United States Academic Pentathlon Science Resource Guide 2024-2025 PDF

United States Academic Pentathlon ® OUR CHANGING CLIMATE...

United States Academic Pentathlon ® OUR CHANGING CLIMATE Texas Pentathlon - TX, TX SCIENCE An Introduction to Environmental Science Resource Guide 2 0 24 – 2 0 25 The vision of the United States Academic Decathlon® is to provide students the opportunity to excel academically through team competition. Toll Free: 866-511-USAD (8723) Direct: 712-326-9589 Fax: 712-366-3701 Email: [email protected] Website: www.usad.org This material may not be reproduced or transmitted, in whole or in part, by any means, including but not limited to photocopy, print, electronic, or internet display (public or private sites) or downloading, without prior written permission from USAD. Violators may be prosecuted. Copyright ® 2024 by United States Academic Decathlon®. All rights reserved.  Table of Contents INTRODUCTION.................. 4 SECTION II: BIODIVERSITY: FROM LOCAL TO GLOBAL.............. 22 SECTION I: FOUNDATIONS OF Biodiversity....................... 22 ENVIRONMENTAL SCIENCE......... 5 What Is Biodiversity and Why Does It What Is Environmental Science?.... 5 Matter?............................. 22 Genetic Diversity.................... 23 Environmental Indicators............ 5 Expressions of Genetic Diversity....... 24 Biological Diversity................... 6 Species Diversity..................... 24 World Human Population.............. 7 Food Production...................... 8 Evolution......................... 24 Global Temperatures and Greenhouse Adaptation through Natural Selection... 26 Gases............................... 8 Adaptation to a Changing Environment.. 26 Texas Pentathlon - TX, TX Air and Water Pollution............... 10 Nonadaptive Evolutionary Processes... 26 The Pace of Evolution................ 27 The Scientific Method............... 11 An Illustration of the Scientific Method.. 13 Changes in Environmental Conditions The Role of Repetition in Science...... 13 and Extinctions................... 28 Understanding How to Interpret Scientific The Fossil Record................... 29 Studies............................. 14 Mass Extinctions.................... 29 Environmental Systems............ 14 Human Activity and Biodiversity... 30 System Dynamics.................... 14 Habitat Fragmentation............... 30 Matter and Energy Exchange.......... 14 The Introduction of Exotic Species..... 31 Open and Closed Systems............. 15 The Human Component of Environmental Linking Biodiversity and Evolution to Systems............................. 15 Ecology........................... 32 The Ecological Perspective........... 32 System Analysis: Determining How Environmental Conditions............ 32 Matter and Energy Flow in the Resources.......................... 32 Environment...................... 15 Inputs, Outputs, and Flux.............. 15 Community Ecology............... 33 Steady State......................... 16 Interspecific Competition............. 33 Accumulation and Depletion........... 17 Predation...........................34 Feedbacks........................... 17 Mutualism.......................... 35 Overshoot........................... 19 Regulating Population Systems........ 19 Ecological Communities........... 35 Food Webs.......................... 35 Section I Summary................ 38 Energy and Trophic Levels............ 36 2024–2025 Science Pentathlon Resource Guide 2  Keystone Species.................... 37 Natural Sources of Air Pollution....... 56 Atmospheric (Thermal) Inversion...... 57 Major Aspects of Ecosystems....... 39 Ecosystem Boundaries............... 39 Energy Use and Sources........... 57 The Biotic Components of Ecosystems.. 39 Generating Electricity................ 57 The Impact of Ecosystem Change on Its Nonrenewable Energy Sources........ 58 Biotic Components................... 39 Coal................................. 58 Petroleum............................ 59 Biomes........................... 40 Oil................................... 59 Biomes and Global Biodiversity....... 40 Natural Gas.......................... 59 Hydraulic Fracturing.................. 59 Biogeochemical Cycles............ 45 Nuclear Power....................... 59 The Water Cycle..................... 45 Renewable Energy................... 62 The Carbon Cycle.................... 46 Direct and Indirect Solar Energy....... 63 The Nitrogen Cycle...................48 Passive Solar Energy.................. 64 Active Solar Energy.................. 64 Section II Summary............... 48 Wind Energy......................... 64 Advantages and Disadvantages of Solar SECTION III: THE HUMAN IMPACT ON and Wind Energy..................... 65 NATURAL RESOURCES........... 50 Hydroelectric Power.................. 66 Biomass Around the World........... 68 Water Pollution................... 50 Modern Carbon vs. Fossil Carbon...... 68 Texas Pentathlon - TX, TX Types of Water Pollutants............. 51 Ethanol.............................. 69 Pathogens............................51 Oxygen-demanding Waste............ 51 Conservation and Efficiency.......... 69 Inorganic Compounds................ 51 Organic Pollutants.................... 52 Global Climate Change............ 72 Sediments........................... 52 The Greenhouse Effect............... 72 Thermal Pollution..................... 52 Greenhouse Gases................... 74 Evidence of Temperature Change Ocean and Shoreline Pollution........ 52 over Time........................... 74 Solid Waste Pollution................ 52 Indicators of Climate Change.......... 75 Wastewater Treatment............... 53 Effects of Global Warming............ 75 Improvements in U.S. Water Quality.... 54 Predicted Future Effects of Global Air Pollution and the Atmosphere... 54 Warming............................ 76 Major Air Pollutants................. 54 Sulfur Dioxide........................ 54 Section III Summary.............. 77 Nitrogen Oxides...................... 54 Carbon Monoxide..................... 55 CONCLUSION......................81 Lead................................. 55 Particulate Matter..................... 55 Ground-Level Ozone................. 55 NOTES............................ 82 Secondary Pollutants................ 56 BIBLIOGRAPHY.................... 83 2024–2025 Science Pentathlon Resource Guide 3  Introduction Environmental science is the study of the impacts that Section II deals with biodiversity, from genes to human activities have on the environment, including ecosystems. You will learn the basics of ecosystem the pollution impact of turning on your lights, the loss ecology—the study of the different ways that living of biodiversity from deforestation and the overfishing and nonliving components are organized together in of the oceans, and the many global impacts of adding nature. We will then focus on nonhuman species— billions of tons of greenhouse gases to the atmosphere. how they have evolved, what controls their distribution However, environmental science is also a tool for and abundance, how they interact with each other, and developing ways to manage those impacts so that how human activities impact them. You will also learn humans, and the other species with whom we share the some of the ways that environmental scientists develop Earth, can have a sustainable future. strategies to protect species and their ecosystems. To study these impacts requires an interdisciplinary In Section III, we deal with three related topics: Texas Pentathlon - TX, TX approach, relying on many aspects of biology, earth 1) water and air pollution; 2) our various energy and atmospheric sciences, fundamental principles sources and how their use causes pollution and of chemistry and physics, and human population other environmental impacts; and 3) how economic dynamics. Section I starts with an overview of how development and increased energy use has impacted environmental science is conducted—what types of our atmosphere and the global environment—global scientific approaches are used and what unique issues change in general and global climate change in environmental science has to deal with. We then particular. The human act of adding greenhouse gases explore how the Earth is made up of interconnected to the atmosphere is impacting us today and will likely systems—living (humans and other species) and impact people in the future even more. We will explore nonliving components (e.g., air, water, minerals) what environmental science can add to the work of joined together by the flow of energy and matter. maintaining a sustainable Earth. Environmental science deals with natural systems like lakes and forests and also domesticated systems like cities and farms. 2024–2025 Science Pentathlon Resource Guide 4  Section I Foundations of Environmental Science WHAT IS ENVIRONMENTAL organism, including the others of its kind, its food sources (prey), any predators that may feed on it, SCIENCE? the weather, the landscape, and any other aspect of Environmental science is the study of the impacts the world in which it lives. A local environment is of human activities on environmental systems. These the area immediately surrounding an organism or human activities include large-scale actions, such as person; an environment, however, can encompass clearing land for agriculture, fishing the oceans for an area of greater scale. An environment can be as food, mining the land for minerals and fuels, and small as a pond or as large as a complete mountain changing our planet’s climate through the emissions range or an ocean. The immensely complicated global of decades worth of greenhouse gases. These activities environment is the sum of all the aspects of the Earth. also include everyday individual actions, like driving a car to the store, turning on your lights, and choosing Environmental science is interdisciplinary, covering Texas Pentathlon - TX, TX whether to use plastic, paper, or reusable containers. many aspects of biology, earth and atmospheric sciences, fundamental principles of chemistry and The environment is the sum total of all the conditions physics, human population dynamics, and biological and and living and nonliving factors that surround an natural resources. Environmental science is a science- based discipline, meaning it is based on the scientific FIGURE 1 method that includes observations, hypothesis testing, field and laboratory research, and other practices, which we will discuss later in this section. One way of studying the environment is to study its different systems and the ways they interact. A system is a set of living and/or nonliving components connected in such a way that changes in one part of the system affect other parts. A particular system can usually be isolated and studied apart from other systems. The Earth is a system and so is an ant colony, a lake ecosystem, and a farm. Because systems are so important to an understanding of the environment, we will devote much of Section I to looking at environmental systems in detail. But first, we will explore how environmental scientists monitor human impacts on environmental systems. ENVIRONMENTAL INDICATORS If we wanted to determine whether a person is healthy, we might measure body temperature, heart rate, blood Environmental science integrates many different physical and social sciences. pressure, and respiration rate. If something is amiss with one or more of these indicators, it is usually a 2024–2025 Science Pentathlon Resource Guide 5  6 Global temperature and atmospheric greenhouse gas levels 6 Pollution levels Biological Diversity Overall biological diversity describes the diversity of genes, species, habitats, and ecosystems on Earth. The number of species on Earth, and whether that number is increasing or decreasing, can help us measure the The amount of new growth on trees can be used as an biological status of the planet. A species is defined as indicator of the health of a forest. a group of organisms that is distinct from other groups Image Source: Smithsonian Environmental Research Center in morphology (body type), physiology, or biochemical properties. Individuals within a species can breed and reliable signal that something is wrong in the human produce viable offspring. There are approximately 1.8 body. What indicators can we use to determine million “known”—that is, identified and catalogued— the vitality of the planet? Evaluating the health of species on Earth today. The actual number of species, the Earth, or even a specific environment, is much while highly debated, is likely to be more than ten times more complex, and we cannot measure every single that number because most species, especially microbial component. However, as with individuals, assessing species, have not yet been identified or catalogued. certain key aspects of the environment gives us an indication of its health. Species extinction is a natural part of the process of life on Earth. Roughly 99.9 percent of the species that An environmental indicator is a measure that reflects have ever lived on Earth are now extinct. Though Texas Pentathlon - TX, TX the environmental health of a system. For example, it is difficult to determine what the “background” the amount of new growth on trees might be used to rate of extinction was before people played a role, indicate the state of a forest. Unfortunately, at present, estimates have been made using “quiet” periods in the there is no single indicator that effectively assesses geologic record (that is, time periods with no massive the whole planet. In addition, the same environmental environmental or biological upheaval). “Background” indicator can tell a very different story depending on extinction rates are now estimated to be two mammal when or where the measurement is taken. Measuring extinctions per 10,000 species per one hundred years.1 new growth on trees over the summer will yield very different data than the same measurements taken over From recent studies, it is clear that human beings have the winter. greatly accelerated species extinction rates to up to a hundred times higher than background. The loss and Likewise, some parts of the world are experiencing degradation of habitat by human beings is considered declines in annual precipitation, while others are the major cause of species extinction today. Attempts seeing increases. Rates of change are also important to estimate species loss by relating it to the area of land when considering environmental indicators. This is that has been altered by human activity suggest that as analogous to taking a person’s temperature multiple many as 40,000 species per year may be going extinct. times during a day to see if it is stable and, if not, how Gains have been made in saving certain species, fast it is changing. The importance of a measurement particularly those that attract the attention of people, may be best understood in the context of a pattern of such as the American bison, peregrine falcon, bald measurements: Is growth increasing? Decreasing? Are eagle, and California condor, but overall, the number the changes global? Or regional? of species on Earth is declining at a rate to rival past There are six categories of environmental indicators on mass extinction events, such as the extinction of the which we will focus: dinosaurs. (See Figure 2.) Biological diversity Species such as the Bengal tiger, the snow leopard, 6 Human population growth and the West Indian Manatee are endangered and 6 Food Production may go extinct if present trends are not reversed. And 6 Resource consumption the loss of species of particular importance within an 6 2024–2025 Science Pentathlon Resource Guide 6  FIGURE 2 The five past mass extinctions events. Current human impacts may be causing another such extinction event. Source: EarthHow Texas Pentathlon - TX, TX The growing human population on the Earth creates a greater demand on Earth’s finite resources. Snow leopards are endangered and may go extinct if present trends are not reversed. the world population was undergoing exponential growth, which is growth that increases as a percentage ecosystem—keystone species—can cause a cascade of the numbers already in the population. While of extinction of species dependent on them, resulting in human population growth has slowed and is no longer harm to or loss of entire ecosystems. The overall rate exponential, world population size will nonetheless at which species go extinct on Earth not only tells us continue to increase for at least fifty to a hundred how biological diversity on Earth is decreasing but is an years. The United Nations projects that world important indicator of the state of land, water, and air population will level off somewhere between 8 and 12 on the planet. If we use species diversity as an indicator billion people by the year 2150. of environmental quality, we must conclude that the situation is getting worse and is not sustainable. Can the Earth sustain so many people? If we use the human population on Earth as an environmental World Human Population indicator, it is encouraging that the rate of population According to the United Nations, the global human growth has slowed, but we still should be concerned population reached eight billion people in November that the total population will continue to increase 2022. Roughly 378,000 infants are born and 148,000 for at least the next fifty years and possibly longer. people die each day resulting in 230,000 new The additional people on Earth will create a greater inhabitants on Earth each day, or almost a million demand on Earth’s finite resources, including energy, new people on Earth every four days. Until the 1960s, food, water, and land and—unless we dramatically 2024–2025 Science Pentathlon Resource Guide 7  future generations. Although there is no single way FIGURE 3 to determine the sustainability of a given society, the rapid depletion of a resource is a clear indication that its use is not sustainable. The human consumption of resources, energy, and land all contribute to a decrease in the sustainability of not only human activities, but of the natural ecosystem on which all species, including humans, depend. However, many of the same human activities that cause adverse impacts can improve the overall quality of life among human beings. Somehow, there must be a balance between utilizing resources to improve life today, saving them for future generations, and protecting the natural environment. Obviously, the larger the population, the greater the Human population size estimates from 1960 to today and a consumption of resources. So, more people, regardless projection to 2100. of their lifestyle or where they live, means a greater Credit: Katie Peek; Data Source: World Population Prospects 2022, United environmental impact. But resource use per person, Nations Population Division. Image Source: Scientific American which varies from region to region and by type of economy and country, is also critical. Patterns of change our industrial society—will produce more resource consumption differ vastly in different parts of pollution and waste for the foreseeable future. the world. For example, a country where most people live in relatively small houses will have less impact Texas Pentathlon - TX, TX Food Production than a country where most people live in large houses, Food grains such as wheat, corn and rice provide more all other factors being equal. And the way people than half the calories eaten by humans. Worldwide heat and light their homes (with kerosene, candles, grain production is a result of the quality of soils, or electricity, for example), will produce different climatic conditions, land area under cultivation, environmental impacts. human labor, energy, and water expended on growing For some resources, a very small portion of the food, and other influences. Therefore, an increase or world’s population may be responsible for most of decrease in the amount of grain grown worldwide for the consumption. The United Nations Development human consumption is an environmental indicator. Program reports that the twenty percent of the people The term “intensity” in the context of agriculture in the world who live in developed countries consume refers to how much food is grown per hectare or acre forty-five percent of all meat and fish, fifty-eight of land. The agricultural practices used to produce percent of total energy, and eighty-four percent of all food vary widely from high-intensity monoculture (one paper, and own eighty-seven percent of the world’s crop) to low-intensity polyculture (many crops). The automobiles and trucks. The poorest twenty percent of yield (tons of grain per unit area of land) from a given the people in the world consume or use five percent or area can indicate both the intensity of agricultural less of each of these items. Thus, while it is true that methods and the quality of the land. High-intensity a larger population translates to more consumption, agricultural practices often lead to soil erosion, runoff more pollution, and more environmental impact, of fertilizers and animal wastes into waterways, and the way people live is also an important predictor of buildup of pesticides, all of which reduce the quality environmental impact. of the land. As land becomes more degraded, its yield begins to decline. Global Temperatures and Greenhouse Gases Resource Consumption The temperature of the Earth is regulated by many Sustainable use occurs when present-day consumption factors, including incoming solar radiation, absorbed of resources allows an adequate supply to remain for solar heat emanating from the Earth, the surface area 2024–2025 Science Pentathlon Resource Guide 8  of ice caps and ocean, and the concentration of certain gases that surround the Earth. These gases trap heat around the Earth, warming the atmosphere—much like the glass around a greenhouse traps heat—so they are sometimes called greenhouse gases. Carbon dioxide and methane are two greenhouse gases that are present in the atmosphere due to both natural processes and human activities. Combustion of fossil fuel is the primary human activity that produces carbon dioxide. For the past 130 years, global temperatures have fluctuated but show an overall increase. (See Figure 4.) During the same period, atmospheric carbon Combustion of fossil fuel is the primary human activity that dioxide and methane concentrations also increased produces carbon dioxide. steadily. (See Figure 5.) Virtually all scientists agree FIGURE 4 Texas Pentathlon - TX, TX Change in global surface temperature (annual average) as observed and simulated using human & natural and only natural factors (both 1850-2020). Source: IPCC 2024–2025 Science Pentathlon Resource Guide 9 FIGURE 5 The major source of lead contamination in the U.S. is drinking water. Lead was also used as an additive to gasoline to improve engine performance of the automobile engine. As the automobile became more widely used throughout the world, the use of lead increased as well, Atmospheric carbon dioxide. and much of the lead production and emissions in the Source: NOAA twentieth century were a result of this use. Sthat the increase in carbon dioxide during the last Beginning in 1975, clean air legislation required Texas Pentathlon - TX, TX two centuries is anthropogenic (a result of human that new cars sold in the United States use gasoline activity), coming especially from the combustion of without lead, and gradually the same requirements fossil fuels and destruction of forests. were imposed in many other parts of the world. This switch from leaded to unleaded gasoline is primarily Air and Water Pollution responsible for the decreases in lead emissions. While The metal lead (chemical symbol Pb) is very useful there is still a great deal of toxic lead produced and because it is soft, malleable (can be shaped with just emitted throughout the world, the substantial decline a hammer), and resists corrosion, but it also impairs in lead emissions is certainly a positive step. If we use human central nervous system function and is toxic global lead emissions as an environmental indicator, to most plants and animals. Developing brains (in we should conclude that the situation is improving. fetuses and children) are particularly sensitive to However, this “easy fix” simply stopped adding a lead. The amount of lead in the atmosphere, water, harmful element to gasoline. There are still significant soils, and plants and animals is an indicator of the quantities of lead emitted in coal, oil and even gasoline amount of pollution that has been introduced into the that we call “unleaded.” natural environment and an indirect indicator of the Lead was also a major ingredient in paint. Although amount of harm that may have occurred from human houses built after 1960 tend to have much lower manipulation of the natural environment. concentrations of lead in paint, there are many houses From five thousand years ago until fairly recently, the built before 1960 that are covered with peeling global production, or mining, of lead has increased. paint that can be composed of 50 percent lead. This In the early years of lead production, relatively small paint can add to the indoor air concentration of amounts of the metal were liberated to the atmosphere lead, and when it peels, it is sometimes ingested by during separation and refinement of the lead from young children. While not part of the atmospheric other metals. Changes in refining techniques that came measurement of lead, this is another important with the Industrial Revolution led to greater releases pathway of lead pollution to human beings. into the atmosphere. In addition, coal and oil contain However, the major source of lead contamination in small amounts of lead, and as more of these fuels were the U.S. today is our drinking water—particularly burned, more lead was released to the atmosphere. from lead pipes and other plumbing material that 2024–2025 Science Pentathlon Resource Guide 10 will corrode over time, especially if the water is any interference by the researcher. When a wildlife highly acidic. While many of these lead pipes have biologist observes hundreds of interactions between been replaced with safer materials, lead plumbing moose and wolves, they are conducting an observational fixtures are still prevalent, especially in lower income experiment. A manipulation experiment is conducted by communities. Lead is but one example of how human changing some aspect—the experimental variable—of activities contaminate our air, water, and land. a natural or controlled environment. The elements being studied are divided into two groups: the experimental THE SCIENTIFIC METHOD and the control. The experimental group is the one that The scientific information that we will cover—including is manipulated; the control group is left undisturbed the information just presented on environmental for comparison. These two groups should be treated indicators—has been collected, analyzed, and identically in every way, with the exception of the one synthesized through a process called the scientific variable that is being tested in the experimental group. method. The scientific method is an objective way to explore the natural world, draw inferences from it, and It is important to have a large enough sample size—the predict the outcome of certain events, processes, or number of individuals tested or samples collected—so alterations. This method is used by scientists in many that the data gathered are representative of the entire parts of the world and is the generally accepted way to population. For example, if you are testing the effect of conduct science. A simple experiment conducted by a a pollutant on the growth rate of a plant species, you first-year college student follows the same principles as would want to test the effect on ten or a hundred plants, a large, multi-million-dollar experiment conducted by a not just one or two. group of investigators at a research institution. 6 Accept, revise, or reject the hypothesis. Reconcile any differences between the Texas Pentathlon - TX, TX Let’s look at each of the major steps in the scientific method. predictions and the results. If findings differ from the hypothesis, the hypothesis is modified 6 Observe the natural world, with or without and retested. This may continue until there is human interference, and ask questions about general agreement between the hypothesis and those observations. the experiment. 6 Generate a hypothesis. Make a general 6 Report findings to others. An essential part statement about the organisms or processes of the scientific method is to inform others under observation that could answer the of what has been done. Reporting to others questions posed. The hypothesis must be can take place through peer-reviewed written testable and falsifiable—that is, the researcher communications in publications or formal must be able to determine whether it is presentations of the results at conferences and incorrect. scientific meetings. 6 Based on existing information, make a 6 Replicate the experiment. For any given preliminary determination of whether the hypothesis, the process described above is hypothesis is true or false. Based on the generally repeated over and over by different hypothesis, the observations, and questions, scientists. When a given hypothesis is tested it is possible to make an informed projection and accepted by many investigators, it may about the hypothesis. become a scientific finding. If a hypothesis Test the hypothesis with an experiment. is widely accepted, it becomes a theory. If a 6 Hypotheses should make predictions about theory is widely accepted and appears to apply the world. Determine whether the hypothesis universally without any exceptions, it is called is false using an observational experiment a universal law. An example of a universal or a manipulation experiment, testing these law is the First Law of Thermodynamics, predictions. which says that energy cannot be created or destroyed, it simply changes form. Even though An observational experiment is conducted by we use the term “law,” no scientific finding is observing phenomena in the natural world without considered definitively proven, because there 2024–2025 Science Pentathlon Resource Guide 11 FIGURE 6 How science works EXPLORATION AND DISCOVERY Making Asking New technology observations questions Personal motivation Practical problem Serendipity Curiosity Surprising observation Sharing data and ideas Finding Exploring the inspiration literature Texas Pentathlon - TX, TX Gathering data Expected Actual Hypotheses results/observations results/observations Interpreting data Supportive, contradictory, surprising or inconclusive data may...... inspire...support a revised hypothesis. assumptions. Feedback and Develop Address Replication technology societal issues peer review... inspire...oppose a revised/new hypothesis. hypothesis. Discussion with Build Inform Publication colleagues knowledge policy TESTING Coming up IDEAS Satisfy Solve everyday Theory curiosity problems with new building questions/ideas BENEFITS AND COMMUNITY OUTCOMES ANALYSIS AND FEEDBACK The process of scientific inquiry. Source: University of California Berkeley, Understanding Science 101 www.understandingscience.org © 2008 The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California 2024–2025 Science Pentathlon Resource Guide 12  is always the possibility of new information that would change the conclusions. Therefore, scientific laws are considered not disproven. An Illustration of the Scientific Method Let’s consider a hypothetical example to see how the scientific method is applied. Scientists have observed that species diversity, one of our environmental indicators, is affected by the alteration of habitat. An environmental scientist in an area of Southern California that is being developed for housing poses the question, “What will happen to the diversity of species of small mammals and shrubs if the size of a natural area is reduced from ten hectares to one The scientific method is an ongoing discussion among hectare?” (1 hectare = 2.47 acres). The scientist phrases researchers this question as a hypothesis: “Reducing the size of the natural area will result in a significant loss in small have a clear experimental variable or manipulation. mammal and shrub species” and predicts that the Sometimes, an observation is made after an event hypothesis is correct. (Alternatively, they could predict has occurred, and an environmental scientist must that it is incorrect.) determine what has happened without having data from before the event. This kind of analysis is a little The researcher then uses the following situation as an bit like detective work, but certain aspects of the Texas Pentathlon - TX, TX experiment to test their hypothesis: scientific method still apply. Five housing developments are to be The Role of Repetition in Science constructed in the suburbs of a major city The scientific method is an ongoing discussion among in Southern California, each on a ten- researchers. Scientists frequently disagree about hectare plot of land with one hectare in hypotheses, experimental conditions, results, and the the middle left as a “natural area.” Before interpretation of results. Two investigators may even the developments begin, the investigator obtain different results from similar experiments, or two conducts inventories of all the species on all interpretations may explain the same set of observations. five ten-hectare areas destined to become Any single finding has limited significance. It is when housing developments, and five similar ten- the same finding is repeated over and over by different hectare areas that will remain undisturbed investigators that we can begin to trust that the observed and act as controls. The survey determines phenomenon is real and significant. In the meantime, the an average number of species per hectare. disagreements and the discussion about contradictory In this example, the experimental variable is the findings are not only normal, but are a valuable part of reduction of habitat size from ten hectares to one the scientific process. hectare. While reporting on two studies that reached opposite Ten years after the housing developments have been conclusions, the popular press often assumes the completed, the investigator returns to the survey discrepancy is the result of bad science or confusion sites and inventories the species again. If the one on the part of scientists. Particularly when a scientific hectare “natural areas” in the housing developments issue is of great popular interest or concerns have fewer species than the undisturbed areas, the policy—questions such as global warming, toxicity investigator could conclude that their hypothesis was of pollutants, or species extinction, for example— not falsified—reducing the size of the natural area did individual preliminary results may be reported to the decrease species diversity—and report their findings general public before scientists have had a chance to to the scientific community. Not all scientific studies reconcile apparent or actual differences. 2024–2025 Science Pentathlon Resource Guide 13 Understanding How to Interpret the system affect other parts. In practice, systems are defined by the person looking at them. For example, Scientific Studies one scientist may spend an entire career studying the If it is important to view scientific findings critically, physiological and anatomical systems of individual how can we judge whether a report is based on good humpback whales to learn how they can dive so deep, science? Sometimes scientific investigators do not swim so far, and survive in such a range of marine differentiate between the control group of subjects and environments. In contrast, the population biologist will the experimental group. Other times, there is not a focus on gathering data on population changes over large enough sample size to draw general conclusions. time, while the community ecologist will be interested Alternatively, the conclusions may be made about one in the whale’s interaction with other species, such as group (for instance, mature trees) when the experiment their prey. And the conservation biologist will likely was done on a different group (seedlings). In order to be most concerned with the adverse impacts of human conduct a scientifically sound study, the investigators fisheries—and the gear used in those fisheries—on must use a large enough sample size and have a the whale population. While all these systems are distinct difference between the experimental group and connected, it is this final one—where human activity the control group. Further, they must demonstrate a has it most serious impacts—where environmental cause-and-effect relationship between a manipulation science will interact with fishery policies, law, and and a result and be able to identify a mechanism economics. that would give rise to the observed result. A simple correlation between one event and another—that is, the Throughout this resource guide, we will define systems two occurring together—does not constitute scientific in terms of the particular environmental issue we are evidence that one caused the other. studying. The largest system studied by environmental scientists, and the one of which all others are part, Texas Pentathlon - TX, TX ENVIRONMENTAL SYSTEMS is our global system—the Earth. The interactions of System Dynamics systems and components within systems are known as A butterfly stirring the air in Beijing can affect weather system dynamics. patterns in New York a month later. This often- paraphrased statement is a poetic way of describing the Matter and Energy Exchange interconnectedness of systems on Earth. The study of Environmental systems, whether small or large, involve the environment is the study of systems. Recall that a the exchange of matter (materials) or energy. One of system is a set of living and/or nonliving components the most important materials involved in environmental connected in such a way that changes in one part of systems is water; some others are fuels (oil, coal, FIGURE 7 An example of the inflow and outflow of energy in the system of a car. Source: Friedland, Andrew and Rick Relyea, Essentials of Environmental Science 2nd ed. W.H. Freeman, New York (2016).] 2024–2025 Science Pentathlon Resource Guide 14  FIGURE 8 Open and closed systems. (a) Earth is an open system with respect to energy. Solar radiation enters the Earth system, and energy leaves it in the form of heat and reflected light. (b) However, Earth is essentially a closed system with respect to matter because very little matter enters or leaves the Earth system. The white arrows indicate the cycling of energy and matter. Source: Friedland, Andrew and Rick Relyea, Essentials of Environmental Science 2nd ed. W.H. Freeman, New York (2016).] etc.), chemicals, and gases (e.g., oxygen). For other include people or run up against human influence in environmental systems, the exchange of energy is the one form or another, many areas of human endeavor, Texas Pentathlon - TX, TX important process. This includes the energy (food) some of which are not scientific at all, are important to a intake of a single animal, the energy flows through systems-based understanding of the environment. Some an ecosystem, the fossil fuel energy used to drive of the most important areas that we will touch on are: modern human society, and the energy on which all environmental systems ultimately depend: the energy 6 Economics from the Sun. 6 Social structures and institutions, including various levels of government Open and Closed Systems 6 Law Systems can be either open or closed. An open system 6 Policy is one where the exchange of matter or energy between 6 Environmental advocacy and action it and other systems occurs. In a closed system, For example, new scientific data on global warming exchange does not occur. The Earth system is open will affect new policies or laws related to greenhouse with respect to energy. Solar energy enters the Earth’s gas production, as well as ways to adapt to a changing atmosphere, and heat energy escapes from the Earth’s climate. atmosphere. However, the Earth system is closed with respect to matter, such as chemical elements. SYSTEM ANALYSIS: DETERMINING Except for the occasional meteorite or space shuttle, no material enters or leaves the Earth system. The ocean HOW MATTER AND ENERGY FLOW is a system that is open to both energy and matter. IN THE ENVIRONMENT Energy from the Sun enters the ocean, and energy Inputs, Outputs, and Flux from the ocean is easily transferred to other systems People who examine systems often conduct a system such as the atmosphere. And matter, such as sediment analysis to determine what goes in, what comes out, and nutrients, enters the ocean via rivers and streams. and what has changed within a given system. This type of analysis is very similar to the kind of analysis you The Human Component of might perform on your personal checking account to Environmental Systems learn your financial status. In your checking account, Because environmental systems almost invariably you start with a sum of money called your balance. 2024–2025 Science Pentathlon Resource Guide 15 Systems analysts call that balance a pool. If you deposit money into your checking account, you are FIGURE 9 adding an input. You also have expenditures—you write checks against your checking account balance or withdraw money from your account. Systems analysts call this an output. In order to determine your financial status, you start with your balance at the beginning of a month, add inputs (deposits), and subtract outputs (checks and withdrawals). This gives you your checkbook balance at the end of the month, or the change in the pool of money. Systems analysts call that change a flux. If you quantify your income in terms of so many dollars per month, you are describing a flux rate, a flow per unit of time. The same kind of analysis can be done for water in a bucket, pollutants in the atmosphere, or nutrients in the ocean. It tells an environmental scientist if the size of the pool is increasing, decreasing, or staying the same. Because it was designed to be done for materials that have mass, it is often called a mass balance analysis— Texas Pentathlon - TX, TX an accounting of the inputs and outputs to determine the fluxes in a given system. All types of balance analyses, whether they be mass, energy, or monetary, can be represented as: Net Flux = Inputs – Outputs Steady State A steady state system does not change over time. The most important aspect of conducting a mass, Source: Friedland, Andrew and Rick Relyea, Essentials of Environmental energy, or monetary balance analysis is learning if Science 2nd ed. W.H. Freeman, New York (2016).] your system is in steady state—that is, if input equals output and the size of the pool does not change over and a flux out of 1 liter per minute. Since the input time. The first step is to determine the size of the pool. equals the output, net flux = 0, and over time there will Sometimes we can measure the pool directly. With be no change in this system. The pool will remain at 10 a bucket of water, for example, we could empty the liters until someone changes one of the fluxes, perhaps bucket into a measured container to determine the size by turning off the faucet or plugging up the holes in the of our pool. If we are trying to determine the size of a bottom of the bucket. This system is in steady state. large or immobile pool, such as a flock of birds or an ocean, we have to calculate or estimate the pool size. Many pools in the natural world are at steady state; the water in the atmosphere is an example. The amount of Next, we want to measure, estimate, or calculate the water that enters the atmosphere from evaporation in net flux into and out of the system (input and output). any given time period is roughly equal to the amount For example, imagine that someone has punched holes that leaves the atmosphere as precipitation over the in the bottom of our bucket, so the water is leaking out, same time. The oceans are also at steady state; the water and at the same time we are running water into it from that enters from rivers and streams is roughly equal a faucet. We can measure input from the faucet and to the water that evaporates. When a community bans output from the holes. As Figure 9 shows, the bucket watering lawns and washing cars and declares a drought has a pool of 10 liters, a flux in of 1 liter per minute, emergency during a dry summer, it is because their 2024–2025 Science Pentathlon Resource Guide 16  sediment. We can calculate: FIGURE 10 Flux = 0 – 1,000 mg/day Flux = –1,000 mg/day At the start, the reservoir holds (10 mg/L) × (1,000,000 liters) = 10,000,000 mg of the pollutant. Losing 1,000 mg/day, the reservoir will contain no pollutant in 10,000 days. In other words, it will take (10,000 days)/(365 days/year) = 27.4 years before the pollutant is totally gone from the reservoir. Feedbacks So far, we have presented fairly simple systems with easily defined inputs and outputs. Any change in the A system that is not in a steady state will change over time. system involves simply increasing or decreasing the inputs or outputs. For other environmental systems, the important factors are not the input and output water supply is no longer at steady state; more water themselves, but the mechanisms that control, or is being lost from the reservoir than is replenished by regulate, these flows. In these regulatory mechanisms, precipitation and streams. If a resource, such as a water a change in the system either leads to further change or supply, is decreasing in size, it means that the system is returns the system to its original state. not being utilized in a sustainable way. Texas Pentathlon - TX, TX Consider your own or your parents’ behavior with It is important to realize that one part of a system respect to a bank account. If you notice that your pool can be in steady state while another part is not. For of money (your checkbook balance) is decreasing, you example, though water in the atmosphere is in a steady may spend less money to reduce the flux of dollars state, carbon dioxide in the atmosphere is not; it is out of your checkbook, or you may work more hours slowly increasing, as we will discuss later. to increase the flux of dollars into your checkbook. Essentially, you alter your behavior in one or more Accumulation and Depletion ways in order to change your cash flow situation. These If a system is not in steady state, we may want to changes in behaviors, called feedbacks, are adjustments determine the rate at which it is accumulating or losing made by a system in response to behavior or events. material. For example, if a pollutant is accumulating in a drinking water reservoir, it may be valuable to know the Balancing your checkbook is an example of a negative time when pollutant concentrations will become toxic feedback loop, in which the behavior always brings the to organisms in the reservoir or to humans drinking the system variable—in this case, your money—back to a water in the reservoir. We can calculate accumulation or starting point. By contrast, a gambler, who bets more depletion rates by using the formula for net flux: and more money as they begin losing, will not return to the starting point—the loss of money will cause Net Flux = Inputs – Outputs increased betting and more losses, until all the money For example, assume that a pollutant is slowly is gone. This is an example of a positive feedback loop, decreasing in concentration in the water because it in which the system variable is continuously moved is interacting with the sediment that lines the bottom away from the stable point—what we often call a of the reservoir. A calculation of the change in the vicious cycle. system can indicate when that water will be safe to Feedback systems are found throughout the drink. Suppose the reservoir holds 1,000,000 liters environment. One major feedback system that is of great of water, and the pollutant is at a concentration of 10 importance to environmental scientists, policy makers, mg/L. Assume no additional pollutant is entering the and citizens is the Earth’s heating system feedback loop. reservoir, and that 1,000 mg/day interacts with the In general, warmer temperatures at the Earth’s surface 2024–2025 Science Pentathlon Resource Guide 17  FIGURE 11 Texas Pentathlon - TX, TX Negative and positive feedback loops. Source: Friedland, Andrew and Rick Relyea, Essentials of Environmental Science, 2nd ed. W.H. Freeman, New York (2016).] Earth warmer, which leads to greater evaporation, and more warming, and the cycle continues. In the absence of other factors that compensate for or balance the warming, this positive feedback loop could continue making temperatures warmer and warmer, driving the system away from the starting point. However, more evaporation also leads to more cloud cover, which would reflect more incident sunlight and possibly lower temperatures, resulting in a negative feedback loop. It is unknown whether or not the sum of these loops would lead to an increase or decrease in temperature. Warmer temperatures at the Earth’s surface lead to greater The balance in many environmental systems is evaporation from oceans and lakes. The additional moisture dependent on the smooth operation of feedback loops. in the atmosphere from evaporation enhances the layer of Sometimes conflicting factors lead to a breakdown in heat-trapping gases, including water vapor, that cover the the negative feedback loop and send the environmental Earth, which makes the Earth warmer, which leads to greater system away from its set point, the stable value for the evaporation, and more warming, creating a positive feedback loop. parameter under examination. This is particularly true when the system involves a conflict between lead to greater evaporation from oceans and lakes. The ecological control factors regulating a natural resource, additional moisture in the atmosphere from evaporation such as a commercial fish or an energy source, and enhances the layer of heat-trapping gases, including economic and social factors driving human use of such water vapor, that cover the Earth. This helps to make the resources. As you study the exploitation of natural resources, both living and nonliving, try to determine 2024–2025 Science Pentathlon Resource Guide 18 FIGURE 12 In most predator-prey systems, such as wolf-deer systems, the amount of predation will increase as the number of prey Because of a slow response to a signal, an action continues increases. This negative feedback cycle will drive the prey long after it should. This is known as overshoot. population back to its starting point. Source: Paul Chefurka, “Population: The Elephant in the Room.”] of individuals of a single species. We will discuss what factors may be disrupting the negative feedback populations in detail in Section II, but for the purpose loop of those systems. of illustrating feedback systems, we need to introduce some basic population concepts here. Overshoot Texas Pentathlon - TX, TX The size of any population is controlled by two inputs— One last system dynamics concept to consider in the number of births and the amount of immigration— both positive and negative feedback systems is the and two outputs—the number of deaths and the amount time between when a signal is generated and when of emigration (individuals leaving the population). it is received and responded to. Consider the bank account example. As soon as you notice that your Net Population Change = Input (Births + Immigration) balance is steadily decreasing, you might alter your – Output (Deaths + Emigration) spending habits or try to make some more money. But what if you don’t have an app that provides you with For most—though not all—populations, births and a continuous update of your account? This delay in deaths greatly outnumber immigration and emigration, receiving the signal might mean that you would keep so it is the former two “flows” that we will concentrate overspending and exceed your intended balance. on. Environmental scientists usually find it easy to estimate birth rates and death rates. What is more Exceeding the stable set point of a system is known difficult, and more interesting, is determining how as overshoot. In the natural world, many systems these two flows are regulated. experience delays in the transmittance of information that lead to overshoot. Overshoot is an important part Environmental scientists study both single population of human and nonhuman population systems. When a systems and systems of interacting populations. In population’s birth rate is high, the factors controlling both cases, the size of any one population can be population growth (disease, reduced fertility, etc.) regulated, through various feedbacks, by abiotic cannot compensate fast enough, and the population (nonliving) components of the environment and by will grow past the maximum number of individuals populations of other organisms (the biotic components that can be supported by its environment, known as of the environment). For example, as a deer population the carrying capacity. The result of such an overshoot increases in size, the amount of food available for will usually be a dramatic population crash from each individual will probably decrease. Less food disease or starvation. means less energy for females to put into reproduction, resulting in fewer births, or less food for newly born Regulating Population Systems fawns—a negative feedback. Environmental scientists define a population as a group 2024–2025 Science Pentathlon Resource Guide 19  FIGURE 13 Texas Pentathlon - TX, TX A negative feedback loop involving populations of predators (wildcats) and prey (rabbits). In more complex systems containing many interacting species per one hundred years), it is certain that populations, one population may be regulated by the human beings have increased extinction rates size of another. A rabbit population may have enough on Earth today. Of the estimated 10 million to food to fuel an increase in population size, but it may 30 million species on Earth, perhaps as many live in an area with many wildcats, which prey upon as 40,000—maybe more—are going extinct the rabbits. In most predator-prey systems, the amount each year. Biological diversity gives a negative of predation will increase as the number of prey indication of the state of the Earth and shows increases (they become easier to find and to hunt). This that we are in a sixth mass extinction event. negative feedback cycle will drive the rabbit population Atmospheric concentrations of carbon dioxide 6 back to its starting point (Figure 13). and other greenhouse gases are steadily increasing due to human activity. Global SECTION I SUMMARY temperatures have risen during the 1900s, 6 Environmental science is the study of the with a particularly rapid increase since 1980. impacts of human activities on environmental It is clear that human activity is causing global systems. There is no single environmental temperature increase and climate change. indicator that offers an accurate, objective assessment of the status of the entire Earth, but 6 Air and water emissions increased steadily a number of indicators in different areas are in the early 1900s and decreased (in the U.S. used. at least) after the early 1970s due to stricter pollution regulations. However, pollution levels 6 There are roughly 8 billion people on Earth remain a global issue, particularly for some today. The total human population continues chemicals. to increase, though the rate of growth has been steadily decreasing since the 1960s. 6 Sustainability is the consumption of resources in the present that allows an adequate supply 6 While the background rate of extinction is to remain for future generations. Resource an estimate (two mammal species per 10,000 consumption varies throughout the world and 2024–2025 Science Pentathlon Resource Guide 20  has different environmental impacts depending mass balance analysis to calculate inputs and on both the number of people and the type outputs to the system pool and the rate of and quantity of resources they use. As an flux through the pool. If there is no overall environmental indicator, resource consumption change to the pool, the system is in steady shows a worsening state of the environment. state. Changes in one input can affect an entire Scientists often study the dynamics of complex system. 6 environmental systems, which are sets of living 6 Systems are regulated by feedback loops. and nonliving components connected in such In negative feedback, changes in the system a way that changes in one part of the system variable bring the system back to its stable affect the other parts. set point. In positive feedback, changes in the Systems can be open or closed to exchanges of variable lead to further changes, bringing the 6 matter, energy, or both. Human activity almost system further away from the set point. always affects environmental system dynamics 6 If there is too long a delay between the time in some way. between when a signal is generated and when A system analysis determines what goes in, it is received and responded to, the system may 6 what comes out, and what has changed within experience overshoot. In some systems, this a given system. Environmental scientists use may lead to exceeding the carrying capacity. Texas Pentathlon - TX, TX 2024–2025 Science Pentathlon Resource Guide 21  Section II Biodiversity: From Local to Global In this section, we will focus on the Earth as a living the plantation may be the same as in an equivalent planet and explore the ways that life is organized area of natural forest, but the diversity of organisms from local to global scales. You will learn about the will be far less. The number of different species in any evolutionary processes that gave rise to the diversity given place is the most common measure of biological of species on our planet, the biological and physical diversity. Variety of species, however, is not the only factors that regulate biodiversity from genes to species, way biological diversity can be measured. Recall from and how living and nonliving components are linked Section I that biological diversity, or biodiversity, is the together into systems—both small and global. The diversity of all the genes, species, and habitats on Earth. major elements you will cover are: The great number of species on Earth is the result of 6 Evolution and Biodiversity − Genetic variation the large amount of genetic diversity within and among resulting in environmentally adaptive traits species. Genetic diversity is the variety of genes, the Texas Pentathlon - TX, TX has resulted in a diverse number and types of chemical building blocks that provide the blueprint species. for how every individual organism develops. Current Community Ecology − how populations of estimates are that humans have approximately 30,000 6 species grow, disperse, and interact with other different genes, which can combine to form a virtually populations limitless variety of individuals. No two people, except for identical twins, will have exactly the same 6 Ecosystems − the integration of living and combination of genes. There is even more genetic nonliving system components in specific diversity between individuals of different species. geographic areas Biomes − variation in global patterns of Biodiversity also includes the different ways that 6 temperature, sunlight, and rainfall are key in FIGURE 14 creating geographic regions distinguished by different dominant forms of plants and animals 6 Global Energy and Matter Cycles − global biogeochemical cycles on which all ecosystems depend BIODIVERSITY What Is Biodiversity and Why Does It Matter? A small plot of land or a tiny pond has dozens or hundreds of different kinds of plants and animals that even the untrained eye can distinguish, as well as thousands of different kinds of microscopic organisms. In contrast, a carefully tended lawn or a commercial tree plantation usually supports only a few types of grasses or trees. The total number of living things in A sample of the range of multi-cellular species diversity. 2024–2025 Science Pentathlon Resource Guide 22 groups of species are organized together on the planet. A forest community will contain different species of FIGURE 15 plants and animals than a community of organisms in a desert, a lake, or the ocean bottom. Finally, biodiversity describes different combinations of living and nonliving components in varied environmental systems of inputs, outputs, and feedbacks. Genetic Diversity At the most basic level, species are distinguished from each other by how different their genes are. Genetic diversity is the ultimate source of biodiversity on Earth. The genetic differences between members of the same species can lead to physical variety such as different eye color, leaf arrangement, or beak size; differences between members of various species can result in dramatically different body plans and capabilities. Over generations, blueprints can change so that sometimes the organism of today bears very Two pea plants with the Bb genotype (purple flowers) produce little resemblance to its ultimate ancestor. This change a mix of purple and white colored offspring. Source: CK-12.org is the result of evolution. Evolution occurs when the genes among groups of individuals within the same Texas Pentathlon - TX, TX species change over time, so that the groups become genotypes: BB, Bb, or bb. The phenotypes produced different enough to be recognized as separate species. by the BB and bb genotypes will differ in some To understand how genetic diversity leads to species way. For example, in pea plants the B allele (and diversity, we need to understand some of the basic therefore the BB genotype) produces purple flowers, principles of genetic diversity. and the bb genotype produces white flowers. The Bb All organisms inherit from their parents the genes genotype contains one allele of each type, and yet pea that provide the blueprint for their development and plants with this genotype are also observed to have function. Some genes contain most, or even all, of purple flowers. In this case, the B allele is said to be the instructions for relatively simple traits. More dominant over the b allele. complex traits, such as body size and shape, are the Taken together, all the different alleles for a particular result of the interaction of more than one gene. All of trait that occur in a population are a pool of genetic these traits, the simple and the complex, are referred diversity. It is impossible to estimate the number of to as an individual’s phenotype, which consists of different alleles for genes of all individuals in any all of an individual’s anatomical, physiological, and natural population, and thus all the potential diversity, behavioral characteristics. All of an organism’s genes but a familiar example can give you some idea of the together comprise its genotype, which is its unique possibilities. All the varieties of Canis familiaris, genetic composition and the code for its phenotype. the domestic dog, share enough genetic material to Genes are chemically made up of the molecule DNA be considered one species. However, by repeatedly and arranged within an organism’s cells on structures breeding individuals with certain desired traits, called chromosomes. breeders have produced dogs as varied as toy poodles Genes frequently have alternative forms that contain and Great Danes. Each different breed is expressing a different instructions for what the gene will produce; different combination of alleles that lead to variations each alternative form is called an allele. If a particular in size, shape, coat texture, color, and so forth. gene in a population has two alleles (we’ll call them There is only one way a new allele can be produced: B and b), an individual in the population who has a mutation, an error made when genetic material two copies of the gene will have one of three possible is copied, can permanently alter the genotype an 2024–2025 Science Pentathlon Resource Guide 23 organism passes on to its descendants. Mutations Expressions of Genetic Diversity occur spontaneously and randomly. Millions of copies The observable characteristics associated with an of genetic material are made within cells, so it’s only organism’s genotype is called its phenotype. In some natural that some mistakes will be made. Mutations simple cases, a phenotype is simply the expression of are even more likely under some environmental a genotype. For instance, a person who inherits the conditions—exposure to anthropogenic chemicals, such genes for blue eyes will have blue eyes whether they as those in tobacco smoke, for instance, or radiation. live in tropical Africa or subarctic Alaska. However,