Sistemas Ecológicos Cerrados

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Closed Ecological Systems

Author(s): Frieda B. TaubSource: Annual Review of Ecology and Systematics, Vol. 5 (1974), pp. 139-160Published by: Annual ReviewsStable URL: http://www.jstor.org/stable/2096884.

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140 TAUBREGENERATIVE LIFE-SUPPORT SYSTEMS FORSPACE FLIGHTManned paceflightrequires life-support ystem hat will supplyman'sneeds-02, H20, and food-and eliminatehis wastes-CO2, urine,feces,and heat. Earlysystems reliedon expendableCO2 absorbants nd storageof water, food, andpressurized xygen; hus the weightof the storedmaterials osesharplywith thedurationof the mission(54). The attractiveness f convertingwastes to needsprompted n evaluation f potential egenerativeystems.For long,multimannedmissions, he weight,powerrequirements,nd complexities f suchsystemswouldbe lessthan thoseof theweightandstorage ystemsof expendablematerials. n themid-1950sno one could predictwhen the need wouldbe critical,but researchwasbegun nthusiastically. egenerativeystems onsideredwereof threemajor lasses:(a) physicochemical,b) photosynthetic,nd (c) chemosyntheticHydrogenomonasbacteria).Physicochemical RegenerativeSystemsSystems angingrom imple iltrationnddistillation f urineandcabincondensateforregenerationf potableH20 to moreelaborate ystems,e.g.electrolysis f H20forrecoveryof 02 (H20 -4 H2 + 1/2 02), to the Sabatier eaction orrecovery fmethaneand water(CO2+ 4H2 CH4+ 2H20) coupledwith crackingofmethane(CH4+ H20 -4 3H2+ CO) for recoveryof the H2to maintain heSabatiereaction, ndpotentiallyosynthesis iapolymerizationo producehumanfood compounds rommethanoland formaldehyde25). Most physicochemicalmethodshad high energyrequirementsut wereamenable o an engineering p-proach.Techniquesof water recoveryhave beenevaluatedand compared 95).Theseeffortsarenowlargelyof historical nterest ince theconcurrent esearch nenergy torage edto the useof theH2-02 fuel cell in placeof the heavierbatteries.The02 requirementsf the fuel cell made the human02 requirementeem petty,and ts wasteproduct f waterwas farmore hanthe humanrequirement.osome,the use of a waste productof the fuel cell to supplya human need wouldbeconsideredycling,but t isactuallymultiple,nonregenerativese. Various hysico-chemicalatmosphericontrolsubsystemswereproposed 2), and a recentsystemwasappraisedn a 90-daytest (35).PhotosyntheticRegenerativeSystemsA multiplicityof systemswas rapidlysuggested.Initially they werejustifiedasC02/02 converters, ut the potentialuseof plantmaterial s food was also consid-ered.Manyweredesignedalso to utilize urineand wash waterandpossibly ecesto supplythe algal nutrients. t was generallyaccepted hat a three-componentsystem (man-wasteprocessing-plant)wouldbe requiredas a minimum;humanwastesnotdirectly uitablewouldbe processed o supply herequired utrients oralgal growth. Various short circuits and alternatepathways(Figure 1) wereproposed.The earliestplan or a photosyntheticife-supportystem s not known o me,butit musthavebeendevelopedbefore1954,whenMyerspublishedherequirements

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CLOSEDECOLOGICAL YSTEMS 141MULTISTAGE COLOGICALYSTEM

SecondaryConsumer WASTESTORAGE

Primary HCE1Consumer

GreenA 0Plants

FigureI A compositemultistageife-supportystem.fora man-day ystem.Its possibilityhadbeensuggestedn 1953by Bowman 8).By 1956,aconference nphotosyntheticasexchangerswassponsored ytheOfficeof NavalResearch93);systemsweredesignedo prolong hesubmergenceapabil-ityof nuclear ubmarines ithout hereleaseof gasbubbles. n 1959Richet al (76)presenteda fairlyadvanced cheme,with waterreclamation, hotosynthetic asexchange,andwastestabilization. ischer 87) discussedvarious ypesof systems:human-yeast-bacteria-algae;igherplant-algae-waste-human;he aboveplusananimal-goat, Daphnia, orslug(?); ydroponicallyrownplantsonabacterial-algalconverter;a Hungatecycle, crew-microbes-plants;nd a van Niel microcycle,Artemia, bacteria, ndalgae.None of theproposed ystemscouldmeet all humanneedsnor recycleall productsandtheywerelargelyprojections f whatcouldbedone.Theparallelbetween heearth's cological ycleandtheproposed pacesystemswas mmediately bviousandwas nfluentialntheir nitialdesign.Surprisingly,ewecologistsbecame nvolved,as is discussedater.Developmentwent argely o civilengineerssewage reatment rocesses), lantphysiologistsmassalgalcultureandhigherplants),medical ndhumanphysiologistshuman equirements),ndchemi-cal engineers scaleupof sewageandalgalsystems).Althoughall studiesclaimedto be directedtowardthe development f totalsystems,most concentrated n the processeswithin a singlesubsystem.Artificialinputswere often used to standardize xperimental onditions,e.g. an air-CO2mixture roma pressurizedankrather hanfromhumanrespiration.Usuallythe



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142 TAUBoutputwasmeasured utnotusedby another ubsystem.Thisuncoupling fsubsys-tems,whilemaking heconductof eachproject asierandindependent,liminatedfeedbacks,nteractions,r the effectsof tracematerials.The studiesreviewedhereareorganized s singlesubsystems, oupled ubsystems, nd theholisticapproach.The clashbetween hesubsystem nd holisticapproachs discussed san introduc-tion to the latter.SINGLE SUBSYSTEMSHumanDaily Balance An enormousamountof medicaland physiological e-searchwas reviewedandperformedo determinehumanrequirementsnd wasteproductsunder he likelystressesof spacetravel.Mostof thepertinent atawerebrought ogethern the BioastronauticsataBook (97).The work s a convenientdocument f human actorvalues.Furthernutritional nd wasteconsiderationsrecompiledin (57). The nominalvalues for regeneration tudies are shown inTable1 (1).Algal Culture Algaloxygenor cell production eceived he overwhelmingffortof the nonmedical tudies. enkins stimatedn 1966 hatabout$30millionhadbeenspenton research nto photosynthetic ioregenerativeystemsduringthe 12-15preceding ears(37). It was sparked nddirectedby twopublicationsn 1953: a)Earlier tudieson massalgal culturewere madeconveniently vailablen AlgalCulturerom Laboratoryo PilotPlant(11),a compilationdesigned o encourageconsideration f masscultures s a sourceof high protein ood to solve the world'sfoodproblem. b) Chlorellayrenoidosa X 71105,a high temperaturetrain,wasdefined s the mostefficient hotosyntheticrganism, nd tsgrowthandproductionrateswere described78).Myerssoonestimatedhatphotosyntheticas exchangefora man-daywouldnecessitate .3kgof Chlorellauspendedn230 litersof liquidhaving24 m2of lightedsurfaceandrequiring 0hp (52).Thehigh powerrequire-ment was basedon anefficiency f 19%for conversion f electricityo fluorescentlight and 10% for conversionof light to photosynthesis.The high volumeandsurfacearearequirements erenecessary ecauseof theself-shadingf densealgalsuspensions.A significant umber f aviation ompanies nduniversities,s wellastheU.S. AirForce, nitiated tudiesalmostsimultaneously. hereprevailed gen-Table 1 Nominal values of the daily materials balance for man in space (1). (Values byother authors are not materially different.)

In OutTotal: 3615 g Total: 3615 gWater: 2400 g Water: 2730 gOxygen: 715 g (22.3 moles) Carbon dioxide: 840 g (19.2 moles)Dry food: 500 g (95% digestible) Dry solids: 45 g(2400 cal, of which protein = 10%,fat = 35%,and carbohydrate = 55%)



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CLOSEDECOLOGICALYSTEMS 143eraloptimism hatthis line of researchwouldprovecrucial o thespaceeffortandmighthaveimportant arthapplications, nda general uppositionwas that thefederalgovernment, ither heU.S. Air Forceor NASA, wouldsupport he morepromisingeams.The information massedon the cultureof algae,especiallyof ChlorellaTX71105, is overwhelming. ignificant ystems (29 in number)were reviewedandcomparedn 1966(49).Therequirementsorone-man upportvaried rom3.5 to3,000 liters,from2.5 to 71 m2, and from7 to 100 kw. In most instancesdenseculturesrequiring ighsurfaceareasbut small volumesweretradedoff for thoseless dense requiringess surfaceareas,becauseof deeperlight penetration, utgreatervolumes.Mostof thosesystemswouldrequiremultiplesor scalingup toachieveone-man upport.Inspiteof thiswork, healgalsystemsdidnot lookfavorableo NASA;especiallyobjectionable ere he unknowns f reliability.Althoughas muchwasknownaboutChlorella s anycell, therewasno hopeof knowingall its components ndtheirseparateand combinedproperties nderall conditions.Becauseof the inefficientconversion f electrical nergyolight(lessthan20%)andthesubsequentnefficientconversionof light to photosynthesisprobablyno more than 20%),at best effi-ciencywouldbe an unacceptable %.The useof sunlightwas rejected s compro-mising he integrity f thespacevehicleshell,requiringonstantorientationo thesun and beingvulnerableo sunbursts nd other unpredictablevents.HigherPlants Becauseof the potentialadvantagesof lower requirementsorwater,andthereforeowerweightof thesystem,andthemorereadyacceptance shuman ood,a limitedeffortwasexpended n higherplantsas potentialphotosyn-theticagents.None of this effortwentbeyond he preliminarytages.Duckweed(severalspeciesof the familyLemnaceae)demonstratedminimumdivisionratesranging rom 12-20 hr (vs 8 hr for thermophilicChlorella), l-thoughthe authorscautioned hat light intensityand otherconditionswerenotcomparable. majoradvantagef the duckweeds thatgaswas exchanged irectlybetweenthe plantand the atmosphere,o that elaborategassingand degassingprocedureswerenot necessary.Harvestingwasalso simpler;heplantsweresepa-ratedby coarsescreensanddidnot haveto becentrifuged96,98).Otheraviationcompanies, uch as RepublicAviation(75) and the MartinCompany 32), weregrowinghigherplants,but their detailedreportswere not in my collectionofliterature.Thepotential ffectsof alteredatmosphere ndgravitationieldsweretestedonsnapbeanandotherplants.Differenceswerenoted,buttheresultswerepreliminary(4).Otherreports n studiesofhigherplantsaregiven n(4).Studies fgravitationaleffectson patterns f plantgrowthhavecontinued n the Biosatellite rogram, utas a basic research ffort.WasteProcessing Biologicalwasteprocessingwas morefrequently tudiedas apartof a coupledsystemthan as a singlesubsystem, ndthe materials reviewedin that section.Whenwasteproductswerenot recycled heycould be storedwitha disinfectant, eleased rom the vehicle,or incinerated.



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144 TAUBCOUPLED SUBSYSTEMSPhotosynthetic-AnimalRespiration Even coupled photosynthetic subsystems wereusuallyopento material ransfer, otably ood.It is probablehatMyersperformedthe initialalga-mouseexperiments etween1955and 1958citedin (9), but I havenot seen the Air Force Reports.TheSchoolof AviationMedicine eported 15 itercultureof Anacystis idulans(a blue-green lga)was coupledwithone 30 g mousefor 80 hr,andsubsequentlywiththree30 g micefor 80 hr (31). In each instance, he abilityof the culture oproduce 2 exceededheanimal espirationndthe02 concentrationoonexceeded30%by volume,whereas he CO2 oncentrationwashighat thestartandwasnotdepleted.Themosttroublesomeindingwas a continuousncreasen the COlevel,attributedo theAnacystis;he problemwaseliminated yinclusion fa COburner(Hocalite,heated o 1250C).A 15 litercultureof Synechocystisalsoa blue-greenalga)was similarlyable to matchthe 02 requirementsf fourmice. In anotherexperimentmentioned utnot reportedn detail, he algalcultureunitmaintainedmicefor 15days.In all of theseexperiments nlygas exchangewascoupled.Themicewerefeda standardab chow,crumbsof whichbecamemixedwith fecesandurine.Thealgalculturesweregrownentirelyon a chemicallydefinedmediumandthe gaseouswasteproductsof the mice.When he 15.5 iteralgalunitwithSynechocystis ascoupledwitha 3 kgprimateit suppliedonlyone sixthof the oxygenneeds,andtheexperimentwasterminatedat 21/2hr (30).At ChanceVoughtAircraft, tudieswereunderway efore1960to demonstratethatthe thermophilictrainof Chlorella an support he 02 requirementsf mice(8). Of eight trials,fivewereterminated ecauseof excessiveCO2andthreewereconsidereduccessful ndwereendedon the 12th,14th,and28thdayformechan-ical problems nrelatedo thebiologicalunctions.Oneof themice olerated 5daysin the regeneratedtmosphere,xperiencingt one timean atmospherewith 10%CO2 nd 10%02. On thelongestruna4 literalgalculture upportedherespiratoryneedsof a 30 g mouse,and oxygenincreasedrom21% to a maximumof 30%.When womicewereused he02 concentration ascontrolled etween 0 and31%afterday 7 anduntilday 15,whereEfter2 was observed o dropslowlyto 10%untilday20 when theexperimentwas terminated.The imbalanceoward he endof theexperimentwas relatedo theaccidentalwettingof theaccumulatedecesandurineand subsequentncreasedactivityand 02 uptakeby the bacteria.Clearly,although his systemcouldproviderespiratoryupport o the mice, it couldnotsupply he biological 2 demandof the accumulatedwasteproducts.Theaerobicmetabolism ssociatedwiththe wasteswasequal o twomice.Methaneand ethanewerenoted.Ina laterexperiment 40 g mousewas kept ngoodhealth or 66days;the 02 increased o 63% and CO2was usuallycontrolledat 0.2% or less. Nomethane, thane,or CO werefound (9).Additional asexchange tudiesbetweena dwarfmouseandChlorella llipsoideaagainresultednexcess02 productionromslightbutpersistentmbalancesetweenthe C02/02 ratiosof the mouseandalga (27). Theseratioscanbe shiftedby the



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CLOSEDECOLOGICAL YSTEMS 145composition f the mousediet andthe formof nitrogen nitrateor urea)suppliedto thealga.Metabolismfwasteproductswasminimized ydrystorage.Twosealedexperiments f 15 and 24 days wereterminated,not becauseof any componentfailure,butbecausean increasen oxygenandtotalgasvolumeexceeded helimitsof a variablevolumecomponent.Theysuggestthat earlierexperiments y othersprobablyhadsignificant as leaks.TheBioregeneratingnit (BRU)was a morecomplex ystembutalsorestrictedto gaseousbalance. t included ulture ystemsof thefungusLinderina ennespora,the hightemperaturetrainof Chlorella yrenoidosa, sewagereactor,anda rat(45).Thefunguswasselected oritsability o convertgaseousammonia o protein,a potentialanimal eedsupplement. he2.5 literalgalculturewassuppliedwith allits requirementsn its growthmediumexceptcarbon, he fungalculturewassup-plied withall of its growthrequirementsn its medium,andthe ratwas providedwith food (unspecified, resumably standard aboratory how) and water.Thefecesandurineof the ratwerestored,but gas products uch as NH3 wouldhavecirculated hrough he air and havebeenavailable or fungal ncorporation. hesewagereactorwas runon ratandrabbit ecescollected romotheranimals.Thusthesystem ested heabilityof thealgalculture o provide 2 for thefungus, ewagereactor, ndrat.Gasbalancewasachieved or 48 hron a trialrunwithout herat.Failureresultedafter22 hrwiththe inclusionof a 65 g rat andsewage oad.Untilthena reasonable2 balancehadobtained, utCO2had ncreased apidlyrom0.08at4 hrto 1.20%.By28 hrthe02 haddeclined o 8.4%andtheCO2hadincreasedto 10%. Thesetrendscontinueduntilthe ratdied,at approximately 5 hr. By 72hrthesedimentableewage olidshadbeenreduced75%,andby92 hrthesewagehadbeendigested.London& West(45) attributedhe gas imbalance o a sudden02 demandby the fungalor sewagesystemandnot to a malfunction f the algalsystem.Theynoted,however,hatthealgal countbegan o peakoffat 40 hr,as intheirearlierexperiments.An improvedBRUhad 9 litersof algalculturewithincreasedightandcontinu-ous medium nputandculturewashover.Thesystemwas run for 174hrwithCO2gasto prime healgalculture;hen a 149g rat,feces,andfungal poreswereaddedandthe systemwas sealed.After24 hrthe CO2hadrisensharply o 7%,whereasthe 02 haddroppedo 11%. At 70 hralgal culturewasshifted romcontinuousobatchoperation, utgasimbalanceontinuedo worsen.During his timeof severestress he ratinspireddeeplyandrapidlybutcontinued o take food andwater.At80 hr, half (1.2 liters)of the fungalculture was removed n order to lessenthe02 demand; yieldof 3gdryweightwasrecovered. hereafterasbalance eturned;the02 increasedo 17%andtheCO2 ell to 2.6%.Additionalmediumwassuppliedto the algalcultureduring his time.At 216 hrthe runwasdiscontinued ecauseof mechanical reakdown.Theratappearedo be healthyand hadgainedweight.A subsequent unof 309 hrresulted n a heavyvacuumandwas thendiscontinued.Theseriesof experimentswas interpreted s showingthe possibility f photosyn-theticregenerationf the atmosphere.Additionalexperimentsndicated hat bac-terialcontaminationf thealgalculturewasnotresponsibleor theproblems.Aftera total of 819 hr (34 days), the algal culturewas still vigorousand capableof



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146 TAUBperformingts roleas a gasexchangemechanism.Fungalgrowthoccurredappar-entlywithout he use of gaseousNH3,the cornsteep liquor n themediumhavingprovidedan adequate upplyof nitrogen.Thefungus,presumablydible,wasnottested.A 1220 g Cebusmonkeywas maintainedby a 57 liter Chlorella yrenoidosaculture or several50 hr periods 99). The 02 gradually osefrom21 to approxi-mately25%.The CO2eveldidnotexceed1%.Themonkey's ctivitywasthemajorcauseof observedluctuationsn 02 andCO2 oncentrations. he02 productionwascontrolledby light intensity,nutrient eed concentration, utrientexchange,andCO2supply.Algalcultureswerealsousedto provideatmosphericontrol orhuman ubjects,.BoeingCompanyresearchersmadethe decision o bypassanimalstudiesandgodirectly o man-supportingystems 7). Multiple ankswithcapacities f 55 literseachwereconstructed; ightwereeventuallyused.LikeGolueke& Oswald 33),they first concentrated n 02 productionper unit volumeand latercameto theconclusionhat02 production erunit areaand lightintensityaremore mportant.In thepreliminary nmannedrials 2 production eaked24 hr afterseedingat 43ml 02/liter hr, or 2.4 liters 02/tank hr. It was estimated hat eighttankswouldprovide19 liters/hr,orabout herequirementf oneman naresting r low-activityenvironment. healgalcultureswereknown o bebacterially ontaminated,utnodeleterious ffectswereseen.A 56 hr mannedrun was successfully ompleted:he02 remainedbetween19 and 21% while the CO2 remainedbelow 2%; minorvariationswererelated o the humansubjects' ctivityand the periodicharvestofthealgalcultures.Subsequenttudieswith smalleralgaltanks ndicatedhata mancouldbe supported n much less thanthe 380 litersused.Algal-AnimalFeedingStudies The literatureon algal-animal eedingstudies sconsiderable nd much of it has been summarized43, 48), but the resultsarefrequentlyonflicting.For instance,Lubitz 46)reportedhat Chlorellawashighlypalatable,wellabsorbed, nd capableof providinghe sole sourceof protein n anotherwise ompletediet for the rat. Conrad& Johnson 16) had poorresultsandassumed hat Chlorellawouldbe poorlydigestedby the rat.Vanderveent al (94)suggested hatbacterial ontaminationmightbe responsibleor some toxiceffectsreportedn human eedings.I suggest hat someof the extremedifferencesn resultswithin heanimalexperi-mentscouldhavebeendue to thedifferent eeding echniques;when Chlorellawasusedas a portionof a completediet it was satisfactory, ut whenprovidedas thesole dietit wasunsatisfactory.amparticularlyoncerned bout helackofcalciumin most algal growthmedia;Chlorellaapparentlydoes not requirecalciuminsubstantial mounts,but ratsdo. In thehuman eeding rialscontrolovertotaldietwas sometimes nadequate.The generalconsensus s that algae,and particularlyChlorella,maynot be suitableas human ood;but no toxinshavebeen identified.I regard he digestibilityo be an openquestion;Lubitz(46) wasthe only one tomeasuret, andhe reported oodassimilation.Others implyquoteearlierworkersas statingthat the wall is resistant o digestion.



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CLOSEDECOLOGICAL YSTEMS 147Human WasteProductso AlgalNutrients The direct or indirectuse of humanwasteproductsorphotosyntheticecyclingwasassumednmostschemes, lthoughadditionalupplementsmightbe deemednecessary.Each methodof treatment adits own advantages nddisadvantages72).Thedirectutilization f wasteswouldrequire combined erobicbacterial-algalreaction hamber.Pipes 72)stated hatthe algaewouldalwaysproduce 2 inexcessof thatrequiredorthe oxidationof the organicmatter f lightandnutritionwereadequate.The criticalproblemwould be the concentration f CO2available orphotosynthesis. ucha systemwas estimated o require detentionperiodof 60-72hr anda capacityof 30 litersper person.It wouldbe greater n size thanthe unitrequired or the otherprocesses, ut would allowother components f the systemto be correspondinglyiminished.The advantages f such a unit were saidto be:95%oxidationof organicmatter,recoveryof potablewaterafterdisinfection ndothertreatment,andproduction f a food supplement onsistingof a mixtureofalgae,bacteria, ungi,protozoa, nd a fewhigher nvertebrates.hefurthestdevel-opmentof such a system was the Algatrons 34), 11 of which, each 18 in. indiameterand4 ft long,wouldbe requiredpermanforgas exchange,waste treat-ment,and waterrecovery. n experiments,Oscillatoriaa filamentous lue-greenalga) gave 02 yields comparableo those of Chlorella,but havingan unpleasant,swampy dor.The unit wasalso substitutednto the microterella, iscussed ater.A manned quivalent f themouseunitwasdesignedermedMECCA Man-Algal-BacterialEcologicalCultureChamber).Directutilization f wasteshadobviousdisadvantages:isease ransmission,ightabsorption,ndastrongpsychologicalevulsiono thepotential stronauts.Numer-ous methods weresuggestedby Pipes (72) to overcome hese:incineration,wetoxidation,chemicaloxidation,aerobicmicrobialdigestion activated ludge),andanaerobic igestion.An electrolyticmethodof breakingdown dailyoutput wasdeveloped,andthe products, ombinedwithadditionalurine as a supplementarynitrogensource, supportedgrowthcomparableo the standardKnop'smedium(50). In further xperimentation icronutrientupplementationndreliability e-tweenbatcheswere ested 51).Theproducts f combustion esultednvery imitedgrowthunless additionalCO2 was supplied;with CO2 and the chelatingagentEDTA(ethylenediamineetraacetic cid) growthyieldswere107and 108cells/ml(74).Themicrobialreatment fwastes, eparated yasemipermeable embraneroman algalculture,was tried(6). Experimentsverperiodsof 21 daysdemonstratedsuccessful lgal growthon thediffusedproductsof bacterial xidation.Thesystemwas not entirely unctional roman engineering ointof viewbecauseof the slow-nessof waterdiffusion.Bieberdorf6) notedthat,duringa 20-dayrun,notonlywasgoodgrowthofalgaeobtained ccompanied ysatisfactory ecompositionf waste,butthe composition f airwithinthe chamber emained onstantat 20%02 and80%N2 even though it was sealedfrom the laboratory tmosphere. t may alsobe worthnotingthat holes developed n the cellophanemembranesn 4-5 dayswhen one membrane eparatedalgae and fungi but not when two membraneswereusedseparated y a barrier f distilledwater.In the actualexperiments,yn-



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148 TAUBthetic wastesconsistingof dehydrated ooked meat, distilled water, and papainwere used.As a test of mesophilic ctivatedludge,cellulose, oaps,detergents, nd vomituswereeachadded.Cellulosewasdegraded fteran initial ag (67). Castile oap, thedetergentodiumdodecyl ulfate,and vomitushad nodeleterious ffects,but nonbi-odegradable etergentswere a problem 68).Human WasteProducts oPotentialFood It was soonrecognized hatsomeof thehumanwasteproductsmightbeused nproducing n alternateoodsource.Tischer& Tischer 89) studied he use of humanurineand feces forthe production f thecrustaceanDaphnia,the mold Rhizopusdelemar(alone or combinedwith thebacterium seudomonas),he protozoanParamecium,ndtheyeastSaccharomycescerevisiae.EarlierTischer 88) hadshown thatR. delemarconvertsup to 50%offecalnitrogen nto fungalprotoplasm.Fecalnitrogenwasnot as gooda sourceofnitrogenorfungalgrowthasnitratenitrogen. mproved ieldsof moldgrowthandefficiencies f conversionmightbe obtainedby supplementationf the feces withcertain orms of nitrogen,carbon,and possiblyvitamins.Moldgrownon humanwastesubstrateswas driedand fedto five hamsters s a sole food for 10daysandwas observed o produceno weightchange.This resultwasinterpreteds showingthat molds cultivatedon humanwastescan be converted nto animal issue.At the Universityof Washingtontudieswere madethat involved eeding ish,Tilapia,on algae and intermediateooplankton rownon humanwasteproducts(81, 82).Three ypesof 17-liter ystemsweretested: a) a feces-supportedommu-nityofalgae,Daphnia, otifers, rotozoa, nd Tilapia, b) asimilar ommunityhatwas unfed,and (c) another hat was fed frozenbrineshrimp.Theywere aeratedduring he 93-dayrunso thattemporary as imbalancewould not be critical.Atthe end of 30 days the fish were weighedand replaced.The fish in the unfedecosystemswereobviously tarving,whereas hosein theecosystem eceivingeceshadgrownalmosthalfas muchas those ntheecosystemedbrine hrimp.Thereaf-ter, two systemswere fedfeces and the thirdbrineshrimp.Theoriginally tarvedfishgrewbut nevercaughtupwith the othergroups n average r totalweight.Thefish ntheecosystemhathad received ecesfrom hebeginningwereapproximatelyof the sameaverageweightas thecontrols,but fewersurvived.Most mortalitiesnthesystemsweredue to theentrapmentf fish ntubes ntended o shelter ooplank-ton,but mortalitieswerehigher n the feces-fed ystems.Although t was intendedthat the fecal materialbe utilizedas a nutrient or the algaeandmicrobes,whichwouldbe eatenby the invertebrates,ndthese, n turn,wouldbe eatenby the fish,we observed nstead hatthe fishactively ed on the fecal materialas it wasbeingadded.Gas analysisof the inputandoutputair indicateda balance n the systemafterthe first few days. No unpleasant dorsdeveloped.The Daphnia, n spiteof theattempt o shelterthem, were all eaten within the first few days.The Chlorellaunderwent successionof bloomsand thensteadilydiminished.Ankistrodesmus,anothergreenalga, becamequite abundantand apparentlymaintained he gasbalanceduring he fluctuationsn abundance f Chlorella.Theprotozoanpopula-



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CLOSEDECOLOGICAL YSTEMS 149tion generally ncreased hroughouthe experiment.Small snailsappearedn thefeces-fed ystem and wereeatenavidlyby the fish.Since heweightof the fishsystemwouldhaveto beminimized, herelationshipsbetweendensityandgrowthwerestudied n volumesranging rom 3.5 to 17liters.Higherdensities,44 g/liter, andlarger ish,18g averageweight,wereobtained nthe 17-liter ontainers.AlthoughTilapiacangrowmuchlarger n ponds, heyarereadily tunted; helargerof thetest fishweremuch ikesardines.Thesecontainerswereopen to the airandfurther eratedwithcompressed irthrougha smallfilterwith activated harcoal, and,andglasswool. Brineshrimpwere fed ad lib daily.The water waschanged f it became ouled,usuallynot more than onceperday.Someof the fish weresteamedand eatenby the researcheam: heywerebonybutotherwisehighly palatable.The experimentswereinterpreted s suggesting hat wasteproductsandexcessalgaecouldbe used to produceanalternate nimal ood for theastronautswithoutan excessive02 demandor weightload. It was reported hat an unidentified s-tronautopined hatfishingmightproviderecreational alue,butthateating eces-reared ishwould be an unlikelypossibility.Algal-Mammal-Waste ycling An algal-microbial-mammalystem, ermed hemicroterella, asmorecoupled hanformer ystems; he waste productsof themiceprovided he algalnutrients, ndcondensedwater romthe systemprovidedwater orthemice(33). Thetotalsystemwassealed na 38.5literchromatographyjar. Spacewas provided or one to fourmice to resideon a meshfloorabovethealgal-bacterial ulture.This areawasequippedwith facilities oreating,drinking,sleeping, and recreation,as well as an air conditioningunit whose condensateprovideddrinkingwater.Fresh ood in the formof pastewassuppliedromoutsidethesystem; o somebatchesalgalpastewas added.Thealgal-microbialommunityoccupied5-7 litersandconsisted f Chlorellapyrenoidosa90-95%),Chlorococcumsp.(4-9%), Scenedesmusbliquus1%),and fecal-derived acteria.Theobjectivesin thesestudieswere(a) to achieveconditions ormaintaining constant02/C02ratio,(b) to test for limits of duration,and (c) to minimize he supportsystemnecessary o maintain hebalance.The firstphase, reported n moredetailin Oswaldet al (70), providednsightsinto the limits of regenerativeystems.The initial seriesof experiments ll led orapid ncreasesn CO2anddecreasesn 02. Variousmodificationsn retentionimeof thecontinuous lgal-microbialommunityo speedgrowthrateand02 percellhad imitedeffect.Reduction f thedepth andvolume)of the culturewasbeneficialsince in the shallowerculturea greaterportionof the algalpopulationwas wellilluminated.Ultimately,headdition fmore ights,especially rom hetop, enableda 5 literalgal-microbialommunityo support he02 requirementsf a mouseandits wasteproducts.Thesecondphasewasconcernedwiththe durationof gaseousregulation y theuse of mousewastesas the majornutrition or the algalcommunity.The culturefluidremoved n the continuous perationof the algal microbial ommunitywascentrifuged ndtheliquidreturnedo the unit.The unitfunctionedwell for 10days;



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150 TAUBwithin 4 days aftersealingthe 02 rose to 25%, during the succeeding 5 days it variedfrom 23 to 25%, and on the 10th day it began to drop. At this time the culture hadbegun to turn yellowish green. Magnesium and phosphate were added, and within2 days the culture became deep green and the 02, which had been 19% on the 11thday, was up to 25%. During the remainder of the 6 week run magnesium andphosphate were added routinely each 5th day, and the 02 remainedbetween 23 and25%. The run was terminated at the end of 6 weeks because Golueke & Oswald (33)felt that no further information would be gained.Additional experiments resulted in reduction of the volume of algal-microbialcommunity required(33). Two points deserve examination: (a) a small volume wasmore effective than a large one, and (b) the microbial uses of 02 probably balancedthe ultimate composition of the gas around 25% 02. A large volume of culture (143ml/g mouse) was offset by inadequate light penetration, so that a smaller volume,25 ml/g of mouse, was as effective. A large part of the increase in yield was reportedto be due to an increase in the portion of the culture receiving an optimum amountof light. The potential self-regulationof the 02 in the mid-20% rangeis in interestingcontrast to the 63% 02 of Bowman & Thomae (9).The further suggestion of homeostatic properties of such systems was made byGolueke & Oswald (33):

The considerablenfluenceof carbondioxide on the systemwas demonstratednexperimentseported lsewhereOswald t al, 1962)concerningransferunctionswithrelation o step inputsof carbondioxide.The step inputswereaccomplished y firstremovingone of two mice fromthe microterellawhen the system was in a state ofequilibrium ithrespecto gas;andthenrestoringhemouseafter heoxygen oncentra-tion hadagainreached quilibrium.heimmediateesponsewas evaluatednbothsteps.Directlyafterremoval f the mouse, heoxygenconcentrationropped.However, fteraninterval f anhourorso, theoxygenconcentrationgainreached quilibrium,suallyat a level close to that beforeremovalof the mouse.Restoration f the mouseagainbrought bouta decline noxygenanda repetition f thepattern bserved ponremovalof the mouse.Apparently,healgalculturebuildsupanalgalpopulation roportionalo thecarbondioxideoutputof the micepresentntheunit.When he mouse oad s suddenly educed,the balancebetween arbondioxideandalgalpopulations upset,algalactivitydeclines,andoxygen production rops.Gradually, owever,a newequilibriums reached.Thesuddenrestoration f theoriginalmouse oad, andconsequent ugmentation f carbondioxide nputagainupsets he equilibrium. ut,as before, he cultureadjusts tself andthe originalequilibriums resumed.The abilityof the systemto adjust tselfshows itshomeostatic roperties.33, p. 526)Unfortunately, I have not been able to locate the experiments describedabove inmy copy of the report cited. Perhaps that experiment was described in another ofthe progress reports from that laboratory.The nutritional closure of the system, though incomplete because the mouse wasnot fed entirely on algae, suggests that nitrogen as well as magnesiumand phosphatemight become limiting. The deficiency of nitrogen in their budget was due largelyto the growth of young mice so that less nitrogen was returned to the algal culturethan was being consumed (70).



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CLOSEDECOLOGICAL YSTEMS 151The authors made special mention of the pleasant woodsy odor of the mi-croterella.

Implications Crudeas these studiesof coupledsystems were, they have severalimplications or a theoryof closed ecologicalsystems.1. Continuousight is not incompatiblewith algalculture; xperimentsn whichgaswas monitored ontinuously idnotindicateany24 hrperiodicitywith reducednighttimephotosynthesis, s mightbe expected f internalmetabolic locksregu-latedphotosynthesis r if metabolites roducedduring he darkwerenecessary orthe next day's photosynthesis.Variations n growthdid occur in these coupledsystems,as theydid in Krauss'Recyclostat 41), but none of the authorsreporteddiurnalcycles.2. The maintenance f the02 concentrationn the lower20%range s probablynot due to any universalhomeostaticmechanism f algal culturesalone, but maybea functionof algal-sewage ommunities, rovided hat lightis adequate.Suchamechanismmightbe hypothesized ince high02 concentrations known o inhibitphotosynthesis. hotosynthesis adbeenreported o decreasewhen he culturewasin equilibriumwith02 pressures bove 160mmHg (91). WhenCO2 s in limitedsupply ts productionby mice or microbesmightcontrolphotosynthesis.3. Carbonmonoxide idnotappearo be aproblem xcept n theblue-green lgalculturesystems.4. Self-inhibitinglgalproductsdid not limit the recyclingof usedalgalcultureliquid,as had beenpostulatedromresultsobtainedbyPratt 73)fromanapparentautoinhibitor e called chlorellin. urlew 12) suggested hatchlorellin, f pro-duced, mightbe destroyedby the bacteria n contaminatedultures,and that anecologicalbalancemightbe established etween he algaland bacterialgrowths.Krauss 42) failed to findany evidenceof an autoinhibitorn his Recyclostat, nwhichbacteria-freelgalculturesweremaintained.The autoinhibitor as not beendemonstratedn Chlorellayrenoidosa, or, accordingo Myers, nany algalstrainother than that usedby Pratt(53).

THE HOLISTIC APPROACH: THE ECOLOGISTS' CONTRIBUTION While closedecologicalsystemswerebeingresearched nd publishedby engineersand plantphysiologistsnthe late1950sandearly 1960s,at leasta few ecologistsried o makesome nput.Particularly . Odum,his studentR. Beyers,and aterE. Odumarguedthatnaturally erived ystemswouldbe more ikely o be successful ecauseof theirinformation ontentandhighly evolvedregulatorymechanisms.To increasecommunication nd facilitateunderstandingetween he engineersandecologistsand betweenbothgroupsand the generalacademicbiological om-munity, organized symposium, SpaceBiology:Ecological. spects, t the 1962meetingof the Aimericannstituteof BiologicalSciences AIBS)at OregonStateUniversity,Corvallis.Thesymposiumwas highlysponsored yvariousAIBSorga-nizations-the EcologicalSociety of America,AmericanSocietyof Zoologists,BotanicalSocietyof America,PhycologicalSocietyof America,Society or Indus-trialMicrobiology, nd AmericanFisheriesSociety,but not by NASA-and waswell attended.



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152 TAUBAs far as I can judge, the symposiumand the subsequentpublicationof thepresentations79) achieved either oal;opinions emained nchanged. omeecolo-gists expressed kepticism hat algae could grow and surviveat the high lightintensities eported 52,000 umensaccording o Matthern& Koch)(47) or undercontinuous ight. Most of the engineersperceived he ecologistsas introducingunnecessary omplexityandpresentingunfeasibledemands, uchas a need for 2acresperman(61) or the needto initiatestudies o gainfurtherunderstandingfnatural ystems 71).The publication f the presentationst the symposiumhas servedas a record.J.Myers 54) opened hemeeting ndstated he differing ointsofviewof ecologistsandengineers. comparedhe present ubsystemplanswiththe trophicorganiza-

tionandpresentedhe research escribed arlier 81). Beyers 5) reviewed alancedaquaticmicrocosmsand emphasizedhat the patternsof net photosynthesis ndnighttimerespirationweresimilarregardless f majororganisms,emperature,rsalinity.H. Odumanalyzed he spacevehicle ife-supportystemas a specialappli-cationof the moregeneral cosystems heory 61).In particular, e stated hat theefficiency-powereciprocity rinciple ictates hat high efficiency f lightutilizationcannotbe achievedwith maximalrate of output.He argued hat the hiddencostof maintaining rtificial lgalsystems s reallygreater han the total cost of usinga multispecies, elf-regulatingcosystem.He proposedconstruction f a systemfrom multiple eeding rom natural ources,which would be unstable or about 2weeks,butwould henbe competitive,elf-sustaining,ndhighlymetabolic.Tischer& Tischer(89) presented xperiments n the productionof Daphria, fungi,andbacteriaromurineand feces(reviewed arliern thispaper).Patten 71) presentedinformation heory as a necessary ool for understanding aturalecosystemsandprobably or wiselydesigning pacesystems.Matthern& Koch(47)described heengineering f massalgalcultures,andWardet al presentedhe uses of algaeandother plants in space systems(96). Of the engineers' ontributions,hat of theMicroterella f Golueke & Oswald was most closely related n conceptto anaturally erived,multispecies cosystem though t was reviewed ereas a coupledsubsystem 33)]. The symposiumncludedan engineering pproach o ecologicalconsiderations f a permanentunarbase(38)as wellas a planfor theinvestigationof extra-terrestrialife. Muchof the presentation t this symposiumwas citedbyCooke, Beyers& Odum(19) andby Cooke(18).Theonlycontributionsyecologists hatI was ableto find nany iteratureikelyto be readby researchersn thespacefieldwere(a) by E. Odumat the DiscussiononRegenerative ystemsn 1963,heldwithinaConferencenHumanEcology 10),(b) a presentation y Cooke,Beyers& E. Odum at the BioregenerativeystemsConferencen 1966 19),andpossibly c) my presentationtthesymposium Foodsin Space 82), which marginally inted at some ecologicalconsiderations.At the RegenerativeSystemsConference,Brown (10), the discussion eader,indicated he lack of inputfrom ecologistsand attributedt to the opinionthatecologistsdid not consider t partof their bailiwick.E. Odumpresented he ap-proachof H. Odum & Beyersof multipleseeding rom naturalcommunitiesol-lowedby closureand self-regulation,ut it was met withoutenthusiasm.Brownopined hat such studiesare of interest o theecologistbut not applicableo space



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CLOSEDECOLOGICAL YSTEMS 153systems.Still later,E. Odumreiteratedhe advisability f usingstabilitymecha-nisms that hadevolved n diversenatural ystems,and Brownagainrejected hisapproach.FremontSmith upportedheecologists' fforts o the extentof advocat-ingpursuit fbothapproaches,lthoughnopractical sewasyetapparent, becausethe resultsthat may come of this line of thoughtareunpredictable. .CookepresentedhepaperbyCooke,Beyers&Odumentitled TheCasefortheMultispecies cologicalSystemwithSpecialReference o Succession ndStability,at the BioregenerativeystemsConferenceponsored y NASA in 1966(19). In itthe authorsstatedthat the engineering pproachof testingand laterassemblingseparate ubsystemswouldsurely ail,whereas heecologicalapproach f allowinggroupsof speciesknown o occurtogether o reassemble ndreorganizen a newenvironmentnto anintegrated,elf-maintainingystem,anecosystem,wouldpro-vide the greatestopportunityor developinga successful ong-term ife-supportsystem.Theysuggestedhemultispecieslimaxecosystem sproposed yH. Odum(61).Theystressedhat lowefficiencywithhighstabilitywouldbefeasible,whereashigh-efficiency onocultures ouldrequire xcessive xternal ontrolrequirements.Theydrewheavilyon thefoodwebstudiesof Paine, hemicroecosystemtudiesofCookeand Beyers,andthe trendstudiesof stagesof ecosystemsby E. Odum.Thediscussion fter hemeeting eflectedheantagonism mong he otherpartic-ipants.Thefollowingobjectionswerestated: his wasmerelyrewordingheprocessof one-by-oneelectionofcomponents; self-regulatingcosystemwouldnotneces-sarilyensure hesurvival f any onecomponent, .g.man; hespacesystem s beingsupported y earth echnology nd it doesnot have to includeall of thefunctionalcomponents f the earth;monocultures the basisof most of our agriculture ndnecessary or evena lunar or Martiancolony;the inclusionof 20 specieswouldrequire 10experiments s a minimum; nd it was questionedwhether he mixedculturesof Oswald& Goluekeweremorestablethanthe two-componentmouse-algasystemsof Myersor the single-alga ulturesof Krauss.In spiteof Cooke'srebuttals, he participantsemained pposed o the conceptof a systemdevelopedby natural eedingandself-controlleduccession o an operational limaxstage.E.Odum,Beyers,andCookedidhavea NASAresearch ontract,NsG 706/11-003, but it was terminatedprematurely.This was the only workon ecologicalecosystems upported o my knowledge. I hada smallgrant(NsG 519) to studythefeasibility f using hedevelopment f Daphniaundernullgravity s a potentialBiosatelliteexperiment,but the experimentwas judgedtoo complexbecauseIplanned o use a lightedcultureof algaeas a sourceof food and02.1ChemosyntheticRegenerativeSystemsWith the increasingdisenchantmentn the partof NASA with photosyntheticsystemsbecauseof their owefficiency f electricalutilization,heHydrogenomonasbacteria ystembegan o lookmorefeasible.Electrolysiswasdeemedmoreaccept-able thanphotosynthesis ecauseof its greater fficiencyOf02 production erunitofelectricity.Bacteria fthegenusHydrogenomonasrecapable futilizing aseoushydrogen s anenergy ource,CO2as a carbon ource,andureaorammoniumaltsas a nitrogen ource.Tracematerialsmust alsobe supplied n a growthmedium.



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154 TAUBTheCO2and urinecould berecycledf H2weresupplied o producebacterial ellsandwater:6H2+ 202 + CO2 (CH20)+ 5H20. Subsequentlyhe watercouldbe electrolyzedto supply 02 for the astronautsand to resupplyH2 for Hy-drogenomonasulture.The cell massmight be a potential ood.Obviously herewouldbe a potential aving n electricalpowerrequirements;ut, as in thecase ofthe algalculture,could a biological ystemhave adequate eliability?NASA's interest n Hydrogenomonasystems sparkeda numberof studiesongrowthand food value.Manyof thesearereviewedn Bioregenerativeystems 56)and n TheClosedLifeSupport ystem 55),especiallyhe papers f Drakeet al (25),Jogowet al (36), and Foster& Litchfield29) in the latter.Publicationn 1972 ofthe paper MassCultivation f Hydrogenomonasutropa n SubmergedCultureby Litchfield 44) suggeststhat NASA is still pursuing his approach.He citesunsuccessful uman eeding rials,but successful nimal rials.A coupledculture-electrolysis ystemappears ot to havebeenstudiedyet;therefore o closedsystemshave beentested.The above s a roughsketchof the U.S. literature elated o space applicationsofclosedecological ystems, ompletelygnoringhe verysubstantialRussianitera-ture that appears o follow the same trends.Access to the total literature an beobtainedby requesting searchfrom NASA usingappropriate ey words. Forinstance,using hekeyword Bioregeneration ASA indexed358 references,ndunder ClosedEcological ystems t indexed 61more 58).TheRussian iterature(translated)s especiallywell covered here.The NationalTechnical nformationService 92)alsosupplied everalhundred eferencesn the title ClosedEcologicalSystems appreciations tendered o the Environmental rotectionAgencyforsupplying his material).NON-SPACE-RELATED STUDIESInspiteof thelackof stimulusby the spaceprogram,he studyof natural ommuni-ties has moved owarda systemsanalysisapproach.Whilenatural ystemnsre notclosedthermodynamically,eitherwere the photosynthetic egenerativeife-sup-port experiments.Both are concernedwith the processeswithinan interactingsystemso defined hat inputsand outputscan be measured.Two experimentalapproacheso the studyof naturalcommunitiesare especiallyrelated o closedecologicalsystems:metabolismof naturalcommunitiesand microcosmstudies.Spacepermitsonly a cursory reatment f either topic.Metabolism of Natural CommunitiesThe zornireefstudy (63) nrldhe SWiey pfimgstudy(%W) w'l tecognized asclassics n thestudyof communitymetabolism.Numerousother studieshaveusedthe same approach 20-23, 64-66). P/R (photosynthesis/respiration)atiosap-proach1in undisturbed,mature ommunities, nd lowervalues, .e. proportionallymorerespiration, re foundunderorganic nputs.Homeostaticmechanismseemto exist. It would be interesting o examine the data in sufficientdetail, or toundertake ewstudies, o seewhether he P/R ratio wouldbe greater han 1 with



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CLOSEDECOLOGICAL YSTEMS 155the removal of organic material, e.g. fishing, and with the replacementof equivalentinorganic nutrients. Community metabolism deserves a review of its own.More detailed studies of community metabolism, or more particularly carbonflow, have been published by Saunders (77) and have been presented by Hobby andalso by Wetzel (personal communications). These three authors have been compar-ing their results to determine whether differentkinds of lakes have the same generalpatterns.Another approach to community metabolism was made by Olson (69), who usedsystem analysis to examine the balance between producersand decomposers and thesubsequent storage. System analysis is being used extensively now.Microcosm ResearchThe research on microcosms has been reviewed recently by Cooke (17); for reasonsof space, the studies in that review will not be discussed here. After reviewing theinformation on diurnal metabolism, ecological succession, P/R ratios, phosphoruscycling, and maturity and stability, Cooke concluded that these laboratory mi-crocosms have demonstrated certain regulatory properties of ecosystems.Because microcosm studies require large populations of numerous interactingorganisms, most have dealt with microbial communities. The entire symposiumpublication tructure ndFunction f FreshwaterMicrobialCommunities13) mayserve as a review itself. In that volume I presented the results of a continuousgnotobiotic ecosystem consisting of an alga, a herbivorous protozoan, and twobacteria (83). Since then I have simplified the continuous cultures to only twoorganisms, the alga and the herbivorous protozoan. The relationship between thenutrient, alga, and protozoan has been modelled mathematically with the help ofD. McKenzie of our laboratory (84, 86). I am now in the process, with N. Pearson,of attempting to verify the predictions of the model. In the course of these studiesI have become aware of another experimental-mathematicaltreatment of stabilityrelationships of continuous predator-preycultures. These studies (14, 15, 24, 26, 39,80, 90) are heterotrophic, being based on an organic compound and bacteria-protozoa interactions. In contrast, my system starts almost devoid of organics andthe protozoa depend on the photosynthesis and growth of the algae as their solesource of food. I believe a reviewon predator-prey continuous culturesis in prepara-tion.Closed Microcosms and Balanced Aquaria Studies3Most of this work, including my own, appearsto be unpublished. Both Beyers andCooke have made observations on closed systems, but have not completed studies

3Since reparinghereview, wopapers n massandenergy low nclosedecosystems avebeen ound.Ulanowicz 100)proposed mathematicalrameworkor linear ystemsrelatingtheparametersfpopulation ynamicsothoseofenergy low;May 101)hasconsideredmorecomplexwebs.Theystated hata necessary nd sufficient onditionorecosystemtabilitysthatenergy ontentperunitbiomassncreasena hierarchicalashion sone climbs hetrophicladder.Other nsights ntrophic elationshipsre ndicated.No experimentalrobservationalresultsareconsidered.Thesemodelsmightprovide he basisfor validation xperiments.



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156 TAUBsuitablefor publication.E. Odum (59) picturedseveraldemonstrationystemsapparently stablishedor teachingpurposes,but no data wereshown.Twocom-pletedstudies rommy laboratorynvolved1.a seriesof pairedalgaland bacterialcultures onnectedonlyby a gasbridge,and 2. naturallyderived ultures nrichedwithvaryingamountsof nutrients.On thesubjectof balanced quaria, was unable o findanydetailed esearches.E. Odum(59) cited a reportby Waringtonof the establishment f a 12 gallonaquariumystem.Atz (3) hadapparentlytatedbalanced quariao beimpossible,atleastas mostaquarists ave ried o establish hem(cited n62). Odum& Johnson(62)agreewith Atz thatsmallsystemswithnumerousish are impossible, utthatthe sealedaquariums not impossiblen concept, givenan adequatebiomassofproducersnddecomposers. alanced quariawerepreparedor sale n 1973by twowomenin Washington tate,AnnetteNormanand SarahWilson.Most of theirsystemswere gallon ugs with sand,water 2/3), air (1/3) and severalplants,ponddetritussnails,and a pairof guppies.Zooplanktondid not persist,as they wererapidlyeaten.The fish tended o live about4 monthsbut rarelyreproduced. hesnailssurvived or about6 monthsin the systemthey gave me, and the plantsappearedhealthyafter 10 months.Their resultsappear o be typicalof most at-tempts.SUMMARYStudies f closedecological ystemsnevermanagedocombine heholisticapproachof the few ecologistsactive in that field with the subsystemsapproachof theengineers ndphysiologists. heonlyhypotheses fferedbytheengineeringtudieswere(a) that a homeostaticmechanismmightbe responsibleor the controlof 02concentrationn the low 20% range,and(b) that some of thesupport ora highertrophicevel(man)mightcomefromusing ecalmaterialo growfungiorfish.Thedetritalcyclesof lakes,estuaries,orests,anddesertsare now receivingncreasedstudy,especially n theInternational iologicalProgram.P. Bissonette nd I havebeenexploring he hypothesis hat muchdetritalmaterial n lakes becomescon-vertedntochironomid iomass ndthechironomidsresubsequentlyatenby fish.The massalgalculture echniquesmayyetbe used n theproduction f agricultureor, sinceharvestinghe smallcells fromthe liquid s a problem, heproduction faquatic ood for aquatic ilterfeeders85).Thespaceefforthas managedhusfar withoutbiological egenerativeystemsofeitherthe photosyntheticr chemosyntheticype.SkyLab,with its crewof threeremainingn excessof 2 months,apparentlymanagedwith storedexpendablemate-rials and probablywaterfrom the fuel cells (28).Sealedecologicalsystemsdo permitexamination f the self-regulationnherentina givenset oforganismswitha finite etof chemical esources.Gaseous xchangeis difficult nd expensiveo measure irectly,and estimatesof 02 andCO2 ransferfrom 2 diffusion ndpHchange equiremeasurementsrestimations f concentra-tion gradientsand mixingcoefficients.Nitrogentransfers evenmore difficult omeasureunlessthere s significantN2fixationor release.Respirometryechniques



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CLOSEDECOLOGICAL YSTEMS 157introduceartifactsbecausethey requiredense concentrations f organismsandextremepH buffering.Theinclusionof an atmospheren a sealedsystempermitsthe water-atmosphereiffusion ndstorage unctions hat occur n the biosphere.In a sealed system, transientconcentrationsOf02 and CO2 can be monitoredcontinuously nd can providea moredetailedrecordof communitymetabolism.This approachmay yet providean excellent tool for studyingtotal communityresponses o manipulations.LiteratureCited

1. Adams,C. C. 1963.Nutritional spectsof space flight.Medicaland BiologicalProblemsof SpaceFlight, ed. G. H.Bourne,Chap.10, 237-44. New York:Academic.289 pp.2. AeronauticalSystems Division, Dir/Aeromechanics, Flight AccessoriesLab., Wright-PattersonAFB, Ohio.1963.Atmospheric ontrol ystemsorSpace Vehicles.Rep. ASD-TDR-62-527, Part I. Arlington,Va.: ArmedServ.Tech.Inf.Agency.247 pp.3. Atz, J. W. 1949. The balancedaquariummyth. Aquarist 14:159-60,179-824. Benjamin,F. B., Taufman,W. I., Hel-vey,W. M. 1962.Biologisticsor SpaceSystems Symposium,242-64. Aero-space Med. Div., 6570th AerospaceMed. Res. Lab., Wright-PattersonAFB, OhioAMRL-TDR-62-1165. Beyers,R. J. 1963.Balancedaquaticmicrocosms-their implications forspace travel. Am. Biol. Teach. 25:422-296. Bieberdorf, . W. 1962.A StudyofMi-crobiologicalWaste TreatmentTech-niques.USAF 6570thAerospaceMed.Res. Lab., Wright-PattersonF Base,Ohio,AMRL-TDR-62-142.83 pp.7. Bovee,H. H. et al 1962.Large algalsystems.See Ref.4, 8-198. Bowman,R. O., Thomae,F. W. 1960.An algae ifesupport ystem.AerospaceEng. 19(12):26-29, 29. Bowman,R. O., Thomae,F. W. 1961.Long-term ontoxic upportof animallife withalgae.Science134:55-5610. Brown,A. H. 1966. Regenerativeys-tems. Proc. Ist Int. InterdisciplinaryConf:,Princeton,NJ., October 3-16,1963,ed.D. H.Calloway, 2-119.NewYork:New YorkAcad.Sci.11. Burlew,J. S. 1961.AlgalCultureromLaboratoryo PilotPlant.WashingtonDC: Carnegie nst. Publ. 600. 357 pp.(First printing1953)12. Burlew, .S. 1961.Currenttatusof the

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