rom the viewpoints of (1)the environment and the demands it places on the organ- isms in it or(2)organisms and how they adapt to their environmental conditions. An ecosystem consists of an assembly of mutually interacting organisms and their environment in which materials are interchanged in a largely cyclical manner. An ecosystem has physical, chemical, and biological components along with energy sources and pathways of energy and materials interchange. The environment in which a particular organism lives is called its habitat. The role of an organism in a habitat is called its niche For the study of ecology it is often convenient to divide the environment into four broad categories The terrestrial environment is based on land and consists of biomes, such as grasslands, savannas, deserts, or one of several kinds of forests. The freshwater environment can be further subdivided between standing-water habitats (lakes, reservoirs) and running-water habitats(streams, rivers). The oceanic marine environment is characterized by saltwater and may be divided broadly into the shallow waters of the continental shelf composing the neritic zone and the deeper waters of the ocean that constitute the oceanic region. An environment in which two or more kinds of organisms exist together to their mutual benefit is termed a symbiotic environment a particularly important factor in describing ecosystems is that of populations consisting of numbers of a specific species occupying a specific habitat. Populations may be stable, or they may grow exponentially as a population explosion. A population explosion that is unchecked results in resource depletion, waste ccumulation, and predation culminating in an abrupt decline called a population crash. Behavior in areas such as hierarchies, territoriality, social stress, and feeding patterns plays a strong role in determining the fates of populations Two major subdivisions of modern ecology are ecosystem ecology, which views ecosystems as large units, and population ecology, which attempts to explain ece stem behavior from the properties of individual units. In practice, the two approaches are usually merged. Descriptive ecology describes the types and nature of organisms and their environment, emphasizing structures of ecosystems and communities, and dispersions and structures of populations. Functional ecology explains how things work in an ecosystem, including how populations respond to nvironmental alteration and how matter and energy move through ecosystems An understanding of ecology is essential in the management of modern industri- lized societies in ways that are compatible with environmental preservation and enhancement. Applied ecology deals with predicting the impacts of technology and development and making recommendations such that these activities will have minimum adverse impact, or even positive impact, on ecosystems 1. 5. ENERGY AND CYCLES OF ENERGY Biogeochemical cycles and virtually all other processes on Earth are driven by energy from the sun. The sun acts as a so-called blackbody radiator with an effective surface temperature of 5780 K (absolute temperature in which each unit is the same as a Celsius degree, but with zero taken at absolute zero).5 It transmits energy to Earth as electromagnetic radiation(see below) with a maximum energy flux at about 500 nanometers, which is in the visible region of the spectrum. A 1 meter C 2000 CRC Press llc
from the viewpoints of (1) the environment and the demands it places on the organisms in it or (2) organisms and how they adapt to their environmental conditions. An ecosystem consists of an assembly of mutually interacting organisms and their environment in which materials are interchanged in a largely cyclical manner. An ecosystem has physical, chemical, and biological components along with energy sources and pathways of energy and materials interchange. The environment in which a particular organism lives is called its habitat. The role of an organism in a habitat is called its niche. For the study of ecology it is often convenient to divide the environment into four broad categories. The terrestrial environment is based on land and consists of biomes, such as grasslands, savannas, deserts, or one of several kinds of forests. The freshwater environment can be further subdivided between standing-water habitats (lakes, reservoirs) and running-water habitats (streams, rivers). The oceanic marine environment is characterized by saltwater and may be divided broadly into the shallow waters of the continental shelf composing the neritic zone and the deeper waters of the ocean that constitute the oceanic region. An environment in which two or more kinds of organisms exist together to their mutual benefit is termed a symbiotic environment. A particularly important factor in describing ecosystems is that of populations consisting of numbers of a specific species occupying a specific habitat. Populations may be stable, or they may grow exponentially as a population explosion. A population explosion that is unchecked results in resource depletion, waste accumulation, and predation culminating in an abrupt decline called a population crash. Behavior in areas such as hierarchies, territoriality, social stress, and feeding patterns plays a strong role in determining the fates of populations. Two major subdivisions of modern ecology are ecosystem ecology, which views ecosystems as large units, and population ecology, which attempts to explain ecosystem behavior from the properties of individual units. In practice, the two approaches are usually merged. Descriptive ecology describes the types and nature of organisms and their environment, emphasizing structures of ecosystems and communities, and dispersions and structures of populations. Functional ecology explains how things work in an ecosystem, including how populations respond to environmental alteration and how matter and energy move through ecosystems. An understanding of ecology is essential in the management of modern industrialized societies in ways that are compatible with environmental preservation and enhancement. Applied ecology deals with predicting the impacts of technology and development and making recommendations such that these activities will have minimum adverse impact, or even positive impact, on ecosystems. 1.5. ENERGY AND CYCLES OF ENERGY Biogeochemical cycles and virtually all other processes on Earth are driven by energy from the sun. The sun acts as a so-called blackbody radiator with an effective surface temperature of 5780 K (absolute temperature in which each unit is the same as a Celsius degree, but with zero taken at absolute zero).5 It transmits energy to Earth as electromagnetic radiation (see below) with a maximum energy flux at about 500 nanometers, which is in the visible region of the spectrum. A 1-square-meter © 2000 CRC Press LLC
area perpendicular to the line of solar flux at the top of the atmosphere receives energy at a rate of 1, 340 watts, sufficient, for example, to power an electric iron This is called the solar flux(see Chapter 9, Figure 9.3) Light and electromagnetic Radiation lectromagnetic radiation, particularly light, is of utmost importance in considering energy in environmental systems. Therefore, the following important points related to electromagnetic radiation should be noted Energy can be carried through space at the speed of light(c), 3.00 x 108 meters per second(m/s)in a vacuum, by electromagnetic radiation which includes visible light, ultraviolet radiation, infrared radiation, icrowaves, radio waves, gamma rays, and X-rays Electromagnetic radiation has a wave character. The waves move at the speed of light, c, and have characteristics of wavelength(2), amplitude, and frequency(v, Greek nu")as illustrated below AAAA-wfAA The wavelength is the distance required for one complete cycle, and the frequency is the number of cycles per unit time. They are related by the where v is in units of cycles per second(s", a unit called the hertz, Hz) andλ Is In meters(m) In addition to behaving as a wave, electromagnetic radiation has char acteristics of particle The dual wave/particle nature of electromagnetic radiation is the basis of the quantum theory of electromagnetic radiation, which states that radiant energy may be absorbed or emitted only in discrete packets called quanta or photons. The energy, E, of each photon is given by where h is Plancks constant, 6.63 x 10-34 J-s joule x second) From the preceding, it is seen that the energy of a photon is higher when the frequency of the associated wave is higher(and the wavelength shorter) C 2000 CRC Press llc
area perpendicular to the line of solar flux at the top of the atmosphere receives energy at a rate of 1,340 watts, sufficient, for example, to power an electric iron. This is called the solar flux (see Chapter 9, Figure 9.3). Light and Electromagnetic Radiation Electromagnetic radiation, particularly light, is of utmost importance in considering energy in environmental systems. Therefore, the following important points related to electromagnetic radiation should be noted: • Energy can be carried through space at the speed of light (c), 3.00 x 108 meters per second (m/s) in a vacuum, by electromagnetic radiation, which includes visible light, ultraviolet radiation, infrared radiation, microwaves, radio waves, gamma rays, and X-rays. • Electromagnetic radiation has a wave character. The waves move at the speed of light, c, and have characteristics of wavelength (l), amplitude, and frequency (n, Greek “nu”) as illustrated below: Amplitude Wavelength Shorter wavelength. higher frequency • The wavelength is the distance required for one complete cycle, and the frequency is the number of cycles per unit time. They are related by the following equation: nl = c where n is in units of cycles per second (s-1, a unit called the hertz, Hz) and l is in meters (m). • In addition to behaving as a wave, electromagnetic radiation has characteristics of particles. • The dual wave/particle nature of electromagnetic radiation is the basis of the quantum theory of electromagnetic radiation, which states that radiant energy may be absorbed or emitted only in discrete packets called quanta or photons. The energy, E, of each photon is given by E = h n where h is Planck’s constant, 6.63 ´ 10-34 J-s (joule ´ second). • From the preceding, it is seen that the energy of a photon is higher when the frequency of the associated wave is higher (and the wavelength shorter). © 2000 CRC Press LLC
Energy Flow and Photosynthesis in Living Systems Whereas materials are recycled through ecosystems, the flow of useful energy is essentially a one-way process Incoming solar energy can be regarded as high-grade energy because it can cause useful reactions to occur, such as production of electricity in photovoltaic cells or photosynthesis in plants. As shown in Figure 1.2, solar energy captured by green plants energizes chlorophyll, which in turn powers metabolic processes that produce carbohydrates from water and carbon dioxide These carbohydrates are repositories of stored chemical energy that can be converted to heat and work by metabolic reactions with oxygen in organisms. Ultimately, most of the energy is converted to low-grade heat, which is eventually reradiated away from Earth by infrared radiation Energy Utilization During the last two centuries, the growing, enormous human impact on energy utilization has resulted in many of the environmental problems now facing humankind. This time period has seen a transition from the almost exclusive use of energy captured by photosynthesis and utilized as biomass(food to provide muscle power, wood for heat)to the use of fossil fuel petroleum, natural gas, and coal for about 90 percent, and nuclear energy for about 5 percent, of all energy employed commercially. Although fossil sources of energy have greatly exceeded the pessimistic estimates made during the energy crisis"of the 1970s, they are limited and their pollution potential is high. Of particular importance is the fact that all fossil fuels produce carbon dioxide, a greenhouse gas. Therefore, it will be necessary to move toward the utilization of alternate renewable energy sources, including solar energy and biomass. The study of energy utilization is crucial in the environmental sciences, and it is discussed in greater detail in Chapter 18, Industrial Ecology Resources, and Energy 1.6. MATTER AND CYCLES OF MATTER Cycles of matter(Figure 1.3), often based on elemental importance in the environment. b These cycles are summarized here and are the viewpoint of various reservoirs, such as oceans, sedin cles can be regarded from discussed further in later chapters. Global geochemical cy nents, and the atmosphere connected by conduits through which matter moves continuously. The movement of a specific kind of matter between two particular reservoirs may be reversible or irre- versible. The fluxes of movement for specific kinds of matter vary greatly as do the contents of such matter in a specified reservoir. Cycles of matter would occur even in the absence of life on Earth but are strongly influenced by life for ms, particularly plants and microorganisms. Organisms participate in biogeochemical cycles, which describe the circulation of matter, particularly plant and animal nutrients, through ecosystems. As part of the carbon cycle, atmospheric carbon in CO, is fixed as biomass, as part of the nitrogen cycle, atmospheric N, is fixed in organic matter. The reverse of these kinds of processes is mineralization, in which biologically bound elements are returned to inorganic states. Biogeochemical cycles are ultimately C 2000 CRC Press llc
Energy Flow and Photosynthesis in Living Systems Whereas materials are recycled through ecosystems, the flow of useful energy is essentially a one-way process. Incoming solar energy can be regarded as high-grade energy because it can cause useful reactions to occur, such as production of electricity in photovoltaic cells or photosynthesis in plants. As shown in Figure 1.2, solar energy captured by green plants energizes chlorophyll, which in turn powers metabolic processes that produce carbohydrates from water and carbon dioxide. These carbohydrates are repositories of stored chemical energy that can be converted to heat and work by metabolic reactions with oxygen in organisms. Ultimately, most of the energy is converted to low-grade heat, which is eventually reradiated away from Earth by infrared radiation. Energy Utilization During the last two centuries, the growing, enormous human impact on energy utilization has resulted in many of the environmental problems now facing humankind. This time period has seen a transition from the almost exclusive use of energy captured by photosynthesis and utilized as biomass (food to provide muscle power, wood for heat) to the use of fossil fuel petroleum, natural gas, and coal for about 90 percent, and nuclear energy for about 5 percent, of all energy employed commercially. Although fossil sources of energy have greatly exceeded the pessimistic estimates made during the “energy crisis” of the 1970s, they are limited and their pollution potential is high. Of particular importance is the fact that all fossil fuels produce carbon dioxide, a greenhouse gas. Therefore, it will be necessary to move toward the utilization of alternate renewable energy sources, including solar energy and biomass. The study of energy utilization is crucial in the environmental sciences, and it is discussed in greater detail in Chapter 18, “Industrial Ecology, Resources, and Energy.” 1.6. MATTER AND CYCLES OF MATTER Cycles of matter (Figure 1.3), often based on elemental cycles, are of utmost importance in the environment. 6 These cycles are summarized here and are discussed further in later chapters. Global geochemical cycles can be regarded from the viewpoint of various reservoirs, such as oceans, sediments, and the atmosphere, connected by conduits through which matter moves continuously. The movement of a specific kind of matter between two particular reservoirs may be reversible or irreversible. The fluxes of movement for specific kinds of matter vary greatly as do the contents of such matter in a specified reservoir. Cycles of matter would occur even in the absence of life on Earth but are strongly influenced by life forms, particularly plants and microorganisms. Organisms participate in biogeochemical cycles, which describe the circulation of matter, particularly plant and animal nutrients, through ecosystems. As part of the carbon cycle, atmospheric carbon in CO2 is fixed as biomass; as part of the nitrogen cycle, atmospheric N2 is fixed in organic matter. The reverse of these kinds of processes is mineralization, in which biologically bound elements are returned to inorganic states. Biogeochemical cycles are ultimately © 2000 CRC Press LLC
powered by solar energy, which is fine-tuned and directed by energy expended by organisms. In a sense, the solar-energy-powered hydrologic cycle(Figure 3. 1)acts as an endless conveyer belt to move materials essential for life through ecosystem herge through Oxygen Synthesis of Figure 1. 2. Energy conversion and transfer by photosynthesis Figure 1.3 shows a general cycle with all five spheres or reservoirs in which matter may be contained. Human activities now have such a strong influence on materials cycles that it is useful to refer to the"anthrosphere'"along with the other environmental"spheres" as a reservoir of materials. Using Figure 1.3 as a model,it is possible to arrive at any of the known elemental cycles. Some of the numerous possibilities for materials exchange are summarized in Table 1.1 C 2000 CRC Press LlC
powered by solar energy, which is fine-tuned and directed by energy expended by organisms. In a sense, the solar-energy-powered hydrologic cycle (Figure 3.1) acts as an endless conveyer belt to move materials essential for life through ecosystems. Figure 1.2. Energy conversion and transfer by photosynthesis. Figure 1.3 shows a general cycle with all five spheres or reservoirs in which matter may be contained. Human activities now have such a strong influence on materials cycles that it is useful to refer to the “anthrosphere” along with the other environmental “spheres” as a reservoir of materials. Using Figure 1.3 as a model, it is possible to arrive at any of the known elemental cycles. Some of the numerous possibilities for materials exchange are summarized in Table 1.1. © 2000 CRC Press LLC
Atmosphere Biosphere Anthrosphere Bi←An Ge→Hv Hydrosphere GeeLy Figure 1.3. General cycle showing interchange of matter among the atmos Endogenic and Exogenic cycles Materials cycles may be divided broadly between endogenic cycles, which predominantly involve subsurface rocks of various kinds, and exogenic cycles which occur largely on Earth's surface and usually have an atmospheric component These two kinds of cycles are broadly outlined in Figure 1. 4. In general, sediment and soil can be viewed as being shared between the two cycles and constitute the predominant interface between them Most biogeochemical cycles can be described as elemental cycles involving nutrient elements such as carbon, nitrogen, oxygen, phosphorus, and sulfur. Mar are exogenic cycles in which the element in question spends part of the cycle in the atmosphere--O, fo N2 for nitrogen, CO2 for carbon. Others, notably the phosphorus cycle, do not have a gaseous component and are endogenic cycles. All sedimentary cycles involve salt solutions or soil solutions(see Section 16.2)that contain dissolved substances leached from weathered minerals. these substances C 2000 CRC Press llc
Figure 1.3. General cycle showing interchange of matter among the atmosphere, biosphere, anthrosphere, geosphere, and hydrosphere. Endogenic and Exogenic Cycles Materials cycles may be divided broadly between endogenic cycles, which predominantly involve subsurface rocks of various kinds, and exogenic cycles, which occur largely on Earth’s surface and usually have an atmospheric component.7 These two kinds of cycles are broadly outlined in Figure 1.4. In general, sediment and soil can be viewed as being shared between the two cycles and constitute the predominant interface between them. Most biogeochemical cycles can be described as elemental cycles involving nutrient elements such as carbon, nitrogen, oxygen, phosphorus, and sulfur. Many are exogenic cycles in which the element in question spends part of the cycle in the atmosphere—O2 for oxygen, N2 for nitrogen, CO2 for carbon. Others, notably the phosphorus cycle, do not have a gaseous component and are endogenic cycles. All sedimentary cycles involve salt solutions or soil solutions (see Section 16.2) that contain dissolved substances leached from weathered minerals; these substances © 2000 CRC Press LLC