Post on 27-Dec-2015
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