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? Oceans 97% Of what’s left: ice: 69 %; groundwater 30 %; all else 1%

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 SINK SOURCE

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.

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

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: 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