1. © 2011 Pearson Education, Inc. MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earth’s air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms.

2. © 2011 Pearson Education, Inc. Effects of Human Activities on Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. Contributing to climate change.

3. © 2011 Pearson Education, Inc. The global carbon cycle

4. © 2011 Pearson Education, Inc. Carbon cycle: other ways to transfer carbon Some processes are significant in transferring carbon Diffusion exchange between atmosphere and oceans Combustion of fossil fuels releases CO 2 to the air Fossilization of dead plants and animals into coal Removed carbon from the atmosphere Burning releases CO 2 to the air Limestone keeps carbon out of circulation Weathering of exposed limestone releases carbon A carbon atom cycles about every six years

5. © 2011 Pearson Education, Inc. Human impacts on the carbon cycle Human intrusion into the cycle is significant We are diverting or removing 40% of the photosynthetic effect of land plants Burning fossil fuels has increased atmospheric CO 2 by 35% Deforestation and soil degradation release significant amounts of CO 2 to the atmosphere Recent reforestation and changed agricultural practices have improved this somewhat

6. © 2011 Pearson Education, Inc. Effects of Human Activities on Carbon Cycle We alter the carbon cycle by adding excess CO 2 to the atmosphere through: Burning fossil fuels. Clearing vegetation faster than it is replaced. Figure 3-28

7. © 2011 Pearson Education, Inc. The phosphorus cycle Mineral elements originate in rock and soil minerals A shortage of phosphorus is a limiting factor Excessive phosphorus can stimulate algal growth As rock breaks down, phosphate is released Replenishes phosphate lost through leaching or runoff Organic phosphate: incorporated into organic compounds by plants from soil or water Cycles through the food chain Broken down in cell respiration or by decomposers Enters into chemical reactions with other substances

8. © 2011 Pearson Education, Inc. The global phosphorus cycle

9. © 2011 Pearson Education, Inc. Human impacts on the phosphorus cycle The most serious intrusion comes from fertilizers Phosphorus is mined and made into fertilizers, animal feeds, detergents, etc. When added to soil, it can stimulate production Human applications have tripled the amount reaching the oceans, accelerating the cycle It can’t be returned to the soil Excess phosphorus in water leads to severe pollution Can cause too many bacteria and fish kills

10. © 2011 Pearson Education, Inc. Effects of Human Activities on the Phosphorous Cycle We remove large amounts of phosphate from the earth to make fertilizer. We reduce phosphorous in tropical soils by clearing forests. We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.

11. © 2011 Pearson Education, Inc. The nitrogen cycle Is a unique cycle Bacteria in soils, water, and sediments perform many steps of the cycle Nitrogen is in high demand by aquatic and terrestrial plants Air is the main reservoir of nitrogen (N) Nonreactive nitrogen: most organisms can not use it Reactive nitrogen (Nr): other forms of nitrogen that can be used by organisms

12. © 2011 Pearson Education, Inc. The global nitrogen cycle

13. © 2011 Pearson Education, Inc. Plants take up nitrogen Plants in terrestrial ecosystems (“non-N-fixing producers”) Take up Nr as ammonium (NO 4 ) and incorporate it into proteins and nucleic acid compounds The nitrogen moves through the food chain to decomposers, releasing nitrogen wastes Soil bacteria (nitrifying bacteria) convert ammonium to nitrate to obtain energy Nitrate is available for plant uptake Nitrogen fixation: bacteria and cyanobacteria can use nonreactive N

14. © 2011 Pearson Education, Inc. Means of nitrogen fixation Bacteria (genus Rhizobium) live in legume root nodules The legume provides the bacteria a place to live and food It receives a source of nitrogen in return Nitrogen enters the food chain from the legumes Three other processes “fix” nitrogen Atmospheric nitrogen fixation: lightning Industrial fixation: in fertilizer manufacturing Combustion of fossil fuels: oxidizes nitrogen Industrial fixation and fossil fuels release nitrogen oxides, which are converted to nitric acid (acid precipitation)

15. © 2011 Pearson Education, Inc. Nitrogen fixation

16. © 2011 Pearson Education, Inc. Denitrification A microbial process in soils and sediments depleted of oxygen Microbes use nitrate as a substitute for oxygen Nitrogen is reduced (it gains electrons) to nitrogen gas Released into the atmosphere Occurs in sewage treatment systems

17. © 2011 Pearson Education, Inc. Human impacts on the nitrogen cycle Human involvement in the nitrogen cycle is substantial Many crops are legumes and draw N from the air Peas, beans, soybeans, alfalfa Increases the rate of nitrogen fixation Nonleguminous crops (corn, wheat, potatoes) are heavily fertilized with nitrogen from industrial fixation We are more than doubling the rate of nitrogen moving from air to land

18. © 2011 Pearson Education, Inc. Serious consequences of fertilization Nitric acid has destroyed lakes, ponds, and forests Atmospheric nitrogen oxides adds to ozone pollution, climate change, and stratospheric ozone depletion Abundant nitrates are not incorporated into organisms They are released into the soil, where they leach calcium and magnesium Eutrophication of waterways Nitrogen cascade: complex of ecological effects as Nr moves through the environment

19. © 2011 Pearson Education, Inc. Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation.

20. © 2011 Pearson Education, Inc. Effects of Human Activities on the Nitrogen Cycle Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. Figure 3-30

21. © 2011 Pearson Education, Inc. Effects of Human Activities on the Sulfur Cycle We add sulfur dioxide to the atmosphere by: Burning coal and oil Refining sulfur containing petroleum. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.

22. © 2011 Pearson Education, Inc. Comparing the cycles Carbon is mainly found in the atmosphere Directly taken in by plants Nitrogen and phosphorus are limiting factors All three cycles have been sped up by human actions Acid rain, greenhouse gases, eutrophication Other cycles exist for other elements (e.g., water) All go on simultaneously All come together in tissues of living things

23. © 2011 Pearson Education, Inc. Nutrient cycles and energy flow