Notes

ch 46 ecosystem ecology

carbon cycle - network of biolgical & physical processes that shuttle carbon among rock, soil, oceans, air, & organisms

charles keeling & measuring changing levels of atmospheric co2:
co2 levels varied by season: concentrations highest in spring and decline by approx. 6 ppm in early fall

keeling curve
-co2 concentrations cycle up & down over a year (highest in spring and decline by approx. 6 ppm in early fall)
-have steadily increased (by 30%) over the last 60 years

short term carbon cycle
-amount of co2 removed from atmosphere by photosynthesis (25%) = amount returned by cellular respiration

-adds co2 to atmosphere: geological inputs (volcaones, mid-cean ridges), biological inputs (respiration), human activities (deforestation, burning fossil fuels, power plants, airplanes, ships, automobiles)
-removes co2 from atmosphere: geological removal (chemical weathering of rocks), biological processes (photosynthesis)

carbon isotopes & atmospheric co2
-ratio of 13c to 12c has declined; total atmospheric co2 has increased (co2 being added to atmosphere has less 13c and more 12c than co2 already in air); only fossil fuels have the right ratios of all 3 carbon isotopes to account for the pattern of isotopic change in atmospheric co2

co2 sinks: ~half of co2 released by human acitivites doesn't end up in the air; the missing carbon is stored as co2 & carbonate & bicarbonate ions dissolved in oceans

cold glacial & warm interglacial periods correlate /w minimum & maximum amtospheric co2 levels respectively (higher concentrations of co2 result in warmer temperatures); atmospheric co2 oscillates /w glacial expansion & retreat (climatic shifts recorded in ice cores)

reservoirs: places where carbon is found on earth - most stored in organisms living on land, decaying organic compounds in the soil, & inorganic carbon & organisms in oceans; largest reservoir is in sediments & sedimentary rock

-fluxes: rates at which carbon flows from one reservoir to another

-food web - traces cycling of carbon from environemnt thru a succession of organisms back to the environment; trophic levels represent an organism's place in the food web
-primary producrs - plants/bacteria/algae generate compounds that provide food for other organisms
-primary consumers - herbivores/grazers consume primary producers
-secondary consumers - predators/scavengers/carnivores consume primary consumers
-tertiary consumers - eat secondary consumers
-decomposers - fungi break down dead tissue & respirate to return carbon fixed by photosynthesis to atmosphere

-10% of biomass is passed from trophic levels; larger biomass at base supports more at higher trophic levels

nitrogen cycle:
-assimilation - primary producers obtain nitrogen as nitrate ammonia or ammonium ion in soil or water
-ammonification - decomposters return nitrogen to soil as ammonia
-denitrification - anaerobic respiration in which nitrate serves as the temrinal electorn acceptor
-nitrification - chemoautotrophic process that uses energy gained from oxidation of ammonia or nitrate by oxygen
-anammox - chemoautotrophy with energy from the reaction of ammonia and nitrate
-nitrogen fixation - reduction of n2 to biologically useful ammonai by bacteria/archaea
9phosphorus & nitrogen are limiting nutrients (decrease disrupts cell membrane production in consumers)