The cycling of matter in ecosystems

1. The cycling of matter in ecosystems • Biogeochemical cycles: circular pathways involving biological, geological, and chemical processes • Biogeochemical cycles include: • Carbon Cycle • Phosphorus Cycle • Nitrogen cycle

2. The Carbon Cycle How carbon (C) moves through our environment • Producers pull carbon dioxide (CO2) from the air and use it in photosynthesis. • Consumers eat producers and return CO2 to the air by respiration. • Decomposition of dead organisms, plus pressure underground, forms sedimentary rock and fossil fuels. This buried carbon is returned to the air when rocks are uplifted and eroded.

3. Carbon cycle: other ways to transfer carbon • Ocean water also absorbs carbon from multiple sources, eventually storing it in sedimentary rock or providing it to aquatic plants. • Limestone keeps carbon out of circulation • Weathering of exposed limestone releases carbon • A carbon atom cycles about every six years

4. The carbon cycle

5. The global carbon cycle

6. Human impacts on the carbon cycle • We have increased CO2 in the atmosphere by burning fossil fuels and deforesting forests. • Atmospheric CO2 concentrations may be the highest now than in 420,000 years. • This is driving global warming and climate change.

7. 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 CO2 by 35% • Deforestation and soil degradation release significant amounts of CO2 to the atmosphere • Recent reforestation and changed agricultural practices have improved this somewhat

8. Summary of Carbon Cycle • Acid rain: from the atmosphere delivers CO2 dissolved in water vapor to earth. • Photosynthesis: turns CO2 into plant biomass • Respiration: converts sugars and starches into energy for organisms and releases CO2. • Decomposition: converts dead plants and animals into CO2 and other inorganic nutrients. http://www.youtube.com/watch?v=irwRzQNS-GI

9. The Phosphorous Cycle How phosphorus (P) flows through our environment • P is most abundant in rocks. Weathering releases phosphate (PO43–) ions from rocks into water. • As rock breaks down, phosphate is released • Replenishes phosphate lost through leaching or runoff • Plants take up phosphates in water, pass it on to consumers, who return it to the soil when they die. • Phosphates dissolved in lakes and oceans precipitate, settle, and can become sedimentary rock.

10. The phosphorous cycle

11. The global phosphorus cycle

12. 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

13. Summary of Phosphorus Cycle • Weathering: of phosphate from rocks delivers phosphorus to soil. • Decomposition: of plant and animal wastes and remains delivers phosphorus to soil. • Humans make phosphates through mining and chemical weathering. http://www.youtube.com/watch?v=3iwL24oVpH4

14. 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

15. The nitrogen cycle

16. The global nitrogen cycle

17. Plants take up nitrogen • Plants in terrestrial ecosystems (“non-N-fixing producers”) • Take up( N) as ammonium (NO4) 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

18. 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) • Denitrification: Microbes use nitrate as a substitute for oxygen

19. Nitrogen Cycle Summary • Nitrification: by bacteria convert NH4 into NO2- and then into NO3- • Denitrification: Conversion of biological nitrogen (proteins-No3- and NH4) into atmospheric nitrogen. • Biological Nitrogen Fixation: bacteria in the roots of legumes fix nitrogen. • Atmospheric Fixation: lightning converts N2 to NO3- and NH4 • Industrial Fixation: factories make fertilizer from atmospheric nitrogen. http://www.youtube.com/watch?v=IaGNSmQQmBc

20. 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

21. 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

22. 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. Nutrient cycles and energy flow