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Midterm

ENV200 Test 1 Textbook Notes

25 Pages
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Department
School of Environment
Course Code
ENV200H1
Professor
Romila Verma

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Chapter 1 – Understanding Our Environment [1.1] Understanding our environment - Environment (French environner = to encircle or surround) = the natural world and the “built” or technological, social, and cultural world - Environmental science = the systematic study of our environment and our place in it o Draws upon many disciplines to help us understanding pressing problems of resource supply, ecosystem stability, and sustainable living (e.g., social sciences, natural sciences) o Uses scientific methods to study processes and systems in the environment o Works in the public interest  E.g., To promote public health by reducing water contamination without necessarily being interested in nature or biodiversity - Environmentalism = working to influence attitudes and policies that affect our environment - The most amazing feature of our planet is its rich diversity of life o Millions of species populate the earth and help sustain a habitable environment o Creates diverse, self-sustaining ecosystems [1.2] Crises and opportunities - There are over 7 billion people on earth, about twice as many as there were 40 years ago o About 80 million people added each year o Between 8 and 10 million people by 2050 - Climate change o Atmosphere normally captures heat near the earth’s surface o Human activities have greatly increased concentrations of greenhouse gases (e.g., CO2)  Atmospheric CO2 concentrations have increased 30% in the past 200 years  Global mean temperatures will increase by 2-6°C compared to 1990  Severe droughts and heat waves  Greater storm intensity and flooding  Disappearing mountaintop glaciers and snowfields - Hunger o Global food production has increased faster than human population growth over the past century, but food resources are unevenly distributed o Biotechnology and intensive farming techniques are too expensive for many poor farmers o About 2/3 of all agricultural lands show signs of degradation o More than 850 million people are chronically undernourished o At least 60 million people face acute food shortages due to weather, politics, or war - Clean water st o Most critical resource in the 21 century o At least 1.1 billion people lack access to safe drinking water o At least 2.2 billion people don’t have adequate sanitation o More than 15 million people (mostly children under age 5) are killed every year from polluted water o About 40% of the world population lives in countries where water demands exceed supplies o At least 75% of us could live under similar conditions by 2025 - Energy resources o Fossil fuels (e.g., oil, coal, natural gas) provide around 80% of the energy used in industrialized countries  Supplies are diminishing  Costs are high (e.g., air and water pollution, mining damage, political conflicts, climate change) o Energy conservation and renewable energy resources (e.g., solar, wind, geothermal, biomass power) are less destructive options - Air quality o Air quality has worsened dramatically in newly industrialized areas (e.g., China, India) o Asian brown cloud = 3 km (2 mile) thick toxic haze of ash, acids, aerosols, dust, and photochemical smog regularly covers the entire Indian subcontinent for much of the year o At least 3 million people die each year from diseases triggered by air pollution o More than 2 billion metric tons of air pollutants (not including CO2 or soil) are released each year o Air pollutants travel easily around the world - Biodiversity loss o Habitat destruction, overexploitation, pollution, and exotic organisms are eliminating species o More than 800 species have disappeared over the past century o At least 10,000 species are considered threatened  50% of all primates and freshwater fish  10% of all plant species o Most bird and butterfly populations have declined by 50-75% over the last 20 years o At least 50% of forests existing before the introduction of agriculture have been cleared - Marine resources o The ocean is an irreplaceable food resource o More than 1 billion people in developing countries depend on seafood as a main source of animal protein o Most commercial fisheries around the world are in steep decline o More than 75% of the 441 fish stocks are severely depleted or in urgent need of better management o About 90% of all the large predators (e.g., Bluefin tuna, marlin, swordfish, sharks, cod, halibut) have been removed from the ocean - There is increasing awareness that is leading to progress in many areas - Population and pollution o Population has stabilized in most industrialized countries and even in some very poor countries o Since 1950, the average number of children born per woman worldwide has decreased from 5 to 2.45 o By 2050, most countries will have fertility rates below the replacement rate of 2.1 children per woman  World population will stabilize at about 8.9 billion, instead of 9.3 billion - Health o Incidence of life-threatening infectious diseases has been reduced o Life expectancies have nearly doubled o Smallpox has been completely eradicated o Polio has vanquished expect in a few countries o More than 800 million people have gained access to improved water supplies and modern sanitation since 1990 o Food insecurity and chronic hunger has declined by about 40 million people, despite the population growth of 1 billion people during the 1990s - Renewable energy o Transition to renewable energy sources (e.g., wind, solar, biomass power) are reducing reliance on fossil fuels - Information and education o Access to knowledge is expanding and essential to progress  Rapid exchange of information on the Internet makes it easier to raise global awareness of environmental problems o Literacy and access to education are expanding  Education for girls is a primary driver for declining birth rates worldwide - Conservation of forests and nature preserves o Deforestation rates has slowed in Asia from over 8% to less than 1% o Brazil has led global deforestation rates for decades, but is now working to protect forests o Nature preserves and protected areas have increased o More than 100,000 parks and nature preserves around the world  20 million km (7.7 million mi )  13.5% of the world’s land area - Protection of marine resources o MPAs and improved monitoring of fishes provide opportunities for sustainable management [1.4] Science helps us understand our world - Science = process for producing knowledge based on observations o Cumulative body of knowledge produced by many scientists o Searches for testable evidence (e.g., more evidence = better answers) o Assumes that the world is knowable and that we can learn about it by careful observation and logical reasoning  Radical departure from religious and philosophical approaches  In the Middle Ages, the ultimate sources of knowledge about matters such as how crops grow, how diseases spread, or how the stars move were religious authorities or cultural traditions - Scientists are skeptical o Cautious about accepting a proposed explanation until there is substantial evidence to support it o Aims to be methodical and unbiased o Scientific tests are subject to review by informed peers  Peer review process = to ensure that scientists maintain good standards in study design, data collection, and interpretation of results - Scientists demand reproducibility o Cautious about accepting conclusions o Must produce the same result consistently to be sure that the first outcome wasn’t a fluke o Must describe the conditions of the study so that someone else can reproduce the findings - Basic principles of science o Empiricism = we can learn about the world by careful observation of empirical (real, observable) phenomena = expect to understand fundamental processes and natural laws by observation o Uniformitarianism = basic patterns and processes are uniform across time and space o Parsimony (Ockham’s razor) = when two plausible explanations are reasonable, the simpler (more parsimonious) one is preferable o Uncertainty = knowledge changes as new evidence appears, and explanations (theories) changes with new evidence o Repeatability = test and experiments should be repeatable such that if the same results cannot be reproduced, then the conclusions are probably incorrect o Proof is elusive = we rarely expect science to provide absolute proof that a theory is correct because new evidence may also improve our current explanations o Testable questions = to find out whether a theory is correct, it must be tested by formulating testable hypotheses - Deductive reasoning = deduce conclusions from general laws that are known to be true (e.g., general to specific) o More logically sound, but only works when the general laws are correct o Often, we do not know the general laws that guide natural systems - Inductive reasoning = rely on observations to produce a general rule (e.g., specific to general) - Insight, creativity, and experience can also be essential in science - Standard scientific steps o Identify question o Propose a testable hypothesis o Develop a test of the hypothesis o Collect data from the test o Interpret the results o Refine and revise original hypothesis o Report for peer review - It is always easier to prove a hypothesis wrong than to prove it true o We usually test our hypotheses with observations, but there is no way to make every possible observation o The elusiveness of absolute proof is a persistent problem in environmental policy and law o The elusiveness of proof often decides environmental liability lawsuits - Theory = proposed explanation of how a process works - Scientific theory = when an explanation has been supported by a large number of tests, and when a majority of experts have reached a general consensus that it is a reliable description or explanation o To many people, a theory is a speculative and unsupported by facts o To a scientist, a theory means that while all explanations are tentative and open to revision and correction, it is supported by an overwhelming body of data and experience, and it is generally accepted by the scientific community - Science involves probability o Probability estimates are based on a set of previous observations or on standard statistical measures o Sometimes probability has to do with random chance (e.g., flipping a coin) o Sometimes probability is weighted by circumstances (e.g., amount of time spent studying) o Sometimes there is a combination of chance and circumstances (e.g., catching a cold) o Probability is often more reliable than proof  Absolute proof is hard to achieve, but we can demonstrate a strong trend or relationship that is unlikely to be achieved by chance - Experimental design can reduce bias o Observable (or natural) experiment = observe natural events that have already happened and interpret a causal relationship between the variables o Manipulative experiment = conditions are deliberately altered and all other variables are held constant  Controlled study = comparing a treatment (exposed) group and a control (unexposed group) o Double-blind experiment = neither the subject nor the researcher knows who is in the treatment group and who is in the control group - Studies have one dependent (or response) variable and one, or more, independent (or explanatory) variables o Dependent variable is affected by the independent variables o Independent variables may be affected by the same environmental conditions as the dependent variable o Explanatory variables explain differences in the dependent variable - Science is a cumulative process o Accumulation of scientific knowledge involves cooperation and contributions from many people o A community of scientists collaborates in a cumulative, self-correcting process o Scientific consensus = general agreement among informed scholars  E.g., Many coral reefs are in danger, as a result of pollution, physical damage, and warming seas  E.g., Global climate conditions are changing, though models differ somewhat on how rapidly they will change in different regions o Paradigm shifts = new ideas emerge that cause major shifts in scientific consensus  Paradigm shifts occur when a majority of scientists accept that the old explanation no longer describes new observations very well - When controversy surrounds science, claims about sound science and accusations of “junk science” often arise o Media will often take a position contrary to the scientific majority to gain publicity, political allies, and money o Baloney Detection Kit  How reliable are the sources? Is there reason to believe that they might have an agenda?  Have the claims been verified by other sources? What data are presented in support of this opinion?  What position does the majority of the scientific community hold in this issue?  How does this claim fit with what we know about how the world works? Is this a reasonable assertion or does it contradict established theories?  Are the arguments balanced and logical? Have proponents of a particular position considered alternative points of view or only selected supportive evidence for their particular beliefs?  What do you know about the sources of funding for a particular position? Are studies financed by groups with partisan goals?  Where was evidence from competing theories published? Has it undergone impartial peer review or is it only proprietary publication? - Scientific uncertainty is frequently invoked as a reason to postpone actions that a vast majority of informed scientists consider to be prudent o Our decisions to accept or dispute scientific evidence often depend on group identity o Our urge to be agreeable to our group can be strong, compared to our interest in critically analyzing evidence o Expectations of group behaviour can shift over time o Resolving differences on environmental policy sometimes requires recognition of group identity in our attitudes toward science, as well as our attitudes toward policies and issues beyond science [1.5] Critical thinking - We evaluate arguments in science with observable evidence or data o Logical reasoning from evidence o Critical evaluation of evidence - Critical thinking = logical, orderly, analytical assessment of ideas, evidence, and arguments o Steps in critical thinking:  What is the purpose of my thinking?  What precise question am I trying to answer?  Within what point of view am I thinking?  What information am I using?  How am I interpreting that information?  What concepts or ideas are central to my thinking?  What conclusions am I aiming toward?  What assumptions am I making?  If I accept the conclusions, what are the implications?  What would the consequences be if I put my thoughts into action? o Steps in critical thinking:  Identify and evaluate premises and conclusions in an argument  Acknowledge and clarify uncertainties, vagueness, equivocation, and contradictions  Distinguish between facts and values  Recognize and assess assumptions  Distinguish source reliability or unreliability  Recognize and understand conceptual frameworks - Analytical thinking = helps break a problem down into its constituent parts - Creative thinking = “how might I approach this problem in new and inventive ways?” - Logical thinking = evaluates whether the structure of the argument make sense - Reflective thinking = “what does it all mean?” - Data change constantly, including our interpretation of data - Although most of us try to be fair and even-handed in presenting controversies, our personal biases and values affect how we see issues and present arguments [1.6] Where do our ideas about the environment come from? - Many of our current responses to problems of environmental degradation are rooted in the writings of relatively recent environmental thinkers o Four distinct stages, but not mutually exclusive:  Resource conservation for optimal use  Nature preservation for moral and aesthetic reasons  Concern over health and ecological consequences of pollution  Global environmental citizenship - Most modern environmental ideas developed in response to resource depletion associated with more recent agricultural and industrial revolutions - Resource waste triggered pragmatic resource conservation (stage 1) o Pragmatic utilitarian (or resource) conservation = forests should be saved, not because they are beautiful or because they shelter wild creatures of the wilderness, but only to provide homes and jobs for people  Resources should be used for the greatest good, for the greatest number, for the longest time  Conservation is the development and use of the natural resources now existing on this continent for the benefit of the people who live here now  There may be just as much waste in neglecting the development and use of certain natural resources as there is in their destruction - Ethical and aesthetic concerns inspired the preservation movement (stage 2) o Preservation = the fundamental right of other organisms – and nature as a whole – to exist and to pursue their own interests o Conservation = positive exercise of skill and insight, not merely a negative exercise of abstinence or caution - Rising pollution levels led to the modern environmental movement (stage 3) o Modern environmentalism (e.g., activism + research) = concerns extend to include both natural resources and environmental pollution - Environmental quality is tied to social progress (stage 4) o Sustainable development = economic improvement for the world's poorest populations is possible without devastating the environment  Core concept of modern environmentalism o Global environmentalism = links between environmental quality and social progress on a global scale [EXPLORING SCIENCE] How do we know the state of population and poverty? - Too large to observe directly - Use data sets, usually collected by governments (e.g., U.S. Census) or by organizations (e.g., UN Food and Agriculture Organization, World Bank) - Census agency o Contacts as many individuals in a country as they can reach o Asks a standard list of questions o Enters all the answers into an enormous set of data tables that anybody can access o Calculate averages, high and low values, changes from previous surveys, or comparisons among regions - International organizations o Unable to contact all persons in the world o Survey governments and attempt to gather answers to a standard set of questions o Sometimes there are “no data” values in global data sets (e.g., Somalia, North Korea) - Data sources provide a large-scale view of issues such as hunger, poverty, education, or health - Both local and global views are often necessary for describing trends in environmental science [KEY CONCEPTS] Sustainable development is a goal - Sustainable development = to meet the needs of people today without compromising resources and environmental systems for future generations - Development = improving access to health care, education, and other conditions necessary for a healthy and productive life o Equitable economic growth supports better education, housing, and health care o Accelerated extraction of natural resources (e.g., more mining, forestry, conversion of forests and wetlands to farmlands) o More efficient use of resources or growth in parts of the economy that don't depend on resource extraction (e.g., education, health care, knowledge-based economic activities) o Some resources can be enhanced and used without depletion for future generations (e.g., reforestation, maintaining fish nurseries, careful management of soil resources) - Ten key factors necessary for sustainable development: o Combating poverty because poverty reduces access to health care, education, and other essential components of development o Reducing resource consumption but wealthy regions are responsible for most of the world's consumption o Population growth leads to ever-greater resource demands because all people need some resources o Health care because without health, economic security is at risk, and poverty can persist through generations o Sustainable cities to ensure that cities are healthy places to live and cause minimal environmental impact because over half of humanity lives in cities o Environmental policy ensures that environmental quality is protected before it gets damaged and sets agreed-upon rules for resource use o Protection of the atmosphere minimizes the rate of climate change and reduces the impact of air pollution on people, plants, and infrastructure o Combating deforestation and protecting biodiversity because much of the world’s biodiversity is in forests and we depend on forests for water resources, climate regulation, and resources  Other key zones of biodiversity include coral reefs, wetlands, and coastal areas o Combating desertification and drought (e.g., better management of water resources) can save farms, ecosystems, and lives o Agriculture and rural development (e.g., more sustainable farming systems, soil steward ship to help stabilize yields, access to land) affects the lives of nearly half of humanity who don’t live in cities and helps reduce populations in urban slums Chapter 2 – Environmental Systems: Matter, Energy, and Life [2.3] Energy - Energy = the ability to do work - Kinetic energy = the energy contained in moving objects - Potential energy = stored energy that is available for use - Chemical energy = stored energy in food and gasoline o An example of potential energy - Energy is often measured in units of heat (calories) or work (joules) o Joule (J) = the work done when one kilogram is accelerated at one meter per second per second o Calorie = the amount of energy needed to heat one gram of pure water one degree Celsius  1 calorie = 4.184 J - Heat = the energy that can be transferred between objects of different temperature o Change in heat content = change in kinetic energy = change in temperature (unless there is change in state)  High heat content, but low temperature (e.g., lake freezing slowly)  Low heat content, but high temperature (e.g., burning match) - Low-quality energy = energy that is diffused, dispersed, and low in temperature is difficult to gather and use for productive purposes (e.g., heat stored in the oceans, alternative energy sources)  hard to use - High-quality energy = energy that is intense, concentrated, and high in temperature is useful in carrying out work (e.g., intense flames of a very hot fire, high-voltage electrical energy, oil, coal, gas)  easy to use - Energy flows in a one-way path o A constant supply of energy (mostly from the sun) is needed to keep biological processes running  Used repeatedly as it flows through the system  Stored temporarily in the chemical bonds of organic molecules  Eventually, it is released and dissipated - Thermodynamics = the rates of flow and the transformation of energy from one form or quality to another - First law of thermodynamics = energy is conserved; neither created nor destroyed; may be transformed - Second law of thermodynamics = energy is degraded and dissipates as it moves through ecosystems o With each successive energy transfer or transformation in a system, less energy is available to do work o Entropy = disorder  Tends to increase in all natural systems  Less useful energy is available at the end of a process than at the start  Everything in the universe tends to fall apart, slow down, and get more disorganized o Organisms are structurally and metabolically organized, which requires a continual supply of energy  Every time some energy is used by a cell to do work, some of that energy is dissipated or lost as heat  If cellular energy supplies are interrupted or depleted, then the result is death [2.4] Energy for life - There are organisms that get energy in other ways o Extremophiles = organisms that get energy through chemosynthesis  Found deep the earth's crust, deep on the ocean floor, and in hot springs  Ecosystems cluster around thermal vents  Thermal vents = cracks where boiling-hot water, heated by magma in the earth's crust, escapes from the ocean floor o Chemosynthesis = extracting energy from inorganic chemical compounds, such as oxidation of hydrogen sulfide (H S) 2 - For nearly all life on earth, the sun is the ultimate energy source o Sun = made up of hydrogen gas  Provides much more energy than biological systems can harness (e.g., more than enough) o Electromagnetic spectrum  Solar radiation = sun emits infrared, visible, and ultraviolet light  Our eyes are sensitive to visible light wavelengths  More than half of incoming sunlight is reflected or absorbed by clouds, dust, and gases  Of the solar radiation that does reach the earth’s surface: o Absorbed by land or water o Reflected into space by water, snow, and land surfaces o 45% infrared, 45% visible, and 10% ultraviolet  Harmful, short wavelengths are filtered out by gases (e.g., ozone) in the upper atmosphere  Terra radiation = earth emits infrared light (e.g., lower energy, longer wavelengths) - Solar energy is essential to life for two main reasons o Provides warmth  Most organisms survive within a relatively narrow temperature range  At high temperatures (above 40°C), most biomolecules begin to break down  At low temperatures (near 0°C), some chemical reactions of metabolism occur too slowly  Water and atmosphere helps to moderate, maintain, and distribute the sun's heat  Atmosphere protects life-forms from harmful doses of ultraviolet and other forms of radiation o Nearly all organisms on the earth's surface depend on solar radiation for life-sustaining energy - Primary producers = create carbohydrates and other organic molecules using sunlight, water, and carbon dioxide o Provide the energy and matter in an ecosystem o Carry out both photosynthesis and cellular respiration o During the day, if light, water, and CO2 are available, then there is a net production2of O and carbohydrates - Photosynthesis = converts radiant energy into high-energy chemical energy in the bonds that hold organic molecules together o 6H O + 6CO + solar energy  C H O + 6O 2 2 6 12 6 2  Energy is captured  Energy is stored temporarily in chemical bonds o Use visible and infrared light wavelengths o Absorb red and blue wavelengths o Reflect green wavelengths o Half of the energy plants absorb is used in evaporating water o 1-2% of the sunlight falling on plants is available for photosynthesis o Occurs within chloroplasts o Chlorophyll = a unique green molecule that can absorb light energy and use it to create high-energy chemical bonds in compounds that fuel all subsequent cellular metabolism  Assisted by other lipid, sugar, protein, and nucleotide molecules o Light-dependent reactions = reactions occur while the chloroplast is receiving light  Extract energy from light  Split water molecules  Release molecular oxygen (O ) 2  Create high-energy molecules, which provide energy for the next set of processes  ATP = adenosine triphosphate  NADPH = nicotinamide adenine dinucleotide phosphate o Light-independent reactions = reactions do not use light directly  Extract energy from ATP and NADPH  Split carbon dioxide molecules  Add carbon atoms (from carbon dioxide) to simple sugar molecules (e.g., glucose) o Glucose = an energy-rich compound that serves as the primary fuel for all metabolic processes of cells  Energy in its chemical bonds can be released by other enzymes  To make other molecules  To drive kinetic processes - Cellular respiration = splitting carbon and hydrogen atoms from the sugar molecule and recombining them with oxygen to recreate carbon dioxide and water o C H O + 6O  6H O + 6CO + released energy 6 12 6 2 2 2  Energy is released  Energy is stored temporarily in chemical bonds o Reverse of photosynthesis o To extract energy and nutrients from organic molecules [2.5] From species to ecosystems - Species (Latin species = kind) = all organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring - Population = all the members of a species living in a given area at the same time - Biological community = all the populations of organisms living and interacting in a particular area - Ecosystem = a biological community and its physical environment o Energy and matter flow through the biological community and its physical environment - Photosynthesis (and rarely chemosynthesis) is the base of all ecosystems - Producers = organisms that produce organic material by photosynthesis o Mainly green plants and algae - Productivity = the amount of biomass (biological material) produced in a given area during a given period of time o Most important property of an ecosystem o Measured by remote sensing from aircraft or satellites o Primary productivity = photosynthesis is the basis for almost all growth in an ecosystem  Net primary productivity will be low if decomposers consume the biomass as rapidly as it is formed by producers - Food web = several types of predators and parasites o Most consumers have multiple food sources o Many species are prey to several types of predators and parasites - Trophic level = an organism's feeding status in an ecosystem o Primary producers (autotrophs) = feed themselves using only sunlight, water, carbon dioxide, minerals o Consumers = an organism that eats the chemical energy harnessed by the producers  Primary consumer (herbivores) = an organism that eats primary producers  Secondary consumer (carnivores) = an organism that eats primary consumers  Tertiary consumer (top carnivores/predators) = highest tropic level o Recyclers = remove and recycle dead bodies and waste products of others; feed on all trophic levels  Scavengers = clean up dead carcasses of larger animals  E.g., jackals, cultures  Dentrivores = consume litter, debris, and dung  E.g., ants, beetles  Decomposers = complete the final breakdown and recycling of organic materials  E.g., fungi, bacteria  Without them, nutrients would remain locked up in the organic compounds of dead organisms and discarded body wastes, rather than being made available to successive generations o Pyramid structure  Broad base of primary producers  Few individuals in the highest trophic levels  Huge number of organisms at lower trophic levels is needed to support few top carnivores - Savanna = a rolling grassland scattered with shrubs and isolated trees, which can be found between a tropical rainforest and desert biome - The complexity of a food chain depends on both the number of species available as well as the physical characteristics of a particular ecosystem o A harsh arctic landscape has a much simpler food chain than a temperate or tropical one [2.6] Biogeochemical cycles and life processes - Biogeochemical cycle = elements and compounds are cycled endlessly through living things and the environment - Hydrologic cycle o Most of the earth's water is stored in the oceans o Steps  Solar energy evaporates water  Wind distribute water vapor around the globe  Water condenses over land (e.g., rain, snow, fog) and supports all terrestrial ecosystems  10% of water evaporated from oceans falls over land  Organisms emit moisture through respiration and perspiration  Re-enters the atmosphere  Enters the lakes and streams  Returns to the ocean o Water is responsible for:  Metabolic processes within cells  Maintaining the flows of key nutrients through ecosystems  Global-scale distribution of heat and energy - Carbon cycle o Carbon serves a dual purpose for organisms  Structural component of organic molecules  Chemical bonds in carbon compounds provide metabolic energy o Photosynthetic organisms take up CO 2  Carbon fixation = carbon is changed from gaseous CO2to less mobile organic molecules o Recycling may be very quick or extremely slow  Organisms can exhale CO during cellular respiration, and plants could take up the CO in the 2 2 same afternoon  Organisms can use carbon atoms in a sugar molecule to make larger organic molecules, so carbon atoms remain a part of the body until death and decay  Wood releases carbon atoms only when digested by fungi and bacteria, which release CO 2 during cellular respiration o Recycling can take a long time  Carbon atoms are released when coal and oil are burned  Coal and oil = compressed, chemically altered remains of plants and microorganisms  Enormous amounts of carbon are locked up in shells and skeletons of marine organisms as calcium carbonate (CaCO )3  Carbon atoms are exposed from limestone deposits by geological events  Limestone deposits = formed calcium carbonate from ancient oceans  Drawn into deep molten layers  Released via volcanic activity o Every carbon atom on the earth has made about 30 round trips over the past 4 billion years o Natural exchanges are balanced, but human sources produce a net increase of CO in 2he atmosphere o Carbon sinks = materials that store carbon (e.g., geologic formations, standing forests)  When carbon is released from these sinks, natural recycling systems may not be able to keep up  Burning fossil fuels  Clearing extensive forests o Extra atmospheric CO c2uld support faster plant growth and speed up some of the recycling processes - Nitrogen cycle o Nitrogen  Primary component of fertilizers  Makes up about 78% of the air around us  Essential component of amino acids, peptides, and proteins o Plants cannot use N 2 but bacteria can  N = the stable two-atom form that is most common in air 2  Plants acquire nitrogen from nitrogen-fixing bacteria (including somecyanobacteria) that live in and around their roots  Nitrogen fixation = conversion of molecular nitrogen to ammonia or ammonium  Nitrogen-fixing bacteria = combine N 2ith hydrogen to make ammonia (NH ) and3ammonium (NH ) 4+ o Bacteria convert ammonia to nitrates  Nitrogen (N 2 + hydrogen (H 2  ammonia (NH ) +3oxygen (O ) 2nitrite (NO ) 2nitrate (NO ) 3− o Plants use nitrates to−create organic nitrog+n  Nitrate (NO 3  ammonium (NH ) 4 o Nitrogen is stored in sediments or converted back to molecular nitrogen o Legumes = members of the bean family  Useful in agriculture  Nitrogen-fixing bacteria live in the root tissues, which adds nitrogen to the soil  Nodule = mass of root tissue containing many bacteria that help convert nitrogen (N ) 2 in the soil to usable forms  Interplant and rotate legumes with crops that use but cannot replace soil nitrates o Nitrogen re-enters the environment in several ways  Death of organisms  Fungi and bacteria decompose dead organisms, releasing ammonia and ammonium ions, which then are available for nitrate formation −  Denitrifying bacteria break down nitrate (NO 3 into nitrogen (N 2 and nitrous oxide (N2O)  Denitrifying bacteria compete with plant roots for available nitrates  Denitrification occurs mainly in waterlogged soils o Low oxygen availability o Large amount of decomposable organic matter  Plants shed leaves, needles, flowers, fruits, and cones  Animals shed hair, feathers, skin, exoskeletons, pupal cases, and silk  Animals produce excrement and urinary wastes that contain nitrogenous compounds  Urine = contains detoxified wastes of protein metabolism o Humans have profoundly altered the nitrogen cycle  Human sources of nitrogen fixation are about 50% greater than natural sources  Using synthetic fertilizers  Cultivating nitrogen-fixing crops  Burning fossil fuels o Excess nitrogen causes:  Eutrophication = algal blooms and excess plant growth in water bodies  Serious loss of soil nutrients such as calcium and potassium  Acidification of rivers and lakes  Rising atmospheric concentrations of nitrous oxide, which is a greenhouse gas  Spreading of weeds into areas where native plants are adapted to nitrogen-poor environments - Phosphorus cycle o Takes millions of years o Phosphorus  Used in energy-transfer reactions  Slowly released from rocks, salt deposits (from ancient sea beds), and mineral compounds  Transported in water  Cycles through ecosystems when it is taken in by organisms  Producers take in inorganic phosphorus, incorporate it into organic molecules, and then pass it on to consumers o Natural movement of phosphorus is slight, involving recycling within ecosystems and some erosion and sedimentation of phosp−3rus-bearing rock o Use of phosphate (PO 4 )fertilizers and cleaning agents increases phosphorus in aquatic systems o Mining of fertilizers has greatly speeded the use and movement of phosphorus in the environment o Most phosphate used for detergents and inorganic fertilizers come from salt deposits from ancient sea beds o Most of the phosphorus used in agriculture ends up in the ocean again, from runoff or sewage waste that is released into rivers o Over millions of years, phosphorus will become part of mineral deposits o On shorter time scales, we could use up our available sources of phosphorus o Excess nitrogen causes:  Eutrophication = algal blooms and excess plant growth in water bodies  Algae bloom = explosive growth of algae and photosynthetic bacteria populations - Sulfur cycle o Sulfur  Minor, but essential component of proteins  Determinants of the acidity of rainfall, surface water, and soil  Critical regulators of global climate  Present mainly underground in rocks, soil, minerals and water  Pyrite = iron disulfide  Gypsum = calcium sulfate  Cycles through ecosystems when it is taken in by organisms  Assumes many oxidation states  Hydrogen sulfide (H2S)  Sulfur dioxide (S2 ) 2−  Sulfate ion (S4 ) o Bacteria sequester sulfur in biogenic deposits or release it into the environment  Type of sulfur bacteria depends on oxygen concentrations, pH level, and light level o Human activities release large quantities of sulfur  Burning fossil fuels produce sulfuric acid, which cause acid rain  Sulfur dioxide and sulfate aerosols  Cause human health problems  Damage buildings and vegetation  Reduce visibility  Absorb UV radiation  Create cloud cover that cools cities  Offset greenhouse effects of rising 2O concentrations o Oceanic phytoplankton release biogenic sulfur  Role in global climate regulation  Dimethylsulfide (DMS)  Accounts for 50% of all biogenic sulfur emissions  Keep temperature within a suitable range for all life  Ocean water is warm single-celled organisms release DS DMS is oxidized to 2O and then SO4− sulfate aerosols act as cloud droplet condensation nuclei  clouds appear  increase the earth’s albedo (reflectivity)  earth is cool  Ocean water is cool  phytoplankton activity decreases  less DMS production decreases  clouds disappear o Weathering, emissions from deep seafloor vents, and volcanic eruptions release inorganic sulfur into the air and water [EXPLORING SCIENCE] A “water planet” - There is an abundance
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