may be deposited as mineral formations, or they may be taken up by organisms nutrients Table l.l. Interchange of Materials among the Possible Spheres of the environment From Atmosphere Hydrosphere Biosphere Geosphere Anthrosphere Atmosphere HO H2S, part- SO2, CO Hydrosphere H2O ICH,O) pollutants Mineral Fertiliz ecosphere H,O HO Organic Hazardou Anthrosphere O2, N, H,O Food Minerals Carbon Cycle Carbon is circulated through the carbon cycle shown in Figure 1.5. This cycle shows that carbon may be present as gaseous atmospheric CO,, constituting a rela- tively small but highly significant portion of global carbon. Some of the carbon is dissolved in surface water and groundwater as HCO3 or molecular CO2(aq). A ver large amount of carbon is present in minerals, particularly calcium and magnesium carbonates such as CaCO3. Photosynthesis fixes inorganic C as biological carbon represented as (CH,O), which is a consituent of all life molecules. Another fraction of carbon is fixed as petroleum and natural gas, with a much larger amount as hydro- carbonaceous kerogen( the organic matter in oil shale), coal, and lignite, represented s CxH2x. Manufacturing processes are used to convert hydrocarbons to xenobiotic compounds with functional groups containing halogens, oxygen, nitrogen, pho phorus, or sulfur. Though a very small amount of total environmental carbon, these compounds are particularly significant because of their toxicological chemical effects An important aspect of the carbon cycle is that it is the cycle by which solar energy is transferred to biological systems and ultimately to the geosphere and anthrosphere as fossil carbon and fossil fuels. Organic, or biological, carbon (CH,O), is contained in energy-rich molecules that can react biochemically with molecular oxygen, O,, to regenerate carbon dioxide and produce energy. This can occur biochemically in an organism through aerobic respiration as shown in Equation 1.4.2, or it may occur as combustion, such as when wood or fossil fuels are Microorganisms are strongly involved in the carbon cycle, mediating crucial bio- chemical reactions discussed later in this section. Photosynthetic algae are the pre dominant carbon-fixing agents in water; as they consume CO, to produce biomass the C 2000 CRC Press LlC
may be deposited as mineral formations, or they may be taken up by organisms as nutrients. Table 1.1. Interchange of Materials among the Possible Spheres of the Environment From Atmosphere Hydrosphere Biosphere Geosphere Anthrosphere To Atmosphere ––– H2O O2 H2S, part- SO2, CO2 icles Hydrosphere H2O ––– {CH2O} Mineral Water solutes pollutants Biosphere O2, CO2 H2O ––– Mineral Fertilizers nutrients Geosphere H2O H2O Organic ––– Hazardous matter wastes Anthrosphere O2, N2 H2O Food Minerals ––– Carbon Cycle Carbon is circulated through the carbon cycle shown in Figure 1.5. This cycle shows that carbon may be present as gaseous atmospheric CO2, constituting a relatively small but highly significant portion of global carbon. Some of the carbon is dissolved in surface water and groundwater as HCO3 - or molecular CO2(aq). A very large amount of carbon is present in minerals, particularly calcium and magnesium carbonates such as CaCO3. Photosynthesis fixes inorganic C as biological carbon, represented as {CH2O}, which is a consituent of all life molecules. Another fraction of carbon is fixed as petroleum and natural gas, with a much larger amount as hydrocarbonaceous kerogen (the organic matter in oil shale), coal, and lignite, represented as CxH2x. Manufacturing processes are used to convert hydrocarbons to xenobiotic compounds with functional groups containing halogens, oxygen, nitrogen, phosphorus, or sulfur. Though a very small amount of total environmental carbon, these compounds are particularly significant because of their toxicological chemical effects. An important aspect of the carbon cycle is that it is the cycle by which solar energy is transferred to biological systems and ultimately to the geosphere and anthrosphere as fossil carbon and fossil fuels. Organic, or biological, carbon, {CH2O}, is contained in energy-rich molecules that can react biochemically with molecular oxygen, O2, to regenerate carbon dioxide and produce energy. This can occur biochemically in an organism through aerobic respiration as shown in Equation 1.4.2, or it may occur as combustion, such as when wood or fossil fuels are burned. Microorganisms are strongly involved in the carbon cycle, mediating crucial biochemical reactions discussed later in this section. Photosynthetic algae are the predominant carbon-fixing agents in water; as they consume CO2 to produce biomass the © 2000 CRC Press LLC
Outline of exogenic cycle. Atmosphere Hydrosphere Sediments v丿 Soil Igneous Metal Magn Outline of endogenic cycle Figure 1. 4. General outline of exogenic and endogenic cycles pH of the water is raised enabling precipitation of CacO3 and Caco, MgCO Organic carbon by microorganisms is transformed by biogeochemical processes to fossil petroleum, kerogen, coal, and lignite. Microorganisms degrade organic carbon from biomass, petroleum, and xenobiotic sources, ultimately returning it to the atmosphere as CO, Hydrocarbons such as those in crude oil and nthetic hydrocarbons are degraded by microorganisms. This is an important C 2000 CRC Press LlC
Atmosphere Hydrosphere Sediments Soil Biosphere Metamorphic rock Igneous rock Sedimentary rock Magma Outline of endogenic cycle Outline of exogenic cycle Figure 1.4. General outline of exogenic and endogenic cycles. pH of the water is raised enabling precipitation of CaCO3 and CaCO3•MgCO3. Organic carbon fixed by microorganisms is transformed by biogeochemical processes to fossil petroleum, kerogen, coal, and lignite. Microorganisms degrade organic carbon from biomass, petroleum, and xenobiotic sources, ultimately returning it to the atmosphere as CO2. Hydrocarbons such as those in crude oil and some synthetic hydrocarbons are degraded by microorganisms. This is an important © 2000 CRC Press LLC
mechanism for eliminating pollutant hydrocarbons, as those that are accidentally spilled on soil or in water. Biodegradation can also be used to treat carbon-containing compounds in hazardous wastes CO2 in the atmosphere degradation publication and chemical processes Phe Soluble inorganic carbon predominantly HCO3 ICH2O)and xenobiotic Chemical precipitation Dissolution with incorporation of Xenobiotics manu- dissolved co minera carbon into microbial shells facture with petrol- Biogeochemical euam StOc processes Fixed organic Insoluble inorganic carbon hydrocarbon, CxHox predominantly CaCO3 and CaCO2·MgCO .5. The carbon cycle. Mineral carbon is held in a reservoir of limeston nay be leached into a min olution as dissolved hydroger when dissolved Co,(aq)reacts with CaCO2. In the atmosphere carbe carbon dioxide is fixed organic carbon is released as CO, by microbial decay of organic matter The Nitrogen Cycle As shown in Figure 1.6, nitrogen occurs prominently in all the spheres of the environment. The atmosphere is 78% elemental nitrogen, N,, by volume and com- prises an inexhaustible reservoir of this essential element. Nitrogen, though consti- tuting much less of biomass than carbon or oxygen, is an essential constituent of proteins. The N, molecule is very stable so that breaking it down into atoms that can be incorporated with inorganic and organic chemical forms of nitrogen is the limiting step in the nitrogen cycle. This does occur by highly energetic processes in lightning discharges that produce nitrogen oxides. Elemental nitrogen is also incorporated into chemically bound forms, or fixed by biochemical processes medi ated by microorganisms. The biological nitrogen is mineralized to the inorganic form during the decay of biomass. Large quantities of nitrogen are fixed synthetically under high temperature and high pressure conditions according to the following overall reaction: N2+3H2→2NH3 (16.1) C 2000 CRC Press LlC
mechanism for eliminating pollutant hydrocarbons, such as those that are accidentally spilled on soil or in water. Biodegradation can also be used to treat carbon-containing compounds in hazardous wastes. CO2 in the atmosphere Photosynthesis Biodegradation Solubilization and chemical processes Soluble inorganic carbon, predominantly HCO3 - Fixed organic carbon, {CH2O} and xenobiotic carbon Dissolution with dissolved CO2 Chemical precipitation and incorporation of mineral carbon into microbial shells Biogeochemical processes Xenobiotics manufacture with petroleum feedstock Fixed organic hydrocarbon, CxH2x and kerogen Insoluble inorganic carbon, predominantly CaCO3 and CaCO3•MgCO3 Figure 1.5. The carbon cycle. Mineral carbon is held in a reservoir of limestone, CaCO3, from which it may be leached into a mineral solution as dissolved hydrogen carbonate ion, HCO3 - , formed when dissolved CO2 (aq) reacts with CaCO3 . In the atmosphere carbon is present as carbon dioxide, CO2 . Atmospheric carbon dioxide is fixed as organic matter by photosynthesis, and organic carbon is released as CO2 by microbial decay of organic matter. The Nitrogen Cycle As shown in Figure 1.6, nitrogen occurs prominently in all the spheres of the environment. The atmosphere is 78% elemental nitrogen, N2, by volume and comprises an inexhaustible reservoir of this essential element. Nitrogen, though constituting much less of biomass than carbon or oxygen, is an essential constituent of proteins. The N2 molecule is very stable so that breaking it down into atoms that can be incorporated with inorganic and organic chemical forms of nitrogen is the limiting step in the nitrogen cycle. This does occur by highly energetic processes in lightning discharges that produce nitrogen oxides. Elemental nitrogen is also incorporated into chemically bound forms, or fixed by biochemical processes mediated by microorganisms. The biological nitrogen is mineralized to the inorganic form during the decay of biomass. Large quantities of nitrogen are fixed synthetically under high temperature and high pressure conditions according to the following overall reaction: N2 + 3H2 ® 2NH3 (1.6.1) © 2000 CRC Press LLC
traces of NO, NO2, HNO,, NH4NO3 罪 Anthrosphere Biosphere NH3, HNO3, NO, NO2 9:8+2z2 ly-bound Inorganic nitrates such as amino ( nh Hydrosphere and Geosphere Dissolved NO,", NH4+ Organically-bound n in dead The production of gaseous N, and N,o by microorganisms and the evolution of these gases to the atmosphere completes the nitrogen cycle through a process called denitrification. The nitrogen cycle is discussed from the viewpoint of microbial processes in Section 6.11 The Oxygen Cycle The oxygen cycle is discussed in Chapter 9 and is illustrated in Figure 9. 11. It involves the interchange of oxygen between the elemental form of gaseous O contained in a huge reservoir in the atmosphere, and chemically bound O in CO2 H,O, and organic matter. It is strongly tied with other elemental cycles, particularly the carbon cycle. Elemental oxygen becomes chemically bound by various energy. yielding processes, particularly combustion and metabolic processes in organisms. It is released in photosynthesis. This element readily combines with and oxidizes other species such as carbon in aerobic respiration(Equation 1. 4.2), or carbon and hydrogen in the combustion of fossil fuels such as methan CH4+202→CO2+2H2O (162) C 2000 CRC Press LlC
Atmosphere N2, some N2O traces of NO, NO2, HNO3 , NH4NO3 Anthrosphere NH3, HNO3, NO, NO2 Inorganic nitrates Organonitrogen compounds Biosphere Biologically-bound nitrogen such as amino (NH2) nitrogen in proteins Hydrosphere and Geosphere Dissolved NO3 -, NH4 + Organically-bound N in dead biomass and fossil fuels Figure 1.6. The nitrogen cycle. The production of gaseous N2 and N2O by microorganisms and the evolution of these gases to the atmosphere completes the nitrogen cycle through a process called denitrification. The nitrogen cycle is discussed from the viewpoint of microbial processes in Section 6.11. The Oxygen Cycle The oxygen cycle is discussed in Chapter 9 and is illustrated in Figure 9.11. It involves the interchange of oxygen between the elemental form of gaseous O2, contained in a huge reservoir in the atmosphere, and chemically bound O in CO2, H2O, and organic matter. It is strongly tied with other elemental cycles, particularly the carbon cycle. Elemental oxygen becomes chemically bound by various energyyielding processes, particularly combustion and metabolic processes in organisms. It is released in photosynthesis. This element readily combines with and oxidizes other species such as carbon in aerobic respiration (Equation 1.4.2), or carbon and hydrogen in the combustion of fossil fuels such as methane: CH4 + 2O2 ® CO2 + 2H2O (1.6.2) © 2000 CRC Press LLC
Elemental oxygen also oxidizes inorganic substances such as iron(l) in minerals 4Fe+O2→>2Fe2O3 (1.6.3) A particularly important aspect of the oxygen cycle is stratospheric ozone, O3 As discussed in Chapter 9, Section 9.9, a relatively small concentration of ozone in the stratosphere, more than 10 kilometers high in the atmosphere, filters out ultra violet radiation in the wavelength range of 220-330 nm, thus protecting life on Earth from the highly damaging effects of this radiation The oxygen cycle is completed by the return of elemental O, to the atmosphere The only significant way in which this is done is through photosynthesis mediated y plants. The overall reaction for photosynthesis is given in Equation 1. 4.1 The Phosphorus Cycle The phosphorus cycle, Figure 1.7, is crucial because phosphorus is usually the limiting nutrient in ecosystems. There are no common stable gaseous forms of phos phorus, so the phosphorus cycle is endogenic. In the geosphere, phosphorus is held largely in poorly soluble minerals, such as hydroxyapatite a calcium salt, deposits which constitute the major reservoir of environmental phosphate. Soluble phosphorus from phosphate minerals and other sources such as fertilizers is taken up by plants and incorporated into nucleic acids which make up the genetic material of Soluble inorganic phosphate as HPO4, H,PO4, and polyphosphates ssimilation by Fertilizer runoff. waste- ecipiianion organisms water, detergent wastes biodegradation Dissolution orus Insoluble inorganic phosphate, predominantly such as Cas(Oh)(POA) or iron phosphates organIc and inorganIc phosphates in sediment Figure 1.7. The phosphorus cycle C 2000 CRC Press LlC
Elemental oxygen also oxidizes inorganic substances such as iron(II) in minerals: 4FeO + O2 ® 2Fe2O3 (1.6.3) A particularly important aspect of the oxygen cycle is stratospheric ozone, O3. As discussed in Chapter 9, Section 9.9, a relatively small concentration of ozone in the stratosphere, more than 10 kilometers high in the atmosphere, filters out ultraviolet radiation in the wavelength range of 220-330 nm, thus protecting life on Earth from the highly damaging effects of this radiation. The oxygen cycle is completed by the return of elemental O2 to the atmosphere. The only significant way in which this is done is through photosynthesis mediated by plants. The overall reaction for photosynthesis is given in Equation 1.4.1. The Phosphorus Cycle The phosphorus cycle, Figure 1.7, is crucial because phosphorus is usually the limiting nutrient in ecosystems. There are no common stable gaseous forms of phosphorus, so the phosphorus cycle is endogenic. In the geosphere, phosphorus is held largely in poorly soluble minerals, such as hydroxyapatite a calcium salt, deposits of which constitute the major reservoir of environmental phosphate. Soluble phosphorus from phosphate minerals and other sources such as fertilizers is taken up by plants and incorporated into nucleic acids which make up the genetic material of Soluble inorganic phosphate, as HPO4 2-, H2PO4 -, and polyphosphates Fertilizer runoff, wastewater, detergent wastes Xenobiotic organophosphates Biological phosphorus, predominantly nucleic acids, ADP, ATP Biological organic and inorganic phosphates in sediments Insoluble inorganic phosphate, such as Ca5(OH)(PO4) 3 or iron phosphates Dissolution Precipitation Biodegradation Assimilation by organisms Figure 1.7. The phosphorus cycle. © 2000 CRC Press LLC