Ecosystems Energy Flow 2. Chemical cycles water, carbon, nitrogen 3. Human effects on cycles

1. Ecosystems Energy Flow 2. Chemical cycles water, carbon, nitrogen 3. Human effects on cycles eutrophication, acid rain

2. Ecosystem = community plus abiotic factors - Conditions (temp, light) Resources (water, nutrients) • Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat • Chemicals are recycled between air, water, soil, and organisms

3. A terrarium ecosystem / Biosphere II Chemical cycling(C, N, etc.) Chemicalenergy Heatenergy Lightenergy Figure 36.8

4. Chemicals are recycled between organic matter and abiotic reservoirs • Water cycle - Carbon cycle • Nitrogen cycle

5. Solar heat Net movementof water vaporby wind (36) Water vaporover the land Water vaporover the sea Evaporationandtranspiration(59) Precipitationover the land(95) Precipitationover the sea(283) Evaporationfrom the sea(319) Oceans Surface waterand groundwater Flow of waterfrom land to sea(36) Figure 36.14

6. salt water = 97.5% freshwater = 2.5% lakes, rivers, and soil 0.03% ice caps and glaciers 1.97% atmosphere 0.001% ground- water 0.5% oceans

7. Carbon cycle • Carbon is taken from the atmosphere by photosynthesis • used to make organic molecules returned to the atmosphere by cellular respiration, decomposers

8. CO2 in atmosphere Plants,algae,cyanobacteria Cellular respiration Burning Photosynthesis Higher-levelconsumers Primaryconsumers Wood andfossil fuels Decomposition Detritivores(soil microbesand others) Detritus Figure 36.15

9. The nitrogen cycle relies heavily on bacteria • Nitrogen is plentiful in the atmosphere as N2 • But plants and animals cannot use N2 • Some bacteria in soil and legume root nodules convert N2 to compounds that plants can use: ammonium (NH4+) and nitrate (NO3–)

10. Legumes and certain other plants house nitrogen-fixing bacteria Shoot • Legumes and certain other plants have nodules in their roots that contain nitrogen-fixing bacteria Nodules Roots Figure 32.14A

11. ATMOSPHERE N2 Aminoacids Nitrogen-fixingbacteria N2 NH4+ NH4+(ammonium) NO3–(nitrate) Soil Nitrifyingbacteria Ammonifyingbacteria Organicmaterial Root Figure 32.13

12. Nitrogen (N2) in atmosphere Amino acidsand proteins inplants and animals Assimilationby plants Nitrogenfixation Denitrifyingbacteria Detritus Nitrogen-fixingbacteria in rootnodules of legumes Nitrates(NO3–) Detritivores Nitrogen-fixingbacteria in soil Decomposition Nitrifyingbacteria Nitrogenfixation Ammonium (NH4+)

13. Human impact on chemical cycles 76% naturally occurring 24% human- caused 24% naturally occurring 58% human- caused 46% available 54% used Atmospheric CO2 concentration Terrestrial nitrogen fixation Accessible surface water

14. Example: acid rain • Sulfur dioxide, nitrogen oxides create strong acids when dissolved in rain water. • Low pH kills aquatic life, leaches nutrients from soil • Calcium deficiency affects everything in food chain: plants, insects, birds. Weak egg shells. • Environmental changes caused by humans can unbalance nutrient cycling over the long term

15. eutrophication • Algal bloom can cause a lake to lose its species diversity

16. Human-caused eutrophication wiped out fisheries in Lake Erie in the 1950s and 1960s • classic experiments on eutrophication led to the ban on phosphates in detergents Figure 36.19B

17. What are the limits to human alteration of chemical cycles and habitats? • What should the limits be? • How do we set priorities for what we value in the natural world? Aesthetic, economic, conservation, humans