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Daily question. Use the second law of thermodynamics to explain why there is such a sharp decrease in usable energy as energy flows through a food chain. Does an energy loss at each step violate the first law of thermodynamics? - PowerPoint PPT PresentationTRANSCRIPT
Daily question• Use the second law of thermodynamics to
explain why there is such a sharp decrease in usable energy as energy flows through a food chain. Does an energy loss at each step violate the first law of thermodynamics?– 1st law: Energy is neither created nor destroyed,
but may be converted from one form to another– 2nd law: When energy is changed from one form
to another, some useful energy is degraded to lower quality, more dispersed, less useful energy
Cycles, watersheds and ecosystem ecology
Energy flows,matter cycles
• Energy enters ecosystems in 2 ways:– Sun– Chemosynthetic bacteria at hydrothermal vents
• Most deep sea ecosystems depend on photosynthesis: how?
• Some: chemosynthetic bacteria
Energy flow• Result of flow—and loss—of energy at
each trophic level is the ecological pyramid– Numbers– Biomass– Especially: Energy
Problem
• Under what conditions would the pyramid of numbers not strictly be a pyramid? ie. Give an example
• Trees are few and large, insects many and small
• Trees and insect herbiroves
Matter
• Earth is open system with respect to energy
• Mostly closed system regarding matter– Elements cycle
•
Biogeochemical cycles
• Involve biological, geological, and chemical interactions
• Matter not created
• 5 cycles representative of all biogeochemical cycles:– Carbon
– Nitrogen
– Phosphorus
– Sulfur
– Water
Essential questions
• How do elements important to life move through the biosphere and geosphere? (this is called ``flux’’)
• Where are these elements stored for long term? (places are called ``sinks’’)
• How are humans altering these cycles? (``anthropogenic effects’’)
Hydrologic cycle
• Water you drink today may have been part of a dinosaur’s urine 75 million years ago.
• OR, in the Passaic River 4 months ago
residence times– Range from days in the atmosphere to
thousands of years deep in the ground
Where is the
water?
http://ga.water.usgs.gov/edu/watercycle.html
Sources vs. sinks• Reservoir = where in the environment
(atmosphere, hydrosphere, geosphere, biosphere) that an element can be found
• Sink = Flow into reservoir is greater than flow out.
• Source = Flow out of reservoir is greater than flow in.
SOURCE SINKFLUX
Carbon cycleReservoirs?
– Sedimentary rocks
– Oceans
– Atmosphere
– Fossil fuels
• Sinks: oceans, atmosphere
• Source: fossil fuels
Carbon cycle
• C found in molecules essential to life (proteins, carbohydrates, etc)– Organic chemistry is the chemistry of C
• Atmosphere: CO2
• Ocean: dissolved carbon dioxide, dissolved organic C
• Earth: – *Sedimentary rocks (ie, limestone)– *Fossil fuels * The major reservoirs
Carbon cycle
• How does C go from atmosphere to biosphere? _____________
• What are various pathways that C can take once in the biosphere?
• How does C go from geosphere/biosphere back to atmosphere? _____________
• Residence times: How long does C remain in reservoirs?
Carbon cycle measurement
Nitrogen cycle
How read this graph?
Nitrogen cycle
• N essential to life: Found in proteins and nucleic acids.
• Where is most nitrogen?_____________
• N2 is so stable, doesn’t readily combine with other atoms
Nitrogen cycle
• 5 main steps:– Nitrogen fixation– Nitrification– Assimilation– Ammonification– Denitrification
• Bacteria involved in all steps except assimilation
Nitrogen fixation N2 NH4
+
• Conversion of gaseous nitrogen (N2) to ammonia (NH4
+)• Fixed means, ``put into a form organisms
can use.’’• Combustion, volcanic action, lightning,
industrial processes all fix N• Bacteria fix N anaerobically.
– Some found inside root nodules, Rhizobium
Nitrification NH4
+ NO3-
• Conversion of ammonia or ammonium to nitrate (NO3
-)
• Soil bacteria
• Bacteria get energy
Assimilation
• Plant roots absorb nitrate, ammonia, or ammonium and assimilate the nitrogen into plant amino acids and nucleic acids
• Animals that consume plants then assimilate the nitrogen into their bodies
Ammonification
• Conversion of biological nitrogen compounds (what are these?) back into ammonia and ammonium ions. DECOMPOSITION
• Step 1: organisms produce nitrogen-rich waste• Step 2: bacteria (decomposers) convert waste into
simpler nitrogen-containing molecules (NH3, NH4+)
Denitrification
• Bacteria reverse the action of nitrogen-fixing bacteria
• Nitrogen released back to atmosphere
Watersheds and the cycles
• Watershed = area of land that drains into a body of water
PROBLEM• Earth’s water in dynamic equilibrium• IF:
– Precipitation to ocean = 385,000 km2/yr
– Evaporation from ocean = 425,000 km2/yr
– What is a good estimate for runoff to ocean?
• 40,000 km3/yr