Download Cycles, watersheds and ecosystem ecology

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.
FLUX
SOURCE
SINK
Carbon cycle
Reservoirs?
–
–
–
–
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 nitrogenfixing 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