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2 Environmental Systems: Matter, Energy, and Ecosystems Chapter Objectives This chapter will help students: 2.1 Describe the nature of environmental systems 2.2 Explain the fundamentals of matter and chemistry, and apply them to realworld situations 2.3 Differentiate among forms of energy and explain the first and second laws of thermodynamics 2.4 Distinguish photosynthesis, cellular respiration, and chemosynthesis, and summarize their importance to living things 2.5 Define ecosystems and discuss how living and nonliving entities interact in ecosystem-level ecology 2.6 Outline the fundamentals of landscape ecology and ecological modeling 2.7 Explain ecosystem services and describe how they benefit our lives 2.8 Compare and contrast how water, carbon, nitrogen, and phosphorus cycle through the environment, and explain how human activities affect these cycles

Lecture Outline I.

Central Case Study: The Vanishing Oysters of the Chesapeake Bay A. Economic decline occurred in Deal Island and other bayside towns due to the collapse of the Chesapeake Bay oyster fishery.

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B. The Chesapeake Bay was once a thriving system, due to nutrients carried to the bay by streams in its drainage basin or watershed—the land area that funnels water to a given body of water. C. The intensive harvest of bay oysters began in the 1830s, and by the 1880s, the bay boasted the world’s largest oyster fishery. D. But by 2010, the bay’s oysters had been reduced to a mere 1% of their historical abundance. E. In addition to overharvesting, one of the biggest impacts on oysters in recent decades is the pollution of the bay with high levels of the nutrients nitrogen and phosphorus from agricultural fertilizers, animal manure, stormwater runoff, and atmospheric compounds produced by fossil fuel combustion. This depletes the oxygen in the water (a condition called hypoxia) and creates “dead zones” in the bay. F. There is hope for the recovery of the Chesapeake Bay system, with the EPA making states reduce nitrogen and phosphorus input to the bay by 2025. Oyster restoration efforts are also showing promise. II.

Earth’s Environmental Systems A. Systems involve feedback loops. 1. A system is a network of relationships among parts, elements, or components that interact with and influence one another through the exchange of energy, matter, or information. The lithosphere is the rock and sediment beneath our feet, the planet’s uppermost mantle and crust. The atmosphere is composed of the air surrounding our planet. The hydrosphere encompasses all water—salt or fresh, liquid, ice, or vapor—in surface bodies, underground, and in the atmosphere. The biosphere consists of all the planet’s organisms and the abiotic (nonliving) portions of the environment with which they interact. 2. Sometimes a system’s output can serve as input to that same system, a circular process described as a feedback loop. In a negative feedback loop, output that results from a system moving in one direction acts as input that moves the system in the other direction. 3. In a system stabilized by negative feedback, when processes move in opposing directions at equivalent rates so that their effects balance out, they are said to be in dynamic equilibrium. Processes in dynamic equilibrium can contribute to homeostasis, the tendency of a system to maintain relatively constant or stable internal conditions. 4. Positive feedback loops have the opposite effect. Rather than stabilizing a system, they drive it further toward an extreme.

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B. Environmental systems interact. 1. The Chesapeake Bay and the rivers that empty into it provide an example of how systems interact. For a scientist interested in runoff—the precipitation that flows over land and enters waterways—and the flow of water, sediment, or pollutants, it may make the most sense to define the bay’s watershed as a system. 2. The dead zones in the Chesapeake Bay are due to the extremely high levels of nitrogen and phosphorus delivered to its waters from the 6 states in its watershed and the 15 states in its airshed—the geographic area that produces air pollutants that are likely to end up in a waterway. 3. The process of nutrient overenrichment, increased production of organic matter, and subsequent ecosystem degradation is known as eutrophication. III.

Matter, Chemistry, and the Environment A. Atoms and elements are chemical building blocks. 1. All material in the universe that has mass and occupies space— solid, liquid, and gas, alike—is called matter. The study of types of matter and their interactions is called chemistry. Matter may be transformed from one type of substance into others, but it cannot be created or destroyed. This principle is referred to as the law of conservation of matter. 2. An element is a fundamental type of matter, a chemical substance with a given set of properties that cannot be broken down into substances with other properties. 3. An atom is the smallest unit that maintains the chemical properties of the element. Atoms of each element contain a specific number of protons (positively charged particles) in the atom’s nucleus (its dense center), and this number is called the element’s atomic number. Most atoms also contain neutrons, which are particles in the nucleus that lack an electrical charge. An atom’s nucleus is surrounded by negatively charged particles known as electrons, which balance the positive charge of the protons. 4. Elements especially abundant on our planet include hydrogen (in water), oxygen (in the air), silicon (in Earth’s crust), nitrogen (in the air), and carbon (in living organisms). Elements that organisms need for survival, such as carbon, nitrogen, calcium, and phosphorus, are called nutrients.

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a) Atoms with differing numbers of neutrons are isotopes. Some isotopes, called radioisotopes, are radioactive and “decay” by changing their chemical identity as they shed subatomic particles and emit high-energy radiation. Each radioisotope decays at a rate determined by that isotope’s half-life, the amount of time it takes for one-half of the atoms to give off radiation and decay. b) Atoms may also gain or lose electrons, thereby becoming ions, which are electrically charged atoms or combinations of atoms. B. Atoms bond to form molecules and compounds. 1. Atoms bond together to form molecules, combinations of two or more atoms. A molecule composed of atoms of two or more different elements is called a compound—one compound is water (one oxygen atom bonded to two hydrogen atoms). Another compound is carbon dioxide, consisting of one carbon atom bonded to two oxygen atoms; its chemical formula is CO2. 2. Some compounds are made up of ions of differing charge that bind with one another to form ionic bonds. Atoms that lack an electrical charge combine by “sharing” electrons in a covalent bond. 3. Elements, molecules, and compounds can also come together without chemically bonding, in mixtures called solutions. C. Hydrogen ions determine acidity. 1. Solutions in which the H+ concentration is greater than the OH– concentration are acidic, whereas solutions in which the OH– concentration exceeds the H+ concentration are basic, or alkaline. 2. The pH scale quantifies the acidity or alkalinity of solutions. D. Matter is composed of organic and inorganic compounds. 1. Organic compounds consist of carbon atoms (and generally hydrogen atoms) joined by covalent bonds, and they may also include other elements. Inorganic compounds, in contrast, lack carbon–carbon bonds. 2. One class of organic compounds that is important in environmental science is the hydrocarbons, which consist solely of bonded atoms of carbon and hydrogen. E. Macromolecules are the building blocks of life. 1. Three types of polymers (long chains of repeated molecules) are essential to life: proteins, nucleic acids, and carbohydrates. Along with lipids (which are not polymers), these types of molecules are referred to as macromolecules because of their large sizes.

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2. Proteins consist of long chains of organic molecules called amino acids. They serve various functions including structural support, energy storage, immune system functions, hormones, and enzymes. 3. Nucleic acids direct the production of proteins. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) carry the hereditary information for organisms. Nucleic acids are composed of a series of nucleotides, each of which contains a sugar molecule, a phosphate group, and a nitrogenous base. Regions of DNA that code for particular proteins that perform particular functions are called genes. 4. Carbohydrates include simple sugars and large molecules three to seven carbon atoms long. Among these is glucose, which fuels living cells and serves as a building block for complex carbohydrates such as starch, an energy storage compound; chitin, a structural component of shells; and cellulose, the most abundant organic compound on Earth, which is found in the cell walls of plants. 5. Lipids are a chemically diverse group of compounds, grouped together because they do not dissolve in water. IV.

Energy: An Introduction A. Energy is always conserved, but it changes in quality. 1. Energy is the capacity to change the position, physical composition, or temperature of matter. Potential energy is the energy of position. Kinetic energy is the energy of motion. Chemical energy is potential energy stored in the bonds between atoms. 2. The first law of thermodynamics states that energy can change from one form to another but cannot be created or destroyed. 3. The second law of thermodynamics states that the nature of energy will change from a more-ordered state to a less-ordered state, as long as no force counteracts this tendency. Systems tend to move toward increasing disorder, or entropy. B. Light energy from the sun powers most living systems. 1. Some organisms use the sun’s radiation directly to produce their own food. Such organisms are called autotrophs, or primary producers, and include green plants, algae, and cyanobacteria. Through the process of photosynthesis, autotrophs use sunlight to power a series of chemical reactions that transform molecules with lower-energy bonds—water and carbon dioxide—into sugar molecules with many high-energy bonds.

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2. Photosynthesis occurs within cellular organelles called chloroplasts where the light-absorbing pigment chlorophyll uses solar energy to initiate a series of chemical reactions called the light reactions. The light reactions produce energy molecules that fuel reactions in the Calvin cycle where sugars are formed. 3. The net process of photosynthesis is defined by the chemical equation: 6CO2 + 6H2O + the sun’s energy → C6H12O6 (sugar) + 6O2. 4. Not all primary production requires sunlight, however. 5. Bacteria in deep-sea vents use the chemical-bond energy of hydrogen sulfide (H2S) to transform inorganic carbon into organic carbon compounds in a process called chemosynthesis. Chemosynthesis occurs in various ways. C. Cellular respiration releases chemical energy. 1. Organisms make use of the chemical energy created by photosynthesis in a process called cellular respiration. Cells use oxygen to convert glucose back into its original starting materials, water and carbon dioxide, and release energy to power all of the biochemical reactions that sustain life. The net equation for cellular respiration is the exact opposite of that for photosynthesis: C6H12O6 (sugar) + 6O2 → 6CO2 + 6H2O + energy. 2. Respiration occurs in autotrophs and also in heterotrophs, organisms that gain their energy by feeding on other organisms. V.

Ecosystems A. Energy flows and matter cycles through ecosystems. 1. An ecosystem consists of all organisms and nonliving entities that occur and interact in a particular area at the same time. 2. An example of an ecosystem is the Chesapeake Bay estuary—a water body where rivers flow into the ocean, mixing fresh water with salt water. 3. Energy flows in one direction through ecosystems. As autotrophs convert solar energy to the energy of chemical bonds in sugar through the process of photosynthesis, they perform primary production. The total amount of chemical energy produced by autotrophs is termed gross primary production. Autotrophs use most of this production to power their own metabolism by cellular respiration, releasing heat energy to the environment as a byproduct. The energy that remains after respiration and that is used to generate biomass is called net primary production.

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4. Some plant biomass is subsequently eaten by herbivores, which use the energy they gain from plant biomass for their own metabolism or to generate biomass in their bodies, termed secondary production. 5. In contrast to chemical energy, nutrients are generally recycled within ecosystems. B. Ecosystems vary in their productivity. 1. Ecosystems differ in the rate at which autotrophs convert energy to biomass. This rate is termed productivity, and the energy or biomass that remains in an ecosystem after autotrophs have metabolized enough for their own maintenance through cellular respiration is called net primary productivity. C. Ecosystems interact across landscapes. 1. Ecosystems occur at different scales. 2. Areas where ecosystems meet may consist of transitional zones called ecotones, in which elements of each ecosystem mix. 3. In a broad-scale approach called landscape ecology, scientists study how landscape structure affects the abundance, distribution, and interaction of organisms. 4. A landscape is made up of patches arrayed spatially over a landscape in a mosaic. Landscape ecology is of great interest to conservation biologists, scientists who study the loss, protection, and restoration of biodiversity. 5. Landscape-level analyses have been greatly aided by satellite imaging and geographic information systems (GIS)—computer software that takes multiple types of data and layers them together on a common set of geographic coordinates. D. Modeling helps ecologists understand systems. 1. In science, a model is a simplified representation of a complicated natural process, designed to help us understand how the process occurs and to make predictions. Ecological modeling is the practice of constructing and testing models that aim to explain and predict how ecological systems function. 2. Ecological models can be mathematically complicated, but they are grounded in actual data and based on hypotheses about how components interact in ecosystems.

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E. Ecosystem services sustain our world. 1. Ecological services are the natural processes that humans benefit from. 2. One of the most important ecosystem services is the cycling of nutrients. VI.

Biogeochemical Cycles A. Nutrients circulate through ecosystems in biogeochemical cycles. 1. Nutrient cycles (or biogeochemical cycles) circulate elements or molecules through the lithosphere, atmosphere, hydrosphere, and biosphere. 2. Nutrients and other materials move from one reservoir, or pool, to another, remaining in each reservoir for varying amounts of time (the residence time). The rate at which materials move between reservoirs is termed a flux. When a reservoir releases more materials than it accepts, it is called a source, and when a reservoir accepts more materials than it releases, it is called a sink. B. The water cycle affects all other cycles. 1. The hydrologic cycle, or water cycle, summarizes how water—in liquid, gaseous, and solid forms—flows through our environment. 2. The oceans are the largest reservoir in the hydrologic cycle, holding more than 97% of all water on Earth. 3. Water moves from surface water and moist soil into the atmosphere by evaporation, the conversion of a liquid to gaseous form. Water also enters the atmosphere by transpiration, the release of water vapor by plants through their leaves. Water returns from the atmosphere to Earth’s surface as precipitation when water vapor condenses and falls as rain or snow. This may be taken up by plants and used by animals, but much of it flows as runoff into surface water bodies. 4. Some water soaks down through soil and rock through a process called infiltration, recharging underground reservoirs known as aquifers. Aquifers are porous regions of rock and soil that hold groundwater, water found within the soil. The upper limit of groundwater held in an aquifer is referred to as the water table. 5. Human activity affects nearly every aspect of the water cycle.

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C. The carbon cycle circulates a vital nutrient. 1. The carbon cycle describes the routes that carbon atoms take through the environment. 2. The largest reservoir of carbon, sedimentary rock, is formed in oceans and freshwater wetlands. 3. Ocean waters are the second-largest reservoir of carbon on Earth. 4. Human activity affects the carbon cycles through our use of coal, oil, and natural gas. 5. Some of the excess CO2 in the atmosphere is now being absorbed by ocean water. 6. Our understanding of the carbon cycle is not yet complete. D. The nitrogen cycle involves specialized bacteria. 1. Nitrogen is an essential ingredient in proteins, DNA, and RNA and, like phosphorus, is an essential nutrient for plant growth. Thus, the nitrogen cycle is of vital importance to all organisms. 2. To become biologically available, inert nitrogen gas must be “fixed,” or combined with hydrogen in nature to form ammonia, whose water-soluble ions of ammonium can be taken up by plants. Nitrogen fixation can be accomplished in two ways: by the intense energy of lightning strikes or by particular types of nitrogen-fixing bacteria that inhabit the top layer of soil. Other types of bacteria then perform a process known as nitrification, converting ammonium ions first into nitrite ions and then into nitrate ions. 3. Animals obtain the nitrogen that they need by consuming plants or other animals. Decomposers obtain nitrogen from dead and decaying plant and animal matter and from the urine and feces of animals. The next step in the nitrogen cycle occurs when denitrifying bacteria convert nitrates in soil or water to gaseous nitrogen. Denitrification thereby completes the cycle by releasing nitrogen back into the atmosphere as a gas. 4. Historically, nitrogen fixation was a bottleneck, a step that limited the flux of nitrogen out of the atmosphere and into water-soluble forms. Once people discovered how to fix nitrogen on massive scales, a process called industrial fixation, we accelerated its flux into other reservoirs. E. The phosphorus cycle circulates a limited nutrient. 1. Sedimentary rocks are the largest reservoir in the phosphorus cycle.

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2. People increase phosphorus concentrations in surface waters through runoff of the phosphorus-rich fertilizers we apply to lawns and farmlands. F. Tackling nutrient enrichment requires diverse approaches. VII.

Conclusion A. Life interacts with its nonliving environment in ecosystems, systems through which energy flows and materials are recycled. B. Applications of chemistry can provide solutions to environmental problems involving agricultural practices, water resources, air quality, energy policy, and environmental health.

Key Terms acidic airshed...