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