exchange

Exchange of carbon across the atmosphere-ocean Exchange of carbon across the atmosphere-ocean interface links carbon cycles of terrestrial and aquatic interface links carbon cycles of terrestrial and aquatic ecosystems.ecosystems.

Oceans contain 50 times as much CO2 as the Oceans contain 50 times as much CO2 as the atmosphere (oceans as sink. Oceans as source?)atmosphere (oceans as sink. Oceans as source?)

Dissolved carbon pool is 30,000 GT, nearly 50 X that of Dissolved carbon pool is 30,000 GT, nearly 50 X that of atmosphere (640 GT).atmosphere (640 GT).

Net atmospheric flux (assimilation/ dissimilation and Net atmospheric flux (assimilation/ dissimilation and exchange with oceans) is 119 GT/yr for mean exchange with oceans) is 119 GT/yr for mean atmospheric residence time (640 GT / 119 GT/yr) of atmospheric residence time (640 GT / 119 GT/yr) of about 5 years.about 5 years.

By 1990: combustion of fossil fuels -> 6 GT / year = ~ By 1990: combustion of fossil fuels -> 6 GT / year = ~ 1% of total atmospheric carbon dioxide1% of total atmospheric carbon dioxide

Read up on climate change - againRead up on climate change - again21

Third class of carbon cycling: Third class of carbon cycling: Precipitation of CarbonatesPrecipitation of Carbonates

Precipitation (and dissolution) of Precipitation (and dissolution) of carbonates occurs in aquatic systems:carbonates occurs in aquatic systems: precipitation (as calcium and magnesium precipitation (as calcium and magnesium

carbonates) leads to formation of limestone carbonates) leads to formation of limestone and dolomite rockand dolomite rock turnover of these sediments is far slower than turnover of these sediments is far slower than

those associated with assimilation/dissimilation those associated with assimilation/dissimilation or ocean-atmosphere exchangeor ocean-atmosphere exchange

carbonate sediments represent the single carbonate sediments represent the single largest compartment of carbon on planet largest compartment of carbon on planet (18,000,000 GT)(18,000,000 GT)

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Most of the earth’s carbon is in Most of the earth’s carbon is in sedimentary rocks (southern Texas)sedimentary rocks (southern Texas)

Precipitation of Precipitation of Calcium and Carbon Through the Calcium and Carbon Through the

AgesAges

COCO22 dissolves in water to form carbonic acid, dissolves in water to form carbonic acid, which dissociates into hydrogen, bicarbonate, which dissociates into hydrogen, bicarbonate, and carbonate ions:and carbonate ions:

COCO22 + H + H22O O H H22COCO33

HH22COCO33 H H++ + HCO + HCO33-- 2H 2H++ + CO + CO33

2-2-

Calcium ions combine with carbonate ions to Calcium ions combine with carbonate ions to form slightly insoluble calcium carbonate, which form slightly insoluble calcium carbonate, which precipitates:precipitates:

CaCa2+2+ + CO + CO332-2- CaCO CaCO33

When precipitationWhen precipitation > respiration (as in algal blooms) – calcium > respiration (as in algal blooms) – calcium tends to precipitate out of the systemtends to precipitate out of the system

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Slow Release of Slow Release of Sedimentary Calcium and CarbonSedimentary Calcium and Carbon

Calcium removed from the water column in Calcium removed from the water column in the oceans is replaced by calcium dissolved the oceans is replaced by calcium dissolved from limestone sediments on land by from limestone sediments on land by slightly acidic water of rivers and streams.slightly acidic water of rivers and streams.

Carbon is also slowly released from oceanic Carbon is also slowly released from oceanic sediments as limestone is subducted sediments as limestone is subducted beneath continental plates, and CObeneath continental plates, and CO22 is is outgassed in volcanic eruptions.outgassed in volcanic eruptions.

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Reef-Builders extract carbon Reef-Builders extract carbon from water.from water.

In neutral conditions of marine ecosystems, In neutral conditions of marine ecosystems, extraction of COextraction of CO22 from water column drives from water column drives precipitation of CaCOprecipitation of CaCO33::

CaCOCaCO33 + H + H22O + COO + CO22 Ca Ca2+2+ + 2HCO + 2HCO33--

Reef-building algae and coralline algae Reef-building algae and coralline algae incorporate calcium carbonate into their incorporate calcium carbonate into their hard structures, forming reefs.hard structures, forming reefs.

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Skeleton of caralline algae made of calcium Skeleton of caralline algae made of calcium carbonatecarbonate

Changes in the Carbon Cycle Changes in the Carbon Cycle Over TimeOver Time

Atmospheric COAtmospheric CO22 concentrations have concentrations have varied considerably over earth’s history:varied considerably over earth’s history: during the early Paleozoic era (550-400 Mya), during the early Paleozoic era (550-400 Mya),

concentrations were 15-20 X those at presentconcentrations were 15-20 X those at present concentrations declined to ca. present level by concentrations declined to ca. present level by

300 Mya (during which saw development of 300 Mya (during which saw development of forests on land), then increased again to 5 X forests on land), then increased again to 5 X present level through the early Mesozoic era present level through the early Mesozoic era (250-150 Mya) and have declined gradually (250-150 Mya) and have declined gradually sincesince

early Paleozoic and early Mesozoic eras were early Paleozoic and early Mesozoic eras were extreme greenhouse times (hot temperatures), extreme greenhouse times (hot temperatures), unlikely to be equaled by effects of current unlikely to be equaled by effects of current human enhancement of atmospheric COhuman enhancement of atmospheric CO22

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YesYes

Read: ‘Ecologists in the Field’Read: ‘Ecologists in the Field’

Read it carefully. All of themRead it carefully. All of them

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Nitrogen - A Most Versatile Nitrogen - A Most Versatile Element!Element!

Ultimate source (largest reservoir) of this Ultimate source (largest reservoir) of this essential element is molecular Nessential element is molecular N22 gas in gas in the atmosphere, which can also dissolve in the atmosphere, which can also dissolve in water to some extent.water to some extent.

Nitrogen is absent from native rock.Nitrogen is absent from native rock.

Nitrogen enters biological pathways Nitrogen enters biological pathways through nitrogen fixation:through nitrogen fixation: these pathways are more complicated than these pathways are more complicated than

those of the carbon cycle because nitrogen has those of the carbon cycle because nitrogen has more oxidized and reduced forms than carbonmore oxidized and reduced forms than carbon

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Biological pathways of the Biological pathways of the nitrogen cyclenitrogen cycle

AmmonificationAmmonification

Plants assimilate inorganic nitrogen into Plants assimilate inorganic nitrogen into proteins, which may be passed through proteins, which may be passed through various trophic levels.various trophic levels.

Ammonification (dissimilation of N) is Ammonification (dissimilation of N) is carried out by all organisms:carried out by all organisms: initial step is breakdown of proteins into initial step is breakdown of proteins into

constituent amino acids by hydrolysisconstituent amino acids by hydrolysis carbon (not nitrogen) in amino acids is then carbon (not nitrogen) in amino acids is then

oxidized, releasing ammonia (NHoxidized, releasing ammonia (NH33))

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NitrificationNitrification

Nitrification is oxidation of ammonia:Nitrification is oxidation of ammonia: first step is oxidation of ammonia to nitrite first step is oxidation of ammonia to nitrite

(NO(NO22--), carried out by ), carried out by NitrosomonasNitrosomonas in soil and in soil and

NitrosococcusNitrosococcus in oceans in oceans nitrite is then oxidized to nitrate (NOnitrite is then oxidized to nitrate (NO33

--) by ) by NitrobacterNitrobacter in soil and in soil and NitrococcusNitrococcus in oceans in oceans

nitrification is an aerobic process; the nitrification is an aerobic process; the nitrifying organisms involved are nitrifying organisms involved are chemoautotrophic bacteriachemoautotrophic bacteria

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DenitrificationDenitrification

Denitrification is the reduction of nitrate to Denitrification is the reduction of nitrate to nitric oxide (NO), which escapes as a gas:nitric oxide (NO), which escapes as a gas: occurs in waterlogged, anaerobic soils, oxygen-occurs in waterlogged, anaerobic soils, oxygen-

depleted sediments, and bottom waters in depleted sediments, and bottom waters in aquatic ecosystemsaquatic ecosystems

carried out by heterotrophic bacteria such as carried out by heterotrophic bacteria such as Pseudomonas denitrificansPseudomonas denitrificans

further N-reductions may lead to production of further N-reductions may lead to production of nitrous oxide (Nnitrous oxide (N22O) and molecular nitrogen (NO) and molecular nitrogen (N22), ), both gasesboth gases

denitrification may be one of the principal denitrification may be one of the principal causes of low availability of nitrogen in marine causes of low availability of nitrogen in marine systemssystems

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Nitrogen FixationNitrogen Fixation

Loss of nitrogen to atmosphere by Loss of nitrogen to atmosphere by denitrification is offset by nitrogen denitrification is offset by nitrogen fixation:fixation: fixation is carried out by:fixation is carried out by:

free-living bacteria such as free-living bacteria such as AzotobacterAzotobacter symbiotic bacteria such as symbiotic bacteria such as RhizobiumRhizobium, living in root , living in root

nodules of legumes and other plantsnodules of legumes and other plants cyanobacteriacyanobacteria

N-fixation is an energy-requiring process, N-fixation is an energy-requiring process, with energy supplied by oxidation of organic with energy supplied by oxidation of organic detritus (free-living bacteria), sugars detritus (free-living bacteria), sugars supplied by plants (bacterial symbionts), or supplied by plants (bacterial symbionts), or photosynthesis (cyanobacteria)photosynthesis (cyanobacteria)

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Significance of Nitrogen Significance of Nitrogen FixationFixation

Nitrogen fixation balances denitrification on Nitrogen fixation balances denitrification on a global basis:a global basis: these fluxes amount to about 2% of total these fluxes amount to about 2% of total

cycling of nitrogen through ecosystemscycling of nitrogen through ecosystems

Nitrogen fixation is often very important on Nitrogen fixation is often very important on a local scale:a local scale: N-fixers dominate early colonizers on N-fixers dominate early colonizers on

nitrogen-poor substrates, such as lava flows nitrogen-poor substrates, such as lava flows or areas left bare by receding glaciersor areas left bare by receding glaciers

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Nodules on the roots of Nodules on the roots of soybeans harbor symbiotic soybeans harbor symbiotic

nitrogen-fixing bacterianitrogen-fixing bacteria

Nitrogen and usNitrogen and us

human beings have more than doubled the human beings have more than doubled the annual transfer of nitrogen into biologically annual transfer of nitrogen into biologically available formsavailable forms Chemical fertilizersChemical fertilizers Pollution from vehicles and industrial plantsPollution from vehicles and industrial plants

N2O has risen in the atmosphere as a result of N2O has risen in the atmosphere as a result of agricultural fertilization, biomass burning, agricultural fertilization, biomass burning, cattle and feedlots, and other industrial cattle and feedlots, and other industrial sourcessources

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Human activitiesHuman activities

The impacts of human domination of the nitrogen The impacts of human domination of the nitrogen cycle that we have identified with certainty include:cycle that we have identified with certainty include: Increased global concentrations of nitrous oxide Increased global concentrations of nitrous oxide

(N2O), a potent greenhouse gas, in the atmosphere as (N2O), a potent greenhouse gas, in the atmosphere as well as increased regional concentrations of other well as increased regional concentrations of other oxides of nitrogen (including nitric oxide, NO) that oxides of nitrogen (including nitric oxide, NO) that drive the formation of photochemical smog;drive the formation of photochemical smog;

Losses of soil nutrients such as calcium and potassium Losses of soil nutrients such as calcium and potassium that are essential for long-term soil fertility;that are essential for long-term soil fertility;

Substantial acidification of soils and of the waters of Substantial acidification of soils and of the waters of streams and lakes in several regions;streams and lakes in several regions;

Greatly increased transport of nitrogen by rivers into Greatly increased transport of nitrogen by rivers into estuaries and coastal waters where it is a major estuaries and coastal waters where it is a major pollutant. pollutant.

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consequencesconsequences

human alterations of the nitrogen cycle have:human alterations of the nitrogen cycle have:

* Accelerated losses of biological diversity, * Accelerated losses of biological diversity, especially among plants adapted to low-especially among plants adapted to low-nitrogen soils, and subsequently, the animals nitrogen soils, and subsequently, the animals and microbes that depend on these plants;and microbes that depend on these plants;

* Caused changes in the plant and animal * Caused changes in the plant and animal life and ecological processes of estuarine and life and ecological processes of estuarine and nearshore ecosystems, and contributed to nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries. long-term declines in coastal marine fisheries.

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The Phosphorus CycleThe Phosphorus Cycle

Phosphorous is an essential element, Phosphorous is an essential element, constituent of nucleic acids, cell constituent of nucleic acids, cell membranes, energy transfer systems, membranes, energy transfer systems, bones, and teeth.bones, and teeth.

Phosphorus may limit productivity:Phosphorus may limit productivity: in aquatic systems, sediments act as a in aquatic systems, sediments act as a

phosphorus sink unless oxygen-depletedphosphorus sink unless oxygen-depleted in soils, phosphorus is only readily available in soils, phosphorus is only readily available

between pH of 6 and 7between pH of 6 and 7

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Phosphorus Phosphorus TransformationsTransformations

Phosphorus undergoes relatively few Phosphorus undergoes relatively few transformations:transformations: plants assimilate P as phosphate (POplants assimilate P as phosphate (PO44

3-3-) and ) and incorporate this into organic compoundsincorporate this into organic compounds

animals and phosphatizing bacteria break animals and phosphatizing bacteria break down organic forms of phosphorus and down organic forms of phosphorus and release the phosphorus as phosphaterelease the phosphorus as phosphate

phosphorus does not:phosphorus does not: undergo oxidation-reduction reactions in the undergo oxidation-reduction reactions in the

ecosystemecosystem circulate through the atmosphere, except as dustcirculate through the atmosphere, except as dust

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Phosphorus cyclePhosphorus cycle

The Sulfur Cycle 1The Sulfur Cycle 1

Sulfur is an essential element and, Sulfur is an essential element and, like nitrogen, has many oxidation like nitrogen, has many oxidation states and follows complex chemical states and follows complex chemical pathways.pathways.

Sulfur reduction reactions include:Sulfur reduction reactions include: assimilatory sulfate reduction to organic assimilatory sulfate reduction to organic

forms and dissimilatory oxidation back to forms and dissimilatory oxidation back to sulfate by many organismssulfate by many organisms

reduction of sulfate when used as an reduction of sulfate when used as an oxidizer for respiration by heterotrophic oxidizer for respiration by heterotrophic bacteria in anaerobic environmentsbacteria in anaerobic environments

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The Sulfur Cycle 2The Sulfur Cycle 2

Sulfur oxidation reactions include:Sulfur oxidation reactions include: oxidation of reduced sulfur when used as an oxidation of reduced sulfur when used as an

electron donor (in place of oxygen in water) electron donor (in place of oxygen in water) by photosynthetic bacteriaby photosynthetic bacteria

oxidation of sulfur by chemoautotrophic oxidation of sulfur by chemoautotrophic bacteria that use the energy thus obtained for bacteria that use the energy thus obtained for assimilation of COassimilation of CO22

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Sulfur in Coal and Oil Sulfur in Coal and Oil DepositsDeposits

Iron sulfide (FeS) commonly associated with Iron sulfide (FeS) commonly associated with coal and oil deposits can result in coal and oil deposits can result in environmental problems:environmental problems: oxidation of sulfides in mine wastes to oxidation of sulfides in mine wastes to

sulfate, which combines with water to form sulfate, which combines with water to form sulfuric acid, associated with acid mine sulfuric acid, associated with acid mine drainagedrainage

oxidation of sulfides in coal and oil releases oxidation of sulfides in coal and oil releases sulfates into atmosphere, which then form sulfates into atmosphere, which then form sulfuric acid, a component of acid rainsulfuric acid, a component of acid rain

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Sulfur cycleSulfur cycle

Acidic streams from refuse of Acidic streams from refuse of coal mines (Pennsylvania)coal mines (Pennsylvania)

Microorganisms assume diverse Microorganisms assume diverse roles in element cycles.roles in element cycles.

Decomposition in anaerobic organic Decomposition in anaerobic organic sediments is dependent on certain sediments is dependent on certain specialized microbes, the denitrifiers:specialized microbes, the denitrifiers:

these heterotrophic organisms use oxidized these heterotrophic organisms use oxidized forms of N, S, and Fe as electron acceptors forms of N, S, and Fe as electron acceptors (oxidizers) in the absence of oxygen(oxidizers) in the absence of oxygen

for example, some anaerobic bacteria utilize for example, some anaerobic bacteria utilize nitrate as an alternative electron acceptor for nitrate as an alternative electron acceptor for the oxidation of glucose:the oxidation of glucose:

glucose + NOglucose + NO33-- CO CO22 + H + H22O + OHO + OH-- + N + N22 + energy + energy

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Biological Nitrogen Biological Nitrogen FixationFixation

Biological nitrogen fixation (by bacteria Biological nitrogen fixation (by bacteria and cyanobacteria) is essential to and cyanobacteria) is essential to counterbalancing N losses associated with counterbalancing N losses associated with denitrification.denitrification.

Nitrogen is often implicated as a limiting Nitrogen is often implicated as a limiting nutrient in terrestrial and aquatic systems.nutrient in terrestrial and aquatic systems.

Nitrogen fixation is critical to ecosystem Nitrogen fixation is critical to ecosystem development in primary succession.development in primary succession.

Continued nitrogen input is essential for Continued nitrogen input is essential for long-term health of natural ecosystems.long-term health of natural ecosystems.

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Autotrophic DiversityAutotrophic Diversity

All autotrophs are capable of assimilating All autotrophs are capable of assimilating (reducing) carbon in CO(reducing) carbon in CO22 into organic forms into organic forms (initially glucose):(initially glucose): photoautotrophs accomplish this by capturing photoautotrophs accomplish this by capturing

energy from sun through photosynthesis:energy from sun through photosynthesis: green plants, algae, and cyanobacteria use green plants, algae, and cyanobacteria use

water as an electron donor (reducing agent) and water as an electron donor (reducing agent) and are aerobicare aerobic

purple and green bacteria use Hpurple and green bacteria use H22S or organic S or organic compounds as electron donors and are compounds as electron donors and are anaerobicanaerobic

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ChemoautotrophsChemoautotrophsChemoautrophs Chemoautrophs are not photosynthetic, are not photosynthetic,

reducing inorganic carbon (from COreducing inorganic carbon (from CO22), ), but using energy obtained from aerobic but using energy obtained from aerobic oxidation of inorganic substrates:oxidation of inorganic substrates: methane - methane - Methanosomonas, MethylomonasMethanosomonas, Methylomonas hydrogen - hydrogen - Hydrogenomonas, MicrococcusHydrogenomonas, Micrococcus ammonia - nitrifying bacteria ammonia - nitrifying bacteria Nitrosomonas, Nitrosomonas,

NitrococcusNitrococcus nitrite - nitrifying bacteria nitrite - nitrifying bacteria Nitrobacter, Nitrobacter,

NitrococcusNitrococcus hydrogen sulfide, sulfur, sulfate - hydrogen sulfide, sulfur, sulfate -

ThiobacillusThiobacillus ferrous iron salts - ferrous iron salts - Ferrobacillus, GallionellaFerrobacillus, Gallionella

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Deep-Sea Vent Deep-Sea Vent EcosystemsEcosystems

Deep-sea vent ecosystems are far below Deep-sea vent ecosystems are far below the penetration of any light, dependent the penetration of any light, dependent on chemoautotrophic production:on chemoautotrophic production: hot water coming from vents is charged with hot water coming from vents is charged with

hydrogen sulfide, Hhydrogen sulfide, H22S ; the hot water is their S ; the hot water is their source of energysource of energy

chemoautrophic bacteria use oxygen from chemoautrophic bacteria use oxygen from seawater to oxidize Hseawater to oxidize H22S, then use the energy S, then use the energy thus obtained for assimilatory carbon thus obtained for assimilatory carbon reductionreduction

other members of vent communities (clams, other members of vent communities (clams, worms, crabs, fish) ultimately depend on worms, crabs, fish) ultimately depend on primary production of these bacteriaprimary production of these bacteria

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Living things are intimately Living things are intimately involved in elemental cycles.involved in elemental cycles.

Elements are cycled through ecosystems Elements are cycled through ecosystems primarily because metabolic activities primarily because metabolic activities result in chemical transformations.result in chemical transformations.

Each type of habitat presents a different Each type of habitat presents a different chemical environment, especially with chemical environment, especially with respect to:respect to: presence/absence of oxygenpresence/absence of oxygen possible sources of energypossible sources of energy

Numerous adaptations have arisen to Numerous adaptations have arisen to meet these challenges.meet these challenges.

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ReviewReview

Energy transformations Energy transformations and element cycling and element cycling are intimately linkedare intimately linked

Ecosystems can be Ecosystems can be modeled as a series of modeled as a series of linked compartmentslinked compartments

Water provides a Water provides a physical model of physical model of element cycling in element cycling in ecosystemsecosystems

The carbon cycle is The carbon cycle is closely tied to the flux of closely tied to the flux of energy through the energy through the biospherebiosphere

Nitrogen assumes many Nitrogen assumes many oxidation states in cycling oxidation states in cycling through ecosystemsthrough ecosystems

The phosphorous cycle is The phosphorous cycle is chemically uncomplicatedchemically uncomplicated

Sulfur exists in many Sulfur exists in many oxidized and reduced oxidized and reduced forms.forms.

Microorganisms assume Microorganisms assume diverse roles in element diverse roles in element cyclescycles

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