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Ecosystems Chapter 47 Part 2 47.7 Carbon Cycle In the carbon cycle, carbon moves though all food webs, to and from its major reservoirs • • • • • • Earth’s crust: 66 to 100 million gigatons World ocean: 38,000 to 40,000 gigatons Fossil fuel reserves: 4,000 gigatons Detritus in soil: 1,500 to 1,600 gigatons Air: 766 gigatons (mostly as CO2) Biomass: 540 to 610 gigatons Movements of Carbon Most of the annual cycling of carbon occurs between the ocean and the atmosphere • Some CO2 in surface waters is converted to bicarbonate (carbon-oxygen cycling) and moved by ocean currents to deep ocean reservoirs Photosynthesis, aerobic respiration, decomposition, and formation of carbonate sediments all contribute to the carbon cycle Carbon Cycling Carbon Cycling Animation: Carbon cycle Deep Ocean Reservoirs Humans Are Altering the Carbon Cycle Each year we withdraw 4 to 5 gigatons of fossil fuel from environmental reservoirs; and put 6 gigatons more carbon into the air than can be recycled to ocean reservoirs Excess CO2 entering the atmosphere may be a factor in global climate change 47.8 Greenhouse Gases, Global Warming Greenhouse effect • Radiant energy from the sun is absorbed by Earth’s surface and radiated back as heat • Gases in the upper atmosphere trap heat like a greenhouse, and radiate it back to Earth • Greenhouse gases: carbon dioxide, water, nitrous oxide, methane, chlorofluorocarbons (CFCs) The Greenhouse Effect Animation: Greenhouse effect Atmospheric Observations Atmospheric CO2 fluctuates annually with patterns of photosynthesis Average concentrations of CO2 and other greenhouse gases are increasing Human activities – mainly burning of fossil fuels – increase greenhouse gases Increasing Greenhouse Gases Global Warming Global warming • A long-term increase in temperature near Earth’s surface, currently about 1.8°C (3.2°F) per century Scientists expect far-reaching effects • Melting glaciers and rising sea levels • Altered global precipitation patterns, droughts and flooding, more intense hurricanes Changes in Global Mean Temperatures Fig. 47-17a, p. 853 Fig. 47-17b, p. 853 Fig. 47-17c, p. 853 Fig. 47-17d, p. 853 Fig. 47-18, p. 853 The Shrinking Antarctic Ice Shelf Fig. 47-24a, p. 859 Fig. 47-24b, p. 859 47.9 Nitrogen Cycle Gaseous nitrogen (N2) makes up about 80 percent of the lower atmosphere • Most organisms can’t use gaseous nitrogen The nitrogen cycle starts with nitrogen fixation • Nitrogen-fixing bacteria convert N2 in the air to ammonia (NH3), then to ammonium (NH4+) and nitrate (NO3-), which plants easily take up Other Nitrogen Inputs Into Ecosystems Ammonification • Bacteria and fungi make additional ammonium available to plants when they break down nitrogen-rich wastes and remains Nitrification • Bacteria convert ammonium to nitrite (NO2-), and then to nitrate, which plants easily take up Losing Nitrogen from Ecosystems Denitrification • Denitrifying bacteria convert nitrate or nitrite to gaseous nitrogen (N2) or nitrogen oxide (NO2) Ammonium, nitrite, and nitrate are also lost from land ecosystems in runoff and by leaching Nitrogen Cycle in a Land Ecosystem gaseous nitrogen in atmosphere food webs on land nitrogen fixation fertilizers excretion, death, uptake by autotrophs decomposition ammonia, ammonium in soil nitrogen-rich wastes, remains in soil ammonification loss by leaching nitrification uptake by autotrophs loss by denitrification nitrate in soil nitrification nitrite in soil loss by leaching Fig. 47-19, p. 854 Animation: Nitrogen cycle Disruptions by Human Activities Deforestation and conversion of grassland to farmland causes nitrogen loss • Plant removal increases erosion and leaching Synthetic ammonium fertilizers increase soil acidity and encourage ion exchange • Calcium and magnesium ions are washed away Burning fossil fuels releases nitrogen oxides • Contribute to global warming and acid rain Nitrogen Oxides: Some Effects of Air Pollution 47.10 The Phosphorus Cycle Phosphorus cycle • A sedimentary cycle that moves phosphorus from its main reservoir (Earth’s crust) through soils and sediments, aquatic habitats, and bodies of living organisms Phosphate and the Phosphorus Cycle Phosphorus in rocks is mainly phosphate (PO43-) • Water moves phosphate through ecosystems Phosphorus is a limiting factor on plant growth • Taken up by plants only in ionized form • Required for ATP, phospholipids, nucleic acids • Depleted when forest is converted to farmland The Phosphorus Cycle mining excretion fertilizers guano agriculture uptake by autotrophs marine food webs uptake by autotrophs weathering dissolved in ocean water leaching, runoff dissolved in soil water, lakes, rivers death, decomposition sedimentation land food webs death, decomposition settling out weathering uplifting over geologic time marine sediments rocks Fig. 47-21, p. 856 Animation: Phosphorus cycle Eutrophication: Too Many Nutrients Eutrophication • Nutrient enrichment of any ecosystem that is otherwise low in nutrients; often a form of nutrient pollution from agricultural runoff or sewage Eutrophication of a lake can cause excessive algal growth, oxygen depletion, and fish kills Eutrophication Phosphorus is often the limiting factor in aquatic ecosystems nitrogen, carbon added nitrogen, carbon, phosphorus added Fig. 47-22, p. 857 47.5-47.10 Key Concepts Cycling of Water and Nutrients The availability of water, carbon, nitrogen, phosphorus, and other substances influences primary productivity These substances move slowly in global cycles, from environmental reservoirs, into food webs, then back to reservoirs Animation: Carbon dioxide and temperature Animation: Effect of air pollution in forests Animation: Food webs Animation: Greenhouse gases ABC video: MTBE Pollution ABC video: Bottle Backlash ABC video: Carbon Offsets ABC video: International Report: Cooling the Planet ABC video: Endangered species threatened by rain ABC video: Water Pollution threatens Millions Video: Bye-bye, blue bayou Video: Cliff nesters