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TheGlobal CarbonCycleand ClimateChange ScalingEcologicalEnergeticsfrom OrganismtoBiosphere
DavidE.Reichle AssociateDirector,retired OakRidgeNationalLaboratory
Elsevier
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Listoffigures Figure3.1 EnergyexchangeoftheEarthandatmosphereforthenorthernhemisphere (100units ¼ 0.485calcm 2 min 1)baseduponasolarconstantvalueof 1.94calcm 2 min 1 17
Figure3.2 Globalmapofglobalhorizontalradiationontheearth’ssurface,kWm 2 19
Figure3.3 Radiationexchangeforaleaf. 19
Figure3.4 Theboundarylayerbetweenaleafanditsenvironment. 25
Figure3.5 TheoakforestofVirelles-Blaimontenergybalancefrom25Mayto24 October,1967(calcm 2). So,extraatmospheresolarradiationona horizontalsurface(shortwaves); aSo,extraatmosphericsolarradiation reflectedbyEarth-atmospheresystem; Soabs,solarradiationabsorbedby atmosphere; S,directsolarradiationonahorizontalsurface; U, extraatmosphericupwardradiation(longwaves); D,diffusescattered radiationonahorizontalsurface(shortwaves); G,globalradiationona horizontalsurface(S þ D)(shortwaves); Te,terrestrialradiation(long waves); A,atmosphericradiation(longwaves); aS,reflectedsolar radiation; aD,reflecteddiffuseradiation, aG,reflectedglobalradiation; aNA,reflectedatmosphericradiation; apG,globalradiationutilizedinnet photosynthesis; Q1,short-waveradiationbalance(G - aG); Q2,long-wave radiationbalance(A - Te); Q,short-andlong-waveradiationbalance (G - aG þ A - aNA - Te); QG,sensibleheatfluxinsoil; QV,sensibleheat fluxinvegetation; K,sensibleheatturbulentflux; V,latentheatin evapotranspiration; QR,latentheatinwatercondensation; Qh,advective sensibleheat; Qprec,sensibleheatfluxinprecipitationwater.Parametersof thestand(perha):biomass,156ton;netprimaryproduction(ground),14.6 ton.Exchangeaerialsurfaces(haha 1):foliage(2faces)oftrees,14;bark oftrees,2;herblayer,2;litter,1.5;totalexchangesurfaces(exceptlitter, 18haha 1).Figuresinbracketsareestimatedvalues(metricton ¼ 106 g).
Figure3.6 Energyexchangeforalizardinitsnaturaldesertenvironment,showingthe energyflowstothedesertsurfaceandtothelizard.
Figure3.7 Core-shell(two-layer)modelforalizardandaschematicrepresentationof thethermalenergyflowswithitsenvironment(Porteretal.,1973).
Figure3.8 Modelpredictedseasonalbehaviorpatternsforthedesertiguana, Diposaurusdorsalis, comparedtobehavioralobservationsshownas solidbars.
Figure4.1 Electromagneticwavelengthdistributionofradiantenergy.
Figure4.2 Schematicofachloroplastfromaplantcell.
Figure4.3 PhotosystemII,thephotolysisofH2O,andPhotosystemI,producerof ATPandNADPH,bothoccurringinthethylakoidmembraneofthe chloroplast.
Figure4.4 TheCalvincycle.Atomsare:black-carbon,white-hydrogen, red-oxygen,pink-phosphorus.
Figure4.5 ADP-ATPcyclefueledbytheglycolysisofaglucosesubstrate.
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Figure5.1 Relationshipbetweenenthalpy(H),freeenergy(G),andentropy(S). 56
Figure5.2 Summaryofanaerobicrespiration:themetabolicpathwayofglycolysis. 60
Figure5.3 ThecitricacidorKreb’scycle. 61
Figure5.4 Radioactiveeliminationcurvefortwocryptozoanspecies(Parcoblatta sp , thewoodroach,and Sphaeroderusstenostomus,asnail-feedingcarabid groundbeetle)fedwith 134Csisotope-taggedfood. 70
Figure5.5 Idealizedrelationshipbetweenthemetabolicrateofamouseand environmentaltemperature. BMR,basalmetabolicrate; MR,maximal rate; Tlc,lowercriticaltemperature; Tuc,uppercriticaltemperature; Tb, bodytemperature. 75
Figure5.6 Energyflowinanorganismshowingthecategoriesofenergyallocation andloss. 76
Figure6.1 Chemicalreactionrateplottedagainsttemperature, C,change. 81
Figure6.2 Comparisonofrespirationandphotosynthesiswithtemperature. 82
Figure6.3 Responseofectothermsandendothermstoincreasingtemperature. 83
Figure6.4 Thephenology,leafexpansionandsenescence,andbiomassgrowth componentsofasoybeansimulationmodelinteractdynamicallyand demonstratehoweachareinfluencedbyweathervariables. TDM,Total abovegrounddrymatter, RDM,Belowgrounddrymatter, LDM,Leafdry matter, STDM,Stemdrymatter, SDM,Seeddrymatter, CG,Cropgrowth, SG,SeedGrowth, MG,Relativematuritygroup, StemTerm,Stem terminationtype(IndeterminatevsSemi-determinate), RH,Relative humidity, ET,Referenceevapotranspiration, Irrig.,Irrigation. 90
Figure6.5 Floweringphenophasesinatemperatedeciduousforest. 91
Figure6.6 Phenologicaldegree-daysummationpredictingfloweringfor133species ofvascularplantsinanoak-hickoryforestatOakRidge,Tennessee. 92
Figure7.1 Schemeofmatterand/orenergyflowforafoodchainortrophiclevel.MR, totalmaterialremovedbytheorganismorpopulation;NU,material removed,butnotconsumed;C,consumption;FU,rejecta;F,egesta;U, excreta;A,assimilation;D,digestedenergy/material;P,production;Pg, productionduetobodygrowth;Pr,productionduetoreproduction;R, respiration; DB,changesinmassoftheindividualorpopulation;E, elimination. NomenclatureafterPetrusewiczandMacfadyen,1970. 98
Figure7.2 Thetimedelaysbetweenpeaksofradioactivityconcentrationsintrophic levelsreflectthetemporaldelayinthefluxofenergyalongfoodchains. 99
Figure7.3 Fluctuationofbiomassandnumbersofahypotheticalpopulationintime. Assumptionsare:alifespanof3years,onelitterperyear,maturationin 1year,completionofgrowthofyoungin4months,andastable populationandreproductiveratefromyeartoyear.Theinsertshows partitioningofbiomassfornetproductionperyear.Thenetproduction exceedsthebiomasspeakbecauseoftheproductionofanimalsdyingprior tothetimeofbiomasspeak.BO,biomassofcurrentgeneration;B1,2 n, cumulativebiomassfromearliergenerations;EO,eliminationandMR, materialremovedbypredation.
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Figure7.4
Foodwebshowingtheinteractionsbetweenorganismsacrosstrophic levelsintheLakeOntarioecosystem.Primaryproducersareoutlinedin green,primaryconsumersinorange,secondaryconsumersinblue,and tertiary(apex)consumersinpurple.Arrowspointfromanorganismthatis consumedtotheorganismthatconsumesit.
Figure7.5 Astylizedtrophiclevelpyramidwiththeareaineachlevelrepresenting biomassorchemicalenergycontent.
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Figure7.6 Ecologicalpyramidscomparingbiomassandenergyfortrophiclevels fromdifferentaquaticecosystems.Notation:C1,primaryconsumer;C2, secondaryconsumer;C3,tertiaryconsumer;P,Producer;S,saprotroph. 109
Figure7.7 Heterotrophbiomassasafunctionofprimaryproductionperunit plantbiomass.Thesixpointsrepresentecosystemtypes:Cs,conespring; Df,deciduousforest;Po0,pond;Sm,saltmarsh;Tu,tundra;Tf,tropical forest. 114
Figure8.1 Oxygenproductionduringthelightbottle:darkbottleexperiment. 125
Figure8.2 Adiagrammaticrepresentationofthepathwaysofenergyandcarbonflux inafreshwaterecosystem:SilverSprings,Florida.Carbonvaluesgivenin Table8.1.
Figure8.3 Conceptualrepresentationsofstreamspiralinganduptakelength affectingcarbonmetabolisminflowingwaters.
Figure8.4 Thebiogeochemicalcycleofcarbonintheoceanecosystem.
Figure8.5 ThecarboncycleinamesicdeciduousforestinTennessee.Trees,leftto right,representunderstory,dominant Liriodendrontulipifera,andallother overstorytrees.Decomposersareseparatedbysurfacelitterandsoilzones. Heterotrophsareinvertebratesonlyforbothherbivoresandcarnivores; valuesdonotincludevertebrates.AllvaluesareingCm 2 forbiomass (boxes,upperleftstandingcrop;lowerright,annualincrement)andingC m 2 yr 1 forfluxes(arrows).
Figure8.6 Approximateturnovertimesinyearsrepresentativeforcarbonin majorworldecosystemtypes:vegetationingreenandsoils/sedimentsin brown,approximateaveragetimesinyearsderivedfromthesources below.
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Figure9.1 Theglobaldistributionofbiomes,or“ecofloristiczones”mappedbythe UnitedNationsFoodandAgriculturalOrganization.Source:Rueschand Gibbs,2008. 159
Figure9.2 Ecofloristiczones(biomes)asdeterminedbymeanannualtemperature andannualprecipitation. 160
Figure9.3 IPCCTier-1GlobalBiomassCarbonMap(aboveandbelow-ground)for theYear2000inmetrictonscarbonperhectare(100gm 2). 174
Figure9.4 Patternsofoceancirculation.
Figure10.1 Thenaturalglobalcycleofcarbonshowingthemajorreservoirs(pools) andpathways(fluxes)ofcarbonflowinthebiosphere,asillustratedin thestructureofanearly,multidimensionalboxmodel.
Figure10.2 InterannualfluctuationsinatmosphericCO2concentrationsreveal the“breathing”ofthebiosphereacrosstheseasonsoftheyear.
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Figure10.3 Contoursofsoilcarbon(kgCm 2)plottedonaHoldridge(1967) life-zonechart. 201
Figure10.4 Acompartmentmodeloftheglobalcarboncyclewithcouplingstoother elements.Themodelconstructincorporatesrapidecologicalprocesses(A) withslowgeologicprocesses(B)averagedoverthelatterportionofpostCambriantime.(A)LandscapesisearlyHolocene(recent)timehad approximatelyequalquantitiesofrapidlycycling(mostlyphotosynthetic) tissuefromwoodyandnonwoodypartsofplants.Thelatterprobablywere ofnegligiblemassbeforethelateSilurianPeriodabout400millionyears ago.EstimatedvaluesanduncertaintiesaregiveninTable10.7.(B) Summaryofoceanicandlithosphericcycles.Note:1molcarbon dioxide ¼ 12gcarbon. 202
Figure11.1 GlobalatmosphericCO2 versusMaunaLoaCO2.MeasurementsatMauna Loareflecttheglobalaveragederivedfrommanyworldwidemonitoring stations. 212
Figure11.2 AtmosphericCO2 levels(partspermillion,ppm)overthepast10,000 years.BluelinefromTaylorDome,Antarcticaicecores.Greenline fromLawDome,Antarcticaicecores.Redlinefromdirectatmospheric measurementsatMaunaLoa,Hawaii. 213
Figure11.3 GlobalsatellitemeasurementsofatmosphericCO2 concentrationsinJuly 2008fromtheNASAAtmosphericInfraredSounder(AIRS)ontheAqua satellite. 214
Figure11.4 TheGreenhouseEffect. 215
Figure11.5 ComparisonofglobaltemperatureandatmosphericCO2 concentrations from1880to2010,withtemperaturedeviationsfromhistoricnorms. 216
Figure11.6 Anestimatein1990ofworldwidegreenhousegasemissions.Valuesare 1012 gCO2-eq.
Figure11.7 Fossilfuelconsumptionbytheworld.
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Figure11.8 Breakdownofannualworldwidegreenhousegasemissionsbyindustrial sectorin2010.Valuesare1012 gCO2-eq. 223
Figure11.9 Theworld’scarboncycleatthebeginningofthe21stcenturyasinfluenced byhumanactivities,showinghowcarbonatomsflowbetweenvarious reservoirsintheEarthsystem.ReservoirsizesareinGt(1015 g)C;fluxes areinGtCyr 1.Therednumbersandarrowsshowtheadditionalfluxes andreservoirchangescausedbyhumans,suchastheburningoffossil fuelsandlandusechanges,averagedover2000 2009.
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Figure11.10 TheairborneCO2 fractionshowingglobalcarbondioxideemissions (asgigatonsofcarbonwithoutoxygenmolecularweightadded)from1960 through2012,andtheamountofemittedCO2 thathasremainedinthe atmosphere.
Figure11.11 Thebiologicalpumpofcarbonintheocean.
Figure11.12 FutureatmosphericCO2 levelsasprojectedforthefourRCPemission scenarios(IPCCSRESReport,2007).Allforcingagents’atmospheric CO2-equivalentconcentrations(inparts-per-million-by-volume(ppmv)) accordingtofourRCPs.
Figure11.13 Radiative-forcingcomponentsusedbytheIPCCin2007inthecalculation ofclimateoutcomesfromfourdifferentrepresentativeconcentration pathways(RCPs)dependentuponpossiblefuturelevelsofgreenhousegas emissions.
Figure11.14 The10hottestyearsglobally.
Figure11.15 Despitetechnologicalimprovementsthatincreasecornyields,extreme weathereventshavecausedsignificantyieldreductionsinsomeyears.
Figure12.1 Schematicdiagramillustratingcurrentand/orprojectedimpactsofclimate changesonmajorcomponentsofmarineandcoastalecosystems.
Figure12.2 Pastandfutureoceanheatcontentchanges(OHC).Annualobservational OHCchangesareconsistentwitheachotherandconsistentwiththe ensemblemeansoftheCMIP5models(Tayloretal.,2012)forhistorical simulationspre-2005andprojectionsfrom2005to2017,giving confidenceinfutureprojectionsto2100(RCP2.6andRCP8.5)(seethe supplementarymaterials).ThemeanprojectedOHCchangesandtheir 90%confidenceintervalsbetween2081and2100areshowninbarsatthe right.TheinsetdepictsthedetailedOHCchangesafterJanuary1990, usingthemonthlyOHCchangesupdatedtoSeptember2018(Chengetal., 2017),alongwiththeotherannualobservedvaluessuperposed.
Figure12.3 Worldwidegreenhousegasemissionin2005.
Figure12.4 Carbonflowsintheenergysystemandsourcesofemissionsinthe UnitedStatesin1995inmillionsofmetrictons(1012 gC).
Figure12.5 Carbonintensityofelectricity:historyandforwardtrendsnecessary toreachazero-carbonelectricitygridbymid-century.
Figure12.6 Theworld’seconomiesvaryconsiderablyinhowefficientlytheir GDPsutilizecarbon-basedfuels.
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Listoftables Table2.1 Unitsofmeasureforenergyinitsvariousformsandtransformations. 6
Table3.1 Transmission(langleysmin 1)ofdirectsolarradiationthroughacanopyof redpineplantation. 20
Table3.2 Totalemissivity, ε,allwavelengthsandshort-waveabsorptivityofcommon bodiesoccurringinthenaturalenvironment(HandbookofChemistryand Physics). 23
Table3.3 Typicalalbedovaluesforenvironmentalsurfacesonearth. 24
Table3.4 Typicalthermalconductivitiesofenvironmentalmedia,biological constituents,andotherreferencematerialsatordinarytemperatures.
Table3.5 Convectioncoefficients(calcm 2 min 1oC)forfreeconvectioninlaminar flow. DTisthetemperaturedifferencein oCbetweenthesurfaceoftheobject andthesurroundingair.Listhedimensionoftheplateinthedirectionof flow.
Table3.6 Ratesofheattransfer(cal cm 2min 1)forforcedconvectionacrossaflat plateasamodelforaplantleafintheenvironment.Values (cal cm 2min 1)areafunctionofthetemperaturedifferentialbetween surfaceandair,dimensionofthesurface,andwindspeed.
Table4.1 Theenergyvalueofdifferentwavelengthsofsolarradiation.
Table4.2 Efficienciesofphotosyntheticradiantenergyconversionintobiomassby plants.
Table5.1 Summaryofaerobicrespiration:TheefficiencyofATPproductionby glycolysis.
Table5.2 Thermalequivalents(kcalL 1)fordifferentcompounds.
Table5.3 HeatsofcombustiontoH2O(L)andCO2 (g)at25 Candconstantpressure.
Table5.4 Energyvaluesforplantpartsandanimaltaxa.
Table5.5 Foodassimilationfordifferentfoodsandbydifferenttrophiclevel consumersreportedinthescientificliterature.
Table5.6 Valuesforthebodyweightexponentialfunction,b,fordifferentanimal types.
Table5.7 Therelationshipbetweenfoodenergyandheatproduction,thecalorigenic effectorspecificdynamicaction(SDA),inadogfed100kcalday-1 of leanmeat(protein)[columns1-4],comparedwiththefoodenergyandheat productionequivalentstobeobtainedfromapurefat[columns5-6]or carbohydrate[columns7-8]diet.
Table5.8 Comparisonofdietaryenergyutilizationinthedomesticpigandcow(values are%foodenergyingested).
Table5.9 Rateofproductionandproductionefficiencyinrelationtodietaryenergy intakeinfarmedanimals.
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Table6.1 Thedevelopmenttimeofseaurchineggsasafunctionoftemperature demonstrateshowenergy(heat)affectsbiologicalprocesses,andhow acclimationtowarmersummertemperatures,orcoolerwintertemperatures, affectsdevelopment.NaturalpopulationsofParacentrotuslividusrange between13 C 28 C. 85
Table6.2 Someexamplesofadaptivestrategiesofplantsandanimalstotheirenergy environment. 86
Table6.3 Someaspectsofanenergybudgetforhummingbirds.
Table7.1 Comparisonofproductivitybetweenmouse,deer,andelephant.
Table7.2 Ecologicalenergeticefficiencies.
Table7.3 Valuesreportedforecologicalenergeticefficienciesfordifferenttrophic levels.
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Table7.4 Calculatedingestion,production,respiration,andegestionbyheterotrophsin agrasslandecosysteminkcalm 2 yr 1 per100kcalm 1 yr 1 netannual primaryproduction. 113
Table7.5 Ecologicalenergeticefficienciesforthreedifferentecosystems (calcm 2 yr 1).
Table8.1 Comparisonofthecarbonbudgetsoffiveaquaticecosystems:SpartinaSalt Marsh,GA(Teal,1962);SilverSprings,FL(Odum,1957);oligotrophic LakeEckarfjarden,Sweden(AnderssonandKumblad,2006);Lake Washington,WA(Eggersetal.,1978);eutrophicLakeLawrence,MI (WetzelandRich,1973).Unitsare:fluxesinkgCm 2 yr 1,standingcropin kgCm 1).
Table8.2 MeanvaluesandrangesforGPP,RE,andNEPforaquaticecosystemsValues aregO2 m 2 day 1).
Table8.3 Comparisonofthecarbonbudgetsofeightterrestrialecosystems:Spruce Forest,Sweden(Karlbergetal.,2007);MesicTulipPoplarforest,TN (Reichleetal.,1973);Oak-Pineforest,NY(WoodwellandBotkin,1970); TropicalRainForest,Thailand(Tanetal.,2010);ShortgrassPrairie,CO (Andrewsetal.,1974);Tundra(afterReichle,1975);Agricultural ecosystemsvaluesfromL.Ryszkowski(Reichle,1981).Unitsare:fluxesin kgCm 2 yr 1,standingcropinkgCm 2).
Table8.4 Comparativemetabolicparametersforsixdifferentforestecosystems.All valuesabovethedottedlineareinkgCm 2 andkgCm 2 yr 1;values belowthedottedlinearedimensionlessindices.
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Table8.5 Comparisoncarbonfluxesoffiveforestecosystemusingeddycovariance: WB¼WalkerBranch;TN,MMSF ¼ MorganMonroeStateForest,IN; HF¼HarvardForest,MA;UMBS¼UniversityofMichiganBiological Station,MI;WC¼WillowCreek,WI.Unitsare:fluxesinkgCm 2 yr 1 , standingcropinkgCm 2 . 150
Table9.1 Conversionfactorsofunitsofmeasureformassandenergyvalues. 159
Table9.2 Summaryofglobalarea,annualnetprimaryproduction(NPP),plantcarbon content,andsoilcarboncontentinbroadlycategorizedterrestrial ecosystems. 162
Table9.3 Primaryproductionandbiomassestimatesforthebiosphere. 164
Table9.4 Netprimaryproductivityintheocean. 167
Table9.5 Secondaryproduction(NSP)byconsumersindifferentecosystems.Values areforspecificconsumergroups,exceptwhereindicatedby “A” ¼ productivityfortheentireanimaltrophiclevel. 170
Table9.6 Variousestimatesoftotalglobalproductionincarbonandenergyunits. 172
Table9.7 Rankingofthenetprimaryproductivityofthebiomesbaseduponthevalues reportedbythereferencescitedinChapter8andTables9.2and9.3. 173
Table9.8 Biomassofecosystemsofthemainbiomeseachwithdistinctvegetative structure.Metrictonha 1 (¼ 102 gm 2).
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Table10.1 Values,anduncertaintiesofparameters,intheglobalcarboncycle. 189
Table10.2 Unitsofmeasurefortheglobalcarboncycle. 191
Table10.3 Atmosphericcarbondioxidefluxes(GtCyr 1 or1015 gCyr 1).Errors represent standarddeviationofuncertaintyestimatesandnotinterannual variabilitywhichislarger.Theatmosphericincrease(firstline)resultsfrom fluxestoandfromtheatmosphere:positivefluxesareinputstothe atmosphere(emissions);negativefluxesarelossesfromtheatmosphere (sinks);andnumbersinparenthesesareranges.Notethatthetotalsinkof anthropogenicCO2 iswellconstrained.Thus,theocean-to-atmosphereand land-to-atmospherefluxesarenegativelycorrelated:ifoneislargertheother mustbesmallertomatchthetotalsink,andviceversa. 194
Table10.4 Estimatedoceaniccarbonpools. 195
Table10.5 Carboninmajorpoolsofthebiosphere.Contemporaryestimatesusing Whittaker&Likens,1973andIPCC2014inparentheses.Percentagesof totalcarbonpools(columns2and3)arebaseduponReiner’s1973 calculationusingBolin’s1970values.
Table10.6 Carbonbalanceinterrestrialdetritusbybiome(Schlesinger,1979).
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Table10.7 Simplifiedglobalcarboninventoryandbudgetestimatesforrecent,early Holocenetimes.Valueshereare1015 gCyr 1 203
Table11.1 Internetsourcesofdatarelativetotheissueofclimatechange. 211
Table11.2 Methanesourcesandsinks,bothnaturalandanthropogenic(Schlesinger, 1997;afterPratheretal.,1995).Unitsare1012 gCH4 yr 1 219
Table11.3 Warmingincreases( C)projectedbytheradiativeforcingfunctionsresulting fromdifferentassumptionsofGHGemissionscenarios.
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Table11.4 EstimatedglobalNPPbyterrestrialecosystems. 242
Table11.5 Futuresealevelrise(inmeters)projectedfromdifferentradiativeforcing functionscenariosfromassumptionsofdifferentGHGemissions. 248
Table12.1 Historicaltimelineofmilestonesinestablishinginternationalclimatepolicy. 261
Table12.2 CumulativeCO2 emissionslimitsfroma2011emissionsbaselinenecessary tolimitglobalwarmingto <1.5 Cand <2 C,withassociatedprobabilities. 263
Table12.3 Thelifecyclecarbonintensityofelectricitysources:greenhousegas emissionsperkilowatt. 266
Table12.4 Thepotentialofdifferentterrestrialbiomestosequestercarbonthatmightbe sustainedovera25 50yearperiod. 270
Table12.5 Relativeconcentrationpathways(RCPs)withpathwaydescriptionsand integratedassessmentmodelsusedbyIPCCfortheyear2100. 277
Table12.6 Futuresealevelrise(inmeters)projectedfromdifferentradiativeforcing functionscenariosfromassumptionsofdifferentGHGemissions. 279
Table12.7 Projectedannualeconomicdamageestimates(in2015$)intheUnitedStates by2090. 280
Table12.8 Estimatedglobalmacro-economiccostsin2030relativetothebaselinefor least-costtrajectoriestowarddifferent,long-termstabilizationlevels. 281
AuthorBio DavidE.Reichle wastheAssociateLaboratoryDirectoroftheOakRidgeNationalLaboratoryforEnvironmental,Life,andSocial Sciences,andtheformerDirectorofits EnvironmentalSciencesDivision.Hewasalso anadjunctProfessorofEcologyattheUniversityofTennessee.Hehasauthoredover 100scientificarticlesonradionuclidesinthe environmentandthemetabolismofecosystems,editedfourbooksonproductivityand carbonmetabolismofecosystems,andled developmentofseveralseminalgovernment reportsongreenhousegasreductiontechnologiesandcarbonsequestration.Hehasserved onmanyscientificadvisoryboardsfortheDepartmentofEnergy,theNational ScienceFoundation,theEnvironmentalProtectionAgency,theNational AcademyofSciences,andotheracademicinstitutionsandbusinessorganizations.HeisafellowoftheAmericanAssociationfortheAdvancementof ScienceandrecipientoftheScientificAchievementAwardfromtheInternationalUnionofForestResearchOrganizations,aDistinguishedService AwardfromtheU.S.DepartmentofEnergy,andtheMuskingumUniversity DistinguishedAlumniServiceAward.Healsoservedonthenationalboardof governorsoftheNatureConservancyandasChairmanofTNC’sTennessee statechapter.
Foreword Bioenergeticshaslongbeenasubjectofresearchinanimalhusbandryand ecologicalresearch,whereitservedasanorganizingprincipleinearly ecosystemresearch(Odum,1959).Themetabolismofecosystemsand ecologicalenergeticsaresubjectareasthatIalwaysfoundtobefascinating, andonesthatwereresearchedintenselyattheOakRidgeNationalLaboratory (ORNL),inOakRidgeTennessee.IwasrecruitedtoORNLasanewPhD fromNorthwesternUniversityin1964tostudythebehaviorofradionuclides infoodchains uptake,bioaccumulation,andpotentialpathwaysleadingto humanexposure.Mypostdoctoralfellowshipwassponsoredbywhatwasthen theUSAtomicEnergyCommission(nowtheUSDepartmentofEnergy).One ofthelittle-knownfactsinthehistoryofAmericanscienceisthattheAEC wasthefirstsignificantsponsorofmodernecologicalresearchintheUnited States,thisroleonlyseveraldecadeslaterbeingassumedbytheNational ScienceFoundation(Egerton,2017).TheManhattanProject’s1943Clinton Laboratories,managedbytheUniversityofChicago’sMetallurgicalLaboratory,wasthepredecessorofORNL;UnionCarbideCorporationassumedresponsibilitiesin1947.BythetimethatIhadarrived,WWIIwasoverand researchhadshiftedtothepeacefulusesofatomicenergy.Myjobtitlewas “biophysicist”intheRadiationEcologySectionoftheHealthPhysicsDivision;theSectionwaslatertobecometheinternationallyrenownedEcological SciencesDivisionatORNL(Auerbach,1993).Ourresearchteam’sscope quicklygrewfromexaminingthefateandeffectsofradionuclidesinfood chainsleadingtohumanstostudyingthenaturalbiogeochemicalcyclesthat governedthemovementofradionuclidesintheenvironment allofwhich wereultimatelyregulatedbythemetabolismofecosystems.
Fewinthescientificcommunity,muchlessinthegeneralpublic,knew whatecologywaswhentheUSAtomicEnergyCommissionbeganits ecologicalresearchprogramsintheearly1950s(ReichleandAuerbach, 2003).Theseprograms,whichantedatedmajorsupportforecosystemresearch bytheNationalScienceFoundationbyseveraldecades,werethefoundation formodernecosystemresearchintheUnitedStates(Coleman,2010).Since ecologistsatORNLhadbeenresearchingecosystemcarbonmetabolism,we becametheUSR&Dcenterforforestecologyandecosystemmodelingwhen USparticipation(1964 74)beganintheInternationalBiologicalProgram (Smith,1968;NAS,2019).Internationalcollaborationcontinuedformany yearsthereafter,andresultsofresearchonthedeciduousforestbiome
culminatedwithpublicationof DynamicPropertiesofForestEcosystems (Reichle,1981).Thisresearchexperiencewasanimportantreasonwhythe AEC’ssuccessor,theEnergyResearchandDevelopmentAdministration,and latertheUSDepartmentofEnergy(DOE),becamealeadingUSagency studyingtheglobalcarboncycle.
ThemissionofDOEanditsnationallaboratorieswastopromotethesafe developmentofallenergytechnologies.Boththescientificexperiencegained fromstudyingthecarbonmetabolismofecosystems(ReichleandAuerbach, 1972)andthedevelopmentofclimatemodelstofollowglobalfalloutfrom weaponstestingandtheconcernabouta“nuclearwinter”fromnuclear weaponsdeployment,thenationallaboratoriesbecameearlyleadersinclimate changeresearch.Thescientificexperiencegainedinearlyenvironmental studiesofthenuclearindustrycamefullcircleinthe1980stoexaminethe environmentalconsequencesofafossilfuel basedenergyeconomy.
Ecologicalenergeticsisthestudyofthemetabolismofplants,animals, microbes,andecosystems.Knowledgeaboutthefunctioningofecological systemsisnecessaryforourunderstandingofthemetabolismofthebiosphere, essentialinadressinghuman-inducedclimatechange,andquitepossibly criticaltoprotectingourglobalenvironment.Thisbookistheproductofa courseinecologicalenergeticsthatIofferedintheearly1970sinthethen GraduatePrograminEcologyattheUniversityofTennessee.Ihadintended thesyllabustobethebasisforatextbookinbioenergetics,butsomehownever foundthetimetowritethebook.Now45yearslaterinretirement,Ihavethe time,thefieldofecologyhasmatured,andbioenergetics,whileaninteresting chapterinbasicecologytextsofthe1950 70s,hasnowassumednewsocietal relevance.Ecologicalenergeticsisthefoundationforbothunderstandingthe metabolismofthebiosphereandalsothebasisforaddressingthepotential futureenvironmentalimpactsofclimatechange.
Thisbookisajourneyintime,scale,andcomplexity.Itwillbeajourney followingthefluxofsolarenergyfromthesun,andcarbonfromtheatmosphere,throughthelivingsystemsonearth.Itwillbeajourneyinscale from milligramstogigatons,fromsecondstoyears,fromsquarecentimetersto hectares,andfromthecelltothebiosphere.Thisjourneyhasruleswhichwill governourpassage theprinciplesofthermodynamics,biochemistry, physiology,andecology.Letusbegin.
SUGGESTEDREADING Coleman,D.C.,2010.BigEcology:TheEmergenceofEcosystemScience.Univ.Calif.Press, Berkeley-LosAngeles-London,p.236. https://epdf.pub/big-ecology-the-emergence-ofecosystem-science.html
Egerton,F.N.,2017.HistoryofEcologicalSciences,Part59:Niches,Biomes,Ecosystems, andSystems. https://www.researchgate.net/publication/320227603_History_of_Ecological_ Sciences_Part_59_Niches_Biomes_Ecosystems_and_Systems/.
Foreword xxv
Odum,E.P.,1959.FundamentalsofEcology,2ndEd.W.B.SandersCo.,PhiladelphiaandLondon, p.546.
Reichle,D.E.,Auerbach,S.I.,2003.U.S.RadioecologicLResearchProgramsoftheAtomic EnergyCommissioninthe1950s.ORNL/TM-2003/280.OakRidgeNationalLaboratory,Oak Ridge,TN. http://www.osti.gov/bridge/.
Smith,F.E.,1968.Theinternationalbiologicalprogramandthescienceofecology.Proc.Nat’l Acad.Sci.USA60(1),5 11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC539127/
Acknowledgments Mycareerinecologyhasbeenstimulatedbyalargenumberofindividuals:my graduateschoolprofessor,OrlandoParkofNorthwesternUniversity,oneof theauthorsof“TheGreatApes,”Alee,EmersonPark,Park,andSchmidt’s PrinciplesofAnimalEcology(1949), oneofthefirstandperhapsbestecology textsfromthe“ChicagoSchool”ofecology;StanleyAuerbach,founderofthe EcologicalSciencesDivision(ESD)attheOakRidgeNationalLaboratory (ORNL),andmentorsandcolleaguesinESD:DacCrossley,JerryOlson, GeorgeVanDyne,FrankHarris;earlyleadersinecologicalenergetics: HowardOdum,GeneOdum,GeorgeWoodwell,BobWhittaker,DickWiegert, DavidGates,JerryFranklin;EuropeanecologistsJohnPhillipson,Amian Macfadyen,JohnSatchel,KasimierzPetrusewicz,LechRyszkowski,Paul Duvigneaud,andHelmutLiethinfluencedmeprofoundly,bothpersonallyand throughtheirseminalpublications.Thebookhasitsorigininacoursein ecologicalenergeticsthatIofferedintheGraduatePrograminEcologyatthe UniversityofTennessee,decadesofresearchatORNL,andhasbeennurtured throughtheencouragementandpatienceofmywife,Donna.BrendaWyatt providedinvaluabletechnicalrecordsassistance,andIamgratefultoORNL forprovidingaccesstoITlibraryresources.
Anintroductiontoecological energeticsandtheglobal carboncycle 1.1RecommendedReading 3
EnergyisessentialforlifeonEarth.Anorganismwithapositiveenergy balanceisgenerallyasuccessfulorganisminnature.Organismsandecosystemshave,consequently,evolvedashighlyefficientthermodynamicsystems. Bioenergeticsdealswiththeenergyrequirementsandtheprocessingofenergy byorganisms.Thetermismostoftenusedinreferencetoanimals,butalso appliestoplants.Plantshaveevolvedtheuniquephotosyntheticprocess,using sunlighttosplitwatermoleculesandmanufactureorganiccarbonmolecules fromatmosphericCO2, thusconvertingradiantenergyintochemicalenergyto supporttheirmetabolicrequirements.Inanimalsystemsbioenergeticsencompassestheprocurementofthechemicalenergyinfood,thedigestionof food,subsequentmetabolism,andtheeventualenergyexpendituresrequired forlivingandreproducing.Bioenergeticsinvolves,therefore,manyaspectsof theorganism’sphysiology,thermalrelationships,andbehavior,andbecomes verycomplexandcomplicatedtoquantify.Bioenergeticshasbecomeavery sophisticatedtoolinanimalhusbandry,foritdealswiththeefficiencyby whichanimalproteincanbeproducedeconomically.Bythe1960s,bioenergeticsasappliedtofree-livinganimalshadbifurcatedintotwofieldsof study,oneapproachemphasizingbehavioralbiologywheretheanimal’sactivitypatternswerestudiedinrelationtoitsenergybalancewithitsenvironment,andanotherphysiologicalapproachdealingwiththemetabolismofthe free-livingorganism.Inactualityboththeseapproachesarenecessarytounderstandthethermodynamicsoforganismsinnature(Reichleetal.,1975).
Bythe1970sthegrowingfieldofecologybegantoutilizebioenergeticsto understandthefunctioningofentireecosystems.Thus,thestudyofecological, orecosystem,energeticsdeveloped.Ecosystemenergeticsaddressestheenergybalanceoftheentireecosystemandallitstrophiclevels.Itconsistsofthe ecosystem’smetabolism itsprimaryproductivity,trophiclevelexchanges,
turnoveranddecompositionofdetritus,growth,andreproduction.Sincebiologicallyutilizedenergyistheenergystoredincarbonmolecules,ecosystem metabolismnecessarilydealswiththecarbonbalanceoftheentireecosystem (Lindeman,1942;Odum,1957;Smalley,1960;Teal,1962;Macfadyen,1964; Phillipson,1966;WoodwellandBotkin,1970;Reichleetal.,1973).Besides plantphotosynthesisandtrophiclevelenergetics,understandingthecarbon metabolismoftheentireecosystem,aboveandbelowground,includesdeath anddecompositiontocompletetheecosystem’scarbonbalance(netecosystem production)withtheenvironment.Thisacademicallyintriguingsubjectsuddenlytookontremendoussocietalrelevancebeginninginthe1980s,withthe growingconcernoverthecombustionoffossilfuelsandtheresultingCO2 emissionstotheatmosphere,leadingtothegreenhouseeffectandglobal warming.
Whatdidweknowabouttheglobalcycleofcarbon?And,whendidwe knowit(Rich,2018)?Ecosystemcarbonbalancesfordifferenttypesofecosystems,whenusedwiththegeographicdistributionofecosystemtypes,or biomes,formedthebasisforearlyglobalcarbonbalancecalculations(Craig, 1957;RevelleandSuess,1957;Bolin,1970).Asthemodelingofecosystem bioenergeticsadvanced,itbecamepossibletoconstructdynamicglobalcarbon modelsofthebiosphere,whichwerefunctionallybasedandcould,consequently,permitquestionstobeaskedaboutthebiosphere’sresponseto changingatmosphericCO2 levelsorrisingtemperaturesorchanginglanduse coverorfeedbackloopssuchasoxidationofArctictundra,glacialmelting, oceanoutgassing,etc(Trabalka,1985;TrabalkaandReichle,1986).These questionsremainverypertinentandcentraltothedebatetodayontheconsequencesofclimatechange.
ThistextbeginswithanintroductiontoecologicalenergeticsinChapter1. Chapter2definesenergyterms,introducesthephysicallawsofenergy,and discusseshowthebasicprinciplesofthermodynamicsgovernbiologicalas wellasphysicalsystems.Chapter3isaprimeronenergyrelationshipsbetweenorganismsandtheenvironment.Chapter4coversthebiologicalenergy transformationsofphotosynthesisandenergyconversionefficiencies.In Chapter5theenergyprocessingbyanimals,theirmetabolism,andenergy budgetsareexamined.Chapter6examineshowspeciesadaptthermallyto theirenvironments.Chapter7addressestheenergyexchangebetweenplants andanimals,ecologicalenergetics,foodchains,andthetrophiclevelconcept. TheninChapter8,thecomplexitiesofenergyflowinecosystemsarecovered. Subsequently,Chapter9examinestheconceptofecosystemproductivity;and theninChapter10theglobalcarboncycleandthebiospherearereviewed. Chapter11examineshowtheanthropogenicemissionsofCO2 andlanduse changehavealteredthenaturalglobalcarboncycleandhaveinfluenced climatechange.Ultimately,humankindwillhavepolicydecisionstomake aboutfossilenergyusetoavoidthenegativeclimaticconsequencesofhaving changedthebiosphere’scarboncycle(Chapter12). 2 TheGlobalCarbonCycleandClimateChange
Anintroductiontoecologicalenergetics Chapter|1 3
Beforecontinuing,Ineedtomakeseveralbriefcommentsaboutreferences. Muchoftheecologicalenergeticsandproductivitydatafromthedecadesofthe mid-1960stothemid-1980s,particularlyduringtheInternationalBiological Program,arecontainedintheproceedingsofinternationalconferences,which arenownearlyinaccessibletomany.Ihaveidentifiedthesepublicationsand extractedpertinentinformationfromthesesourcessothatitcanremaininthe mainstreamofscientificliterature.Secondly,Ihavesoughtpermissionto reproduceselectgraphsandillustrationscontainedinbenchmarkpublications undercopyrightbypublishersofbooksandscientificjournals,sothattheyare availabletothosewithouttheprivilegesofaccesstothesesourcesthrough institutionallibraryITagreements.Andlastly,whenpossible,Ihavereferenced keydatawhenevertheywerepublishedingovernment-sponsoredsymposiaand reports;andsincetheyareinthepublicdomain,Ihaveprovidedtheirurlsfor convenient,directITaccessbythereader.
1.1RecommendedReading Bolin,B.,Degens,E.T.,Kempe,S.,Ketner,P.(Eds.),1979.TheGlobalCarbonCycle.SCOPE,13. JohnWileyandSons,NewYork,p.491. https://www.researchgate.net/publication/40170880_ The_Global_Carbon_Cycle_SCOPE_Report_13/
Odum,H.T.,1957.TrophicstructureandproductivityofSilverSprings,Florida.Ecol.Monogr.25, 55 112. https://doi.org/10.2307/1948571.
Phillipson,J.,1966.Ecologicalenergetics.St.Martin’sPress,NewYork,p.57. https://www. worldcat.org/title/ecological-energetics/oclc/220312888/.
Reichle,D.E.,O’Neill,R.V.,Harris,W.F.,1975.PrinciplesofEnergyandMaterialExchangein Ecosystems.In:W.H.vanDobbenandR.H.Lowe-McConnell(Ed.),UnifyingConceptsin Ecology.W.JunkPub,TheHague,pp.27 43,302pp. https://link.springer.com/chapter/10. 1007/978-94-010-1954-5_3/
Chapter2 Thephysicalandchemical basesofenergy 2.1Energy,work,andpower
CaloriesandJoules
2.2Thedifferentformsofenergy
Chemicalenergy
Radiantenergy
Heatenergy
2.3TheLawsofThermodynamics
TheFirstLawofThermodynamics
Work
Enthalpy
TheSecondLawofThermodynamics
Entropy
2.4Gaiahypothesis
2.5Carbonandenergy
Theformsofcarbon
Measuresofcarbon
Carbonchemistry
2.6Recommendedreading
Thereisnobetterwaytobeginthestudyofecologicalenergeticsthanby startingwithanunderstandingofthepertinentdefinitionsandterminologyof physicsandphysicalchemistry.Learnthisterminologyearly,become comfortablewiththeunitsofmeasure,knowthebasicconcepts,andbioenergeticswillcomealoteasier.
2.1Energy,work,andpower Energyisthecapacitytodowork.Theunitofmeasureforenergyistheerg, whichistheworkperformedwhenaforceofonedyneactsthroughadistance ofonecentimeter.Theunitofforce,thedyne,yieldstoamassofonegramthe accelerationofonecentimeterpersecond(cms 1).Sinceanergofenergyis suchasmallquantity,alargerunit,thejoule,whichisequalto107 ergs,becomesamoreconvenientunitofmeasure.Aunitofheatusedfrequentlyin
physicalchemistryisthecalorie(¼ 4.184J).Thecalorieistheheatenergy requiredtoraisethetemperatureofonegramofwaterfrom14.5 oCto15.5oC. Thecalorieisdefinedasbeingequalto4.1840absolutejoules.Thecalorieisa relativelysmallunitofmeasure,andformostchemicalandbiologicalcalculationsthekilocalorie(103 calories)isused.Thekilocalorie(kcal)istheunit whichistypicallyusedindiscussingdietaryintakeandisoftenwrittenas Calorie.ACalorieequals103 calories,orakcal.
CaloriesandJoules. Acalorieistheenergyneededtoraisethetemperatureof 1gofwaterthrough1 C(alsoexpressedas4.1868J,theunitofenergyinthe InternationalSystemofUnits).Ajouleistheenergyexpendedwhen1kgis moved1mbyaforceof1Newton(N).Useofjoulesisnowrecommendedby internationalconventionandisthepreferredstandardunittomeasureheat (FAO,2003).Nutritionistsandfoodscientistsconcernedwithlargeamountsof energygenerallyusekiloJoules(kJ ¼ 103 J)ormegaJoules(MJ ¼ 106 J).For manydecades,foodenergyhasbeenexpressedincalories,andstudiesinthe fieldofecologicalenergeticshavetraditionallyusedcaloriesasthemeasurefor energy.Inordertoretainconsistencywithresearchreportedinthescientific literature,valuesusedforenergyinthisbookareincalories.Theconversion factorsforjoulesandcaloriesare:1cal ¼ 4.184Jand1J ¼ 0.239cal.
2.2Thedifferentformsofenergy Energycanexistinvariousforms,butthoseofgreatestimportancetoliving organismsaremechanical,chemical,radiant,andheatenergy(Table2.1). Mechanicalenergyhastwoforms:kineticandpotential.Kineticenergy,or freeenergy,canbedescribedasthe“usefulenergy”whichabodypossessesby
TABLE2.1 Unitsofmeasureforenergyinitsvariousformsand transformations.
EnergyIntensityCapacity
Mechanical(ergs)Force(dynes)Changeindistance(cm)
Kinetic(ergs)Velocity(cms-1) 1/2 Mass(g)
Potential(ergs)Heightxaccereraltion(cms-2)Mass(g)
Chemical(calories)Heatofcombustion(calg 1)Mass(g)
Radiant(calories)Radiationflux(calcm 2)Surfacearea(cm2)
Heat(calories)Differenceintemperature(o C)Heatcapacity(calper oC)
Vol.expansion(ergs)Pressure(dynescm-2)Changeinvolume(cm3)
Electrical(joules)Differenceinpotential(volts)Coulombs(ampsxsec.)
Surface(ergs)Surfacetension(ergscm 1)Changeinarea(cm2)
Thephysicalandchemicalbasesofenergy Chapter|2 7
valueofitsmotion,andismeasuredbytheamountofworkwhichisdonein bringingthatbodytorest.ExampleswouldbeamovingballortheBrownian movementofmolecules.Potentialenergyisstoredenergy,whichisonly potentiallyusefuluntilitsconversionintothekineticorfreeenergywhereit becomesavailabletoaccomplishwork.Energymaybestoredinasystemby virtueofposition,asforexample,astoneabovetheEarth’ssurface,asteel springundercompression,orbyvirtueofchemicalpropertiesduetothe arrangementofatomsandelectronswithinamolecule.Conversionofenergy fromthepotentialformtothekineticforminvolvesmovement,i.e.,motion.
Chemicalenergy. Allorganismsmustworktolive,andtheyrequireasource ofpotentialenergywhichcanbeutilizedinordertoperformthelifeprocesses. Thisenergycanbefoundintheformofthechemicalenergyofbiomassused asfood.Energycanalsobeintheformofthechemicalenergyofinorganic moleculesutilizedasanalternativeenergysourcetoradiantenergybychemotrophs.Assembliesofatomsinmattercanberearrangedintodifferent groups;thus,bythemovementofatomsandthecreationofdifferentatomic bonds,chemicalenergyisliberated.Thecombustion(oxidation)ofcoalina furnaceorfoodbytherespiratoryprocessesinacellreleasesenergywhichcan beusedtoaccomplishwork.Bothoftheseprocessesillustratetheconversion ofchemicaltomechanicalenergy.LifeprocessesonthisEarthhaveevolved aroundcarbonchemistry,andmostchemicalenergysourcesarederivedfrom organiccompounds.However,asweshallseeshortly,therearesomenotable exceptions.
Radiantenergy. Thesun,avastincandescentsphereofgas,releasesenergy bythenucleartransmutationofhydrogentohelium,anditisuponthisenergy sourcethatlifeonEarthdepends.Radiantenergyistheenergyofelectromagneticradiation.Becauseelectromagneticradiationcanbeconceptualized asastreamofphotons,radiantenergycanbeviewedasphotonenergy. Alternatively,EMradiationcanbeviewedasanelectromagneticwave,which carriesenergyinitsoscillatingelectricandmagneticfields.Thesetwoviews arecompletelyequivalentandarereconciledtooneanotherinquantumfield theory.Solarradiationisenergyintheformofelectromagneticwaves involvingarhythmicexchangebetweenpotentialandkineticenergy.Electromagneticradiationcanhavefrequencies,orwavelengths,ofdifferentenergycontentandinteractions(e.g.,absorptivities)withmatter.
Heatenergy. Thisisaveryspecialformofenergyresultingfromtherandom movementsofmolecules,whichbyvirtueoftheirmotion,possesskinetic energy.Heatisevolvedwhenallotherformsofenergyaretransformedand workisperformed.Allwork,includingthegrowthandreproductionofliving organisms,representthetransformationofenergyandultimatelyresultsinthe productionofheat.Forexample,whenananimalduringrespirationreleases thepotentialenergyofglucose,approximatelytwo-thirdsofitisconverted
intomechanicalenergytobeusedforwork(activityandgrowth)andonethirdsisgivenoffasheat.
Thereareinstancesofworkwhereheatisabsorbed(endodermicprocesses):thecoolingunitofarefrigeratororthefixationofatmosphericnitrogen bycertainbacteriaareexamples;but,theseprocessesarenotself-supporting energetically.Nitrogenfixationisalwaysaccompaniedbytheexothermic breakdownoforganicsubstrates.Heatenergyreleasedbyanexothermic processisneverusedwithcompleteefficiencybytheendergonicprocess,and sowheneverworkisdonethetrendisalwaystowardheatproduction.In naturalprocesses,changesfromoneformofenergytoanother(excepttoheat) arenormallyincomplete,becausethemovement,alreadyshowntobenecessaryforenergyconversion,involveseitherfrictionorheatproduction.
Temperature istherelativemeasurewhichisusedtocharacterizethe amountofheatpresentinasystem.Severalcommonsystemsareused,only twoofwhichconcernus:theCelsiusandtheKelvinscales.TheCelsius (centigrade)scale(oC)establisheszero(0 )asthefreezingpointofwaterand 100degreesastheboilingpointofwater.TheKelvinscaleisanabsolute measurewhichestablisheszeroatthetemperature( 273 C)atwhichall molecularmotionceases.Becausefreezingandboilingpointslimitlifeprocesses,wewillconventionallyutilizetheCelsiusscale.Heatmaybecharacterizedbythepropertiesoftwophases:sensibleheatandlatentheat. The significanceofeachofthesephaseswillshortlybecomeapparent.Sufficeat presenttodistinguishbetweenthetwophasesasfollows:sensibleheatisthat whichcanbemeasuredbyanincreaseintemperatureofabody,forexample, thewarmingactionofsunlightirradiatingametalplate.Latentheatistheheat absorptionbyabodywithoutanequivalentincreaseintemperature,suchas theheatsoffreezingorvaporizationofwater(heatofvaporizationof water ¼ 539calat100 C).Energyflowisexpressedastheproductoftwo factors:(1)anintensityfactor(orgradient),and(2)acapacityfactor(amount).
Energy,work,andheatareallexpressedinthesameunits:calories,joules, orergs.Itshouldbeevidentthatthedifferentenergiesmaybecompared,but thatnorelationshipexistsbetweenthecapacityfactorsalone.Forexample, electricenergymaybeconvertedintoheatenergy,buttheriseintemperature cannotbecalculatedfromthevoltage,unlessthenumberofcoulombsandthe heatcapacityofthesystemareknown.Itisalsoclearthatthesamequantityof workcanbeaccomplishedbyasmallquantityofwaterpassingthrougha turbinefromagreatheightasbyalargequantityofwaterpassingthrough fromashortdistance.
Thus,arisesoneofthefundamentalprinciplesofthermodynamics the interconvertibilityofenergyformsaswellasthe“trade-offs”betweenthe intensityandcapacityfactors.Allformsofenergyareinterconvertible;when conversionsdooccur,theydosoaccordingtorigorouslawsofexchange. ThesearetheLawsofThermodynamics.
2.3TheLawsofThermodynamics TheFirstLawofThermodynamics. TheFirstLawofThermodynamicsis alsoknownastheLawofConservationofEnergy,sinceitdefinesthatthesum ofallenergiesinanisolatedsystemisconstant.Inotherwords,energymaybe transformedfromonestatetoanother,butitcanneitherbecreatednor destroyed.Thetotalenergyinuniverseremainsconstant,butitiscontinuously becomingmorediffusethroughouttheuniverse.
Rememberthatthecapacityfactorformechanicalandchemicalenergyis mass(m).Thus,Einsteinshowedthatifthereisachangeinmass, Dm, Energy ¼ Dmc2,(2.1) where:
cisthevelocityoflight(3 1010 cms 1).
Therefore,1gofwaterisequivalentto9 1020 ergsofenergy.Itshouldbe evidentthattheLawofConservationofEnergyandtheLawofConservation ofMassareessentiallythesame,andthatnoviolationofthermodynamics occurswhenenergyisconvertedintomassormassisconvertedintoenergy. However,achangeinenergyofasystemwillbebroughtaboutifthesystem doeswork,orifitabsorbsorevolvesheat.Thus,whenachangeofanykind occursinaclosedsystem(wheretheamountofmatterisfixedbutenergyis abletoenterorleave)anincreaseordecreaseoccursintheinternalenergy (E)ofthesystemitself;heat(q)isevolvedorabsorbed,andwork(w)isdone:
Work. Theworkperformedbyasystemistheenergytransferredbythe systemtoitssurroundings.Thenegativevalueofworkindicatesthatapositive amountofworkdonebythesystemhasledtoenergybeinglostfromthe system.
TheFirstLawofThermodynamicsalsoencompassesthemorespecific relationshipofconstantheatsums,whichisofconsiderableimportanceto biologistsinterestedinenergytransformations.Itstatesthatthetotalamount ofheatproduced,orabsorbed,fromachemicalreactionwhichtakesplacein stagesisequaltothetotalamountofheatevolved,orconsumed,whenthe reactionoccursdirectlyinonestep.Theevolutionoflivingsystemshasutilizedbiochemicalmechanismsbywhichchemicalcompoundscanbereduced insteps,thusenablingmoreefficientenergycaptureandutilizationtooccur.A goodbiologicalexampleisthemetabolicoxidationofglucosetocarbondioxideandwater:
Directreaction(combustion)
Two-stagereaction(fermentation)
(a) C6H12O6 /2C2H5OH þ 2CO2 þ 18kcalofenergy
(b) 2C2H5OH þ 6O2 /6H2O þ 4CO2 þ 655kcalofenergy
(a) þ (b) C6H12O6 þ 6O2 /6H2O þ 6CO2 þ 673kcalofenergy
Thus,nomatterwhichpathwayaparticularreactionfollows,thetotal amountofheatevolved,orabsorbed,isalwaysthesame.Therewillbemore discussionaboutthebiologicalsignificanceofthisphenomenonlater.Several otherenergyrelationshipsarealsopertinenttobioenergetics.
Enthalpy. Enthalpyisthetotalpotentialenergyofasystem.Inmanycasesthe onlywork“w”doneonasystemresultsinchangeincalorificvalueofthe availablemass.Inotherwords:
Therefore,theheatabsorbed(q)inaprocess,measuredunderconditionsof constantvolume,isequaltotheinternalenergyincrease.Accordingtothis equation,ifnooutsideworkisdone,theenergyabsorbedbythesystemis equaltothepotentialinternalincrease.Abiologicalexampleofthiswouldbe thereverseofthepreviouschemicalreaction,orphotosynthesis:
6CO2 þ 6H2O þ 709kcal / C6H12O6 þ 6O2,{caloricdifference ¼ change invol.ofCO2 versusO2}
Enthalpyisdefinedastheheatcontentofasystem.Bondenergyisamount ofenergyrequiredtobreakachemicalbond.Thetotalbondenergyisequivalent tothetotalpotentialenergyofthesystem,aquantityknownasenthalpy(H). Theheatabsorbedinaprocessatconstantpressureisequaltothechangein enthalpy, DH.Sinceachangeinenthalpycanoccurthroughbothachangein pressureorvolume,aswellasinternalenergy,anothertermisintroducedto describetheheatcapacityofasubstance:
Thespecificheatofasubstanceisdefinedasthequantityofheatrequired toraisethetemperatureof1gofsubstanceby1 Celsius.Thisisanextremely importantrelationshipforbiologicalsystems.Itexplainstheimportanceof waterasa“thermalbuffer,”sincewhencomparedtoothersolventswater possessesrelativelyhighheatsofvaporizationandfreezing.
TheSecondLawofThermodynamics. Weareallfamiliarwiththefactthat manyenergeticprocessesoccurspontaneously.Forexample,waterruns downhill;gasesexpandfromregionsofhighpressuretoregionsoflow pressure;chemicalreactionsproceedtoequilibrium;andheatflowsfrom warmbodiestocoolerbodies.TheSecondLawofThermodynamicsstatesthat processesinvolvingtransformationswillnotoccurspontaneously,unlessthere isadegradationofenergyfromanonrandom(ordered)formtoarandom
DH ¼ DE þ D (pv)(2.4)
(disordered)form.Innaturalsystems,spontaneousenergytransformations resultinthedegradationoftheenergystateofthesystemfromausefulformto adissipatedandlessusableformofheat.Obviously,asspontaneousprocesses occurinasystemthesystemlosestheabilitytodowork.
Living(biological)systemshaveevolvedtoexploitthesenaturalenergytransformationsandtoutilizeenergyasitpassesfromorderedtorandomstates.
Allsystemstendtoapproachstatesofequilibrium inthermodynamic properties;thismeanscompleterandomnessorenergydegradationofthe system.Asameasureoftheextenttowhichthisequilibriumhasbeenreached, anotherthermodynamicterm,entropyisintroduced.
Entropy. Entropyisameasureofthedisorder,orrandomness,ofasystem. Organized,usableenergyhaslowentropy,whereasdisorganizedentropysuch asheathashighentropy.Themorethemoleculesinasystemaredistributedin adisorderedorrandommanner,themoreprobableisthearrangementandthe greateristheentropy.TheFirstLawofThermodynamicsrecognizesthe interconvertibilityofallformsofenergy,butitdoesnotpredicthowcomplete theconversionswillbe.Thisappliestoallenergyconversions,exceptthe transformationtoheat,whichisapropertyofmoleculesmovingaroundat random.Bycontrast,allotherformsofenergyresultfromanordered, nonrandomarrangementoftheelementaryparticlesofmatter.Heatistheonly fromofenergyduetodisorderorrandommovement,anditisthemostlikely energyformtooccur.
2.4Gaiahypothesis TheGaiaHypothesisproposedbyJamesLovelock(1972)suggeststhatliving organismsontheplanetinteractwiththeirsurroundinginorganicenvironment toformasynergeticandself-regulatingsystemthatcreated,andnowmaintains,theclimateandbiochemicalconditionsthatmakelifeonEarthpossible. Gaiabasesthispostulateonthefactthatthebiosphere,andtheevolutionor organisms,affectsthestabilityofglobaltemperature,salinityofseawater,and otherenvironmentalvariables.Forinstance,eventhoughtheluminosityofthe sun,theEarth’sheatsource,hasincreasedabout30%sincelifebeganalmost fourbillionyearsago,thelivingsystemhasreactedasawholetomaintain temperaturesatalevelsuitableforlife.Cloudformationovertheopenoceanis almostentirelyafunctionofoceanicalgaethatemitsulfurmoleculesaswaste metaboliteswhichbecomecondensationnucleiforrain.Clouds,inturn,help regulatesurfacetemperatures.
LovelockcomparedtheatmospheresofMarsandEarth,andnotedthatthe Earth’shighlevelsofoxygenandnitrogenwereabnormalandthermodynamicallyindisequilibrium.The21%oxygencontentoftheatmosphereisan obviousconsequenceoflivingorganisms,andthelevelsofothergases,NH3
andCH4,arehigherthanwouldbeexpectedforanoxygen-richatmosphere. BiologicalactivityalsoexplainswhytheatmosphereisnotmainlyCO2 and whytheoceansarenotmoresaline.GaiapostulatesthatconditionsonEarth aresounusualthattheycouldonlyresultfromtheactivityofthebiosphere (LovelockandMargulis,1974).
2.5Carbonandenergy Aftertheoriginoftheuniversesome13 18billionyearsagowiththeBig Bang,acondensingsunbegantocollapseandincreasingpressureallowed heliumto“burn”toformcarbon.
4He þ 4He 4 8Be(2.5) 8Be þ 4He / 12C(2.6)
Hydrogen,H,andhelium,He,weretheoriginalbuildingblocksofthe universe.Approximately3.8billionyearsagowhensurfacetemperatures cooledto100 C,watercondensedoutoftheatmospheretoformtheprimitive oceans.Watervaporandcarbondioxide bothdegassingfromtheEarth’s crust servedasanearlygreenhouse.Thisprimordialatmospherekeptearly Earthfromfreezing.WithoutthepresencetodayofwatervaporandCO2 inthe atmospherethatcreatesasignificantgreenhouseeffect,theEarthwouldbe about33 Ccoolerandcoveredbyice(Ramanathan,1988).
Theformsofcarbon. Carbonoccursinmanydifferentmaterialsinmany differentforms.Inbioenergetics,oneisinterestedinthecarboncontentof organicmolecules.Carboncontentmaybecategorizedas:
TotalCarbon(TC) allthecarboninthesample,includingboththe inorganicandtheorganiccarbon,
TotalInorganicCarbon(TIC) oftenreferredtoasinorganiccarbon (IC),carbonate,bicarbonate,anddissolvedcarbondioxide(CO2),
TotalOrganicCarbon(TOC) materialderivedfromdecayingvegetation, bacterialgrowth,andmetabolicactivitiesoflivingorganismsorchemicals, and
ElementalCarbon(EC) charcoal,coal,andsoot.Resistanttoanalytical digestionandextraction,ECcanbeafractionofeitherTICorTOCdepending upontheanalyticalapproach.
Carbonmassmaybecalculatedfromtheproportionalcompositionof carboninthesubstrateifitsmoleculecompositionisknown,i.e.,
proportionalmassofelement ¼ massofelementincompound totalmassofcompound (2.5)
Therefore,theproportionofcarbontimestheweightofthecompoundyields themassofcarbonpresent.MeasurementofCO2,aswellasO2 andCH4,gas
