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Ecosystems The Earth’s Spheres 1. The hydrosphere is the zone of water that covers over three-quarters of the earth. a. The ability of water to absorb and release great quantities of heat keeps climate within livable range. 2. The atmosphere is the gaseous layer near earth. a. The atmosphere is concentrated in lowest 10 kilometers; extends thinly out to 1,000 km. b. Major gases are nitrogen, oxygen and carbon dioxide. 3. The lithosphere is a rocky substratum that extends about 100 kilometers deep. a. Weathering of rocks supplies minerals to plants and eventually forms soil. b. Soil contains decayed organic material (humus) that recycles nutrients to plants. 4. The biosphere is the thin layer where life is possible between the outer atmosphere and the lithosphere. Ecosystems can range from a microcosm, such as an aquarium – To a large area such as a lake or forest Regardless of an ecosystem’s size • Its dynamics involve two main processes: energy flow and chemical cycling – Energy flows through ecosystems – While matter cycles within them Factors affecting Ecosystems • Biotic: Living • Abiotic: Nonliving Clip Energy flows through an ecosystem – Entering as light and exiting as heat Tertiary consumers Microorganisms and other detritivores Detritus Secondary consumers Primary consumers Primary producers Heat Key Chemical cycling Energy flow Sun Energy flows through an ecosystem • First law of thermodynamics – energy can neither be created nor destroyed; it can only be changed from one form of energy to another. • Energy in an ecosystem is transformed by the organism and passed through the food chains • Second law of thermodynamics: – when energy is transformed from one form to another, there is always some loss of energy from the system, usually as low grade heat. Energy flows through an ecosystem: Food Chains and Webs • A food chain represents passage of energy through populations in a community. – A trophic level is a feeding level of one or more populations in a food web. Quaternary consumers Carnivore Tertiary consumers Carnivore Carnivore Carnivore Herbivore Secondary consumers Primary consumers Primary producers Animation Carnivore Plant A terrestrial food chain Carnivore Zooplankton Phytoplankton A marine food chain Energy flows through an ecosystem: Humans Food Webs • A food web – Is a branching Baleen food chain with whales complex Crab-eater seals trophic interactions Birds Smaller toothed whales Leopard seals Fishes Sperm whales Elephant seals Squids Carnivorous plankton Euphausids (krill) Copepods Phytoplankton Ecological Pyramids • Shows the trophic structure of an ecosystem and the energy content that is passed to each successive trophic level in a food web. All of the solar energy that enters an ecosystem is eventually lost as heat Pyramid of energy Ecological Efficiency • When a caterpillar feeds on a plant leaf • Only about one-sixth of the energy in the leaf is used for secondary production Plant material eaten by caterpillar 200 J Feces 100 J 67 J 33 J Growth (new biomass) Cellular respiration Ecological Efficiency Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next Ecological Pyramids and Efficiency This rapid loss of energy is the reason… food chains have from three to four links, rarely five. there are few large carnivores. Tertiary consumers Secondary consumers Primary consumers Primary producers 10 J 100 J 1,000 J 10,000 J 1,000,000 J of sunlight Primary productivity • Rate at which autotrophs capture and store energy within organic compounds over a length of time. Amount of light energy converted to chemical energy (glucose) • i.e. •Net primary production (NPP) •Is equal to GPP minus the energy used by the primary producers for respiration •Only NPP •Is available to consumers Measuring Primary Productivity • Rate of O2 production • Gross primary productivity is the amount available to heterotrophs • GPP is NPP + R Since some of the O2 is used in respiration: NPP= GPP - R AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity • You will… – Measure primary productivity based on changes in dissolved oxygen. – Investigate the effects of changing light intensity on primary productivity. Biological Magnification – Ex: bald eagle 1950s -DDT • DDT interferes with the deposition of calcium in eggshells • DDT is now outlawed Concentration of PCBs • Organisms at higher trophic levels have greater concentrations of accumulated toxins stored in their bodies. PCBs: polychlorinated biphenyls Herring gull eggs 124 ppm Lake trout 4.83 ppm Smelt 1.04 ppm Zooplankton 0.123 ppm Phytoplankton Biogeochemical Cycles • Life on Earth – Depends on the recycling of essential chemical elements • Nutrient circuits that cycle matter through an ecosystem – Involve both biotic and abiotic components and are often called biogeochemical cycles Hydrologic cycle Carbon Cycle Nitrogen cycle Phosphorus cycle Clip • Gaseous forms of carbon, oxygen, sulfur, and nitrogen – Occur in the atmosphere and cycle globally • Less mobile elements, including phosphorous, potassium, and calcium – Cycle on a more local level 1. In the hydrologic cycle, freshwater evaporates and condenses on the earth. 2. Evaporation of water from the oceans leaves behind salts. 3. Rainfall that permeates the earth forms a water table at the surface of the ground water. 4. An aquifer is an underground storage of fresh water in porous rock trapped by impervious rock 5. Freshwater makes up about 3 percent of the world's supply of water and is a renewable resource. 6. Freshwater becomes unavailable when consumption exceeds supply or is polluted so it is not usable. 1. Terrestrial and aquatic organisms exchange carbon dioxide with the atmosphere. 2. Photosynthesis removes CO2 from atmosphere; respiration and combustion add CO2 to atmosphere. 3. CO2 from the air combines with water to produce bicarbonate (HCO3), which is a source of carbon for aquatic producers, primarily algae. 4. Similarly, when aquatic organisms respire, the CO2 they release combines with water to form HCO3. 5. The amount of HCO3 in the water is in equilibrium with the amount of CO2 in the air. Animation 6. The reservoir for the carbon cycle is largely composed of organic matter, calcium carbonate in shells, and limestone, as well as fossil fuels. Carbon Dioxide & Global Warming • CO2, nitrous oxide and methane are gasses that contribute to the rise in atmospheric temperature Global Warming (proposed) Possible consequences of Global Warming • Rising sea levels • Increasing ocean temperatures • Severe weather 1. Nitrogen gas (N2) is 78% of the atmosphere, yet nitrogen deficiency often limits plant growth. 2. In the nitrogen cycle, plants cannot incorporate N2 into organic compounds and therefore depend on various types of bacteria to make nitrogen available to them. 3. Nitrogen Gas Becomes Fixed a. Nitrogen fixation is the process whereby N2 is reduced and added to organic compounds. b. Some cyanobacteria in water and free-living bacteria in soil are able to reduce N2 to ammonium (NH4+). c. Other nitrogen-fixing bacteria, living in nodules on the roots of legumes, make reduced nitrogen and organic compounds available to the host plant. d. Plants cannot fix atmospheric nitrogen but take up both NH4+ and nitrate (NO3-) from the soil. e. After plants take up NO3-, it is enzymatically reduced to NH4+ used to synthesize amino and nucleic acids. Animation 4. Nitrogen Gas Becomes Nitrates a. Nitrification is the production of NO3-. b. Nitrogen gas is converted to NO3in the atmosphere when cosmic radiation, meteor trails, and lightning provide the high energy for nitrogen to react with oxygen. c. Nitrifying bacteria convert NH4+ to NO3-. d. Ammonium in the soil is converted to NO3- by nitrifying bacteria in the soil in a two-step process: 1) First, nitrite-producing bacteria convert NH4+ to nitrite (NO3-). 2) Then, nitrate-producing bacteria convert NO2 - to NO3-. e. Denitrification is conversion of NO3- to nitrous oxide (N2O) and N2. f. There are denitrifying bacteria in both aquatic and terrestrial ecosystems. g. Denitrification counterbalances nitrogen fixation, but not completely; more nitrogen fixation occurs. h. Humans contribute much to the nitrogen cycle when they convert N2 to ammonium and urea in fertilizers. i. Eutrophication (over enrichment) results from fertilizer runoff; when rampant algae dies off, decomposers use up available oxygen during cellular respiration, and this results in a massive fish • 5. Nitrogen and Air Pollution a. Production of fertilizers and burning of fossil fuels adds three times the nitrogen oxides to the atmosphere as normal. b. Acid deposition occurs when nitrogen oxides and sulfur oxides combine with water vapor. c. Photochemical smog results when nitrogen oxides and hydrocarbons react in presence of sunlight; smog contains ozone and peroxyacetylnitrate (PAN) and causes respiratory problems. d. Air pollutants are trapped near the ground by thermal inversions where cold air is trapped near the ground by warm air above. • 1. In phosphorus cycle, weathering makes phosphate ions (PO4 and HPO4 2-) available to plants from the soil. 2. Some phosphate runs off into aquatic ecosystems where algae incorporate it into organic molecules. 3. Phosphate that is not taken up by algae is incorporated into sediments in the oceans. 4. Sediment phosphate only becomes available when geological upheaval exposes sedimentary rocks. 5. Phosphate taken up by producers is incorporated into a variety of organic compounds. 6. Animals eat producers and incorporate some of phosphate into long-lasting teeth, bones, and shells. 7. Decay of organisms and decomposition of animal wastes makes phosphate ions available again. 8. Available phosphate is generally taken up quickly; it is usually a limiting nutrient in most ecosystems. Animation Phosphorus and Water Pollution 1. Humans boost the supply of phosphate by mining phosphate ores for fertilizers, detergents, etc. 2. Run-off of animal wastes from livestock feedlots and commercial fertilizers from cropland as well as discharge of untreated and treated municipal sewage can all add excess phosphate to nearby waters. 3. Eutrophication is the name of this overenrichment and can lead to algal blooms; when the algae die off, decomposers use up the oxygen 5. Oil spills add over 5 million metric tons of oil a year to oceans. 6. Human activities including fishing have exploited ocean resources to the brink of extinction. Human Impact • • • • • • • • Greenhouse effect Ozone depletion Acid Rain Desertification Deforestation Pollution Reduction in species diversity Introduction of nonendemic species Rising Atmospheric CO2 • Due to the increased burning of fossil fuels and other human activities 390 1.05 380 0.90 0.75 370 Temperature 0.60 360 0.45 350 0.30 340 CO2 330 0 320 0.15 310 0.30 300 1960 1965 1970 1975 Figure 54.24 0.15 Temperature variation (C) CO2 concentration (ppm) – The concentration of atmospheric CO2 has been steadily increasing 0.45 1980 1985 1990 1995 2000 2005 Year • Modeling ecosystems - trophic components