Nutrient cycles

2. Nutrient cycles

3. Ecosphere Photo

4. Earth Photo

5. Nutrient cycles • Nutrient cycles, or “biogeochemical cycles,” involve natural processes that recycle nutrients in various chemical forms in a cyclic manner from the non-living environment to living organisms and back to the non-living environment again • Types of nutrient cycles: • Hydrologic cycle • Atmospheric cycles • Sedimentary cycles

6. The water cycle

7. No water, no life • determines ecosystem structure; water-living (aquatic) communities important for supporting life on land • affects nutrient availability • Evaporation and transpiration lead to condensation, to precipitation, to percolation and runoff, and all over again • Powered by energy from the sun and gravity • 84% of water vapor from the oceans (71% of the Earth’s surface) • 77% of precipitation falls back into the sea • Some precipitation locked in glaciers

8. runoff, erosion, moves soil and weathered rock • primary sculptor of the earth’s landscape • dissolves many nutrient compounds, transporting nutrients • Percolation dissolves minerals and moves them into groundwater • Times for water to cycle through various pathways: • Water table: 300-4600 years; Lakes: 13 years; Streams: 13 days; Atmosphere: 9 days; Ocean: 37,000 years; Glaciers: 16,000 years • Evaporation = natural distillation; also purified by chemical and biological processes in the soil • Hydrologic, atmospheric or sedimentary?

9. The carbon cycle

10. Essential to life • Basic building block of carbohydrates, fats, proteins, nucleic acids and all other organic compounds • CO2 is a heat-trapping greenhouse gas; regulates heat, with major impacts on ecosystem function • Cycling times for CO2: Atmosphere, 3 years; Soil, 25-30 years; Oceans, 1,500 years • Hydrologic, atmospheric or sedimentary?

11. The phosphorous cycle

12. essential nutrient of plants and animals, used in DNA, nucleic acids, fats, cell membranes, and bones, teeth and shells • from phosphate deposits on land and shallow ocean sediments to living organisms and slowly back to the land and ocean • Very little in the atmosphere, only as small particles of dust • much more rapidly through living components than through geological formations; animals get by eating producers or animals that eat producers • Animal wastes and decay return much of this phosphorous to the soil, streams, and eventually to ocean bottom and into rock cycle • Hydrologic, atmospheric or sedimentary?

13. The nitrogen cycle

14. Nitrogen is necessary for vital organic compounds such as amino acids, proteins, DNA and RNA • In short supply in both terrestrial and aquatic ecosystems • N2 = 78% of the volume of the troposphere • Cannot be directly used by organisms • Must be converted to compounds that can enter food webs by the process of “nitrogen fixation”

15. Nitrogen fixation: • Specialized bacteria convert N2 to ammonia (NH3) by the reaction N2 + 3H2 = 2NH3 • Cyanobacteria in soils and water, and Rhizobium bacteria in small nodules in legume root systems • Nitrification – NH3 converted by specialized aerobic nitrite (NO2-), toxic • Converted to nitrate (NO3-) ions, which are easily taken up by plants as nutrients

16. Nitrogen fixation: • Assimilation – NO3- taken up by plants and used to make nitrogen-containing organic molecules • Animals get nitrogen by eating plants or plant-eating animals • Decomposers convert to NH3 and ammonium (NH4+); ammonification • Denitirification - specialized bacteria convert NH3 and NH4+ back into NO2- and NO3, and then to N2 and N2O, released into the atmosphere

17. Easily leached by water, limiting productivity potential. • Hydrologic, atmospheric or sedimentary?

18. Back to the Ecosphere

20. How do humans affect nutrient cycles?

21. Water cycle: • Drain fresh water from streams, lakes, and underground sources • Clear vegetation increasing runoff, reducing infiltration, increasing erosion and risk of flooding • Modify water quality by adding nutrients (phosphates) and changing ecological processes that naturally purify water

22. Carbon cycle: • Put more CO2 in the atmosphere than plants can remove • Deforestation reduces the amount of vegetation to remove CO2 • Burning fossil fuels and wood releases more CO2 than natural processes • What happens when we have to much heat-trapping gas?

23. Phosphorous cycle: • Mine large phosphate rock for fertilizers and detergents • Cutting tropical forests; little phosphorous in soil, all bound up in organic matter which usually rapidly recycles; but we remove the biomass or burn it, allowing it to be rapidly washed away by runoff, leaving the land unproductive • Add excess phosphate to aquatic ecosystems in runoff from agricultural operations, causing explosive plant growth creating surface mats which block sunlight; dying plants feed bacteria which uses up most of the oxygen in the water.

24. Nitrogen cycle: • Emit nitric oxide (NO) when burning fuels; leads to acid rain • Emit heat-trapping nitrous oxide (NO2) into the atmosphere • Remove nitrogen from the earth’s crust for fertilizers, harvesting nitrogen-rich biomass, and increase leaching through irrigation • Remove nitrogen from topsoil when burning grasslands and clearing forests; also emits nitrous oxides • Add excess through runoff and sewage – promotes overgrowth of algae, which dies, breaks down, and decomposition by bacteria depletes the water of oxygen; disrupts aquatic systems; reduces aquatic biodiversity • Add excess nitrogen to atmosphere; allowing weedy plants to outcompete other plants, reducing biodiversity

25. Experimental impacts on nitrogen cycling in a disturbed habitat

26. Nitrogen cycles in an experimental ecosystem