emergy synthesis 2 - university of florida · a consequence of successive energy transformations....

EMERGY SYNTHESIS 2:Theory and Applications of the Emergy Methodology

Proceedings from the Second Biennial Emergy Analysis Research Conference,Gainesville, Florida, September, 2001.

Edited byMark T. Brown

University of FloridaGainesville, Florida

Associate EditorsHoward T. Odum

University of FloridaGainesville, Florida

David TilleyUniversity of Maryland

College Park, Maryland

Sergio UlgiatiUniversity of Siena

Siena, Italy

December 2003

The Center for Environmental PolicyDepartment of Environmental Engineering Sciences

University of FloridaGainesville, FL

The Center for Environmental PolicyP.O. Box 116450

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Chapter 15. Emergy Analysis of the Prehistoric Global Nitrogen Cycle

15Emergy Analysis of the Prehistoric Global Nitrogen Cycle

Daniel E. Campbell

ABSTRACT

In this analysis of the prehistoric global nitrogen cycle, relationships between the emergy per unit mass and the mass concentration of nitrogen were examined. A monotonic increase in the emergy per unit mass (the specific emergy) as a function of increasing material concentrations is predicted by energy hierarchy principles and was observed in the data. This pattern is expected when energy transformation is accompanied by an increase in the concentration of material in higher transformity units. Among nitrogen species in the troposphere a different pattern was observed, where transformity and the emergy per unit mass are greater for the more reactive but lower concentration nitrogen species. In this case, lightning discharges create nitrogen species of higher transformity by breaking the stable triple bond of diatomic nitrogen and increasing its chemical reactivity. The nitrogen flows through living systems are arranged in an energy capturing order-disorder loop upon which a trophic hierarchy is built. The emergy per unit mass increases as energy is transformed and nitrogen is concentrated through the trophic web. Planetary nitrogen flows through living systems are large compared to geochemical fluxes and as a consequence they have lower specific emergies. In general living systems have greater mass concentrations of nitrogen which supports the hypothesis that emergent properties of an element or elements ,e.g., life, arise when a threshold of mass concentration is exceeded. Energy principles and the data on global nitrogen flows indicate that the specific emergy of pathway flows may approach a minimum value as the system approaches a state of maximum empower.

INTRODUCTION

The distribution of energy and materials within the global ecosystem can be understood by examining the network of energy transformations that gives rise to these patterns. Odum (1996) showed that the generation of hierarchal organizations follows as a consequence of the properties of energy being transformed in a manner that maximizes power in a network. He proposed this principle as a fifth law of thermodynamics that explains the ubiquity of hierarchical patterns in the universe. The maximum power principle was first put forward as a fourth law of thermodynamics (sensu lato) by Lotka (1922a&b). The fourth law (as modified by Odum 1996) states that network designs which maximize empower prevail in competition with alternatives. Such designs develop positive feedback loops that capture and use more energy, building a network structure that maximizes empower or emergy per unit time. When positive feedbacks of energy develop from multiple levels of organization, e.g., as in the organization of cities, the eddy structure of the ocean, the trophic webs of the sea, etc., a hierarchy is established. Competition among alternative system designs releases a goal seeking mechanism inherent in the structure of hierarchical networks that becomes the means to maximize empower. (Campbell 2001).

The properties of hierarchies of energy transformation are, in part, determined by the second law of thermodynamics, because the quantity of available energy or exergy must decrease with each transformation according to the second law of thermodynamics, whereas the total emergy input to the network which is required to accomplish each successive transformation is not diminished. The

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transformity of a network flow is the ratio of these two quantities. For example, the emergy required to produce the flow along a pathway in solar equivalent joules (sej) is divided by the actual energy moving on the pathway to obtain the transformity of that pathway. The energy hierarchy (fifth?) law (Odum 1996) states that flows of energy in the universe are organized into hierarchies by energy transformation and that position in a hierarchy is measured by transformity. General patterns of organization are expected as a consequence of the this law, e.g., it implies that hierarchies will have many low transformity units with small support areas distributed throughout a given space with progressively fewer higher transformity units that have progressively larger support areas and thus are more widely distributed in space as they

Macroscopic mini-model of the Global Nitrogen Cycleas two coupled order-disorder loops.(1) Outer geochemical loop(2) Inner biochemical loop(3) Coupling from (2) to (1) by dentrification(4) Coupling from (1) to (2) by nitrogen fixation

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Figure 1. An overview energy systems model of the global nitrogen cycle diagramed as two coupled order-disorder loops. The outer geochemical loop (1), shown as dark gray lines, is coupled to the inner biochemical loop (2), shown as black lines, through denitrification (3) and nitrogen fixation (4), shown as dashed lines.

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require more energy for their support.Odum (2000a) observed that when a self-organizing process (one with positive feedbacks)

converges and concentrates energy in centers, materials are also concentrated. He proposed a thermodynamic principle to account for this observation and suggested it as a possible a sixth law of thermodynamics. This principle states that the coupling of matter flows in biogeochemical cycles to the hierarchy of energy transformations explains the widely observed skewed (log normal) distribution of materials with concentration (Aherns, L.H. 1954). Aherns (1954) proposed the log normal distribution of the elements as a law of geochemistry based on his observations on the concentrations of 20 elements in igneous rocks. Emergy researchers have obtained a fairly good understanding of the operation of the proposed fourth and fifth laws in ecosystems (Odum 1971a, Brown 1981, Fontaine 1981, Odum 1994, Hall 1995, Campbell 2000a); however, the operation of the sixth law has not been thoroughly investigated. An investigation of the biogeochemical cycle of lead in relation to the energy hierarchy (Odum 2000c) was the primary empirical study used to demonstrate this law. Additional, information on phosphorus from Brandt-Williams (1999) was used to confirm patterns observed for lead. In this paper I examined the prehistoric global nitrogen cycle to look for patterns in the emergy per unit mass of nitrogen called specific emergy by Ulgiati in this volume. Graphs of the specific emergy of nitrogen species as a function of concentration and other plots were compared with expectations derived from the energy hierarchy principles mentioned above.

A CONCEPTUAL MODEL OF THE GLOBAL NITROGEN CYCLE

The nitrogen cycle is complex which may explain why most representations of this global cycle have focused on fluxes between compartments (Delwiche, 1970; Soderlund and Svensson,1976; Jaffe 1992; Stedman and Shetter,1983; Galloway, 1998) or budgets for individual species, e.g., ammonia (Schlesinger and Hartley,1992) rather than on developing overview models that capture the structure and function of the global nitrogen network as a system. Energy systems language is a tool designed for the analysis of networks and the simplification of complexity. The biogeochemical cycle of nitrogen can be represented as two coupled order-disorder cycles or Michaelis-Menton loops (Odum 1994). Figure 1 shows an overview of the global nitrogen cycle diagramed using the energy systems language (Odum 1971b, 1994). Both cycles are driven by the earth’s three primary energy sources; solar radiation, the earth’s deep heat, and the gravitational attraction of the sun and moon. By definition, disordered forms are either chemically simpler or less concentrated than the ordered forms of nitrogen.

The outer cycle (Figure 1) shows geochemical nitrogen flows moving from a dilute form in the rocks of the lithosphere (53 gN m-3) to N2, a more concentrated form (963 gN m-3) in the atmosphere. In a prehistoric steady state condition, before human agricultural and industrial activities altered global nitrogen flows, most of the nitrogen added annually to the atmosphere eventually made its way back to the lithosphere (Stedman and Shetter 1983). The available energy of nitrogen species concentrated in the atmosphere and in the primordial ocean interacted with the external energy sources to the earth, as well as other material storages, to develop a second inner cycle of nitrogen circulating through a network of biochemical interactions. This inner cycle (Figure 1) moves nitrogen from the relatively disordered inorganic species, e.g., ammonia, nitrate, nitrite, to more complex forms, e.g., amino acids and proteins present in living organisms. Living systems build trophic hierarchies that further concentrate nitrogen as a consequence of successive energy transformations. The exterior geochemical cycle and the interior biochemical cycle of nitrogen are marked (1) and (2), respectively, in Figure 1. These two cycles are coupled from (2) to (1) through the process of denitrification (3) in Figure 1. Nitrogen fixation (4) completes the coupling by establishing a connection from cycle (1) to cycle (2). After an undetermined number of passages through the biosphere, a nitrogen atom will eventually be deposited in sediments where it is eventually returned to the crust in the formation of sedimentary rocks.

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A Brief Account of the Evolution of the Nitrogen Cycle

It may be instructive to consider the evolution of the global nitrogen cycle as outlined by Burns and Hardy (1975) to see how these two coupled cycles may have come into being. The upward arm of the outer cycle marked (1) is driven by the geochemical nitrogen fluxes from crustal outgassing and volcanic eruptions that have supplied N2 and NH3 to the atmosphere since the rocks of the primordial earth first solidified. Schlesinger (1997) points out that the atmosphere of the earth was probably dominated by N2 an other moderately reduced gases when life first developed. After a long period of abiotic organic chemical evolution (Oparin 1953), perhaps facilitated by the introduction of amino acids in meteors (Schlesinger 1997), concentrations of nitrogen and other elements necessary for life in the oceans of the primordial earth are thought to have been exploited by self-organizing, biochemical processes culminating in the development of cells with nitrogen as one of the key constituents. Death and decomposition of cellular life forms, most probably by autolysis, produced ammonia which closed the primordial inner loop. These primitive early life forms were anaerobic organisms dependent on the most accessible and abundant nutrients to support their metabolism. Ammonia is considered to be the primary nitrogen compound supporting early life forms because of the almost universal capacity of organisms to utilize it. The primordial reducing environment of the earth would have supported an easy interchange between the disordered forms of nitrogen in the environment and the more ordered forms of nitrogen in living organisms (Burns and Hardy 1975).

The evolution of the nitrogen cycle cannot be separated from the development of the other global biogeochemical cycles, i.e., carbon, oxygen, phosphorus, sulfur, etc. upon which life depends (Deevey 1970). The development of photosynthesis was an event of particular importance to the cycling of all the biogeochemical elements because it produced increasing concentrations of oxygen in the atmosphere, which promoted the chemical synthesis of oxidized forms of the other elements. Increased concentrations of oxygen in the troposphere, produced by photosynthesis, allowed the oxidation of large quantities of ammonia to nitrate. As nitrate accumulated in the environment, life developed the capacity to use this additional energy source through assimilatory nitrate reduction and denitrification (the reduction of nitrate to a gaseous form, most commonly N2 or N2O). With the development of denitrification as a major pathway, coupling the biological nitrogen cycle to the geochemical one, diatomic nitrogen could be indefinitely sustained in the atmosphere along with oxygen. Nitrogen fixation may have developed as reactive oxygen accumulated in the atmosphere and ammonia become scarce (Burns and Hardy 1975). Alternatively, the earliest organisms may have had limited supplies of nitrogen available for protein synthesis (Schlesinger 1997) and nitrogen fixation may have developed in anaerobic conditions as a means of increasing available nitrogen supplies in the primordial ocean by drawing on the large storage of atmospheric nitrogen. There is little evidence available to fix the time at which biological nitrogen fixation developed (Schlesinger 1997) , but in either case, it acted as a feedback pathway capable of alleviating any nitrogen shortage in the biosphere that might prevent the biosphere as a whole from obtaining the optimum loading of nitrogen (Odum and Pinkerton 1955) needed to develop maximum empower in the global biogeochemical network.

METHODS

Energy systems language (Odum 1971b, 1994) was used to diagram the global nitrogen cycle (Figures 1 and 2). The model of the prehistoric global nitrogen cycle (Figure 2) was evaluated using information from Stedman and Shetter (1983) and other references including four additional evaluations of the global nitrogen cycle performed between 1970 and 1983 (see Table 1). I made several assumptions in addition to those made by Stedman and Shetter (1983) to allow a reasonable estimate of prehistoric nitrogen flows through the network shown in Figure 2. First, global nitrogen flows were assumed to have reached a steady state condition prior to intervention by mankind. This steady state assumption was used to balance all storages in the network given initial values from Stedman and Shetter (1983) and the other

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sources and calculations documented in Table 1. Second, the emergy per unit mass for all storages and flows in the model was calculated based on the fact that the emergy around a completely interconnected closed loop is a constant. The global network of nitrogen flows (Figure 2) was assumed to approximate a completely interconnected closed loop, and therefore, the emergy driving these flows is the emergy supplied to the earth by its independent energy sources, i.e., solar radiation, the earth’s deep heat, and the gravitational attraction of the sun and moon (Odum 1996, Campbell 2000b). The emergy required to place a gram of nitrogen in storage was determined by multiplying the annual emergy input to the earth by the turnover time of the storage in years, since this is the time required to completely replace the material stored. This value was divided by the mass of the storage to give the specific emergy of the storage in sej g-1. The specific emergy of flows was determined by dividing the annual emergy inflow to the earth (sej) by the annual nitrogen flux in grams flowing along a pathway in the global network

RESULTS

The results of this study consist of (a) a conceptual model of the global nitrogen cycle (already presented), (b) a model of nitrogen flows through a four compartment global model (Figure 2) and an evaluation of that model for prehistoric conditions, (c) an analysis of relationships between the specific emergy of network storages and the degree to which nitrogen has been concentrated in those storages and (d) an analysis of the relationship between the magnitude of nitrogen fluxes and the specific emergy of those fluxes. The results from (c) and (d) above will be compared to the results expected from the energy hierarchy principles described earlier and in Odum (2000a).

An energy systems model of the global network of nitrogen storages and flows is shown in Figure 2 and further documented in Table A-1(given as an Appendix) . Item labels in the table are also found on the appropriate storage or flow in the diagram. The three external forcing functions driving flows of nitrogen through the global network were evaluated in emergy units. The global system is modeled using four large compartments: (1) The lithosphere includes the crust where nitrogen is stored in igneous rocks, sedimentary rocks, and fossil fuel; and the mantle with its stored nitrogen. (2) The troposphere has nitrogen stored as diatomic nitrogen, N2; ammonia gas, NH3; nitrous oxide, N2O; and organic nitrogen. In addition, the nitrogen stored as nitric oxide, NO, and nitrogen dioxide, NO2 in the troposphere are combined into the NOx variable and ammonia and NOx in the aqueous phase are shown as storages of the ammonium ion, NH4

+ and nitric acid, HNO3-. (3) The oceans contain nitrogen stored in plant biomass, animal biomass,

sediments, dissolved organic matter or DON, particulate organic matter or PON; as well as, storages of diatomic nitrogen, N2, ammonium, NH4, nitrous oxide, N2O, and NOx that are dissolved in seawater. (4) The land compartment contains nitrogen stores in plant and animal biomass, litter, soil organic matter, soil microbes; as well as nitrogen present in the inorganic pool including insoluble and soluble forms. The links between compartments are shown as thicker lines and intra-compartment links are designated with thinner lines. Gray lines indicate the flow of used energy to the heat sink. Over seventy fluxes within and among compartments have been identified and documented in Table A-1.

The primary connections between the four major compartments of the model are as follows: Out-gassing and volcanic eruptions, J1, is the major nitrogen flow linking the lithosphere to the troposphere. The lithosphere is also linked to the land systems through weathering of sedimentary and igneous rocks, J2. Nitrogen returns to the lithosphere when ocean sediments are subducted into the earth, J60, and transformed into sedimentary rock. The troposphere is linked to the ocean and land compartments through the wet and dry deposition of NH3, J21, J22, J23, and NOx, J13, J14. Also, there is a net flux of N2O, J7, from the troposphere to the stratosphere and a return flow of N2, J64, and NOx, J65, from the stratosphere to the troposphere. The flow of N2 is produced by the decomposition of N2O, either by direct photolysis or through reaction with photolytically activated oxygen atoms (Anderson 1983). In addition, N2 and N2O are returned to the atmosphere from the land and ocean compartments through denitrification, J27, J29, J6,J16, and land and ocean systems take-up atmospheric N2 through biological nitrogen fixation, J57, J26, J28. In addition to the fluxes already mentioned ammonia volatilization from soils, J20, and animal excreta, J18, link the land compartment with the troposphere and water runoff carries several nitrogen species from

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land to the oceans. Ammonia is also volatilized from the oceans, J19, and sea spray, J25, carries DON into the atmosphere resulting in a net flux of nitrogen in this form, J24, from the ocean to the land compartment (Soderlund and Svensson,1976).

The key flow governing the steady state balance of nitrogen in the land and water compartments in Figure 2 is the nitrogen flux back to the lithosphere in subducted ocean sediments. This flow was estimated based on a turnover time of 200 million years for rocks in the crust which is the average value determined by Pierrou (1975) using the global phosphorus cycle. The storage of sedimentary rock in the crust was assumed to be in steady state with 6 Tg y-1 entering from the ocean sediments and 3 Tg y-1 leaving through weathering, 1 Tg y-1 going into the fossil fuel formed in a year, and 2 Tg y-1 returning to the mantle through anatexis or remelting. The flux of nitrogen from the mantle to the crust is assumed to balance the weathering of igneous crustal rocks and outgassing. The second key flow that keeps the global system in steady state is the nitrogen flux from the troposphere to the stratosphere balanced by a return flow of diatomic nitrogen gas. The magnitude of these flows (Table A-1) was determined from estimates for natural nitrous oxide production in the oceans, J5, and on land, J6, given by Prather et al.(1995).

Figure 2. An evaluated energy systems model of the global nitrogen cycle before it was altered by human activities. All stocks are shown in teragrams, Tg, or 1012 g and flows are given as Tg y-1.Hexagons placed on pathways indicate the microbial transformation of nitrogen as follows: black, nitrification; dark gray, nitrogen fixation; light gray, denitrification and white, ammonification. Nitrogen storages that appear as trace amounts in other material are shaded.

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There is a small net loss of nitrogen from the stratosphere to space that has not been considered here. All storages and flows within the global nitrogen network are evaluated and documented in Table A-1. Figure 3 shows the result of plotting the ratio of the earth’s annual emergy inflow to the grams of nitrogen found in selected global storages versus the concentration of nitrogen in those same storages, as determined by the mass of nitrogen per unit volume of the substrate. The pattern found was the one described by Odum (2000a) with the emergy to mass ratio monotonically increasing from left to right as a function of concentration as expected for a hierarchical network of interactions. Figures 4, 5, and 6 show plots of the emergy necessary to place a gram of nitrogen in a given storage as a function of the concentration of nitrogen (gN’-3 substrate). The emergy per gram for material in the compartments of the lithosphere is plotted in Figure 4 as a function of the concentration of nitrogen per cubic meter of the substrate, e.g., the mass of nitrogen contained in a cubic meter of coal was determined to find the x coordinate of the point labeled coal in Figure 4. The pattern made by the four points in Figure 4 increases monotonically from left to right as in Figure 3, but the slope of the curve in this plot abruptly increases between the second and third points. This occurs because the specific emergy of nitrogen in sedimentary rocks is an order of magnitude larger than the specific emergy of diatomic nitrogen gas in the troposphere. This difference is attributable to the differences between the turnover times of the two storages.

The specific emergy of the nitrogen stored in various forms in the troposphere versus the concentration of those forms in gN per cubic meter of air is shown in Figure 5. In this case the pattern is different, displaying a line of points that progressively decrease in magnitude from left to right. This pattern is in part produced by lightning acting on individual molecules of highly unreactive diatomic nitrogen to break its triple bond and create nitrogen species of greater chemical reactivity. The point on the far right is relatively unreactive diatomic nitrogen which has the lowest emergy per unit mass.

Figure 6 shows a plot of the specific emergy and mass concentration of components in the oceans compartment. The specific emergy of the components plotted in this figure fall into two groups: (1) those that are part of the nitrogen cycling through the inner loop (solid triangles) and (2) those that are a part of the outer geochemical loop (open circles). The land compartment components of the inner biochemical loop are not plotted, because they show a similar pattern to that seen in the oceans. The pattern shown in Figure 6, and repeated with somewhat different values by the biological components of the land compartment; is not, at first, recognizable as belonging to either of the two patterns identified through examination of Figures 4 and 5. Both the land and ocean components show that ammonia has the lowest specific emergy of all the nitrogen species examined and that plants and plant derived organic matter have a specific emergy similar to but slightly higher than ammonia. The specific emergy of animals is 5 to10 times greater than that of plants, but nitrogen is only slightly more concentrated in the animal form. The oxidized forms of nitrogen, i.e., NOx, have greater specific emergy and slightly higher concentration than ammonia in both land and ocean systems. These relationships are shown in aggregate form in Table 1 where the specific emergies of the various forms of nitrogen are determined based on their annual global throughput.

Figure 7 plots the log of the material throughput of the components in the ocean compartment against the log of the specific emergy of the flux. Two distinct groups of points are shown on the material flow plot reflecting the two groups of components distinguished in Figure 6. Greater mass flux occurs for lower specific emergy components within each group, as well as for both groups together. The two coherent groups that appear in this plot may reflect the different larger system properties that control nitrogen flow in the biochemical and in the geochemical loops of the global nitrogen cycle.

DISCUSSION

The results of this study can be interpreted and understood by first considering the properties of the energy transformation process responsible for the creation of the hierarchy upon which a set of observations was made. If the observed set of observations is from a hierarchical series of energy transformations, transformity will always accurately define the position of any unit in the hierarchy. The results of this

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study indicate that the specific emergy may also accurately define the position of a unit in the hierarchy (Figure 7). However, the relationships between specific emergy and mass concentration examined in this study (Figures 3,4,5) show that increased concentration of mass does not always follow the increase of specific emergy seen in higher transformity units of a hierarchy. For there to be a relation between the specific emergy and the mass concentration of an element, mass must be concentrated as part of the energy transformation process. The data presented here show that the concentration of mass accompanies energy transformation in many hierarchies that increase the energy stored in higher transformity units by increasing the mass of those units, e.g., turbulent eddies in the ocean, food webs in the sea, cities, etc. But energy transformation can increase the energy per unit in a different manner, e.g., by increasing the chemical reactivity or the velocity of a molecule rather than by concentrating mass, and as a result the positive correlation between the concentration of a material and its specific emergy is not observed (Figure 5). In Figure 5, the specific emergy and the transformity of nitrogen has been increased by changing the chemical reactivity of the element rather than by concentrating its mass. The concentrations of nitrogen species found in the troposphere are also determined by nitrogen flows to and from the land and ocean compartments, (see particularly the values of NH3 (g), NH4 (aq) and organic N in Figure 5) and by the solubility and reactivity of the various nitrogen species themselves (more reactive species have lower residence times). In general, the fundamental assumption that mass is concentrated in higher transformity units does not apply to hierarchies of molecular velocity or chemical reactivity such as those found in the gaseous state. However, the specific emergies of nitrogen species in the troposphere are consistent with the energy hierarchy principle (5th law) when plotted as the number of molecules in a volume of air versus the emergy per gram of each species. These observations support the view that the principle of mass concentration with energy transformation (proposed 6th law) may be a corollary of the more general energy hierarchy principle (5th law).

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Figure 3. The ratio of the earth’s annual emergy inflow to the grams of nitrogen stored in various components of the global network plotted against the mass of nitrogen per unit volume of substrate.

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Because mass is commonly concentrated as the means of concentrating energy in higher transformity units, the energy hierarchy principle explaining mass concentration in biogeochemical systems can be expected to have broad applicability and considerable explanatory power in interpreting patterns in nature. For example, Odum (2000a) showed that a simple relation between the emergy per unit mass and concentration is expected for free elements such as lead that act largely outside the constraints supplied by a more complex structure. When an element is only a part of a more complex structure the relationship between specific emergy of the element and its mass concentration will be shaped by the properties of the complex system of which it is a part. The pattern of specific emergy of nitrogen with its mass concentration in the ocean (Figure 6) and land compartments of the global model (Figure 2) is to a large degree determined by the unique manner in which living systems use nitrogen and the other biologically active elements to capture energy and build organized structures. For example, the points plotted as triangles in Figure 6 show the pattern that living systems have imposed on the specific emergy and mass concentrations of nitrogen species in the ocean. The initial energy capturing step for the ecosystem converts relatively disordered elements, C, N, P, S, O, etc. into more ordered organic matter. The specific emergies of the ordered and disordered forms of nitrogen around the loop are approximately the same implying that the nitrogen in plant matter and in ammonia are of similar quality and will have limited energy barriers to free exchange between the two forms. The relatively free exchange of nitrogen between its ordered and disordered forms may have deep evolutionary roots as noted by Burns and Hardy (1975). In contrast, the nitrogen in plant and organic matter in the oceans is approximately a million times more concentrated than the ammoniacal nitrogen in seawater. This extreme increase in mass concentration of the nitrogen in plant matter over that found in the sea is a consequence of the unique structural and functional properties of living matter which are dissipative systems that exist far from the equilibrium conditions that govern the disordered forms of nitrogen in the sea. Ammonia is

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Figure 4. The emergy required to place a gram of nitrogen in the designated storages of the lithosphere as a function of the concentration of nitrogen per cubic meter of substrate.

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the disordered form of lowest specific emergy in both ocean (3.66E9 sej g-1) and land (3.8E9 sej g-1) compartments and in the global system as a whole (Table 2). The further transformation of energy captured by this initial order-disorder loop of cycling elements is used to build hierarchical networks in which the mass of the constituent elements is hypothesized to become more concentrated in higher transformity network components. The nitrogen data from this study supports this hypothesis at a highly aggregated level because nitrogen is somewhat more concentrated in oceanic animals than it is in phytoplankton. The specific emergy of nitrogen in the higher trophic levels represented by oceanic animals is about and order of magnitude higher than that found in phytoplankton as predicted by the energy transformation and mass concentration principle. Oxidized forms of nitrogen appear in slightly higher concentration than ammonia but with specific emergy an order of magnitude higher than ammonia. These forms must be synthesized from ammonia by nitrifying bacteria or reduced to ammonia through assimilatory nitrate reduction before being used by plants. The additional energy transformations required to make or utilize NOx may account for the increase in its specific emergy (1.8E10 sej g-1 in the oceans and 3.4E10 sej g-1 on land) over that of ammonia.

Figure 7 shows that flows through the storages in the inner biochemical loop are two orders of magnitude greater than the outer geochemical flows. The high concentrations of nitrogen in inner loop components and the increased magnitude of nitrogen flow through this loop indicate that nitrogen is being used in a dynamically different manner by the living systems of the inner loop and that the hierarchical organization of nitrogen flows in these systems is differentiated from, although still connected to, the slow, low flow nitrogen cycle of the outer loop. The accumulation and cycling of nitrogen and other elements by autocatalytic living systems has produced unique organizational properties, e.g., greater empower flow

1E-10 1E-8 1E-6 0.0001 0.01 1 100 10000

Concentration in gN per cubic meter of air

1.00E+10

1.00E+11

1.00E+12

1.00E+13E

merg

y per

gN

(se

j/g)

N2

N2O

NH3 (g)

NOX (aq)

NH4 (aq)

NOX (g)

Organic N

Figure 5. The emergy required to place a gram of nitrogen in the designated storages in the troposphere compartment plotted against the mass concentration of nitrogen per cubic meter of air.

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and more structural complexity, than are possible in a system driven by geochemical processes alone. One might conclude that a distinguishing property of living systems is the ability to accumulate and cycle high concentrations of the biologically active elements or ,alternatively, that life is an emergent property of the biologically active elements and their compounds when concentrations exceed a threshold.

The Carnot ratio from thermodynamics implies that there is a maximum thermodynamic efficiency that can be obtained through design improvements for any real production process. This observation has been combined with the maximum empower principle to deduce that there is a minimum transformity for any storage or flow that indicates that the item is being produced at the optimum efficiency for maximum power (Odum1996). If mass flux commonly follows energy flow the lower specific emergy of the inner loop flows shown in Figure 7 may be a result of the development of a design to maximize empower in earth’s biogeochemical network; i.e., the flows of energy and mass are highest for a given emergy base in the design that is operating at the optimum loading for maximum power (Odum and Pinkerton 1955). Thus, a maximum mass flux per unit of available emergy may be associated with the thermodynamic minimum transformity for a network operating at maximum power. The patterns of specific emergy and global nitrogen flows in the living systems of the oceans and land observed in this study were consistent with design criteria that result in maximizing empower on earth.

0.0001 0.01 1 100 10000 1000000


1.00E+9

1.00E+10

1.00E+11

1.00E+12E

merg

y per

gN

(se

j/g)

NH4

NOX

N2O N2

Animals

Sediments

PON, DON, Phytoplankton

Figure 6. The emergy required to place a gram of nitrogen in the designated storages of the oceans compartment plotted as a function of the mass concentration of nitrogen per cubic meter of substrate. Nitrogen storages that are part of the inner biochemical loop are indicated with a solid triangle, whereas, nitrogen storages that are part of the outer geochemical loop are shown as open circles. In this case N2 and N2O are the concentrations of these gases dissolved in seawater.

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ACKNOWLEDGMENTS

I thank Jim Latimer, Giancarlo Cicchetti, Cathy Wigand, Curt Norwood, Dennis Swaney, and Norbert Jaworski for reviewing the manuscript. I also thank H.T. Odum without whose insight and inspiration this work would not have been possible. Although the research described in this article has been funded by the U.S. Environmental Protection Agency, it has not been subjected to Agency review. Therefore, it does not necessarily reflect the views of the Agency. This paper is contribution number AED-02-017 of the Atlantic Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, United States Environmental Protection Agency.

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its subsidiary). Geochimica et Cosmochimica Acta 5:49-73.Bidigare, R.R., 1983. Nitrogen excretion by marine zooplankton, pp. 385-409. In: Carpenter, E.J., Capone,

1.00E+9 1.00E+10 1.00E+11 1.00E+12 1.00E+13

Log specific emergy (sej/g)

10

100

1000

10000

Log

mat

eria

l flo

w (T

gN/y

)

NH4, Phytoplankton, DONPON

NO3

Animals

N2

N2OSediment N

Figure 7. A plot of the log of nitrogen fluxes through the components in the oceans compartment as a function of the log of the specific emergy of the flux.

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Table 1. The specific emergy of global nitrogen flows based on the annual throughput of the various species. The annual solar emergy input to the earth is 15.83E24 sej y-1 (Odum 2000b)____________________________________________________________________Item

Nitrogen Flow, Tg y-1 S p e c i f i c Emergy, sej g-1

_________________________________________________________________________________

Ammonia (NH3 and NH4) 6688a 2.37E9

Particulate organic nitrogen 6543b 2.42E9

Dissolved organic nitrogen 5250c 3.02E9

NOx ( NO, NO2 and NO3) 1358d

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New York.Deevey, E.S. 1970. Mineral Cycles. Scientific American 223(3):149-158..Delwiche, C.C. 1970. The Nitrogen Cycle. Scientific American 223(3):137-146.Fontaine, T.D. 1981. A self-designing model for testing hypotheses of ecosystem development, pp. 281-

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Galloway, J.N. 1998. The global nitrogen cycle: changes and consequences. Environmental Pollution 102(S1):15-24.

Hall, C.A.S. (ed) 1995. Maximum Power. The Ideas and applications of H.T. Odum. University of Colorado Press, Niwot. 454 pp.

Jaffe, D.A. 1992. The nitrogen cycle, pp. 263-284. In: Butcher, S.S., Charlson, R.J., Orians, G.H., and Wolfe, G.V. (eds) Global Biogeochemical Cycles. Academic Press, San Diego, CA.

Krause, H.R. 1962. Investigation of the decomposition of organic matter in natural waters. FAO Fish. Biol. Rep. No. 34, pp. 19.

Lotka, A.J. 1922a. Contribution to the energetics of evolution. Proc. Natl. Acad. Sci. 8:147-151.Lotka, A.J. 1922b. Natural selection as a physical principle. Proc. Natl. Acad. Sci. 8:152-154.Lui, S.C., Cicerone, R.J., Donahue, T.M. Chambers, W.L. 1977. Sources and sinks of atmospheric N2O

and possible ozone reduction due to industrial fixed nitrogen fertilizers. Tellus 29:251-263.Odum, H.T. 1971a. Environment, Power, and Society. Wiley, New York. 331 pp.Odum, H.T. 1971b. An energy circuit language for ecological and social systems, its physical basis, pp.

139-211. In: Patten, B. (ed) Systems Analysis and Simulation in Ecology, Vol. 2. Academic Press, New York.

Odum, H.T. 1994. Ecological and General Systems: an Introduction to Systems Ecology (Revised Edition). University of Colorado Press, Niwot, CO.

Odum, H.T. 1996. Environmental Accounting: Emergy and Environmental Decision Making. John Wiley and Sons, NY. 370 pp.

Odum, H.T. 2000a. An energy hierarchy law for biogeochemical cycles, pp. 235-248. In: Brown, M.T. (ed) Emergy Synthesis. Proceedings of the First Biennial Emergy Analysis Research Conference, The Center for Environmental Policy, Department of Environmental Engineering Sciences, Gainesville, FL.

Odum, H.T. 2000b. Handbook of Emergy Evaluation . Folio #2 Emergy of Global Processes. Center for Environmental Policy, Environmental Engineering Sciences, University of Florida, Gainesville, FL. 30 pp.

Odum, H.T. (ed) 2000c. Heavy Metals in the Environment. Using Wetlands for Their Removal. Lewis Publishers, Boca Raton. 326 pp.

Odum, H.T.; Pinkerton, R.C. 1955. Time’s speed regulator: The optimum efficiency for maximum power output in physical and biological systems. American Scientist 43:321-343.

Oparin, A.I. 1953. Origin of Life. Dover Publications ,Inc. New York. 270 pp.Parsons, T.R., Tagahashi, M. 1973. Biological Oceanographic Processes. Pergamon Press, Oxford.Pierrou, U. 1975. The global phosphorus cycle, pp.75-88. In: Svensson, B.H. & Soderlund, R.

(eds) Nitrogen, Phosphorus, and Sulfur – Global Cycles. SCOPE Report 7. Ecol. Bull. 22, Stockholm.

Prather, M., Derwent, R., Ehhalt, D., Fraser, P., Sanhueza, E., Zhou, X. 1995. Other trace gases and atmospheric chemistry, pp. 77-118. In: Houghton, J.T., Meira, L.G., Filho, J.B., Hoesung Lee, Callander, B.A., Haites, E., Harris, N., Maskell, K. Climate Change 1994. Cambridge University Press, Cambridge.

Rayleigh, L., 1939. Nitrogen, argon, and neon in the earth’s crust with applications to cosmology. Proc. Roy. Soc. London, Ser. A 170:451-464.

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Rosswall, T. 1976. The internal nitrogen cycle between microorganisms, vegetation and soil, pp. 157-167. In: Svensson, B.H. & Soderlund, R. (eds) Nitrogen, Phosphorus, and Sulfur – Global Cycles. SCOPE Report 7. Ecol. Bull. 22, Stockholm.

Schlesinger, W.H. 1997. Biogeochemistry: An Analysis of Global Change, 2nd edition . Academic Press, San Deigo, CA. 588 pp.

Schlesinger, W.H.& Hartley. A.E., 1992. A global budget for atmospheric NH3. Biogeochemistry 15:191-211.

Soderlund, R. & Svensson, B.H. 1976. The Global Nitrogen Cycle, pp. 23-73. In: Svensson, B.H. & Soderlund, R. (eds) Nitrogen, Phosphorus, and Sulfur – Global Cycles. SCOPE Report 7. Ecol. Bull. 22, Stockholm.

Smith, R. (ed) 1999. Encyclopedia of Geology. Fitzroy Dearborn Publishers, Chicago. Stedman, D.J., Shetter, R.E. 1983. The global budget of atmospheric nitrogen species, pp. 411-454. In:

Swartz, S.E. (ed) Trace Atmospheric Constituents: Properties, Transformations, and Fates. John Wiley, New York.

Ulgiati, S. et al. 2002. This volume.

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Table A-1. Definitions, values, and sources for the external forcing functions, nitrogen storages and flows shown in Figure 2, a diagrammatic representation of the global nitrogen cycle prior to the beginning of the industrial age.

__________________________________________________________________________________

Item Definition Value Source___________________________________________________________________________________ External forcing functions, units sej y-1

Solar Radiation Emergy of the annual planetary insolation. 3.93E24 Odum (2000b)Earth Deep Heat Emergy of annual heat flux from earth. 8.06E24 Odum (2000b)Gravitation Emergy supplied by the gravitational attraction of the sun and moon. 3.84E24 Odum (2000b) Storages, units Tg nitrogen (1 Tg = 1012 g) Mantle Nitrogen in the earth’s mantle 8.15E10 Cailleux (1968)1 Crust Nitrogen in igneous rock of the crust. 2.0E8 Considine(1976) 2 Sed. Rock Nitrogen in sedimentary rock in the crust. 1.4E9 Considine(1976) 3

Troposphere N2 Diatomic nitrogen gas in the troposphere. 3.9E9 Stedman & Shetter (1983)N2O Nitrous oxide in the troposphere. 1400 Stedman & Shetter (1983)NOX (g) NO and NO2 in the troposphere 0.21 Stedman & Shetter (1983)NH3 (g) Ammonia gas in the troposphere. 0.3 Stedman & Shetter (1983)NOX (aq) NOX in aqueous phase mostly as HNO3. 0.1 Stedman & Shetter (1983)NH4 (aq) NH4 in the aqueous phase 0.6 Stedman & Shetter (1983)Organic N Organic nitrogen in the troposphere. 1 Soderlund & Svensson (1976) Oceans N2 Diatomic nitrogen dissolved in the sea. 2.2E7 Delwiche (1970)N2O Nitrous oxide gas dissolved in the sea. 200 Soderlund & Svensson (1976)NH4 Nitrogen in the sea as ammonium ion. 7000 Soderlund & Svensson (1976)NOX Nitrogen in the sea as nitrate and nitrite. 5.75E5 Soderlund & Svensson (1976)Plants Nitrogen in phytoplankton. 300 Soderlund & Svensson (1976)Animals Nitrogen in marine animals. 170 Soderlund & Svensson (1976)DON Nitrogen as dissolved organic nitrogen. 5.3E5 Soderlund & Svensson (1976)PON Nitrogen as particulate organic nitrogen. 2.4E4 Soderlund & Svensson (1976)OM Nitrogen in the sediment organic matter. 5.4E5 Burns & Hardy (1975)Land Plants Nitrogen in land plants. 1.35E4 Soderlund & Svensson (1976) 4

Litter Nitrogen in plant litter. 2800 Soderlund & Svensson (1976) 4

Organic matter Nitrogen in soil organic matter. 3.24E5 Soderlund & Svensson (1976) 4

Microbes Nitrogen in bacteria and fungi. 500 Soderlund & Svensson (1976)

Animals Nitrogen in land animals. 216 Soderlund & Svensson (1976)Soluble N Soluble nitrogen in soil. 1000 Burns & Hardy (1975)5

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Insoluble N Nitrogen bound with inorganic matter. 1.0E5 Burns & Hardy (1975)

Table A-1. Continued__________________________________________________________________________________

Item Definition Value Source___________________________________________________________________________________ Global Nitrogen Flows, units Tg y-1

Lithosphere J1 Nitrogen out-gassing and volcanic gases. 1 Jaffe (1992) J2 Nitrogen leaving the crust by weathering. 4 Smith(1999)6

J2’ Nitrogen from weathering that is soluble 3 Split 3:1 soluble: insoluble J2” Nitrogen in weathered particulate matter 1 Split 3:1 soluble: insoluble J3 Nitrogen entering the crust from the mantle 2 Balances nitrogen losses J4 Nitrogen in sedimentary rocks going into 3 By difference to balance sed. fossil fuel formation and anatexis rock storage J59 Nitrogen in subducted organic matter 5 Burns & Hardy (1975)7 J60 Nitrogen entering in subducted sediments 6 Stedman & Shetter (1983)8

J61 Nitrogen in crust reabsorbed into the mantle 2 Assume it balances crystallizationJ62 Nitrogen incorporated into fossil fuel 1 By difference9 J63 Nitrogen in subducted inorganic matter 1 A s s u m e i t b a l a n c e s weatheringTroposphere J5 Net flux N2O from denitrification at sea. 3 Prather et al. (1995)J6 Net flux N2O from denitrification on land. 6 Prather et al. (1995)J7 Loss by diffusion to the stratosphere. 9.3 Stedman & Shetter (1983)J8 Gain from oxidation of NOx by ozone 0.3 Stedman & Shetter (1983) J9 Lightning and combustion 5 Stedman & Shetter (1983) J10 NH3 oxidized to NOx 0.3 Stedman & Shetter (1983) J11 NOx evolved from soil microbes 5 Balances NOx (g) storageJ12 NOx dissolving in aqueous phase 5 Stedman and Shetter (1983)J13 NOx (g) deposited in dry deposition 5 Stedman & Shetter (1983)10

J13’ NOx (g) deposited by dry deposition to sea 1.2 Stedman & Shetter (1983)10 J13” NOx (g) deposited y dry deposition 3.8 Stedman & Shetter (1983)10 J14 Wet deposition of NOx 5 All dissolved rains out.J14’ Wet deposition of NOx to sea 1.2 Schlesinger & Hartley (1992)11

J14” Wet deposition of NOx to land 3.8 Schlesinger & Hartley (1992)11

J15 Net flux of N in N2 from oceanic fixation and denitrification 9 Stedman & Shetter (1983) J16 Net flux of N in N2 from terrestrial fixation and denitrification 8 Stedman and Shetter (1983) J17 NH3 solution in aqueous phase 22 By difference, balances inflowsJ18 NH3 volatilization from wild animals 3 Soderlund &Svensson (1976)J19 Ammonia volatilization from the sea 13 Schlesinger & Hartley (1992)J20 Ammonia volatilization from soil 10 Schlesinger & Hartley (1992)J21 NH3 dry deposition on land 5 Schlesinger & Hartley (1992)

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J22 NH4 rain out on the land 16 Schlesinger & Hartley (1992)J23 NH4 rain out on the ocean 6 Schlesinger & Hartley (1992))

Table A-1. Continued__________________________________________________________________________________

Item Definition Value Source___________________________________________________________________________________ J24 DON aerosolized in sea foam 10 Soderlund & Svensson (1976) J25 DON rain out on land 10 Soderlund &Svensson (1976) J64 N2 return flow from stratosphere 8.3 Assumed to balance N2O fluxJ65 NOx return flow from stratosphere 1 Stedman & Shetter (1983) Biosphere: Oceans J26 Nitrogen fixation in water column 30 Stedman & Shetter (1983)12 J27 Denitrification in water column to N2 19.5 Stedman and Shetter (1983)J28 Sediment N fixation 10 Soderlund & Svensson (1976)J29 Sediment denitrification producing N2 11.5 Burns & Hardy (1975)13 J29’ Sediment denitrification 15 Burns & Hardy (1975)14 J30 N2O from sediment denitrification 3.5 Stedman & Shetter (1983)13 J31 Conversion of NOx to N2O 19 By difference, bal. N2O tankJ32 Uptake of NOx by plants 857 S o d e r l u n d & S v e n s s o n (1976)15 J33 NOx in runoff 5 Stedman & Shetter (1983)J34 Ammonia converted to NOx in nitrification 869 By difference, bal. NOx tankJ35 Ammonia uptake by plants 3440 S o d e r l u n d & S v e n s s o n (1976)15 J36 Ammonia in runoff 0.5 Stedman & Shetter (1983)J37 Ammonification of DON 4088 By difference, bal. NH4 tankJ38 Plant production of PON 2862 By difference, balances plant st. J39 Plant production of DON 635 Parsons & Tagahashi (1973)16

J40 Plants grazed by animals 800 Parsons & Tagahashi (1973)17

J41 PON produced by animals 445 Parsons & Tagahashi (1973) 18

J42 DON produced by animals 127 Parsons & Tagahashi (1973)19

J43 NH4 excreted by animals 228 Parsons & Tagahashi (1973)20

J44 PON in runoff 3 S o d e r l u n d & S v e n s s o n (1976)21 J45 PON settling out 10 Burns & Hardy (1975)J46 PON converted to DON 3330 By difference, to balance DONJ47 DON in runoff 6 S o d e r l u n d & S v e n s s o n (1976)21 Biosphere: Land J48 N in Litter produced by land plants 1900 Soderlund & Svensson (1976) J49 Nitrogen uptake in NPP 2200 Soderlund & Svensson (1976)J50 Nitrogen consumed by land animals 300 By difference on plant biomassJ51 Nitrogen in feces and mortality 297 By difference, animal biomassJ52 N in litter decaying to organic matter 1700 Soderlund & Svensson (1976) J53 N leached from litter 497 By difference, balances litter

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st. J54 N in Organic matter consumed by microbes 3200 Rosswall (1976)J55 N returned to organic matter by microbes 1503 Rosswall (1976)J56 N remineralized by microbes 1807 Soderlund & Svensson (1976)J57 Nitrogen fixation 110 Stedman & Shetter (1983)J58 Insoluble nitrogen in runoff 1 Runoff balances the tank__________________________________________________________________________________

Notes to Table A-1

1 Cailleux (1968) 4.075E15 Tg mass of mantle times 20 ppm N from Rayleigh (1939)2 9.8E24 g Considine (1976) X 20 ppm from Illinois State Survey web site, http://www.sws.uiuc.edu/

nitro/detail.asp?lpg=areas&type=geosphere.3 Use Considine (1976) to get volume and mass of the crust in relation to igneous volume to get weight

of sedimentary rocks X 500 ppm N, (200ppm to 4000 ppm from Illinois State Survey web site). This checks with estimate in Stedman and Shetter (1983).

4 Times 1.08 to reflect pre-industrial conditions from Stedman and Shetter (1983)5 Estimated as 1% of insoluble inorganic nitrogen.6 Split 3:1 between sedimentary and igneous rock.7 Decreased by half for prehistoric conditions and checked with turnover time of crustal rocks.8 Chosen from range to balance prehistoric runoff.9 T he storage shown is coal only. The nitrogen in oil and gas should be added.10 Dry deposition is assumed to be about equal to wet deposition under prehistoric conditions.11 Wet deposition is split 0.75 to land and 0.25 to sea.12 Minus 10 Tg fixed by sediment from Soderlund and Svensson (1976)13 Lui et al. (1977) N2O : N2 =.23 in denitrification.14 A 5 Tg recycle from sediments exceeds fixation by 515 Codispoti (1983) estimated new nitrogen supplies 25% of total production in world oceans. 16 Exudation of DOC is 15% of total fixed carbon assume DON is exuded in a similar manner.17 Transfer efficiency is 10-20% per trophic level, assume 15% for first level and 20% for 2 succeeding

levels, 18.6%18 Fraction fecal is 0.375 from Butler et al. (1970) + fraction mortality that is particulate, 0.50 to 0.8,

average 0.675 from Krause (1962).

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