Chapter 3 Part II: Matter Cycling in Ecosystems

Unit III: Ecosystem Ecology

I. Nutrient CyclesI. Nutrient Cycles

BIOGEOCHEMICAL CYCLES: natural processes that involve the flow of nutrients through ecosystems: atmosphere, hydrosphere, lithosphere, organisms.

•The BIG SIX

Carbon, Nitrogen, Oxygen, Hydrogen, Sulfur, Phosphorus-all critical to life.

•Each cycle takes various pathways and has various reservoirs and varies in time depending on chem reactivity and whether or not element is in gaseous phase.

•Can be disturbed by humans.

Fig. 4–6© Brooks/Cole Publishing Company / ITP

II. Carbon Cycle-Why it is Important

The most important element in living organisms: *20% body weight; basis of organic molecules that form membranes, tissues, proteins, carbs, energy

Important to the climate system (nature’s thermostat) which sets the background for our environment: *carbon dioxide (CO2 ) and methane (CH4 ) are greenhouse gases which help determine global temperatures

Carbon CycleCarbon Cycle

Fig. 4–23 © Brooks/Cole Publishing Company / ITP

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Processes That Drive the Carbon CyclePhotosynthesisRespirationExchangeSedimentationBurialExtractionCombustion

Carbon Exchange between atmosphere and ocean

Oceans: CO2 dissolved in water, marine sediments, marine organisms.

When CO2 enters the ocean, it participates in a series of reactions

Solution: CO2(atmospheric) ⇌ CO2(dissolved)

Conversion to carbonic acid:CO2(dissolved) + H2O ⇌ H2CO3

Ionization:H2CO3 ⇌ H+ + HCO3− (bicarbonate

ion) HCO3

− ⇌ H+ + CO32-(carbonate ion)

http://www.whoi.edu/home/oceanus_images/ries/calcification.html

Sedimentation and BurialIn the oceans, bicarbonate can combine with calcium to form limestone (calcium carbonate, CaCO3, with silica), which precipitates to the ocean floor and form limestone via sedimentation. Slow, but has accumulated much C over time!

A small fraction of organic carbon in dead biomass is buried in ocean sediments before it can be decomposed-fossilizes-fossil fuels

Extraction, Combustion and other Human Influences

Removal of fossil fuels from earth

Burning of fossils fuelsEquationCH4 + 2O2 CO2 +2 H2O

In absence of human disturbance the exchange of C between Earth surface and atmosphere in a steady state.

Large Scale Deforestation without Reforestation

Carbon SinksOceans, Land Plants,

Sedimentary Rocks, Fossil fuels in lithosphere

Old Carbon vs. New Carbon

III. Nitrogen CycleIII. Nitrogen Cycle

Role of Nitrogen:

• building block of various essential organic molecules – especially proteins & nucleic acids;

• Plant chlorophyll-photosynthesis- requires nitrogen

• limiting nutrient in many ecosystems – typically, addition of N leads to increased productivity.

© Brooks/Cole Publishing Company / ITP

Nitrogen CycleNitrogen Cycle

Fig. 4–24 © Brooks/Cole Publishing Company / ITP

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Element Main Nonliving

Storehouse

Main Forms in Living

Organisms

Other Nonliving Storehouse

Nitrogen (N) Atmospheric: nitrogen gas (N2)

Proteins & other nitrogen-containing organic molecules

Hydrologic: dissolved ammonium (NH4

+), nitrate (NO3

-), & nitrite (NO2

-)

© Brooks/Cole Publishing Company / ITP

Element Main Nonliving

Storehouse

Main Forms in Living

Organisms

Other Nonliving Storehouse

Nitrogen (N) Atmospheric: nitrogen gas (N2)

Proteins & other nitrogen-containing organic molecules

Hydrologic: dissolved ammonium (NH4

+), nitrate (NO3

-), & nitrite (NO2

-)

Nitrogen Cycle ProcessesNitrogen Cycle ProcessesNitrogen Fixation: N2 NH3/NH4

+

Nitrification: NH3/NH4+ NO2-/NO3

-

Assimilation: NO2-/NO3

- organic compounds

(proteins)Ammonification: organic NH3

Dentrification: NO3- N2

Nitrogen CycleNitrogen Cycle

Sinks: Atmosphere, Biomass, Continental ShelfHuman Influences:•Burn fuels at high temps. Releases NO2 (NOx) –acid rain•Commercial fertilizers and livestock waste•Release N stored in plants and soils as gaseous compounds through destruction of forest, grasslands and wetlands•add excess N to aquatic systems-runoff-eutrophication © Brooks/Cole Publishing Company / ITP

IV. Phosphorus CycleIV. Phosphorus CycleRole of Phosphorus:

• essential nutrient for plants & animals – DNA, other nucleic acids

• limiting nutrient in many ecosystems – addition of P increases productivity, especially for freshwater aquatic systems.

Phosphorus Cycled slowly-no gaseous phase. Water-Crust-Living organisms

Sinks: Sedimentary and Igneous Rock, Ocean sediments

Human Effects: Remove to make fertilizer, reduce when we cut tropical forests, disrupt aquatic systems with runoff, detergents

© Brooks/Cole Publishing Company / ITP

Phosphorus CyclePhosphorus Cycle

Fig. 4–25 © Brooks/Cole Publishing Company / ITP

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Phosphorus CyclePhosphorus Cyclemain processes:

• weathering: P slowly released from rock or soil

minerals as phosphate (P043-), which dissolves in

H20 & is readily leached;

• uptake: by plants to form organic phosphates;

• movement through food web;

• break down of organic forms: to phosphate

(P043-) by decomposers;

• leaching: P043- from soil;

• burial in ocean sediments. © Brooks/Cole Publishing Company / ITP

V. Sulfur CycleV. Sulfur CycleStored in underground rocks, minerals and

soilPlants take up sulfur as sulfate-cycles

through food webH2S organic matter in swamps and bogs.SO2 enters atmosphere from volcanoes SOX (SO2 and SO3) lead to acid precipitation.Humans Effect on Sulfur

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Nutrient Cycling & Sustainability•ecosystems tend toward equilibrium with respect to energy flow & nutrient cycling; may appear self–contained;

• “immature” natural ecosytems -- major shifts in energy flow & nutrient cycling;

• ecosystems not self-contained -- considerable exchange of water & nutrients of ecosystems with adjacent ecosystems;

• human modification of nutrient cycles can lead to major shifts in ecosystem function.

© Brooks/Cole Publishing Company / ITP

VI. Ecosystems Respond to DisturbanceNatural Disturbances include hurricanes, ice storms, tsunamis, tornadoes, volcanic eruptions, forest fires

Anthropogenic include human settlements, agriculture, air pollutions, clear cutting forests, mountain top removal.

Occur both short term and long scale.

How do disturbances effect flow of energy and cycling of matter?Resistance is the when the ecosystem can

resist disturbance; productivity remains relatively unchanged after a disturbance.

Can an ecosystem resist the impact and can it recover?Resilience measures the rate at which an

ecosystem returns to its original state after a disturbance.

Restoration Ecology: Restore damaged ecosystems; Chesapeake Bay

Ecosystem ServicesInstrumental Value

ProvisionsRegulating ServicesSuport SystemsResilienceCultural Services

Intrinsic Value