Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 55 Ecosystems PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Overview: Ecosystems, Energy, and Matter • An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Ecosystems can range from a microcosm, such as an aquarium – To a large area such as a lake or forest Figure 54.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Regardless of an ecosystem’s size – Its dynamics involve two main processes: • Energy flows through ecosystems • While matter cycles within them • *so ecosystems are transformers of energy(enters as light and exits as heat) and processors of matter. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 55.1: Ecosystem ecology emphasizes energy flow and chemical cycling • Ecosystem ecologists view ecosystems – As transformers of energy and processors of matter Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystems and Physical Laws • The laws of physics and chemistry apply to ecosystems – Particularly in regard to the flow of energy • Energy is conserved – But degraded to heat during ecosystem processes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Relationships • Energy and nutrients pass from primary producers (autotrophs) – To primary consumers (herbivores) and then to secondary consumers (carnivores) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Figure 54.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sun Biogeochemical Cycles: • Nutrients cycle within an ecosystem • Decomposition links all trophic levels. – (main detritivores are fungi and bacteria) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Detritivores, mainly bacteria and fungi, recycle essential chemical elements – By decomposing organic material and returning elements to inorganic reservoirs Figure 54.3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 55.2: Physical and chemical factors limit primary production in ecosystems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Primary production- the amount of light energy converted to chemical energy by autotrophs during a given time period in the ecosystem. • *P.P. sets the energy budget for the ecosystem. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Global Energy Budget • The amount of solar radiation reaching the surface of the Earth – Limits the photosynthetic output of ecosystems • Only a small fraction of solar energy – Actually strikes photosynthetic organisms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gross and Net Primary Production • GPP (gross primary production)-total primary production in an ecosystem – (Not all of this production is stored as organic material in the growing plants) NPP (net primary production)-amount available to consumers (not used by producers) * Tropics have greatest NPP for the area, oceans overall most NPP only due to size. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Different ecosystems vary considerably in their net primary production – And in their contribution to the total NPP on Earth Open ocean Continental shelf Estuary 5.2 0.3 0.1 0.1 Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice 4.7 Desert and semidesert scrub Tropical rain forest 3.5 3.3 2.9 2.7 Savanna Cultivated land Boreal forest (taiga) 1.6 Tropical seasonal forest Temperate deciduous forest 1.5 1.3 1.0 0.4 Temperate evergreen forest Swamp and marsh Lake and stream Marine 10 3.0 90 0.04 0.9 2,200 22 900 7.9 9.1 600 9.6 800 600 700 5.4 3.5 0.6 140 1,600 7.1 1,200 1,300 4.9 3.8 2.3 0.3 2,000 250 20 30 40 50 60 (a) Percentage of Earth’s surface area 0 500 1,000 1,500 2,000 2,500 (b) Average net primary production (g/m2/yr) Terrestrial Freshwater (on continents) 0.9 0.1 500 0.4 0 1.2 2,500 1.7 Tundra 24.4 5.6 1,500 2.4 1.8 Temperate grassland Woodland and shrubland Key 125 360 65.0 Figure 54.4a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0 5 10 15 20 (c) Percentage of Earth’s net primary production 25 • Oceans provide the most NPP even though they are low in nutrients and unproductive in a defined area. Their vast size gives them a high NPP. • Tropical forests are very high in NPP despite being small because they are very productive. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Overall, terrestrial ecosystems – Contribute about two-thirds of global NPP and marine ecosystems about one-third North Pole 60N 30N Equator 30S 60S South Pole 180 120W 60W Figure 54.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0 60E 120E 180 Light Limitation • The depth of light penetration – Affects primary production throughout the photic zone of an ocean or lake Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutrient Limitation • More than light, nutrients limit primary production in different regions of oceans and lakes. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What limits NPP? • Both Nutrients and Light can determine NPP. • Limiting Nutrient-element needed to increase productivity. In oceans, usually N and P. • ***If you want to test the hypothesis that a certain nutrient is LIMITING …. ADD it and see if NPP increases. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A limiting nutrient is the element that must be added – In order for production to increase in a particular area • Nitrogen and phosphorous – Are typically the nutrients that most often limit marine production – Iron has been found to limit also. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Nutrient enrichment experiments – Confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean EXPERIMENT Pollution from duck farms concentrated near Moriches Bay adds both nitrogen and phosphorus to the coastal water off Long Island. Researchers cultured the phytoplankton Nannochloris atomus with water collected from several bays. 30 21 19 15 5 4 Coast of Long Island, New York. The numbers on the map indicate the data collection stations. Figure 54.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 11 Shinnecock Bay Moriches Bay Atlantic Ocean Inorganic phosphorus 5 4 3 2 1 8 7 6 5 4 3 2 1 0 0 2 4 5 11 30 15 19 21 Station number Great Moriches South Bay Bay 30 Phytoplankton (millions of cells per mL) Phytoplankton 8 7 6 Inorganic phosphorus (g atoms/L) Phytoplankton (millions of cells/mL) RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth (b). 24 Ammonium enriched Phosphate enriched Unenriched control 18 12 6 0 Shinnecock Bay (a) Phytoplankton biomass and phosphorus concentration Starting 2 algal density 4 5 11 30 Station number Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 19 (b) Phytoplankton response to nutrient enrichment Since adding phosphorus, which was already in rich supply, had no effect on CONCLUSION Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem. Figure 54.6 15 21 • Experiments in another ocean region – Showed that iron limited primary production Table 54.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The addition of large amounts of nutrients to lakes – Has a wide range of ecological impacts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Eutrophication of Lakes: • If too much of the limiting nutrient is added (pollution or sewage), the critical load (amt. that can be absorbed) can be exceeded. • An algae bloom results and leads to decay, loss of oxygen…eutrophication. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In some areas, sewage runoff – Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes Figure 54.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary Production in Terrestrial and Wetland Ecosystems • In terrestrial and wetland ecosystems climatic factors – Such as temperature and moisture, affect primary production on a large geographic scale Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The contrast between wet and dry climates – Can be represented by a measure called actual evapotranspiration Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Actual evapotranspiration – Is the amount of water annually transpired by plants and evaporated from a landscape – Is related to net primary production Net primary production (g/m2/yr) 3,000 Tropical forest 2,000 Temperate forest 1,000 Mountain coniferous forest Desert shrubland Temperate grassland Arctic tundra 0 0 500 1,000 1,500 Actual evapotranspiration (mm H2O/yr) Figure 54.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • On a more local scale – A soil nutrient is often the limiting factor in primary production EXPERIMENT Live, above-ground biomass (g dry wt/m2) Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogen to other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls. Adding nitrogen (N) boosts net primary RESULTS production. 300 NP 250 200 150 N only 100 Control 50 P only 0 July June August 1980 Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots. CONCLUSION Figure 54.9 These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 55.3-Trophic Efficiency (% transferred to each level) • Energy transfer between trophic levels is usually only 10% efficient • The secondary production of an ecosystem – Is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time (only a fraction of what it eats) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Production 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 67 J Feces 100 J 33 J Figure 54.10 Growth (new biomass) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration • The production efficiency of an organism – Is the fraction of energy stored in food that is not used for respiration Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Efficiency and Ecological Pyramids • Trophic efficiency – Is the percentage of production transferred from one trophic level to the next – Usually ranges from 5% to 20% Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Pyramids • 1. Energy (Production)-shows only 10% transferred. • 2. Biomass-shows living matter (still about 10% but some aquatic are inverted because producers are consumed too quickly)• 3. Numbers-shows number of organisms, so not always a true pyramid due to size differences. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyramids of Production • This loss of energy with each transfer in a food chain – Can be represented by a pyramid of net production Tertiary consumers Secondary consumers Primary consumers Primary producers Figure 54.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 10 J 100 J 1,000 J 10,000 J 1,000,000 J of sunlight Pyramids of Biomass • One important ecological consequence of low trophic efficiencies – Can be represented in a biomass pyramid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Most biomass pyramids – Show a sharp decrease at successively higher trophic levels Trophic level Dry weight (g/m2) Tertiary consumers 1.5 Secondary consumers 11 Primary consumers Primary producers (a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida. Figure 54.12a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 37 809 • Certain aquatic ecosystems – Sometimes have inverted biomass pyramids(usually because producers are consumed too quickly to accumulate) Trophic level Dry weight (g/m2) Primary consumers (zooplankton) 21 Primary producers (phytoplankton) 4 (b) In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton). Figire 54.12b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyramids of Numbers • A pyramid of numbers – Represents the number of individual organisms in each trophic level (not always a pyramid shape) Trophic level Tertiary consumers Number of individual organisms 3 Secondary consumers 354,904 Primary consumers 708,624 Primary producers Figure 54.13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5,842,424 • The dynamics of energy flow through ecosystems – Have important implications for the human population • Eating meat – Is a relatively inefficient way of tapping photosynthetic production Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Worldwide agriculture could successfully feed many more people – If humans all fed more efficiently, eating only plant material Trophic level Secondary consumers Primary consumers Primary producers Figure 54.14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Green World Hypothesis • According to the green world hypothesis – Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors… Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The green world hypothesis proposes several factors that keep herbivores in check – Plants have defenses against herbivores – Nutrients, not energy supply, usually limit herbivores – Abiotic factors limit herbivores – Intraspecific competition can limit herbivore numbers – Interspecific interactions check herbivore densities Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Most terrestrial ecosystems – Have large standing crops despite the large numbers of herbivores Figure 54.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 55.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A General Model of Chemical Cycling • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A general model of nutrient cycling – Includes the main reservoirs of elements and the processes that transfer elements between reservoirs Reservoir a Organic materials available as nutrients Living organisms, detritus Assimilation, photosynthesis Figure 54.16 Reservoir b Organic materials unavailable as nutrients Fossilization Coal, oil, peat Respiration, decomposition, excretion Burning of fossil fuels Reservoir c Reservoir d Inorganic materials available as nutrients Inorganic materials unavailable as nutrients Atmosphere, soil, water Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Weathering, erosion Formation of sedimentary rock Minerals in rocks • All elements – Cycle between organic and inorganic reservoirs – Also--Remember: decomposition is the key to the rate of cycling. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biogeochemical Cycles • The water cycle and the carbon cycle (p. 1232) THE CARBON CYCLE THE WATER CYCLE CO2 in atmosphere Transport over land Photosynthesis Solar energy Cellular respiration Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Precipitation over land Burning of fossil fuels and wood Evapotranspiration from land Percolation through soil Runoff and groundwater Figure 54.17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carbon compounds in water Higher-level Primary consumers consumers Detritus Decomposition • Water moves in a global cycle – Driven by solar energy – Main reservoir is the ocean • The carbon cycle – Reflects the reciprocal processes of photosynthesis and cellular respiration – Many reservoirs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The nitrogen cycle and the phosphorous cycle THE PHOSPHORUS CYCLE THE NITROGEN CYCLE N2 in atmosphere Rain Geologic uplift Runoff Assimilation NO3 Nitrogen-fixing bacteria in root nodules of legumes Plants Weathering of rocks Denitrifying bacteria Consumption Sedimentation Decomposers Ammonification NH3 Nitrogen-fixing soil bacteria Nitrifying bacteria Nitrification Soil Plant uptake of PO43 Leaching NO2 NH4+ Nitrifying bacteria Figure 54.17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition Nitrogen Cycle key players: • Nitrogen fixing bacteria-take N from air to soil. 2 • Nitrifying bacteria-convert ammonia in soil to nitrates and nitrites. • Denitrifying bacteria--convert nitrates in soil to nitrogen gas in the air. • Legumes-plants with nitrogen fixing bacteria in the roots. • All plants-take in nitrates and pass them through the food chain for all organisms. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Most of the nitrogen cycling in natural ecosystems – Involves local cycles between organisms and soil or water – Main reservoir is the atmosphere (makes up 80% of atmosphere!) • The phosphorus cycle – Is relatively localized, main action is the weathering of rocks and uptake of plants – Main reservoir is sedimentary rocks Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition the Key! • *The key to the rate of Nutrient Cycling is the rate of Decomposition. • This rate varies due to moisture, temps., etc. • Rate of decomp. VERY fast in tropics and slow at the poles. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NITROGEN CYCLE ACTIVITY! • The nitrogen cycle is the one cycle students seem to struggle with so I have set up a role playing activity to help make it more real. • You will be a nitrogen molecule and travel throughout the ecosystem. • At the end of the activity, you will draw the path you took and then LABEL the arrows with the names of the processes you went through. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings RULES FOR DRAWINGS: • If you travelled to a reservoir multiple times, you do not need to draw it more than once, just add more arrows to the place. • After drawing it: Label the arrows with the proper term: – Nitrification -nutrient run-off/moving – Nitrogen fixation -take-up by plants – Denitrification -death – Decomposition -excretion -trophic transfer -dissolved into ground -chemical reaction -precipitation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition and Nutrient Cycling Rates • Decomposers (detritivores) play a key role – In the general pattern of chemical cycling Consumers Producers Decomposers Nutrients available to producers Abiotic reservoir Figure 54.18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Geologic processes • The rates at which nutrients cycle in different ecosystems – Are extremely variable, mostly as a result of differences in rates of decomposition (affected by temperature, moisture, nutrient availability) – Decomposition in rain forest is very rapid. Nutrients do not accumulate, they are rapidly absorbed by plants so soil is very poor. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest • Nutrient cycling – Is strongly regulated by vegetation – See case study-- p. 1234 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Long-term ecological research projects – Monitor ecosystem dynamics over relatively long periods of time • The Hubbard Brook Experimental Forest – Has been used to study nutrient cycling in a forest ecosystem since 1963 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The research team constructed a dam on the site – To monitor water and mineral loss Figure 54.19a (a) Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In one experiment, the trees in one valley were cut down – And the valley was sprayed with herbicides Figure 54.19b (b) One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Net losses of water and minerals were studied – And found to be greater than in an undisturbed area • These results showed how human activity Nitrate concentration in runoff (mg/L) – Can affect ecosystems 80.0 60.0 40.0 20.0 4.0 3.0 2.0 1.0 0 Deforested Completion of tree cutting 1965 Figure 54.19c Control 1966 1967 1968 (c) The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 55.5: The human population is disrupting chemical cycles throughout the biosphere • As the human population has grown in size – Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human Disruptions to Cycles: • 1. Disrupt N-cycling with harvesting, fertilizing, etc. • 2. Biological Magnification- adding chemicals that build up in food chain. • 3. Acid Rain-adding chemicals that change the pH and thus chemical properties of ecosystems • 4. Increased C emissions- (global warming again!) • 5. Ozone Depletion- CFC’s break down ozone layer and allow more UV radiation to enter Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutrient Enrichment • In addition to transporting nutrients from one location to another – Humans have added entirely new materials, some of them toxins, to ecosystems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Agriculture and Nitrogen Cycling • Agriculture constantly removes nutrients from ecosystems – That would ordinarily be cycled back into the soil Figure 54.20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Nitrogen is the main nutrient lost through agriculture – Thus, agriculture has a great impact on the nitrogen cycle • Industrially produced fertilizer is typically used to replace lost nitrogen – But the effects on an ecosystem can be harmful Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Contamination of Aquatic Ecosystems • The critical load for a nutrient – Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • When excess nutrients are added to an ecosystem, the critical load is exceeded – And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Sewage runoff contaminates freshwater ecosystems – Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acid Precipitation • Combustion of fossil fuels – Is the main cause of acid precipitation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • North American and European ecosystems downwind from industrial regions – Have been damaged by rain and snow containing nitric and sulfuric acid 4.6 4.3 4.6 4.3 4.6 4.1 4.3 4.6 Europe Figure 54.21 North America Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • By the year 2000 – The entire contiguous United States was affected by acid precipitation Figure 54.22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Field pH 5.3 5.2–5.3 5.1–5.2 5.0–5.1 4.9–5.0 4.8–4.9 4.7–4.8 4.6–4.7 4.5–4.6 4.4–4.5 4.3–4.4 4.3 • Environmental regulations and new industrial technologies – Have allowed many developed countries to reduce sulfur dioxide emissions in the past 30 years Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Toxins in the Environment • Humans release an immense variety of toxic chemicals – Including thousands of synthetics previously unknown to nature • One of the reasons such toxins are so harmful – Is that they become more concentrated in successive trophic levels of a food web Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In biological magnification – Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower Concentration of PCBs Herring gull eggs 124 ppm Figure 54.23 Lake trout 4.83 ppm Smelt 1.04 ppm Zooplankton 0.123 ppm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phytoplankton 0.025 ppm • In some cases, harmful substances – Persist for long periods of time in an ecosystem and continue to cause harm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Atmospheric Carbon Dioxide • One pressing problem caused by human activities – Is the rising level of atmospheric carbon dioxide Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 0.15 0 Temperature variation (C) CO2 concentration (ppm) – The concentration of atmospheric CO2 has been steadily increasing 320 0.15 310 0.30 300 1960 1965 1970 1975 Figure 54.24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0.45 1980 1985 1990 1995 2000 2005 Year How Elevated CO2 Affects Forest Ecology: The FACTS-I Experiment • The FACTS-I experiment is testing how elevated CO2 – Influences tree growth, carbon concentration in soils, and other factors over a ten-year period Figure 54.25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Greenhouse Effect and Global Warming • The greenhouse effect is caused by atmospheric CO2 – But is necessary to keep the surface of the Earth at a habitable temperature Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Increased levels of atmospheric CO2 are magnifying the greenhouse effect – Which could cause global warming and significant climatic change Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Depletion of Atmospheric Ozone • Life on Earth is protected from the damaging effects of UV radiation – By a protective layer or ozone molecules present in the atmosphere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Satellite studies of the atmosphere – Suggest that the ozone layer has been gradually thinning since 1975 Ozone layer thickness (Dobson units) 350 300 250 200 150 100 50 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Figure 54.26 Year (Average for the month of October) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The destruction of atmospheric ozone – Probably results from chlorine-releasing pollutants produced by human activity 1 Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and oxygen (O2). Chlorine atoms O2 Chlorine O3 ClO O2 Figure 54.27 3 Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again. ClO Cl2O2 Sunlight Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 Two ClO molecules react, forming chlorine peroxide (Cl2O2). • Scientists first described an “ozone hole” – Over Antarctica in 1985; it has increased in size as ozone depletion has increased (a) October 1979 Figure 54.28a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) October 2000 • Good news? • Since CFC’s have been regulated by many nations, the ozone depletion is slowing. • However, the chlorine still in the atmosphere will still have effects for 50 years. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings