1. 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

2. Cycles, watersheds and ecosystem ecology

3. 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

4. Energy flow
Result of flow—and loss—of energy at each trophic level is the ecological pyramid
Numbers
Biomass
Especially: Energy

5. 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

6. Matter Earth is open system with respect to energy
Mostly closed system regarding matter
Elements cycle

8. Biogeochemical cycles
Involve biological, geological, and chemical interactions
Matter not created
5 cycles representative of all biogeochemical cycles:
Carbon
Nitrogen
Phosphorus
Sulfur
Water

9. 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’’)

10. 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

11. Where is the water? Oceans 97%
Of what’s left: ice: 69 %; groundwater 30 %; all else 1%

13. 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.
FLUX
SINK
SOURCE

14. Carbon cycle Reservoirs? Sinks: oceans, atmosphere
Sedimentary rocks
Oceans
Atmosphere
Fossil fuels
Sinks: oceans, atmosphere
Source: fossil fuels
Carbon coming from fossil fuels and being added to atmosphere, and therefore also to the ocean.

15. 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

16. 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?

17. Carbon cycle measurement

18. Nitrogen cycle
Sink: atmosphere, living things. Increasing flux from animal wastes and fertilizers

19. How read this graph?

21. 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

22. Nitrogen cycle 5 main steps:
Nitrogen fixation
Nitrification
Assimilation
Ammonification
Denitrification
Bacteria involved in all steps except assimilation

23. 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

24. Nitrification NH4+  NO3-
Conversion of ammonia or ammonium to nitrate (NO3-)
Soil bacteria
Bacteria get energy

25. 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

26. 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+)

27. Denitrification
Bacteria reverse the action of nitrogen-fixing bacteria
Nitrogen released back to atmosphere

28. Watersheds and the cycles
Watershed = area of land that drains into a body of water

30. PROBLEM Earth’s water in dynamic equilibrium IF: 40,000 km3/yr
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