Energy Flow and Geochemical Cycling in an Ecosystem

1. “All flesh is grass” -Isaiah 40:6 Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass.  -- G. Tyler Miller, Jr., American Chemist (1971) +++++++++++++++++++++++++++++++++++++++++++

2. Energy Flow and Geochemical Cycling in an Ecosystem Energy flow and geochemical cycling

3. Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling • Energy flows through ecosystems while matter cycles within them

4. Conservation of Energy – The first law of thermodynamics • States that energy cannot be created or destroyed, only transformed • Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat

5. The second law of thermodynamics states that every exchange of energy increases the entropy of the universe • Entropy is commonly understood as a measure of molecular disorder within a macroscopic system. • In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat

6. Conservation of Mass • The law of conservation of mass states that matter cannot be created or destroyed • Chemical elements are continually recycled within ecosystems

7. In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water • Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

8. Energy, Mass, and Trophic Levels • Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source. • Heterotrophs depend on the biosynthetic output of other organisms • Trophic level – hierarchy describing how organisms obtain their energy

9. (reactants)

10. Photosynthesis

11. Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores) Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores)

12. Detritivores,or decomposers, are consumers that derive their energy from detritus, nonliving organic matter • Prokaryotes and fungi are important detritivores • Decomposition connects all trophic levels

13. Fig. 55-3

14. Concept 55.2: Energy and other limiting factors control primary production in ecosystems • Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period

15. The Global Energy Budget • The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems • Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength

16. Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient • Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time

17. Production Efficiency • When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production • An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration

18. Fig. 55-9 • *one-sixth of the leaf’s energy is used for secondary production • Plant material • eaten by caterpillar • *Energy transfer between trophic levels is typically only 10% efficient • 200 J • 67 J • Cellular • respiration • 100 J • 33 J • Feces • Growth (new biomass)

19. Trophic Efficiency and Ecological Pyramids • Trophic efficiency is the percentage of production transferred from one trophic level to the next • It usually ranges from 5% to 20% • Trophic efficiency is multiplied over the length of a food chain

20. Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer • A pyramid of net production represents the loss of energy with each transfer in a food chain Go Bobcats!!!

21. Fig. 55-10 • Tertiary • consumers • 100 J • Secondary • consumers • 1000 J • Primary • consumers • 10,000 J • Primary • producers • 100,000J • 1,000,000 J of sunlight

22. Biomass Pyramid • Each tier represents the dry weight of all organisms in one trophic level • Shows sharp decrease at successively higher trophic levels

23. Concept 55.4: Biological and geochemical processes cycle nutrients between organic and inorganic parts of an ecosystem • Life depends on recycling chemical elements • Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

24. Biogeochemical Cycles • Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally • Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level

25. Fig. 55-14a The Water Cycle • Transport • over land • Solar energy • Net movement of • water vapor by wind • Precipitation • over land • Precipitation • over ocean • Evaporation • from ocean • Evapotranspiration • from land • Percolation • through • soil • Runoff and • groundwater

26. The Carbon Cycle • Carbon-based organic molecules are essential to all organisms • Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere • CO2 is taken up and released through photosynthesis and respiration; additionally, volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere

27. Photosynthesis

28. Fig. 55-14c The Nitrogen Cycle • N2 in atmosphere • Assimilation • Denitrifying • bacteria • NO3 • – • Nitrogen-fixing • bacteria • Decomposers • Nitrifying • bacteria • Ammonification • Nitrification • NH3 • NH4 • NO2 • – • + • Nitrogen-fixing • soil bacteria • Nitrifying • bacteria

29. The Terrestrial Nitrogen Cycle • The pathway in which nitrogen moves through the ecosystem • Nitrogen is a component of amino acids, proteins, nucleic acids (DNA), ATP • The main reservoir of nitrogen (N2) is the atmosphere, 78% . N2 gas must be converted to other forms.

30. 4 processes of the Nitrogen Cycle • Nitrogen Fixation - process converts N2 into • NH4+ (ammonium ions). Done by nitrogen fixing bacteria found in soil or nodules on roots of legumes • Examples of legumes: peas, beans, alfalfa, peanuts, clover

31. Nitrification • NH4+ by ammonification, and NH4+ is decomposed to NO2- and often to NO3– by nitrification • Nitrifying bacteria convert NH4+ in soils • Plants absorb nitrates through roots Bashan, Y. and Levanony, H. (1987)

32. Ammonification • Breakdown of nitrogen compounds back into ammonia products NO3- → NH4+

33. Denitrification • Conversion of NH4+, NO2-, NO3- back to N2 gas (bacteria do this).

34. Energy Flow and Geochemical Cycling in an Ecosystem Humans & the Biosphere

35. Fig. 55-17

36. Fig. 55-18 • Winter • Summer

37. Fig. 55-16 • (a) Concrete dam • and weir • (b) Clear-cut watershed • 80 • Deforested • 60 • 40 • 20 • Nitrate concentration in runoff • (mg/L) • Completion of • tree cutting • 4 • 3 • Control • 2 • 1 • 0 • 1965 • 1966 • 1967 • 1968 • (c) Nitrogen in runoff from watersheds

38. Fig. 55-14b The Carbon Cycle • CO2 in atmosphere • Photosynthesis • Cellular • respiration • Photo- • synthesis • Burning of • fossil fuels • and wood • Phyto- • plankton • Higher-level • consumers • Primary • consumers • Carbon compounds • in water • Detritus • Decomposition

39. Photosynthesis

42. Toxins in the Environment • Humans release many toxic chemicals, including synthetics previously unknown to nature • In some cases, harmful substances persist for long periods in an ecosystem • One reason toxins are harmful is that they become more concentrated in successive trophic levels • Biological magnification concentrates toxins at higher trophic levels, where biomass is lower

43. PCBs and many pesticides such as DDT are subject to biological magnification in ecosystems • In the 1960s Rachel Carson brought attention to the biomagnification of DDT in birds in her book Silent Spring

44. Fig. 55-20 • Herring • gull eggs • 124 ppm • Lake trout • 4.83 ppm • Concentration of PCBs • Smelt • 1.04 ppm • Zooplankton • 0.123 ppm • Phytoplankton • 0.025 ppm

45. Depletion of Atmospheric Ozone • Life on Earth is protected from damaging effects of UV radiation by a protective layer of ozone molecules in the atmosphere • Satellite studies suggest that the ozone layer has been gradually thinning since 1975

46. Fig. 55-23 • 350 • 300 • 250 • Ozone layer thickness (Dobsons) • 200 • 100 • 0 • ’60 • ’80 • 1955 • ’70 • ’75 • ’85 • ’90 • ’95 • ’05 • ’65 • 2000 • Year

47. Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity

48. Fig. 55-24 • Chlorine atom • O2 • O3 • Chlorine • ClO • O2 • ClO • Cl2O2 • Sunlight

49. Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

50. Fig. 55-25 • (a) September 1979 • (b) September 2006