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Contents lists available at SciVerse ScienceDirect

Ecological Modelling

jo ur n al homep ag e: www.elsev ier .com/ locate /eco lmodel

mergy evaluations of the global biogeochemical cycles of six biologically activelements and two compounds

aniel E. Campbell a, Hongfang Lub,∗, Bin-Le Linc

US EPA, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882,nited StatesKey Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Science, Guangzhou 510650, ChinaResearch Institute of Science for Safety and Sustainability, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan

r t i c l e i n f o

rticle history:vailable online xxx

eywords:mergy evaluationiologically active elementsitrogenarbonhosphorusulfur

a b s t r a c t

Estimates of the emergy carried by the flows of biologically active elements (BAE) and compounds areneeded to accurately evaluate the near and far-field effects of anthropogenic wastes. The transformitiesand specific emergies of these elements and of their different chemical species are also needed to quantifythe inputs to many ecological and economic production functions. In this study, we performed emergyevaluations of the global biogeochemical cycles of the BAE, carbon, C, nitrogen, N, sulfur, S, phosphorus,P, oxygen, O2 and silica, Si, as well as the global cycles of two compounds (+2), methane, CH4 and water,H2O. We assembled budgets for the global flows of the “BAE + 2” from the literature for the PreindustrialEra and the Industrial Age. The emergy basis for these elemental flows was obtained by documentingthe global inflows of renewable and nonrenewable emergy for the Preindustrial Era (i.e., circa 1850)and for the Industrial Age. The nonrenewable emergy inputs in the Industrial Age were documentedusing a variable time window corresponding to the period of observation when the different elementalbudgets were evaluated. We calculated specific emergies and some transformities of the total flows of theelements and of some of their chemical species. The elemental cycles were diagrammed in Energy SystemsLanguage (ESL) and tables of specific emergies are provided for use in subsequent emergy evaluations.The accuracy of evaluating the global cycles of the BAE + 2 at intermediate complexity was assessed bycomparison to the results of an earlier detailed analysis of the global N cycle. Joint evaluation of theBAE + 2 allowed us to examine these elemental cycles with respect to commonalities and differencesin their structure, function, and potential impacts of their perturbations on the global ecosystem. We
characterize the coupling of the BAE in terms of a fast biogeochemical loop and a slow geochemicalloop, an insight which emerged from the process of diagramming the nitrogen cycle in ESL. Finally, wecompared our emergy evaluation results to other means of ranking greenhouse gases (GHGs) and otherwastes and developed specific recommendations that more research and management attention shouldbe focused on N2O, S and CH4, while continuing present efforts to better understand and manage CO2
and reactive N.© 2013 Elsevier B.V. All rights reserved.

. Introduction

Human impacts on global biogeochemical cycles are nowroadly recognized (Vitousek et al., 1997a,b) and observableffects such as climate change, loss and degradation of ecosystems,

Please cite this article in press as: Campbell, D.E., et al., Emergy evaluations

and two compounds. Ecol. Model. (2013), http://dx.doi.org/10.1016/j.ecolm

nd declines in biodiversity are progressively becoming the focus ofanagement efforts to prevent environmental damage by modify-

ng human behavior that is destructive to the environment (Doney,

∗ Corresponding author. Tel.: +86 20 37084273; fax: +86 20 37252711.E-mail addresses: [email protected] (D.E. Campbell),

[email protected] (H. Lu), [email protected] (B.-L. Lin).

304-3800/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecolmodel.2013.01.013

2010; Lehman and Geller, 2004). In addition, where environmentshave been damaged by the wastes from economic production pro-cesses managers seek to establish policies that require mitigationof that damage through ecosystem restoration and other palliativemeans (e.g., http://co.humboldt.ca.us/planning/salt-river-eir.pdf;http://water.epa.gov/lawsregs/guidance/wetlands/mitbankn.cfm).An accurate evaluation of the effects of wastes on the globalbiogeochemical cycles of the biologically active elements (BAE)and compounds such as methane and water (+2) is a crucial aspect

of the global biogeochemical cycles of six biologically active elementsodel.2013.01.013

of understanding the current environmental crises confrontingthe world. One obstacle to establishing successful programs toexert socioeconomic pressure to alter human behavior or tomake laws and policies that require mitigation or restoration of

dx.doi.org/10.1016/j.ecolmodel.2013.01.013


http://www.sciencedirect.com/science/journal/03043800

http://www.elsevier.com/locate/ecolmodel

mailto:[email protected]



http://co.humboldt.ca.us/planning/salt-river-eir.pdf

http://water.epa.gov/lawsregs/guidance/wetlands/mitbankn.cfm


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nvironmental damage is that a quantitative method for establish-ng fair equivalence between socioeconomic and environmentalutcomes has not been agreed upon.

Emergy evaluation (Odum, 1996) is an objective method forstablishing equivalences among economic, environmental andocial outcomes based on accounting for the available energy ofne kind (i.e., solar joules) that is required for each of the outcomeso occur within the system under evaluation. Emergy evaluation isased on the quantification of production functions of all kinds byccounting for all of the inputs to the production process using aormalized measure of the available energy required for the prod-ct or service. So the fundamental equation of emergy analysis is:

mergy =n∑

i

Available Energyi × Transformityi

here n is the number of inputs to the production function and is an individual input. For each i the quantity of available energy inoules of the input required to make the product or service must benown as well as the transformity of that input, i.e., the quantity ofmergy in solar emjoules required to make one unit of the input,n this case one joule of available energy of input i. The units ofmergy are solar emjoules (semj), the units of available energy ornergy with the potential to do work are joules (J), and the units ofransformity are then solar emjoules per joule (semj/J). This equa-ion can be modified to accept inputs measured in other units, buthe transformity, or more broadly, the emergy per unit measure orhe Unit Emergy Value (UEV) must also be modified to match theltered measure of the input. For example, if mass in grams is usedo quantify the inputs to a production process, the emergy per unitactor is the specific emergy (semj/g).

Although many emergy evaluations have been performedOdum et al., 1987; Brown and Ulgiati, 2002; Brown anduranakarn, 2003) and many UEVs have been calculated (Odum,996; Buranakarn, 1998; Bastianoni et al., 2009; Campbell and Ohrt,009; Heberling and Hopton, 2010), the information set needed formergy evaluations is presently incomplete, because there are stillany critical values for products and services that are unknown or

ot well documented. For example, transformities for the BAE + 2re needed to establish equivalences among the gaseous and otherastes produced by economic production processes in order to

stimate the expected concomitant environmental damage causedy these wastes and for the development of fair trading and mit-

gation schemes. Since the set of possible inputs to all kinds ofroduction functions is large, there are many additional transfor-ities and other UEVs that are needed. However, in this paper,e focus on establishing transformity and specific emergy values

or six BAE (carbon, C, nitrogen, N, sulfur, S, phosphorus, P, oxy-en, O2, and silica, Si) and two compounds (methane, CH4 andater, H2O) through performing emergy analyses of their globalass budgets. We believe that emergy evaluations of these global

ycles are particularly important in understanding and prioritizingesearch on the effects of perturbations of these flows on the globalcosystem, because such evaluations may help in finding work-ble strategies that will result in the establishment of viable, i.e.,air, trading systems to protect the planet. Because of the presentlobal crises mentioned above and the needs of on-going researcht the US Environmental Protection Agency (EPA) and at othernstitutions concerned with the environmental impact of wastes,here is an immediate need for accurate values of these elementalows.



A few emergy evaluations of global cycles of the BAE + 2 haveeen carried out in the past. Odum et al. (1998) and Buenfil2001) evaluated the global hydrological cycle obtaining transfor-

ities and specific emergy values for many global water flows and

PRESSdelling xxx (2013) xxx– xxx

storages. Campbell (2003a) compared selected transformities forglobal water flows obtained from an evaluation of five global hydro-logical cycles and Campbell (2003b) evaluated the specific emergyof the flows of six forms of N in the prehistoric (i.e., prior to thedevelopment of agriculture) N cycle based on an evaluation of adetailed global N budget. Transformities and other unit emergyvalues for N and P used as fertilizers were calculated by Odum(1996). Tonon and Mirandola (2003) calculated a transformity forO2 and Campbell and Ohrt (2009) calculated the specific emergy ofS produced as a by-product of petroleum refining using data fromBastianoni et al. (2009). Recently, Watanabe and Ortega (2011) cal-culated specific emergies for water and for several N and C speciesthat are important greenhouse gases (GHGs), e.g., N2O, CO2 andCH4, with the purpose of estimating an emergy-based value forecosystem services such as carbon sequestration, denitrification,and aquifer recharge.

One of the primary reasons for the success of industrial civ-ilization is that mankind developed the technological capabilityto break the tightly controlled biogeochemical cycles of the Earth(Lovelock, 1979); thereby, extracting energy and materials for useto support human purposes, e.g., economic uses (Odum, 2000;Campbell et al., 2009). However, the extraction and use of theBAE also displaced them in space and time, so that today the bio-geochemical processes that had adapted over millions of years ofco-evolution with life on Earth have been stretched to their limits(e.g., Hughes et al., 2003; Hoegh-Guldberg and Bruno, 2010). Manyof the primary materials essential for economic production are alsothe elements that are essential to support the structure and func-tion of living systems, i.e., the BAE, C, N, S, P, O, Si, as well as thecompounds CH4 and H2O (i.e., BAE + 2).

There are several theoretical and practical questions that arise inconsidering human domination of the global biogeochemical cyclesof the BAE. Campbell et al. (2009) point out that the emergy signa-ture of the Earth changed dramatically from around 1850 to thelatter half of the 20th century, i.e., the emergy base for the Earthor the amount of emergy used in a year increased more than 5-fold over this time. This increase was almost entirely due to theincreased use of fossil fuels and minerals to expand and develophuman civilization. As a result of these activities the global fluxesof the BAE + 2 have changed to varying degrees. This implies thatthe specific emergies and transformities of these elements maybedifferent today than they were in 1850, i.e., prior to the IndustrialAge.

Practically, one of the unique strengths of the emergy method-ology is that it provides a unified, self-consistent objective methodfor quantifying the relative value of material and energy flows in theeconomy and in the environment on equal terms; i.e., solar equiva-lent joules. The implication is that emergy evaluations can help findfair value for the economy and for the planet to help structure mar-ket mechanisms, as well as other means, for controlling and treatingthe wastes of economic production processes. Human agency hasplayed a large role in altering the global fluxes of C, N, S, P, and CH4(e.g., Lal, 2008; Vitousek et al., 1997a,b; Brindlecombe et al., 1989;Kvenvolden and Rogers, 2005), thus the results of these emergyevaluations may be practically useful in establishing equivalencesamong these elements to support trading and other socioeconomiccontrol mechanisms. One goal of this study was to obtain specificemergies of the global flows of six biologically active elements andtwo compounds for use in environmental accounting for the impactof wastes and for establishing emergy values to guide environmen-tal management policies, e.g. on climate change. A second goal wasto compare the specific emergies of global element flows during


the Industrial Age to those in the Preindustrial Era to determinehow these values have changed, and to assess the sensitivity of theglobal biogeochemical system to the 5-fold increase in the emergyuse of the global system over the past 160 years (Campbell et al.,


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Fig. 1. A conceptual model of the global system showing socioeconomic pathways (orange) that carry flows of the biologically active elements and compounds as well asother minerals. Green lines show ecosystem pathways that carry flows of these elements. The heavy solid black line carries renewable emergy inflows, the dotted (blue) linesc ney ana P, grosi to the

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009). Our intent was to better understand the significance of anybserved changes by cross comparison of the structure of the globalycles examined.

. Theory and models

Three conceptual models were used to guide our thinking onerforming emergy evaluations of the global cycles of the BAE.irst, we modeled the global system showing the pathways of massow mediated by the global economy. Next we illustrate the multi-ompartment model used to evaluate flows of the BAE + 2. Finally,e show a conceptual model of the global N cycle represented as

coupling between a fast and a slow order–disorder process sim-lar to the Michaelis–Menten model for activated and deactivatedubstrates in chemistry (Odum, 1994).

.1. Conceptual model of the global system

The Energy Systems Language, ESL (Odum, 1971, 1983, 1994),as applied to draw a conceptual model of the global system

Fig. 1). The model gives an overview of the storages and flows ofhe BAE + 2 in the context of the global system. The pathways (inrange) carry flows of the BAE + 2 mediated by human agency. Eco-ogical pathways carrying the BAE + 2 are shown in green driveny flows of renewable emergy, Ra, that enter from the left (black

ines). Pathways of money flow shown by dashed purple lines andnformation flow shown with dotted blue lines are higher orderocioeconomic functions that depend on the underlying materialnd energy flows.

.2. The multi-compartment model used to evaluate the cycles ofhe biologically active elements

In this study, the individual global element cycles for the BAE + 2



re modeled using a five compartment model of the biogeosphereimilar to that used by Campbell (2003b) to model the global Nycle. For the Prehistoric Era,1 this model includes compartments

1 The detailed global N model was evaluated for prehistoric times, i.e., before theevelopment of agriculture; whereas, the intermediate complexity global cyclesere evaluated for preindustrial times, i.e., circa 1850, with little fossil fuel use butith perturbations to the global cycles caused by the agriculture of that time.

d the gray lines carry energy no longer available for use. BAE + 2, the biologicallys world product; SI, shared information; P, photosynthesis; and R, respiration.(For

web version of the article.)

for the troposphere, lithosphere, the oceans, and land (Fig. A.1).A fifth compartment, the anthroposphere is added to completethe representation of the global system in the Industrial Age(Fig. A.2).

2.3. A conceptual model of the global nitrogen cycle

The N cycle is complex which may explain why up until recentlymost representations of this global cycle have focused on fluxesbetween compartments (Delwiche, 1970; Soderlund and Svensson,1976; Jaffe, 1992; Stedman and Shetter, 1983; Galloway, 1998;Lin et al., 2000) or budgets for individual species, e.g., ammonia(Schlesinger and Hartley, 1992) rather than on developing overviewmodels that capture the structure and function of the global N net-work as a system as in Campbell (2003b) and Galloway et al. (2008).Energy Systems Language was designed for the analysis of networksand the simplification of complexity. Through the process of dia-gramming the global N cycle in ESL, Campbell (2003b) found thatthe biogeochemical cycle of N can be represented as two coupledorder–disorder cycles or Michaelis–Menten loops (Odum, 1994).Fig. 2 shows an overview model of the global N cycle diagrammedusing ESL. Both cycles are driven by the earth’s three primary energysources; solar radiation, the earth’s deep heat, and the gravitationalattraction of the sun and moon, i.e., tidal energy. By definition, dis-ordered forms are either chemically simpler or less concentratedthan the ordered forms of N.

The outer cycle (Fig. 2) shows geochemical N flows moving froma dilute form in the rocks of the lithosphere (53 g N/m3) to N2,a more concentrated form (963 g N/m3) in the atmosphere. In aprehistoric steady state condition, before human agricultural andindustrial activities altered global N flows, most of the N addedannually to the atmosphere eventually made its way back to thelithosphere (Stedman and Shetter, 1983). The available energy ofN species concentrated in the atmosphere and in the primordialocean interacted with the external energy sources of the Earth, aswell as other material storages, to develop a second inner cycleof N circulating through a network of biogeochemical interactions.This inner cycle (Fig. 2) moves N from the relatively disorderedinorganic species, e.g., NH3/NH4

+, NO3−, NO2

−, to more complex


forms, e.g., amino acids and proteins present in living organisms.Living systems build trophic hierarchies that further concentratenitrogen as a consequence of successive energy transformations.The exterior geochemical cycle and the interior biogeochemical


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Fig. 2. Fast biogeochemical cycle (dark gray lines) and slow geochemical cycle (blacklines) of nitrogen identified by Campbell (2003b). The figure shows a macroscopicmini-model of the global nitrogen cycle as two coupled (dotted lines) order–disorderloops: (1) outer geochemical loop, (2) inner biochemical loop, (3) coupling from (1)to (2) by nitrogen fixation and (4) coupling from (2) to (1) by denitrification. Lightg

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ate complexity, we first compiled the data from the figures providedin Reeburgh (1997) and organized this information into three cat-

ray lines carry used energy to the heat sink.

ycle of N are marked (1) and (2), respectively, in Fig. 2. Thesewo cycles are coupled from cycle (1) to cycle (2) through therocess of N fixation (3). Denitrification (4) completes the cou-ling by establishing a connection from cycle (2) to cycle (1).fter an undetermined number of passages through the biosphere,n atom of N will be deposited in sediments where it may beventually returned to the crust in the formation of sedimentaryocks.

Fig. A.1 shows that flows through the storages in the inner bio-eochemical loop are two orders of magnitude greater than theuter geochemical flows. The high concentrations of N in inneroop components and the increased magnitude of N flow throughhis loop indicate that N is being used in a dynamically different

anner by the living systems of the inner loop and that the hier-rchical organization of N flows in these systems is differentiatedrom, although still connected to, the slow, low flow N cycle of theuter loop. The accumulation and cycling of N and other elementsy autocatalytic living systems has produced unique organiza-ional properties, e.g., greater empower flow and more structuralomplexity, than are possible in a system driven by geochemicalrocesses alone. One might hypothesize that a distinguishing prop-rty of living systems is the ability to accumulate and cycle highoncentrations of the BAE or, alternatively, life is an emergent prop-rty of the BAE and their chemical species when concentrationsxceed a threshold.

The evolution of the N cycle cannot be separated from the devel-pment of the other global biogeochemical cycles, i.e., C, O2, P, S,tc. upon which life depends (Deevey, 1970). A question of interests to what extent do other BAE evaluated in this study manifest theast–slow cycles observed for N and to what extent has the coupling



f these two cycles developed in the cycling of the other BAE thatave co-evolved with N?


3. Methods

In a past study (Campbell, 2003b), we found that documentingthe complete global cycle of a BAE, i.e., N, by creating and evaluatinga complex ESL model required 6 months to a year of work (see theAppendix Table A.1 and Fig. A.1). Nevertheless, as mentioned above,there is an immediate need for reasonably accurate values of theseelemental flows for use in current emergy research projects aimedat evaluating the potential far-field effects of gaseous wastes. Onesolution is to evaluate the global cycles of the BAE + 2 in a simplerform, i.e., with the global flows aggregated by similar function tocreate a less complex version of the global cycle. Before applying theemergy methodology to evaluate global budgets of the elements ata reduced level of complexity, we wanted to be sure that we couldobtain reasonably accurate numbers for global flows evaluated atan intermediate level of complexity.

Campbell (2003a) evaluated five annual global water budgetsand found that 95% of the values of the transformity of the chem-ical potential energy of rain on the continents fell within 11.6% ofthe mean value and that 95% of the values of the transformity ofthe chemical potential energy in river water fell within 6.8% of themean value. From this we inferred that there is an expected uncer-tainty in the measurements required to estimate the transformityof the global water budget flows of 7–12%. If we could attain num-bers that were close to this level of uncertainty from an emergyevaluation of global element budgets estimated at an intermediatelevel of complexity, these evaluations might be suitable for estab-lishing trading equivalences and for other regulatory purposes. Werealized that we might compare the values obtained from interme-diate complexity models for N and water to those obtained fromthe detailed model for N constructed by Campbell (2003b) and thedetailed hydrologic budget analyzed by Buenfil (2001) as well asthe five water budgets analyzed by Campbell (2003a) to determineif the values obtained were within a specified level of uncertainty(e.g., ±10% of the mean). With this verification method in mind, wedecided to evaluate the global cycles of several biologically activeelements. The only remaining difficulty was to find a reliable sourcefor data on global budgets at an intermediate level of complexity.

3.1. Database for the evaluation

The global element cycles summarized at an intermedi-ate level of complexity by Reeburgh (1997), and on his website http://www.ess.uci.edu/∼reeburgh/figures.html, were used toconstruct the cycles for the elements C, N, S, P, O, Si as well asfor the compounds CH4 and H2O, supplemented by other refer-ences, e.g., Siegenthaler and Sarmiento (1993) for the C budget inthe Preindustrial Era, Galloway et al. (2004) for the preindustrial Ncycle, Schlesinger (1997) for the S cycle and Kvenvolden and Rogers(2005) for the CH4 emitted during coal, oil, and gas production.Reeburgh (1997) used the C budget as the base for determining thebiological reservoirs in some of the other element cycles, e.g., N andP. All of the original sources for the numbers compiled by Reeburgh(1997) are not cited directly in this paper, but they can be found onhis web site. By using the intermediate complexity global budgets ofReeburgh (http://www.ess.uci.edu/∼reeburgh/) as a base, we wereable to perform an emergy evaluation of the BAE + 2 in a few monthsrather than in several years.

3.2. Emergy evaluation methods and assumptions

To construct evaluated ESL diagrams of the BAE + 2 at intermedi-


egories: storages, flows, and turnover times on spreadsheets. Nextwe drew ESL diagrams for each of the elements and compounds


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nd placed numbers on every known storage and pathway basedn the data presented in Reeburgh and in the other sources men-ioned above. Two diagrams, one for preindustrial global cycles andne for the global cycles during the Industrial Age were constructedor C, N, S and CH4. An evaluated set of forcing functions was usedo show the emergy base for each time period.

Campbell (2003b) made several assumptions in addition tohose made by Stedman and Shetter (1983) that allowed him to

ake a reasonable estimate of prehistoric N flows through the net-ork shown in Fig. A.1. A similar set of assumptions were made

n evaluating the global budgets provided by Reeburgh (1997). Thessumptions that we applied to perform the emergy evaluationsf the global cycles of the BAE + 2 were as follows: first, the globalows of N in the detailed model were assumed to have reached ateady state condition prior to intervention by mankind or in thease of the Reeburgh (1997) for C, N, S, and CH4, prior the Industrialge, i.e., prior to 1850. This steady state assumption was used to bal-nce all storages in the network given initial values from Stedmannd Shetter (1983) for the detailed N model and for the data on, N, S, and CH4 given by Reeburgh (1997) to which minor adjust-ents were made, since this assumption had been applied as a

st order approximation to the data on his web site. Second, in allases the emergy per unit mass values for all storages and flowsn the evaluated models were calculated based on the fact that themergy around a completely interconnected closed loop is a con-tant. For example, the global network of N flows (Fig. A.1) andll other preindustrial and industrial era budgets were assumed topproximate a completely interconnected closed loop. Therefore,he emergy driving these flows is the emergy supplied to the Earthy its independent energy sources, i.e., solar radiation, the Earth’seep heat, and the gravitational attraction of the sun and moonOdum, 1996; Campbell, 2000) plus fossil fuels, minerals, and ero-ion for the detailed 1970s N budget and for the budgets of C, N, S, P,, Si, CH4 and H2O measured during the Industrial Age. The emergyase of the Earth in the Preindustrial Era was taken as the sum of theenewable emergy inputs to the planet, 9.26E+24 semj/y (Campbell,000). The emergy driving the global element cycles of the Earthuring the Industrial Age includes massive inputs of emergy inhe minerals and fuels used to support civilization along with thenflows of renewable emergy mentioned above. The emergy sup-orting the Industrial Age was determined by adding the averagelobal emergy of fossil fuels, nuclear energy and minerals used androsion during the period over which the measurements of thelobal element cycles were made to the renewable emergy base ofhe Earth. Note that under these assumptions it is not necessary tonow all of the connections of the forcing functions within the sys-em to evaluate the specific emergy of the global element flows, andhus these connections are not fully specified in the models shown.

.3. Emergy base of the earth in the Industrial Age

We determined the emergy base for the earth during thewo time periods corresponding to the times when data on thelobal element cycles were observed, i.e., the 1970s for N, P,nd H2O and the 1980s for C, S, O2, Si, and CH4. The time win-ows used were 1972–1976 for the 1970s and 1980–1989 for the980s. Before industrialization of the planet, the biogeochemicalrocesses of the Earth slowly generated storages of fossil fuelsnd minerals within the crust, driven by the renewable emergyase of the Earth, 9.26E+24 semj/y (Campbell, 2000). This situ-tion has changed since the industrialization of the planet, asore and more fossil fuels and minerals have been extracted



rom the earth to fill the demand generated by social and eco-omic growth and development. The extraction and use of theseesources has brought about dramatic land use change, as wells, pollution and degradation of many of the Earth’s ecosystems.

PRESSdelling xxx (2013) xxx– xxx 5

The emergy of the annual consumption of four kinds of nonre-newable energy (oil, natural gas, coal and nuclear energy) based onthe British Petroleum Corporation (BP) statistical review of worldenergy (http://www.bp.com/statisticalreview) and the emergydelivered to the global system by 53 kinds of minerals found inthe US Minerals Yearbook (http://digital.library.wisc.edu/1711.dl/EcoNatRes.MinYB1975v3) were compiled and averaged to quan-tify the emergy driving the biogeochemical cycles of the Earth afterindustrialization, i.e., during the 1970s and 1980s as mentionedabove. Soil erosion during this time was assumed to be the sameas that found in 1995, i.e., 1.38E+19 J/y or 1.00E+24 semj/y (Brownand Ulgiati, 1999). We approximated the emergy input from erodedsoils, because this value was small compared to the emergy inputsfrom fuels and minerals and because we did not have reliable globalestimates of erosion over the time periods of interest.

3.4. The specific emergy of elements and the expected impact ofperturbations in their mass flows

Combining information on the flows of an element or its chem-ical species given on the ESL diagrams with the emergy base of theEarth established at a given time allowed us to calculate the specificemergy (semj/g) of the global flows of an element and of its chem-ical species. We counted the flow on every pathway of the modelto determine the total flow of an element or one of its species. Theemergy required for placing a gram of an element or compound ina global storage was determined by multiplying the annual emergyinput to the earth by the turnover time of the storage in years, sincethis is the time required to completely replace the material stored.This value was divided by the mass of the storage to give the specificemergy of the storage in semj/g. For storages with long turnovertimes, the emergy of the storage was determined using the elemen-tal flows appropriate for the Preindustrial Era. The specific emergyof flows was determined by dividing the annual emergy inflow tothe earth (semj) by the annual flux of an element or compound ingrams flowing along a pathway in the global network.

The Environmental Loading Index (ELR) is a commonly usedmeasure of the potential impacts of waste and nonrenewableemergy used on the environment (Brown and Ulgiati, 2002). TheELR is the ratio of the nonrenewable emergy that can potentiallyproduce an impact to the renewable emergy of the system, which isviewed as a measure of the system’s capacity to process the wastesor the damages caused by nonrenewable emergy use (Brown andUlgiati, 1997). We used a similar approach to show the potentialdamage to the global ecosystem due to changes in the mass flux ofthe various biologically active chemical species. The ratio of theemergy of a mass perturbation to the global renewable emergybase gives the potential impact as a percent of the base. The annualchallenge that must be met to counter a mass flow perturbationis the percent of the global renewable emergy that must be usedin each year to counter the emergy of the mass flux perturbationassuming that all effects of the mass flow change will have negativeconsequences.

4. Results

The results of this study are presented as a series of evaluatedESL diagrams, i.e., diagrams with values assigned to the forcingfunctions, pathways and storages, that comprise the global cyclesof the BAE + 2 (C, N, S, P, O, Si, CH4 and H2O). The global cycles of theBAE + 2 are shown within a five compartment model of the globalsystem as described above. Evaluated ESL diagrams are shown


for C, N, S, and CH4 during the Preindustrial Era. Evaluated ESLdiagrams are shown for C, S, Si, CH4 and O2 for the 1980s and for N,P and H2O for the 1970s. Data tables are given showing the fluxesof each element and some of their chemical species in each time


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eriod. The tables also give the specific emergies of the variousows and show how they have changed from preindustrial to

ndustrial times. The results of determining the planetary emergyase, i.e., the annual emergy inputs to the global system, during thewo time windows of the Industrial Age (IA) that were evaluatedre given first, followed by presentation of the evaluated globalycles. Next, we compare our estimates of the specific emergiesf the various compounds, elements and their chemical species toarlier estimates from the literature. Finally, we examine the pro-ected impact of changes in the mass flow on the global ecosystemnd the significance of this work within the context of the need toffectively manage GHGs and other biogeochemical wastes.

.1. Planetary emergy base in 1970s and 1980s

The emergy of both the energy and mineral consumption oflobal society has grown rapidly in the 150 years following indus-rialization (Campbell et al., 2009; Brown and Ulgiati, 1999). Themergy of the minerals consumed was approximately two timeshat of the emergy of the nonrenewable energy consumed duringhe two periods examined (Table 1). The average global emergyase for the Earth (i.e., the annual emergy inputs that drive the bio-eosphere) increased to 4.38E+25 and 4.89E+25 semj/y in the 1970snd the 1980s, respectively, compared to the preindustrial estimatef 9.26E+24 semj/y (Campbell, 2000). These values are 4.74 and 5.28imes the natural renewable emergy inflow to the Earth during thereindustrial Era. Overall oil was the largest energy source useduring the periods evaluated after industrialization, but oil con-umption fluctuated over the time, while the consumption of thether three energy sources continuously increased (Fig. A.3). Ironre, manganese, and barite (the main constituent of drilling mud),n that order, were the three largest minerals consumed in the early970s and the 1980s based on their emergy. All of these major

nflows varied over the two time periods examined (Table A.4).

.2. Global nitrogen cycle

The results of evaluating the global N cycle at an intermedi-te scale of resolution are shown in Fig. 3a and b. The N flow datan Fig. 3a are from Galloway et al. (2004) and they characterizehe global N cycle in 1860, which for the purposes of this analysisill be considered equivalent to “circa 1850”. The primary flows

etween the compartments of the global model are given with thexception of the lithosphere. The emergy driving these global flowsomes from solar radiation, the deep heat of the Earth and the grav-tational attraction of the sun and moon (emergy flows are in boldype on all figures). The detailed model of the N cycle for prehis-oric times, i.e., without any anthropogenic flows from fossil fuels orgriculture, is given in Fig. A.1 and Table A.1, and briefly describedn A.1. The results reported in Table A.1 are mainly based on resultsrom Anderson (1983), Bidigare (1983), Burns and Hardy (1975),utler et al. (1970), Cailleux (1968), Codispoti (1983), Considine1976), Lui et al. (1977), Parsons and Tagahashi (1973), Pierrou1975), Prather et al. (1994), Rayleigh (1939), Rosswall (1976), andmith (1999). An evaluation of the global N cycle in the Industrialge (1970s) from Reeburgh (1997) is shown in Fig. 3b. Similar to

he preindustrial budget of Galloway et al. (2004) the focus is onhe primary flows between the compartments of the global model,ut in this case, the emergy flows of minerals and fossil fuels fromhe lithosphere have been added.

The N storages (the tank symbols) are the pool sizes of Reeburgh



1997) and the pathway flows are his fluxes. Turnover of storage cane calculated by dividing the storage by the largest flow followingeeburgh (1997). These representations and relationships hold forll of the intermediate complexity global cycles evaluated in this


study where Reeburgh’s data were used, i.e., C, N, for the IndustrialAge and the evaluations of O2, S, P, Si, CH4 and H2O.

A detailed model of the N cycle in the 1970s is presented in theappendix (Fig. A.2 and Table A.2). This evaluation was performedat the same time as Campbell (2003b), but it was not presented asa part of that study. Detailed flows within and between compart-ments are represented in this model incorporating the estimationsof changes in these flows that occurred between prehistoric timesand the Industrial Age (Table A.3).

Key features of the global N cycle shown in the intermediatecomplexity models presented here (Fig. 3a and b) are modified fromReeburgh (1997) and listed as follows: N2O is a long-lived GHG thatis destroyed by photolysis in the stratosphere; NO3

− is the ther-modynamically stable form of N in the global cycle rather than N2;however N2 is the largest N storage, because it is relatively inertand depends on biologically mediated N fixation to be converted toNO3

−, which is then quickly taken-up by plants when it is presentin the biosphere (Reeburgh, 1997); the fast biogeochemical cycleand the slow geochemical cycles of N are linked by two biologicallymediated processes, N fixation and denitrification; N fixation hasbeen augmented by anthropogenic processes in the Industrial Ageso that at present 60% of the N fixed is due to anthropogenic pro-cesses (calculated from the data in Table 1 of Galloway et al., 2004);in the long run denitrification balances the budget by returning Nfrom the fast biogeochemical to the slow geochemical part of theglobal cycle.

Table 2 shows the emergy analysis results for a comparativeanalysis of the detailed representation of the global N cycle in pre-historic times (Table A.1) and in the Industrial Age (Table A.2). Thespecific emergies and the global flows are shown for six N speciesand the total N flow. Only the flows of N2 and N2O are markedlydifferent from their flows prior to global industrialization, whereas,the emergy base for the global system increased more than 4-foldover this time. Ammonia and the ammonium ion have the lowestspecific emergy of all the forms of N examined and N2O has thehighest.

We compared the results of our calculation of the specificemergy of N2 from the detailed model to that obtained from theintermediate complexity model of the global N budget for both pre-historic time (PI, Table 3) and the Industrial Age (IA, Table 3). Theratio was 1.04 for the PI estimates and 1.32 for the IA estimates.Since the internal compartment flows were not well represented inthe intermediate complexity models we were not able to determinethis ratio for other N species.

4.3. Global carbon cycle

An ESL diagram of the global C cycle for the Preindustrial Era(Fig. 4a) and for the Industrial Age during the 1980s (Fig. 4b)revealed a pattern that was, in part, consistent with the couplingof fast and slow cycles observed for N, but the major atmosphericstorage, i.e., a reservoir or pool in Reeburgh (1997), had a muchfaster turnover time (5 y for CO2 compared to 107 y for N2). Theevaluations at both times show that the largest C storages are inthe lithosphere occurring primarily as limestone and kerogen, thedeep ocean constitutes the primary storage of C occurring withinthe land, oceans and atmosphere. Atmospheric C occurring as CO2 isclosely coupled to the biological C reservoir, i.e., C storage, in plantsand animals through photosynthesis and respiration. In the Prein-dustrial Era the figure shows that C flows in the whole system werein balance. In contrast, during the 1980s the accumulated effectsof industrial civilization (e.g., fossil fuel consumption and land use


change) combined with the small size of the atmospheric C pool andits relatively slow equilibrium with the large deep oceanic C reser-voir have resulted in a system that is out of balance (Reeburgh,1997). The primary observable effect of this imbalance has been





Table 1Global emergy base in the Industrial Age: the 1970s and 1980s (semj/y).

Time Year Energy consumption Mineral consumption Global emergy base* Average for period

1972 1.03E+25 2.07E+25 4.12E+251973 1.10E+25 2.22E+25 4.35E+25

1970s 1974 1.10E+25 2.28E+25 4.40E+25 4.38E+251975 1.10E+25 2.32E+25 4.45E+251976 1.17E+25 2.41E+25 4.60E+251980 1.26E+25 2.56E+25 4.85E+251981 1.24E+25 2.55E+25 4.82E+251982 1.23E+25 2.73E+25 4.98E+251983 1.24E+25 2.24E+25 4.51E+25

1980s 1984 1.30E+25 2.39E+25 4.71E+25 4.89E+251985 1.33E+25 2.58E+25 4.93E+251986 1.37E+25 2.50E+25 4.90E+251987 1.41E+25 2.48E+25 4.92E+251988 1.47E+25 2.59E+25 5.09E+251989 1.50E+25 2.64E+25 5.17E+25

* The global emergy base for a given year was determined by adding the emergy of the nonrenewable energy and minerals consumed and a constant factor of1.026E+25 semj/y for the renewable emergy inflows (9.26E+24 semj/y) and soil erosion (1.0E+24 semj/y, Brown and Ulgiati, 1999).

Table 2Nitrogen flows and the specific emergy of N species before (PI) and after the Industrial Age (IA). For this table the values are from Campbell (2003b) and PI is actuallyprehistoric, i.e., before the development of agriculture.

N species NH3–NH4 PON DON NOx N2 N2O Total N

Prehistoric (PI) global emergy: 9.26E+24 semj/yNitrogen flow E+12 g N 8701.8 6687.6 8196 1783 406 60.6 25835Specific emergy semj/g 1.06E+09 1.38E+09 1.13E+09 5.19E+09 2.28E+10 1.53E+11 3.58E+08

Industrial Age (IA) global emergy in 1970s: 4.38E+25 semj/yN flow in 1970s E+12 g N 8878.5 6695 8192 1963 640 104.7 26473.2Specific emergy semj/g 4.93E+09 6.54E+09 5.35E+09 2.23E+10 6.84E+10 4.18E+11 1.65E+09

Sensitivity of N flows to human developmentRatio flows (IA/PI) 1.0203 1.0011 0.9995 1.1010 1.5764 1.7277 1.0247

p(tttsimms

oftflCewte

TE

Ratio Sp. Em. (IA/PI) 4.65 4.72 4.73

rogressively increasing concentrations of CO2 in the atmosphere+3.4E+15 g/y in the 1980s, Fig. 4b). Reeburgh (1997) note thathe major long term sink for C is the deep oceanic sediments andhat the removal of a small amount (0.1%) of net primary produc-ion each year over geologic time has resulted in the present largetorage of O2 in the atmosphere (i.e., the burial of 0.2E+15 g C/yn Fig. 4a). Geological processes complete the C cycle by uplifting

arine shale and through seepage of oil and gas releases and inodern times the pumping of fossil fuels from the earth and their

ubsequent combustion.Table 4 gives the flows and specific emergies of various forms

f C around 1860 and during the 1980s. The flows of the complexorms of C, i.e., DOC and POC, do not appear to have changed, whilehe annual flux of DIC has increased about 1%. In contrast, the globalux of CO2 has increased 7% during this time. The specific emergy ofO2 in the Preindustrial Era was 1.75E+07 semj/g C and its specificmergy in the 1980s was 4.92 times higher (8.62E+07 semj/g C),hich is calculated based on a planetary baseline augmented by



he emergy use from nonrenewable fuels, mineral resources androsion.

able 3stimates of the specific emergy of N2 in the intermediate complexity model (Galloway e

Model N2, Preind

PI – Galloway et al. (2004), IA – Reeburgh (1997) 2.37E+10

PI – Campbell (2003b), IA – this paper 2.28 E+10

Ratio: Intermediate complexity/complex model 1.04

4.30 3.00 2.74 4.62

4.4. Global oxygen cycle

Fig. 5 shows an ESL diagram of the global O2 cycle, whichincludes the major fluxes of O2 among the compartments and someof the internal storages within the compartments of the globalmodel. The numbers for O2 in the storages (reservoirs) and flowsare given in E+15 moles of O2 (Reeburgh, 1997). The atmosphereis the largest O2 storage apart from the lithosphere. The oxygenstored in the atmosphere (37,000E+15 moles O2) is approximately200 times larger than the two next largest storages, the O2 storedin long-lived, land plant biomass (180E+15 moles O2) and the O2stored in the deep ocean water (219E+15 moles O2). Major fluxesare the exchange of O2 across the ocean surface (140E+15 molesO2 flows in and out) and the coupling of the slow turnoveratmospheric storage with the fast-turnover biologic storages ofland and water through photosynthesis and respiration. FollowingReeburgh (1997), we show the ocean sediments as an O2 source,because the long term storage of C in ocean sediments leads to a


slight O2 surplus, which has accumulated in the atmosphere overtime.

t al., 2004 and Reeburgh, 1997 and in the complex model Campbell, 2003b).

ustrial (PI) (semj/g) N2, Industrial Age (IA) (semj/g)

9.01E+106.84E+101.32




8 D.E. Campbell et al. / Ecological Modelling xxx (2013) xxx– xxx

a

Atmosph ere

N23.95E9

Land

Land Bio mass3.5E4

Soils9.5E4

Lithosp hereFossil Fuels

Global N itrogen Cycle, Preindu strial Storages 1012 g N; Flows 1012 g N y-1

N2O1.4E3

N fixed1.35E3

Natu ralFixa �on

120

NaturalFixa�on

121

Leguminous crops

15

Minerals

Rivers27

Oceans

Phy toplankton300

Inorganic6E5

Surface

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Anim als170

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Den itrifica� on98

Weathering5

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Gravita �onalForces1.26 G

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N23.95E9

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Soils9.5E4

Lithosp here

AssetsPeople

Fossil Fuels

Global Nitrogen C ycl e 1970s Storages 1012 g N; Flows 1012 g N y-1

N2O1.4E3

N fixed1.35E3

Natu ralFixa �on

190

NaturalFixa �on

40

Leguminous cro ps40

Minerals

Chem. Fer�lizer20

Combu s�on20

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Denitrifica�on30

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Weathering5

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F for thg lobal

eflflot

ig. 3. Energy systems language diagrams of the global nitrogen cycle representedlobal nitrogen cycle (data sources: Galloway et al., 2004; Reeburgh, 1997). b. The g

In Table 5 the specific emergy of O2 in the Preindustrial Era wasstimated by removing the O2 consumed by combustion from the



ows in Fig. 5. This resulted in an estimate of 9.43E+5 semj/g of O2owing in the global cycle before industrialization. Global O2 flowsnly increased 0.2% as the emergy base of the Earth increased 5.28imes from 1850 to the 1980s.

e Preindustrial Era (1860) and after industrialization (1970s). a. The preindustrialnitrogen cycle in the 1970s (data sources: Reeburgh, 1997).

4.5. Global sulfur cycle


An ESL diagram of the global S cycle for the Preindustrial Era(Fig. 6a) and for the Industrial Age during the 1980s (Fig. 6b)revealed a pattern somewhat different from that of C with a muchshorter turnover time for the major atmospheric storage (8 d for





a

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SolarRadia�on

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Surface100 m

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Lithosp hereFossil fu els

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Global Carbon Cycle, Preindustrial Storages 1015 gC; Flows 1015 gC y-1

GPP90

Minerals

74 74Exchange

Animals Resp.90 Rivers

0.2 DOC0.2 POC

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E

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Downmixing90

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6

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Peat360 POC

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SoilsMineral700

GPP100

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Anthroposphere

SolarRadia�on

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Ear thDeep Heat

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Land

Plants550

Peat360 POC

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SoilsMineral700

Methaneclat hrates

11E3Kerogen

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DOC40

POC3

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+10 y-1

DIC38100+1.6 y-1

Surface100 m

Dee p> 100 m Surfa ce

Sedim ent s150

Lithosp here

AssetsPeople

Fossil fu els3580

Global Ca rbon Cycl e 19 80 to 1989 Storages 1015 g C; Flows 1015 g C y-1

GPP90

Minerals

92 90Exchange

GPP100

Animals Resp.90

Animals

Respira�on50

Rivers0.2 DOC0.2 POC

G

E

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SEG

Downmixing91.6

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DOC700POC

25

Se�ling4

Burial 0.2

6Soil respir a�on50

50

6

13.3 33.2

Erosion1.0


1020+ 0.4 y

F l Era (T

Spotuf

ig. 4. Energy systems language diagrams of the global carbon cycle in Preindustriahe global carbon cycle in the 1980s.

Ox and 5 y for CO2) and with a smaller fraction of the total S fluxassing through the biota. The turnover times for oceanic storages



f S are E+6 years and the geologic storages of S have even longerurnover times (E+8 y). The inter-compartmental flows of the nat-ral S cycle are dominated by the flux of particulate material in theorm of salt from the sea and dust from the land to the atmosphere

1860) and in the Industrial Age (1980s). a. The Preindustrial global carbon cycle; b.

and the subsequent return of this material to the ocean and landsurface in rainfall. Note that in the Preindustrial Era the net flux of


S was from the oceans to the land.The evaluated ESL model of the S cycle for the 1980s (Fig. 6b)

shows the changes that have occurred in global S flows primarilyas a result of the combustion of fossil fuels, as well as, mining S, and





Anthroposphere

SolarRadia�on

3.93

EarthDeep He at

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Atmosphere

O237000

Sedim entaryRocks (OC)

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Oceans

DO6

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Surface100 m

Dee p> 100 m

Lithosph ere

Assets

People

Global Oxygen Cycl e 19 80 to 19 89 Storages 1015 moles O2; Fl ows 1015 moles O2 y-1

Land

Short -Li vedBiota (OC)

11

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Long-Li vedBiota

Soil

Li�er 180(OC)

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GPP9.2

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Weatheri ngVolcanism

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140140

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Export0.4 (OC)

OceanSediments Sedimenta�on

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SEG


33.2

Erosion1.0

13.3

Figure 5.

Fig. 5. Energy systems language diagram of the global oxygen cycle in the Industrial Age (1980s). Flows and storages with OC in parentheses have been based on equivalentcomponents in the global carbon cycle.

Table 4Carbon flows and the specific emergy of C species before and after the Industrial Age.

C species CO2 POC DOC DIC Total C

Preindustrial (PI) global emergy: 9.26E+24 semj/yCarbon flow E+15 g C 528.6 13.8 12.4 190.0 744.7Specific emergy (semj/g) 1.75E+07 6.73E+08 7.49E+08 4.87E+07 1.24E+07

Industrial Age (IA) global emergy in 1980s: 4.89E+25 semj/yC flow E+15 g C 567.4 13.8 12.4 191.6 785.1Specific emergy (semj/g) 8.62E+07 3.55E+09 3.96E+09 2.55E+08 6.23E+07

mftRitE

teflt

4

A

TO

Ratio flows (IA/PI) 1.07 1.00

Ratio Sp. Em. (IA/PI) 4.92 5.28

ore intensive use of land. Wastes from the combustion of S richossil fuels produce SO2, which is oxidized to SO4 in the atmospherehat, in turn, is washed out by rainfall onto the oceans and land.eeburgh (1997) notes that a characteristic feature of the S cycle

n the Industrial Age is that the net flux of S is now from the lando the oceans rather that the reverse as it was in the Preindustrialra.

Table 6 shows the specific emergy of S (1.22E+10 semj/g) inhe Preindustrial Era (the natural S cycle) compared to its specificmergy (3.76E+10 semj/g) in the Industrial Age (1980s). Global Sows increased by 71% from the Preindustrial Era to the 1980s ashe emergy base of the Earth increased 5.28 times.



.6. Global phosphorus cycle

An ESL diagram of the global P cycle (Fig. 7) for the Industrialge (1970s) revealed a pattern of fast biogeochemical cycling and

able 5xygen flows and the specific emergy values of O2 before and after the Industrial Age.

Oxygen Preindustrial (PI) Industrial Age (IA)

Flow E+15 g O2 Specific emergy (semj/g) Flow E+15 g O2

O2 9824.6 9.43E+05 9843.2

1.00 1.01 1.055.28 5.24 5.01

slower geochemical cycling of the element similar to that observedfor N, C, and O, but the amount of P in the atmosphere is very smallwith a turnover time of about 2 days. The dust from the land thatenters the atmosphere is quickly washed out by rainfall. As a resultthe global cycle of P is confined to the oceans (liquid phase) andland (solid phase). The majority of P cycling occurs in the oceanand the major sink for P is the ocean sediments. Over time thesesediments form phosphate rich rock, which has been mined in theIndustrial Age to manufacture fertilizer; thereby, reintroducing Pinto the global ecosystem. The preindustrial flows of P were esti-mated by removing phosphate rock mining from the Industrial Agebudget.

Table 7 shows the specific emergy of P (3.91E+09 semj/g) in the


Preindustrial Era compared to its specific emergy (1.84E+10 semj/g)in the Industrial Age (1970s). Global P flows increased by only 1%from the Preindustrial Era to the 1970s as the emergy base of theEarth increased 4.74 times.

Ratio flows (IA/PI) Ratio Sp. Em. (IA/PI)

Specific emergy (semj/g)

4.97E+06 1.002 5.28


Please cite this article in press as: Campbell, D.E., et al., Emergy evaluations of the global biogeochemical cycles of six biologically active elementsand two compounds. Ecol. Model. (2013), http://dx.doi.org/10.1016/j.ecolmodel.2013.01.013




SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosphe re

SOx3.2

Oceans

Marin e Bi ota30

Surface100 m

Dee p> 100 m

OceanSediments

3E8

LithosphereRocksMinerals

2.4E10 Fossil fuels

Global Sulfur Cycle, Natu ral Storages 1012 g S; Flows 1012 g S y-1

SOx1.6Over Oc eans

Over Land

Land

Land Biota

LakesRivers300

Soils3E5

SO4

1.3E9

Sea Salt140

Biogen ic30

Dep osi �on159

Rivers104

Buri al135

24Air Fl ow13

Bio genic22

Dust20

Deposi �on63

G

E

S

Vol canoes10


a

Anthropo sph ere

SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosphe re

SOx3.2

Oceans

Mari ne Biota30

Surface100 m

Dee p> 100 m

OceanSediments

3E8

AssetsPeople

LithosphereRocksMinerals

2.4E10 Fossil fuels

Global Sulfur Cycl e Mid-1980s Storages 1012 g S; Flows 1012 g S y-1

SOx1.6Over Oc eans

Over Land

SO4

1.3E9

Sea Salt140

Biogen ic30

Deposi� on231

Rivers213

Buri al135

20Air Fl ow81

Anthropogenic93

Biogen ic2.5

Dust20

Dep osi �on84

G

E

S

Consump�on From

Lithosphere150

SEG

Land

Land Biota

LakesRivers300

Soils3E5

Bio genic22

Dust20

Volcanoes10


33.2

1.0

13.3

Waste57

b

Fig. 6. Energy systems language diagrams of the global sulfur cycle in its natural state (comparable to our PI classification) and in the Industrial Age (1980s).

Table 6Sulfur flows and the specific emergy values before and after the Industrial Age.

Sulfur Preindustrial (PI) Industrial Age (IA) Ratio flows (IA/PI) Ratio Sp. Em. (IA/PI)

Flow g S E+12 Specific emergy (semj/g) Flow g S E+12 Specific emergy (semj/g)

S 761.00 1.22E+10 1301.00 3.76E+10 1.71 3.09





Lithosp here

Anthroposphere

SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosphe re

PO40.02 8

Minea ble PO4Rock

1.0 E4

Oceans

PO42700Ocean Bi ota

140

PO48.7E4

Surface300 m

Dee p3000 m

Assets

People

Global Phosphorus Cycl e 19 70s Storages 1012 g P; Fl ows 1012 g P y-1

Land

Land Biota3000

Peat Soil

Li�er 2E5

OceanSediments

4E9

To 60 cm

G

E

S

RiversReact.1.7-2.7Total20

Minerals

2.4E10 Fossil fuels

1842

58

1.9

12

SEG

Dust4.6

4.61065

1065

12

20

64 64

Buri al100

Soil forma� on100


1130.1

Erosion1.0

f the

4

Ibfcgtitwtorn2cittegwt

P

TP

Fig. 7. Energy systems language diagram o

.7. Global silica cycle

An ESL diagram of the global silica (SiO2) cycle (Fig. 8) for thendustrial Age (1980s) showed that the SiO2 cycle is dominatedy processes in the world oceans. Within the oceans a pattern ofast biochemical cycling in the surface waters and slower biogeo-hemical cycling in the deep waters was revealed. Silica has noaseous phase of importance in the global cycle and the eolianransport of dust into the atmosphere was not well characterizedn the database. Silica dissolves from rock during weathering and isransported to the oceans largely in dissolved and colloidal forms,here it is taken-up in photosynthesis by diatoms in high lati-

udes and radiolarians in the tropics (Reeburgh, 1997). When theserganisms die and fall to the ocean sediments, SiO2 is eventuallyeturned to rock through burial over time. The global SiO2 cycle isot as well known as the cycles of, C, N, P, and S (Laurelle et al.,009). Furthermore, anthropogenic effects on the global SiO2 cyclean both enhance (through increased erosion and global warm-ng) and diminish (through dam construction) the input of SiO2o the world oceans. Because of this uncertainty we assumed thathe preindustrial flows of Si were approximately the same as thosestimated for the 1980s. We believe that it is more likely that thelobal dissolved silica input to the oceans is somewhat less than it



as in 1850 due to the overriding effects of dam construction sincehe 1950s (Laurelle et al., 2009).

Table 8 shows the specific emergy of Si (4.43E+08 semj/g) in thereindustrial Era compared to its specific emergy (2.34E+09 semj/g)

able 7hosphorus flows and the specific emergy values before and after the Industrial Age.

Phosphorus Preindustrial (PI) Industrial Age (I

Flow E+12 g P Specific emergy (semj/g) Flow E+12 g P

P 2369.9 3.91E+09 2381.9

global phosphorus cycle during the 1970s.

in the Industrial Age (1980s). Global SiO2 flows appear to be littlechanged compared to the Preindustrial Era while the emergy baseof the Earth has increased 5.28 times.

4.8. Global methane cycle

An ESL diagram of the global CH4 cycle for the Preindustrial Era(Fig. 9a) and for the Industrial Age during the 1980s (Fig. 9b) showsthat CH4 flows are dominated by biologically based processes onthe land, i.e., bacterially mediated production of CH4 in rice paddiesand natural wetlands, CH4 produced by termites and cattle andthrough biomass burning. Storages of CH4 are found in natural gasassociated with fossil fuels in the lithosphere, in hydrated formsin the oceans, and in the atmosphere. The storage of CH4 in theatmosphere is the smallest and it has a turnover time of around 9.6years.

Table 9 shows the specific emergy of CH4 (4.33E+09 semj/g)in the Preindustrial Era compared to its specific emergy(2.14E+10 semj/g) in the Industrial Age (1980s). Global CH4 flowsincreased by 7% from the Preindustrial Era to the 1980s as theemergy base of the Earth increased 5.28 times.

4.9. Global water cycle


An ESL diagram of the global water cycle (Fig. 10) evaluatedmostly during the 1970s shows the major inter-compartmentalflows of water and the quantities of water in storage in the oceans

A) Ratio flows (IA/PI) Ratio Sp. Em. (IA/PI)


1.84E+10 1.01 4.71





Anthroposphere

SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosphe re

SiO40?

Oceans

Phytopla nkton

Surface

Dee p

Lithosp here

Assets

People

Global (Ocean) Sili ca Cycl e 19 80s Storages 1012 moles Si; Fl ows 1012 moles Si y-1

Land

Soil

OceanSediments

6E7

SiO49E4

G

E

S

SEG


240 SiO4

Export120

120

Dissolu�on

Uptake

114.5Upwelling

Dee pDissol u�on

90.9Rai n 29.1

Abyssal Sedimenta�on

29.1Benthic Dissolu�on

23W 0.4 H 0.2

Rivers

5.6

E.S.0.6

5

EolianTransport

0.5

W is Weat heri ngH is Hy drothermal E.S. is Estuarine Sedim enta�on

FuelsAnd

Minerals

46.5

Erosion1.0

Fig. 8. Energy systems language diagram of the global silica cycle in the Industrial Age (1980s). Flows and storages are given as teramoles of Si.

Table 8Silica flows and the specific emergy values before and after the Industrial Age. We have assumed no measurable change due to anthropogenic inputs.

Silica Preindustrial (PI) Industrial Age (IA) Ratio flows (IA/PI) Ratio Sp. Em. (IA/PI)

Flow E+12 g Si Specific emergy (semj/g) Flow E+12 g Si Specific emergy (semj/g)

(i(vm2

wvBvgrb(vtm

TM

Si 20918.5 4.43E+08 20918.5

1.37E+09 km3), in various storages on land the largest of whichs polar ice and glaciers (2.9E+07 km3) and in the atmosphere13,000 km3). Table 10 gives the specific emergy and transformityalues for various global flows of water. The estimates of transfor-ity are based on a uniform conversion factor of 4.74 J/g (Campbell,

003a).A comparison of the values given in Table 10 for three global

ater flows commonly used in emergy analyses shows that thealues for evaporation on land and rain on land estimated byuenfil (2001) and Reeburgh (1997) fall within ±10% of the meanalue determined by Campbell (2003a) using the average of fivelobal water budgets. The value estimated by Reeburgh (1997) forunoff also meets this criterion, but the value for runoff estimatedy Buenfil (2001) falls within 16% of the average from Campbell2003a). When the calculation is corrected for difference in the



alue for Gibbs free energy used to determine the chemical poten-ial energy of the water, Buenfil’s number falls within 11% of the

ean from Campbell (2003a).

able 9ethane flows and the specific emergy values before and after the Industrial Age.

Methane Preindustrial (PI) Industrial Age (IA

Flow E+12 g CH4 Specific emergy (semj/g) Flow E+12 g CH4

CH4 2136.6 4.33E+09 2288.6

2.34E+09 1.00 5.28

4.10. Impacts on the global biogeochemical cycles as indicated byemergy analysis

Table 11 presents the specific emergy of some of the importantchemical species of the BAEs calculated in this study, in order fromthe lowest to the highest. Water in the atmosphere has the low-est specific emergy followed by O2, and CO2, while S compoundsand N2O have the second highest and the highest specific emergy,respectively. The ratios of the elements and compounds specificemergies (IA/PI) indicate that S and N2O flows have undergone thelargest changes on a percentage basis over the time period from1850 to the time of their cycle evaluations, (i.e., because the annualflow of the element is in the denominator of the expression forspecific emergy).

Table 12 shows a comparison of several measures of the relative


harmfulness of chemical species evaluated in this study when theyare released as pollutants. The rank order of the predicted harmful-ness of these substances is similar for the global warming potential

) Ratio flows (IA/PI) Ratio Sp. Em. (IA/PI)


2.14E+10 1.07 4.93





SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosph ere

CH41950

Land

Wetla ndsBoreal and Trop.

Oceans

Surface100 m

Deep> 100 m

Hydrates1.0E7

Lithosp here

Global Me thane Cycle, Preindu strial Storages 1012 gCH4; Flows 1012 g CH4 y-1

Ter mites

Ca�le +Rice Produ c�on

Land Pl ants

G

E

S

MineralsCoal

GasOil

10

85.3

Photochemical Oxida�on420

80

55

44

142

Soils1.0E7

Soil consump� on40

Oceans and La kes75.3

5

27

577Rice477

24

BiomassBurning

30


Geo.Source45

a

Anthroposphere

SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosph ere

CH44800

Land

Wetla ndsBoreal and Trop.

Land fill sOceans

Surface100 m

Dee p> 100 m

Hydrates1.0E7

Lithosphere

Assets

People

Global Me thane Cycl e 19 80s Storages 1012 gCH4; Flows 1012 g CH4 y-1

Ter mites

Ca�le +Rice Produ c�on

Land Pl ants

G

E

S

MineralsCoal

GasOil

10

85.3

Photochemical Oxida�on485

80

55

44

62

SEG Coal Prod.40

Gas Prod.25

142

Soils1.0E7

Soil co nsump�on40

Oceans and La kes75.3

5

27

577Rice477

24

BiomassBurning

22

30


33.2

Erosion1.0

13.3

Geo.Source

45

b

F dustrib

(ttienT

ig. 9. Energy systems language diagrams of the global methane cycle in the Prein. The global methane cycle in the 1980s.

GWP), Public Health Impact (PHI), price of the waste in Europe andhe relative specific emergy with the exception that NOx is judgedo have greater effects on health than CH4. The GWP was released



n IPCC’s 4th Assessment Report. The public health impact consid-red the impacts on plants, buildings and materials, and impactsot quantified but potentially significant (Rabl and Spadaro, 2000).he economic valuation of the impacts considered the valuation of

al Era and in the Industrial Age (1980s). a. The preindustrial global methane cycle.

premature death and cancers, with a 3% discount rate. The ratiosof the specific emergy of the GHG pollutants (Table 12) to that ofCO2 as a base showed that a unit perturbation of the flow of N2O


or NOx in preindustrial times would have been expected to causegreater harm to the global ecosystem than would a similar pertur-bation occurring in the Industrial Age. This difference is primarilydue to the fact that the flows of N2O and NOx increased 1.73 and





Anthroposphere

SolarRadia�on

3.93

EarthDeep He at

4.07


Atmosphe re

H2O13

(527)

Lithosp here

Assets

People

Global Water Cycl e 19 70s Storages 103 km3; Fl ows 103 km3 y-1

Land

Soil Moisture

67(87.4) Ground water

4000(13.33)

S. Lakes104

(0.21)

Polar IceGlaci ers29000(1.81)

F.W.La kes125(2.5)

Rivers1.2

(27.38)

Oceans

Surface300 m

Dee p3000 m

H2O1370000

(37.0)

G

E

S

SEG

Emergy in Bo ld X 1.0E24 se mj/y

40

Rivers385

Rain 485Evapora�on

71

Rain

Evapor a�on111

40Oceansto Lan d

FuelsAnd

Minerals41.1

Numbe rs in paren the sis ar e thr oughputflows es �mated from turnover �mes.

Erosion1.0

m of t

1sfl

gmilg

TE

Fig. 10. Energy systems language diagra

.1 times, respectively, from PI to IA, thus causing their ratios to thepecific emergy of CO2 to decrease implying that a unit change inux would be less stressful under conditions prevalent in the IA.

Table 13 shows the calculation of the potential impacts on thelobal ecosystem (see Section 3) that may result from changes in the



ass fluxes of the BAE + 2 that have been caused by the industrial-zation of the world since 1850. Only the chemical species with theargest impacts are shown and of these changes in S flux have thereatest potential impact and changes in N2O the second greatest.

able 10mergy evaluation of global water flows during the 1970s (Reeburgh, 1997) and compari

Item Storage 1000 km3 Turnover time y

Atmosphere 13 0.02466

Rain on the seaRain on land

Ocean water 1,370,000 37,000

Evaporation

Water on landPolar ice, glaciers 29,000 16,000

Freshwater lakes 125 50

Saline lakes 104 500

Rivers 1.2 0.04

Soil moisture 67 0.77

Groundwater 4000 300

Evaporation

Runoff

Selected numbers from Buenfil (2001)a

Evaporation, land

Rain on land

Runoff

Polar ice, glaciers 29,000 16,000

Selected numbers from Campbell (2003a)Evaporation, land

Rain on landRunoff

a Buenfil (2001) used 4.94 J/g for the Gibbs free energy of water. His numbers have bee

he global water cycle during the 1970s.

The potential impact of the change in S flux on the global ecosystemis an order of magnitude greater than the potential impact of CO2.

5. Discussion


It is fair to ask whether we met our burden of proof that theglobal cycles of the BAE + 2 will be represented within a speci-fied limit of accuracy with respect to a detailed model of the samecycle. Reeburgh (1997) model of the global water cycle falls within

son with values from Buenfil (2001) and Campbell (2003a).

Flow 1000 km3/y Sp. emergy (semj/g) Transformity (semj/J)

527 1.76E+04 3.71E+03385 2.41E+04 5.07E+03111 8.34E+04 1.76E+04

37.0 2.50E+05 5.28E+04425 2.18E+04 4.60E+03

1.81 5.11E+06 1.08E+062.5 3.70E+06 7.81E+050.21 4.45E+07 9.39E+06

27.4 3.38E+05 7.14E+0487.3 1.06E+05 2.24E+0413.3 6.95E+05 1.47E+0571 1.30E+05 2.75E+0440 2.32E+05 4.88E+04

65 1.42E+05 2.88E+04105 8.82E+04 1.79E+04

33 2.86E+05 5.79E+045.21E+06 1.05E+06

70 1.32E+05 2.81E+04108 8.57E+04 1.81E+04

39.2 2.36E+04 5.01E+04

n converted to the 9.26E+24 semj/y baseline.





Table 11The specific emergies of important chemical species of the biologically active elements estimated for preindustrial times (PI) and in the Industrial Age (IA) in this study arecompared with estimates of the same chemical species from prior studies.

Chemical species Units PI IA Watanabe andOrtega (2011)

Campbell andOhrt (2009)

Tonon and Mirandola(2003)

Odum(1996)

Ratio Sp. Em.(IA/PI)

H2O semj/g H2O No data 1.76E+04 NAO2 semj/g O2 9.43E+05 4.97E+06 9.26E+06 5.27CO2 semj/g CO2 4.78E+06 2.35E+07 4.92C semj/g C 1.24E+07 6.23E+07 5.02CO2 semj/g C 1.75E+07 8.62E+07 7.43E+07 4.92SiO2 semj/g SiO2 2.07E+08 1.09E+09 5.28N semj/g N 3.58E+08 1.65E+09 4.61NH3, NH4 semj/g NH3 7.45E+08 3.45E+09 4.87E+10 4.64NOx semj/g NO2 1.58E+09 6.79E+09 1.03E+09 4.30P semj/g P 3.91E+09 1.84E+10 1.78E+10 4.71CH4 semj/g CH4 4.33E+09 2.14E+10 4.94CH4 semj/g C 5.78E+09 2.85E+10 9.38E+09 4.93S semj/g S 1.22E+10 3.76E+10 1.58E+11 3.09N2O semj/g N2O 9.72E+10 2.66E+11 6.62E+10 2.74

Table 12Relative global warming potential, estimated public health impact and the cost per kg in Europe of several pollutants compared to the ratio of the specific emergies of theseGHG pollutants to the specific emergy of CO2, which is used as an indicator of their total capacity to harm the global ecosystem based on their relative emergy values.

GHGs GWP* PHI, Euro/kg** Sp. Em. GHG/Sp. Em. CO2, PI Sp. Em. GHG/Sp. Em. CO2, IA

CO2 1 0.029 (1) 1 1CH4 25 0.58 (20) 906 911N2O 298 – 20335 11319NO – 16.0 (551.7) 331 289

onacGddfmtwtdo

iaOgatttff

TEu

x

* Global warming potential, Solomon et al. (2007).** Public Health Impact, Rabl and Spadaro (2000).

ur data quality objective (±10% of the mean) for the determi-ation of global flows when compared to Buenfil’s more detailednalysis and Campbell (2003a) analysis of five global hydrologi-al budgets at an intermediate level of detail. A comparison of thealloway et al. (2004) data for preindustrial N2 flows with theetailed model of Campbell (2003b) met our criteria with only a 4%ifference between the estimates. However, there was a 32% dif-erence between the estimates of Reeburgh (1997) and the detailed

odel of N2 flows in the 1970s. This difference is primarily due tohe fact that Reeburgh (1997) did not include the internal N2 flowsithin compartments and the detailed model (Campbell, 2003b)

ook this into account. The N model of Reeburgh (1997) has feweretails on the intra-compartmental flows than his models of thether BAE + 2.

Another check on our results is to compare them with past stud-es that calculated the specific emergy values of the same elementsnd compounds. The closest past study to ours is Watanabe andrtega (2011) and, in general, their specific emergy estimates arereater than ours after conversion to the 9.26E+24 semj/y renew-ble baseline (e.g., CO2 4×, NH3 65×, CH4 1.62×) indicating thathey are counting less mass flow than we do. For example, for CH4



hey only counted emissions without considering uptake leadingo a lower estimate of total flow. Watanabe and Ortega’s estimateor the specific emergy of N2O is less than the value that we foundor the same chemical species and this may be due to the fact they

able 13xpected impact of the observed changes in the mass flux of the chemical species of biolsing emergy analysis. The renewable emergy base for the earth is 9.26E+24 semj/y.

Chemical species Change in flux E+12 g Sp. emergy (semj/g) Total imp

NH3–NH4 176.7 7.45E+08 1.32E+23

NOx 180 1.58E+09 2.85E+23

NH3–NH4, NOx 4.16E+23

CO2 38,800 4.78E+06 6.80E+23

CH4 152.0 4.33E+09 6.59E+23

N2O 44.1 9.72E+10 4.29E+24

S 540 1.22E+10 6.57E+24

appear to have assessed flows of N2O and N2 together, possiblyleading to a greater estimate of N2O mass flow. Campbell and Ohrt(2009) estimated a value for the specific emergy of S that was 12.95times the one estimated here; however, they used petroleum refin-ing of which S is a by-product to estimate the specific emergy of S.Also, they acknowledged that their estimate was probably a highvalue. In summary, even though it would be good to have moredata, we believe that our numbers are reasonable based on the evi-dence indicating that for the most part we have met our data qualityobjectives and that our results are interpretable within the contextof past estimates of the specific emergy values for the BAE + 2.

5.1. Dynamic equilibrium and anthropogenic perturbation of theglobal cycles of the BAE + 2

It is clear from the results of this study that both the emergybase for the Earth and many of the global flows of the BAE + 2 exam-ined have changed markedly since the 1850s, which is our chosenmarker for the beginning of the Industrial Age. In most cases, a causeand effect relationship can be established between the changed


global flux of an element and some aspect of the increased emergyinputs to the global system, e.g., the increases in global CO2 andSO2 flows are largely attributable to the waste products of fossil fuelcombustion. However, the observed changes in the global fluxes are

ogically active elements and compounds on the global ecosystem as characterized

act semj Total impact % Ren. base Annual impact %/y Time IA–PI

1.42% 0.011% 1253.07% 0.025% 1254.49% 0.036% 1257.34% 0.054% 1357.11% 0.053% 13546.31% 0.370% 12570.96% 0.530% 135


ING Model

E

cal Mo

nb

optihpWottitsotwttfttatAc5ttioWwepr

tia“flootthoetolsiimiflaocsbt



ot directly proportional to the magnitude of the changed emergyase of the earth.

Energy Systems Theory (EST) predicts that the total change inrder and organization of the global system between 1850 and theeriod evaluated in the Industrial Age should be proportional tohe increase in the potential to create that order as indicated in thencreased emergy of the inputs. This proposition assumes that thereas been sufficient time for the necessary processes to create theredicted level of complexity through self-organization processes.hile this may be true when the social and economic organization

f society in the modern world is considered, we will not attempto demonstrate this condition in this paper, which is focused onhe emergy evaluation of the global cycles of the BAE + 2. A moremportant observation to help us understand the significance ofhe changes in the emergy inputs to the world system is that theuites of time constants governing the flows of the BAE + 2 stretchver a broad range from very fast to extremely slow. This situa-ion implies that many of the global flows of the BAE + 2 (i.e., thoseith turnover times of more than 30 years assuming it takes five

urnover times to reach a new steady state) will not have had timeo reach a dynamic equilibrium that is in harmony with the 5-old increase in the emergy driving these flows that characterizeshe Industrial Age compared to the Preindustrial Era. We believehat for the present time it is prudent to perform our analyses andssess the relative organizing power of the BAE + 2 by referring toheir specific emergies and transformities prior to the Industrialge, since this represents the state attained by the global biogeo-hemical system over millions of years. We hypothesize that the-fold increase in the emergy base of the Earth from around 1850o the 1970s and 1980s, at present, can be viewed as a perturba-ion of the long term steady state, which has created imbalancesn some flows, but in the long run may only be a transient signaln the established patterns based on renewable emergy inflows.e also note that the trend toward increasing emergy use by theorld’s socioeconomic systems has continued from the time of our

valuations to the present day and that evaluations like the oneserformed here need to be repeated as global budgets for moreecent times become available.

We consider the question, “Has the global system of the cycles ofhe BAE + 2 attained or is it seeking a new steady state?” Recogniz-ng that some of the global flows of the BAE + 2 in the Industrial Agere much larger than in the Preindustrial Era, the question becomes,Is this additional emergy required for the observed Industrial Ageows of the elements or one of their chemical species?” One piecef evidence that we can use to illuminate this question is the datan the observed changes in the global flows of the elements andheir species. For example, by the mid 1980s, the emergy base ofhe world had increased 5.28 times, but the global flow of oxygenad only increased 0.2%. During the same time, the specific emergyf O2 apparently increased 5.27 times. A large change in the globalmergy inflows caused little environmental impact to the worldhrough driving the global O2 cycle away from its PI balance. On thether hand, anthropogenic impacts on the global S cycle have beenarge, with the global flow of S increasing to 1.71 times its steadytate value in the Preindustrial Era by the 1980s. In this case, thencreased emergy base for the global system has increased S flowsn the global environment. There is a question with regard to how

uch of the new emergy base for the world system is going intoncreasing global flows of the BAE + 2. To this extent the alteredow would be expected to have higher specific emergy based onn increase in its concentration. However, the relative abundancer rarity of S may not have changed that much compared to other



hemical species with which it has co-evolved; and therefore, itspecific emergy or transformity in the Preindustrial Era may be aetter measure of its expected impacts relative to other factors. Ahird example is that the global P flow increased only 1% up to the


1970s. The impact of industrialization on the balance of the globalP cycle is apparently much less than that observed for the S and Ccycles, but larger than that of the O2 cycle; however, the averagechanges in the global cycle neglect large changes that occur locallyor in a part of the system, e.g., P runoff from agriculture.

5.2. Structural similarities and differences in the global cycles ofthe BAE + 2

One advantage of diagramming the global cycles of the BAE + 2 isthat this process facilitates comparison of the cycles and the iden-tification of structural similarities and differences among them.Reviewing these diagrams and the associated figures shows thatone distinguishing factor among the BAE + 2 is the amount ofstored material that appears in the atmosphere. In decreasing order,the preindustrial atmospheric mass storages of the BAE + 2 are N(3.95E+21 g), O2 (1.18E+21 g), H2O (1.3E+19 g), C (6.0E+17 g), CH4(1.95E+15 g), S (4.8E+12 g), P (2.8E+10 g), Si (unknown). The cou-pling of fast biogeochemical cycling with slow geochemical cyclingas observed for N is clearly present through photosynthesis andrespiration for C, P and Si. While this coupling is also present inthe global cycles of S and O, there is a lower flow of the ele-ment in the biogeochemical cycle compared to physical exchangewith the atmosphere, thus making these elements more suscepti-ble to physical controls. However, the S cycle should be modeledin greater detail, including explicit representation of bacteriallymediated flows to confirm this observation. While photosynthesisand respiration are the major processes establishing the couplingbetween fast and slow cycles for N, C, P, O and Si and to a lesserextent for S, N is the only BAE for which alternatives to photo-synthesis and respiration have evolved to link disordered (i.e., NH3,NOx) to ordered forms of the element (i.e., DON, PON) and vice versa.Phosphorus, which is often considered to be the ultimate limitingelement (Tyrell, 1999; Correll, 1999; Vitousek et al., 2010), does nothave a gaseous phase and thus there is no easily and widely avail-able pool of this resource available to alleviate shortages that canlimit production. From this perspective and given that N often hasbeen shown to limit primary production (Vitousek et al., 2010), thedevelopment of N fixation and denitrification as separate links tojoin the ordered and disordered forms of this BAE may be seen asan evolutionary innovation that makes it easier to maximize powerin primary production and by extension in ecological networks byalleviating the second most common bottleneck limiting greaterproductivity, if not the first. The N cycle’s unique property of doublecoupling between its fast and slow global cycles also implies thatit will have the capacity to better adjust to changes that are causedby anthropogenic perturbations compared to the other BAE + 2.

Methane accounts for less than 1% of the global C budget, butit is an important GHG that is currently out of balance. Pathwaysfor global CH4 flows are governed by a diverse suite of land-basedprocesses that are closely coupled with CH4 in the atmosphere. Themajor sink for CH4 is photochemical oxidation in the upper atmo-sphere, which has increased from the Preindustrial Era to the 1980salong with the increase in anthropogenic sources of methane, e.g.,coal and gas production and landfills. The fast biogeochemical andslow geochemical cycles are evident from the evaluated pathwaysin Fig. 9, but they appear in a somewhat different manner, becausethe fast-turnover, biogeochemical pathways are almost exclusivelyland-based and the CH4 flows are not directly dependent on uptakefor primary production and release in respiration.

Cross comparison among the global element cycle models con-structed in this study revealed a common structural pattern of


coupling between fast biogeochemical and slow geochemical mate-rial cycles, which was followed by C, N, P, Si, and O and to alesser extent by S. Methane exhibited a global cycle dominatedby land-based processes that were less dependent on P-R and


ING Model

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1 cal Mo

mece

5e

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8 D.E. Campbell et al. / Ecologi

ore dependent on total ecosystem processes, e.g., bacteria, cattleructation and termites. The water cycle was dominated by physi-al processes of evaporation, rainfall and transport with some of thevaporation being contributed by the transpiration of land plants.

.3. Relationship between mass throughput and the specificmergy of the chemical species

The storage size divided by the turnover time determines thehroughput of the storage. The greater the throughput of the stor-ge the smaller the specific emergy of a unit of mass flow of thehemical species and the smaller is the expected impact on thelobal cycle of the element per unit mass due to an imbalance inhat chemical species. Using C as an example and assuming prein-ustrial global cycles are approximately in balance, DOC has the

argest specific emergy, followed by POC, DIC and CO2. The specificmergy of CO2 is just 0.02 and 0.03 times that of DOC and POC, andnly 0.36 times that of DIC, which shows that CO2 is not expectedo be the C species to which the global ecosystem is most sensitiveer unit of change in mass flow.

The order of the specific emergy values in Table 11 can be vieweds an indicator of the efficiencies of production for the chemicalpecies and flows of the BAE in the global biogeochemical sys-em. The lowest specific emergy indicates the mass flow that iseing most efficiently created by the global ecosystem. Perhaps, it

s no surprise that atmospheric water appears as the base materialupporting the planetary ecosystem. The second most efficientlyenerated mass flux is O2, and the third is CO2, the fourth is SiO2,ollowed by NH3–NH4, NOx and P in that order. The specific emergyalues of these BAE range over five orders of magnitude and estab-ish the range of specific emergy that is expected to be compatible

ith the usual P-R processes of the global ecosystem. The remaininghree materials CH4, S and N2O have specific emergy values 906,552, and 20335 times that of CO2, respectively, indicating thathese materials will be potent wastes if created in excess of thelobal ecosystem’s ability to process them.

.4. Changes in the flows of the “BAE + 2” and the predicted effectsn the global ecosystem

We can first judge the effects of a disturbance in the mass fluxf a chemical species of an element by examining the magnitude ofts changes relative to other chemical species. For example, by the980s, industrialization had caused a 7% increase in the global CO2ow, and a 1% increase in the DIC flow, but no measurable change

n the POC and DOC flows. By the 1980s, the mass flow of an aver-ge gram of C in the global C cycle had increased 5%. Thus, the totalmpact on the global ecosystem caused by perturbation of the CO2ycle over the time period from 1850 to 1985 was 6.80E+23 semj;hereas, that of the next greatest impact, the change in DIC massow in the world oceans, was almost an order of magnitude less or.80E+22 semj. Judging the magnitude of the CO2 effect in relationo the renewable emergy inflows to the Earth we find that it mayave caused damages equal to 7.34% of the total annual inflow over

period of 135 years or about 0.054% per year (Table 13). If themergy impacts of increased CO2 concentration in the atmospherere all negative (and there may be some positive effects from CO2ertilization etc.) we may expect a 1:1 negative impact on globalcosystem functioning from atmospheric increases in CO2. Thisrediction assumes that a threshold of change will not be crossed byhe gradual increase of CO2 in atmosphere. The relative impacts ofll the major mass flow perturbations examined in this study when



xpressed on an emergy basis show that perturbations of the S flowave the greatest potential impact on the global ecosystem. Usinghe emergy measure of annual impact (Table 13), S is expected toave an order of magnitude more impact than either CO2 or CH4,


which are approximately equal in their predicted impacts based onthe annual perturbations of their mass flows. Nitrous oxide is pro-jected to have the second greatest impact on the global ecosystemor about 70% of that expected for perturbations of the S flow andthe combined effects of N enrichment are predicted to have about2/3 of the impact caused by CO2.

5.5. Application of the results to manage change produced by thewastes of global society

If we assume that the preindustrial global cycles of the BAE + 2were in balance, by the 1980s, the global cycle balances of the ele-ments N, C, O, S, P and Si, had moved 2.5%, 5%, 0.2%, 71%, 1%, 0%(or unknown) away from the dynamic equilibrium that we assumeexisted circa 1850. Based on the perturbation of mass flux overtime, S is the element, whose global cycle should be managed mostcarefully, followed by C and N. Detailed analysis of the flows ofthe various chemical species showed that the flow of N2O and CO2increased 73% and 7%, respectively, which indicates a severe imbal-ance in the global cycle of N2O and a moderate imbalance in theglobal CO2 cycle. The relationship between their respective specificemergy values indicates that the overall environmental impact ofthe N2O imbalance on the global ecosystem may be more than 10times greater than that of the CO2 imbalance. The GWP of CO2, CH4,and N2O (Solomon et al., 2007) ranks these three chemical speciesin the same order of harmfulness as that indicated by their rela-tive specific emergy values. In contrast, the Public Health Impact(PHI) and the price of the waste in Euros places NOx ahead of CH4(Rabl and Spadaro, 2000), which is the reverse of the order indicatedby their relative specific emergy values. This discrepancy betweenthese values indicates caution in assessing the relative effects ofCH4, because some of its PHI may have been overlooked, or CH4 maybe causing environmental effects that are not captured in the PHImarket mechanism. We have seen from the impact analysis givenabove that the greatest emergy change due to mass flow changessince the Preindustrial Era has been seen in the global cycles of theelement S and a chemical species of N, N2O, and that both havepotential environmental impacts over 10 times that of CO2. Fur-thermore, the specific emergy of N2O and S are over 20,335 and2552 times that of CO2. The global flow of CH4 has increased 7%with industrialization, the same as CO2, and its specific emergy(5.78E+09 semj/g C) is 330 times that of CO2 (1.75E+07 semj/g C),which shows that per unit mass of C the potential environmentalimpact of CH4 is much larger than that of CO2. Based on these obser-vations we recommend that more research should be focused onthe further analysis, documentation and verification of the envi-ronmental impacts of N2O, S and CH4 as well as CO2. Given theuncertainty about the impact of the changes in the fluxes of thesechemical species and their large potential impacts as indicated byemergy analysis, it would be logical for managers to take a pre-cautionary approach by putting initiatives in place to reduce theanthropogenically derived mass fluxes of these chemicals.

6. Conclusion

• We determined the specific emergies of six BAE (C, N, S, P, O, andSi) and two compounds (CH4 and H2O) through performing anemergy evaluation of their global biogeochemical cycles.

• We used the values obtained to estimate the relative far-fieldeffects of GHGs (CO2, CH4, and N2O) and other chemical wasteson the global ecosystem.

• We compared our emergy evaluation results to other means


of ranking GHGs and other wastes and developed specific rec-ommendations that more research and management attentionshould be focused on N2O, S and CH4, while continuing presentefforts to better understand and manage CO2 and reactive N.


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In the future emdollar values of the BAE + 2 based on the ratioof the emergy flows supporting the global system to the WorldGross Domestic Product should be used to establish fair marketsfor pollutant trading.

cknowledgments

The research described in this article resulted from a collab-ration between South China Botanical Garden of the Chinesecademy of Sciences, Guangzhou, China (supported, in part, byroject Science Foundation of China (31070483, 31170428)), theational Institute of Advanced Industrial Science and Technology

AIST), Tsukuba, Japan and the United States Environmental Protec-ion Agency (USEPA), Office of Research and Development (ORD),ational Health and Environmental Effects Research Laboratory

NHEERL), Atlantic Ecology Division (AED). We thank John Kiddon,risten Hychka, Jim Latimer, Joe Livolsi, Tim Gleason, Wayne Munnsnd two external reviewers for helpful comments on the paper.lthough the research described in this article has been funded,

n part, by the USEPA, it has not been subjected to Agency leveleview; and therefore, it does not necessarily reflect the views ofhe Agency.

ppendix A. Supplementary data

Supplementary data associated with this article can be found,n the online version, at http://dx.doi.org/10.1016/j.ecolmodel.013.01.013.

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