ecological engineering: a ﬁeld whose time has come...w.j. mitsch, s.e. jørgensen / ecological...

Ecological Engineering 20 (2003) 363–377

Ecological engineering: A field whose time has come

William J. Mitscha,∗, Sven E. Jørgensenb

a Olentangy River Wetland Research Park and School of Natural Resources, The Ohio State University, Columbus, OH 43210, USAb Environmental Chemistry, Royal Danish School of Pharmacy, Copenhagen, DK, Denmark

Received 10 May 2002; received in revised form 14 December 2002; accepted 1 May 2003

Abstract

Ecological engineering is defined as “the design of sustainable ecosystems that integrate human society with its naturalenvironment for the benefit of both.” It involves the restoration of ecosystems that have been substantially disturbed by humanactivities such as environmental pollution or land disturbance; and the development of new sustainable ecosystems that haveboth human and ecological value. While there was some early discussion of ecological engineering in the 1960s, its developmentwas spawned later by several factors, including loss of confidence in the view that all pollution problems can be solved throughtechnological means and the realization that with technological means, pollutants are just being moved from one form toanother. Conventional approaches require massive amounts of resources to solve these problems, and that in turn perpetuatescarbon and nitrogen cycle problems, for example. The development of ecological engineering was given strong impetus in thelast decade with a textbook, the journalEcological Engineeringand two professional ecological engineering societies. Fiveprinciples about ecological engineering are: (1) It is based on the self-designing capacity of ecosystems; (2) It can be the acidtest of ecological theories; (3) It relies on system approaches; (4) It conserves non-renewable energy sources; and (5) It supportsbiological conservation. Ecology as a science is not routinely integrated into engineering curricula, even in environmentalengineering programs, while shortcoming, ecologists, environmental scientists, and managers miss important training in theirprofession—problem solving. These two problems could be solved in the integrated field of ecological engineering.© 2003 Elsevier B.V. All rights reserved.

Keywords:Ecotechnology; Self-design; Self-organization; Ecological conservation

1. Introduction

We are now in a position to make a substantialcontribution to the “greening” of the planet throughecological engineering. The present era’s approach tohuman history is retrospective, both politically andecologically. While not necessarily questioning all we

∗ Corresponding author. Tel.:+1-614-292-9774;fax: +1-614-292-9773.

E-mail address:[email protected] (W.J. Mitsch).

have built and engineered to date, we should be deter-mining (1) whether to continue practices as usual (andwhether we can afford to do so), and (2) what newapproaches are available to engineers for restoringthe “bodily functions” of nature on which we depend.Signs all around us indicate that a paradigm shift istaking place both within and outside the engineeringprofession to accommodate ecological approaches towhat was formerly done through rigid engineeringand a general avoidance of any reliance on naturalsystems. For example, engineers, ecologists, resource

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364 W.J. Mitsch, S.E. Jørgensen / Ecological Engineering 20 (2003) 363–377

managers, and even politicians are now redesign-ing the plumbing in the southern Florida Evergladesto a plan that is friendlier to the natural environ-ment. As part of that effort, the Kissimmee River inFlorida is being “restored”—at an enormous cost—tosomething resembling its former self before it wasstraightened 20 years ago (Fig. 1). Discussions arenow in progress as to how and where to restore theMississippi River Basin to a more natural state by re-moving dikes, restoring wetlands and riparian forests,and even letting the Louisiana Delta flood once againto save the enormous cost of floods and to save theGulf of Mexico from its terrible hypoxia that nowspreads over an area the size of New Jersey (Mitsch

Fig. 1. Part of the Everglades area restoration includes restoration of the Kissimmee River from central Florida to Lake Okeechobee. Atleft is a restored meander and at right is the channelized river. Illustration courtesy of Lou Toth, photo by Paul Whalen, South FloridaWater Management District, West Palm Beach, FL, reprinted with permission.

et al., 2001). A restoration of 4000 ha of coastal saltmarshes is currently occurring in the Delaware Estu-ary in eastern USA (Fig. 2). Agricultural engineers,known for the efficiency with which they drainedthe landscape, are retooling in many locations torebuild wetlands and reverse the drainage. Civil en-gineers, long the nation’s river straighteners, are nowinvolved in removing dams and restoring meanders.In Jutland, Denmark, engineers and scientists arepresently bringing the Skern River, Denmark’s largestriver, back to its old meandering course (Fig. 3).This is now the century of ecological engineer-ing and ecosystem restoration in many parts of theworld.

W.J. Mitsch, S.E. Jørgensen / Ecological Engineering 20 (2003) 363–377 365

Fig. 2. Maurice River Township salt marsh restoration site, one of several locations of coastal marsh restoration along Delaware Bay ineastern United States (photo by W.J. Mitsch).

2. Definition of ecological engineering

We now defineecological engineering as the designof sustainable ecosystems that integrate human societywith its natural environment for the benefit of both(seeMitsch, 1996, 1998). This definition varies slightlyfrom the definition we gave (Mitsch, 1993; Mitschand Jørgensen, 1989), where ecological engineeringwas defined as “the design of human society withits natural environment for the benefit of both.” Wenow believe, with hindsight, that “the design of hu-man society” was perhaps too ambitious a goal for afledgling field and would be much more than engi-neers and scientists can or should do. In fact, it wouldbe social engineering. But “the design of sustainableecosystems” is clearly a sustainable goal that can be

achieved for individual projects, watersheds, and evenlandscape scales.

In a word, ecological engineering involves creatingand restoring sustainable ecosystems that have valueto both humans and nature. Ecological engineeringcombines basic and applied science for the restora-tion, design, and construction of aquatic and terrestrialecosystems. The goals of ecological engineering andecotechnology are:

1. the restoration of ecosystems that have beensubstantially disturbed by human activities suchas environmental pollution or land disturbance;and

2. the development of new sustainable ecosystemsthat have both human and ecological value.


Fig. 3. Restoration of the Skern River in western Denmark back to its old meandering course: (a) straight stream prior to restoration; (b)meandering stream after channel restoration (photos by W.J. Mitsch; fromMitsch and Jørgensen, 2004, reprinted with permission, Wiley).


It is engineering in the sense that it involves thedesign of the natural environment through quantita-tive approaches and that our approaches rely on basicscience. It is a technology whose primary tool is theself-designing ecosystem. It is biology and ecology inthe sense that the components are all of the biologicalspecies of the world.

3. History of ecological engineering

The term ecological engineering was coined byHoward T. Odum in the 1960s and has since been usedextensively in the North America, Europe, and China.Odum defined ecological engineering as “those casesin which the energy supplied by man is small rela-tive to the natural sources, but sufficient to producelarge effects in the resulting patterns and processes”(Odum, 1962) and “environmental manipulation byman using small amounts of supplementary energyto control systems in which the main energy drivesare still coming from natural sources” (Odum et al.,1963). Odum (1971)elaborated on the breadth of eco-logical engineering in his bookEnvironment, Powerand Societyby stating that “the management of natureis ecological engineering, an endeavor with singularaspects supplementary to those of traditional engi-neering. A partnership with nature is a better term.”He later stated inSystems Ecology(Odum, 1983) that“the engineering of new ecosystem designs is a fieldthat uses systems that are mainly self-organizing.”

Concurrent but separate from the development ofecological engineering concepts in the West was a sim-ilar development of the term “ecological engineering”in China. Under the leadership of Ma Shijun, knownas “the father of ecological engineering in China,”ecologists in China began using the term “ecologicalengineering” in the 1960s, with much of that workwritten in Chinese language publications. In one of thefirst publications in western literature,Ma (1985)de-scribed the application of ecological principles in theconcept of ecological engineering in China. Much ofthe approach to environmental management in Chinabegan as an art, but in the past two decades there hasbeen explicit use of the term “ecological engineering”in China. It was first used to describe a formal “de-sign with nature” philosophy for wastewater.Ma(1988)later defined ecological engineering as: “. . . a

specially designed system of production process inwhich the principles of the species symbiosis and thecycling and regeneration of substances in an ecologi-cal system are applied with adopting the system engi-neering technology and introducing new technologiesand excellent traditional production measures to makea multi-step use of substance.” He suggested thatecological engineering was first proposed in China in1978 and is now used throughout the whole country,with about 500 sites in 1988 that were practicingagro-ecological engineering, defined as an “applica-tion of ecological engineering in agriculture” (Ma,1988). That number was updated to about 2000 appli-cations of ecological engineering in China by the early1990s (Yan and Zhang, 1992; Yan et al., 1993). Qiand Tian (1988) suggested that “the objectiveof ecological research [in China] is being trans-formed from systems analysis to system designand construction,” stating that ecology now has agreat knowledge base from observational and ex-perimental ecology and is in the position to meetglobal environmental problems through ecosystemdesign, the main task of ecological engineering.Yanand Yao (1989)describe integrated fish culture man-agement as it is practiced in China as ecological en-gineering because of its attention to waste utilizationand recycling. Part of the Chinese special approachto ecological engineering is based on China’s histor-ical background (Yan et al., 1993), some facets ofwhich are compatible with modern ecological theory.The most influential theory in Chinese philosophyis the yin-yang. The symbol for yin-yang resemblestwo fish, one eating the tail of the other. The dots,while resembling an eye, suggest that to prevent anyforce from reaching an extreme, the system containsa seed of its opposite to maintain a balance. A relatedphilosophy is that of five elements in which there ismutual restraint of five elements—fire, water, wood,metal, and soil. This outlook suggests, as does theyin and yang, the balance of promotion and restraint(Yan et al., 1993).

With these philosophies, a concept close to ecologi-cal engineering developed in China and the East prob-ably centuries ago. The emphasis of our recent defini-tions of ecological engineering in the West has been apartnership with nature and research has been carriedout primarily in experimental ecosystems with somefull-scale applications in aquatic systems, particularly


shallow ponds and wetlands. Ecological engineering,as pioneered by Ma and others in China, however,has been applied to a wide variety of natural resourceand environmental problems, ranging from fisheriesand agriculture, to wastewater control and coastlineprotection. A more detailed comparison of westernand Chinese approaches to ecological engineering arediscussed inMitsch (1991, 1995)and Mitsch et al.(1993).

Meanwhile, there was a similar development ofthe field of ecotechnology in central Europe in themid-1980s.Uhlmann (1983), Straskraba and Gnauck(1985) and Straskraba (1993)defined ecotechnologyas the “use of technological means for ecosystemmanagement, based on deep ecological understand-ing, to minimize the costs of measures and theirharm to the environment.”Straskraba (1993)furtherelaborated on this point and called ecotechnology“the transfer or ecological principles into ecologicalmanagement.” In this paper, we consider ecologicalengineering and ecotechnology as similiar but agreethat the former term involves mostly creation andrestoration of ecosystems while the latter term in-volves managing ecosystems. Which is the more en-compassing term is difficult to say but it could be, asStraskraba (1993)suggested that “Ecotechnology isin a sense broader [than ecological engineering,] be-ing that environmental management [ecotechnology]is considered not only the creation and restoration ofecosystems.”

The marine scientist John Todd in New EnglandUSA was also a leader in applying both the term andthe concepts of ecological engineering to wastew-ater treatment, first at his New Alchemy Instituteand later at his Ocean Ark Center. The term “eco-logical engineering” was applied to the treatment ofwastewater and septage in ecologically based “greenmachines,” with indoor greenhouse applications builtboth in Sweden and the United States in the late1980s (Guterstam, 1996; Guterstam and Todd, 1990;Peterson and Teal, 1996; Teal and Peterson, 1991,1993). Here the applications are described as “environ-mentally responsible technology [that] would providelittle or no sludge, generate useful byproducts, use nohazardous chemicals in the process chain and removesynthetic chemicals from the wastewater” (Guterstamand Todd, 1990). All applications within this subsetof ecological engineering have the commonality of

using ecosystems for treatment of human wastes withan emphasis on truly solving problems with an eco-logical system rather than simply shifting the problemto another medium.

The field of biospherics, which was interested inthe eventual habitation of humans in space, becameanother field with connections to ecological engineer-ing, particularly when Biosphere 2, a glass-enclosedset of ecosystems, was built in the Arizona desert. Thisproject, described in detail in a special issue ofEcolog-ical Engineering(Marino and Odum, 1999) may havebeen on the outer fringe of ecological engineering, asit needed a 10 MW power plant for its fans to move air,its HVAC systems to keep temperatures reasonable,and its pumps to create a hydrologic cycle. The im-portant value of Biosphere 2 is clear: “. . . we shouldappreciate and try to understand the workings of theecosystems in the biosphere that we have” (Mitsch,1999).

Our 1989 book entitled “Ecological Engineer-ing: An Introduction to Ecotechnology” (Mitsch andJørgensen, 1989) and the subsequent initiation ofthe scientific journalEcological Engineering: TheJournal of Ecotechnologyin 1992 brought ecolog-ical engineering principles and practice to a muchwider audience. A 1993 workshop in Washington,DC, sponsored by the US Scientific Committee onProblems in the Environment (SCOPE), led to theestablishment of an international project on “Eco-logical Engineering and Ecosystem Restoration” inParis in 1995 as part of the SCOPE project. Thatcommittee, developed several special issues basedon workshops held around the world that have beensubsequently published inEcological Engineering(Table 1). These volumes give a good glimpse ofthe array of international approaches to ecologi-cal engineering, in developed economies (Hüttl andBradshaw, 2001; Lefeuvre et al., 2002), in develop-ing economies (Wang et al., 1998), and in economiesin transition (Mitsch and Mander, 1997). In themeantime, the International Ecological Engineer-ing Society (IEES) was established in Utrecht, TheNetherlands, in 1993 and the American EcologicalEngineering Society (AEES) in Athens, Georgia in2001. Our bookEcological Engineering and Ecosys-tem Restoration(Mitsch and Jørgensen, 2004), illus-trates how far the field has developed since the 1989book.


Table 1Workshops and subsequent special issue publications of Scientific Committee on Problems in the Environment (SCOPE) project “EcologicalEngineering and Ecosystem Restoration” (fromMitsch and Jørgensen, 2004)

Workshop title Workshop location and date Special issue publication

Ecological engineering in central and easternEurope: remediation of ecosystems damagedby environmental contamination

Tallin, Estonia 6–8 November 1995 Mitsch and Mander (1997)

Ecological engineering in developing countries Beijing, China 7–11 October 1996 Wang et al. (1998)Ecological engineering applied to river and

wetland restorationParis, France 29–31 July 1998 Lefeuvre et al. (2002)

Ecology of post-mining landscapes Cottbus, Germany 15–19 March 1999 Hüttl and Bradshaw (2001)

4. Basic concepts in ecological engineering

There are some basic concepts that collectively dis-tinguish ecological engineering from more conven-tional approaches to solving environmental problemswith engineering approaches. These include the fol-lowing concepts about ecological engineering:

(1) It is the based on the self-designing capacity ofecosystems;

(2) It can be the acid test of ecological theories;(3) It relies on system approaches;(4) It conserves non-renewable energy sources; and(5) It supports biological conservation.

These concepts are discussed in more detail below.Much of this text is fromMitsch and Jørgensen (2004).

4.1. Self-design

Self-design and the related concept of self-organization are important properties of ecosystems tounderstand in the context of creation and restorationof ecosystems. In fact, their application may be themost fundamental concept of ecological engineering.

Table 2Systems categorized by types of organization (fromPahl-Wostl, 1995)

Characteristic Imposed organization Self-organization

Control Externally imposed; centralized control Endogenously imposed; distributed controlRigidity Rigid networks Flexible networksPotential for adaptation Little potential High potentialApplication Conventional engineering Ecological engineering

Examples Machine OrganismFascist or socialist society Democratic societyAgriculture Natural ecosystem

Self-organization isthe property of systems in gen-eral to reorganize themselves given an environmentthat is inherently unstable and non-homogeneous.Self-organization is a systems property that appliesvery well to ecosystems in which species are con-tinually introduced and deleted, species interactions,e.g., predation, mutualism, etc., change in dominance,and the environment itself changes. Since ecologicalengineering often involves the development of newecosystems as well as the use of pilot-scale modelssuch as mesocosms to test ecosystem behavior, theself-organizing capacity of ecosystems remains anenigma to ecologists yet an important concept forecological engineering.

There are two ways that systems can be organized—by rigid top-down control or external influence (im-posed organization) or by self-organization (Table 2).Imposed organization, such as done in many conven-tional engineering approaches, results in rigid struc-tures and little potential for adapting to change. Thisof course is desirable for engineering design wherepredictability of safe and reliable structures are nec-essary such as for bridges, furnaces, and sulfur scrub-bers. Self-organization, on the other hand, develops


flexible networks with a much higher potential foradaptation to new situations. It is thus the latter prop-erty that is desirable for solving many of our eco-logical problems. Here, when biological systems areinvolved, the ability for the ecosystems to change,adapt, and grow according to forcing functions andinternal feedbacks is most important.

We define self-design as the application ofself-organization in the design of ecosystems. Thepresence and survival of species in ecosystems aftertheir introduction by nature or humans is more up tonature than to humans. Self-design is an ecosystemfunction in which the chance introduction of speciesis analogous to the chance development of mutationsnecessary for evolution to proceed (Mitsch, 1998).Multiple seeding of species into ecologically engi-neered systems is one way to speed the selectionprocess in this self-organization (Odum, 1989). In thecontext of ecosystem development, self-design meansthat if an ecosystem is open to allow “seeding” ofenough species and their propagules through humanor natural means, the system itself will optimize itsdesign by selecting for the assemblage of plants, mi-crobes, and animals that is best adapted for existingconditions. The ecosystem then “designs a mix ofman-made and ecological components [in a] patternthat maximizes performance, because it reinforces thestrongest of alternative pathways that are provided bythe variety of species and human initiatives” (Odum,1989).

A whole-system ecosystem experiment that hasdeveloped for almost a decade involves wetlands atthe Olentangy River Wetland Research Park in Ohio,USA, where continual introduction of river waterover a decade has accelerated the natural process ofself-design.Mitsch et al. (1998)describe how 2500individuals of 12 plant species were introduced to onewetland basin while the other remained an unplantedcontrol, essentially testing the self-design capabilitiesof nature with and without human help. Both basins(Fig. 4) had identical inflows of river water and hy-droperiods. After only 3 years, there was convergenceof wetland function of the planted and unplantedbasins with 71% of functional indicators essentiallythe same in the two basins. This convergence in year3 followed the second year where only 12% of theindicators were similar. Most importantly, hundredsof taxa, both aquatic and terrestrial, were continually

Fig. 4. Olentangy River Wetland Research Park at Ohio StateUniversity, Columbus, OH, USA, showing two kidney-shaped ex-perimental wetlands. Basin on right was planted with 12 speciesof wetland plants; basin on left was not planted. Photo is aftersix growing seasons in 1999. This represents a long-term exper-iment in self-design. Photo courtesy of Olentangy River WetlandResearch Park.

introduced to these wetland basins, primarily becausethe wetland basins were hydrologically open systems,and many taxa survived. In 3 years, over 50 speciesof macrophytes, 130 genera of algae, over 30 taxa ofaquatic invertebrates, and dozens of bird species foundtheir way naturally to the wetlands. After 6 years,there were over 100 species of macrophytes but a con-tinued effect of the initial planting was still observedin ecosystem function. The continual introductionof species, whether introduced through flooding andother abiotic and biotic pathways, appeared have amuch more long-lasting effect in development of theseecosystems than did the introduction of a few speciesof plants. But both are important in self-design.

By contrast to the self-design approach, the ap-proach that is more commonly used today by manybiologists for much of what we call ecological restora-tion may be even closer to conventional engineering


than is ecological engineering. There has sometimesbeen reference to this idea of a forceful “design” ofecosystems as the designer approach and the producedecosystems asdesigner ecosystems(van der Valk,1998). There is more honesty in this term than manyare willing to acknowledge. This designer approach,while understandable because of the natural human(not only engineer’s) tendency to control events, isless sustainable than an approach that relies more onnature’s capacity to self-design. In these cases, theintroduction of specific organisms is the goal and thesurvival of these organisms becomes the measure ofsuccess of the project. Systems are being designed inboth cases, perhaps without the precision of systemsthat engineers design with physics and chemistry astheir main sciences. Biology adds to the variabilityof the systems but otherwise design and predictablestructures are carried out and desired.

As we described in our early book (Mitsch andJørgensen (1989): “Ecological engineering is engi-neering in the sense that it involves the design of thisnatural environment using quantitative approaches andbasing our approaches on basic science. It is technol-ogy with the primary tool being self-designing ecosys-tems. The components are all of the biological speciesof the world.”

4.2. The acid test

Restoration ecologists have long suggested the tiebetween basic research and ecosystem restoration,stating that the best way to understand a system,whether a car, a watch, or an ecosystem, is to “at-tempt to reassemble it, to repair it, and to adjust itso that it works properly” (Jordan et al., 1987). Eco-logical engineering will be the ultimate test of manyof our ecological theories.Bradshaw (1987)has de-scribed the restoration of a disturbed ecosystem asthe “acid test of our understanding of that system.”Cairns (1988)was more direct: “One of the mostcompelling reasons for the failure of theoretical ecol-ogists to spend more time on restoration ecology isthe exposure of serious weaknesses in many of thewidely accepted theories and concepts of ecology.”Bradshaw (1997)calls ecosystem restoration, whendone properly, “ecological engineering of the bestkind.” Ecological theories that have been put forwardin the scholarly publications over the past 100 years

must serve as the basis of the language and the prac-tice of ecological engineering. But just as there isthe possibility of these theories providing the basisfor engineering design of ecosystems, there is also apossibility of finding that some of these ecologicaltheories are wrong. Thus ecological engineering isreally a technique for doing fundamental ecologicalresearch and advancing the field of ecology.

4.3. A systems approach

Pahl-Wostl (1995) argues that just as self-organization is a property of a system as a whole, itis meaningless at the level of the parts. Ecologicalengineering requires a more holistic viewpoint thanwe are used to doing in many ecosystem manage-ment strategies. Ecological engineering emphasizes,as does ecological modeling for systems ecologists,the need to consider the entire ecosystem, not justspecies by species. Restoration ecology, a sub-fieldof ecological engineering, has been described as afield in which “the investigator is forced to study theentire system rather than components of the systemin isolation from each other” (Cairns, 1988).

Conversely, the practice of ecological engineeringcannot be supported completely by reductive, ana-lytic experimental testing and relating. Approachessuch as modeling and whole-ecosystem experimen-tation are more important, as ecosystem design andprognosis cannot be predicted by summing parts tomake a whole. One must also be able to synthesizea great number of disciplines to understand and dealwith the design of ecosystems.

All applications of technologies, whether ofbiotechnology, chemical technology, or ecotechnol-ogy, require quantification. Because ecosystems arecomplex systems, the quantification of their reactionsbecomes complex. Systems tools, such as ecologicalmodeling, represent well-developed approaches tosurvey ecosystems, their reactions, and the linkageof their components. Ecological modeling is able tosynthesize the pieces of ecological knowledge, whichmust be put together to solve a certain environmentalproblem. Ecological modeling takes a holistic view ofenvironmental systems. Optimization of subsystemsdoes not necessarily lead to an optimal solution ofthe entire system. There are many examples in envi-ronmental management where optimal management


of one or two aspects of a resource separately doesnot optimize management of the resource as a whole.Ecological engineering projects, while they usuallyhave one or more specific goals, will try to balancebetween the good of humans and the good of nature.

4.4. Non-renewable resource conservation

Because most ecosystems are primarily solar-basedsystems, they are self-sustaining. Once an ecosystemis constructed, it should be able to sustain itself indef-initely through self-design with only a modest amountof intervention. This means that the ecosystem, run-ning on solar energy or the products of solar energy,should not need to depend on technological fossil en-ergies as much as it would if a traditional technologicalsolution to the same problem were implemented. Thesystem’s failure to sustain itself does not mean thatthe ecosystem has failed us (its behavior is ultimatelypredictable). It means that the ecological engineeringhas not facilitated the proper interface between natureand the environment. Modern technology and envi-ronmental technology, for the most part, are based onan economy supported by non-renewable (fossil fuel)energy; ecotechnology is based on the use of somenon-renewable energy expenditure at the start (the de-sign and construction work by the ecological engineer)but subsequently dependence on solar energy.

A corollary to the fact that ecological engineers’systems use less non-renewable energy is that theygenerally cost less than conventional means of solvingpollution and resource problems, particularly in sys-tems maintenance and sustainability. Because of thereliance on solar-driven ecosystems, a larger part ofland or water is needed than would be technologicalsolutions. Therefore, if property purchase (which is,in a way, the purchase of solar energy) is involvedin regions where land prices are high, then ecologi-cal engineering approaches may not be feasible. It isin the daily and annual operating expenses in whichthe work of nature provides subsidies and thus lowercosts for ecological engineering alternatives.

4.5. Ecosystem conservation

We solve human problems and create ones for na-ture. That has been the history of mankind, at leastin the western world. We need to adopt approaches to

solving (at least) environmental problems not only toprotect streams, river, lakes, wetlands, forests, and sa-vannahs. We need to work symbiotically with naturewhere we use her public service functions but recog-nize the need to conserve nature as well. The idea ofnature conservation is so important that it needs to be-come a goal of engineering, not just one of its possibleoutcomes. We must seek additional approaches to re-duce the adverse effects of pollution, while at the sametime preserving our natural ecosystems and conserv-ing our non-renewable energy resources. Ecotechnol-ogy and ecological engineering offer such additionalmeans for coping with some pollution problems, byrecognizing the self-designing properties of naturalecosystems. The prototype machines for ecologicalengineers are the ecosystems of the world.

Ecological engineering involves identifying thosebiological systems that are most adaptable to the hu-man needs and those human needs that are most adapt-able to existing ecosystems. Ecological engineers havein their toolboxes all of the ecosystems, communi-ties, populations, and organisms that the world hasto offer. Therefore, a direct consequence of ecologi-cal engineering is that it would be counterproductiveto eliminate or even disturb natural ecosystems unlessabsolutely necessary. This is analogous to the con-servation ethic that is shared by many farmers eventhough they may till the landscape and suggests thatecological engineering will lead to a greater environ-mental conservation ethic than has been realized up tonow. For example, when wetlands were recognized fortheir ecosystem values of flood control and water qual-ity enhancement, wetland protection efforts gained amuch wider degree of acceptance and even enthusi-asm than they had before, despite their long under-stood values as habitat for fish and wildlife (Mitsch andGosselink, 2000). In short, recognition of ecosystemvalues provides greater justification for the conserva-tion of ecosystems and their species. A corollary ofthis is the point made by Aldo Leopold that the tinker’sfirst rule is to not throw away any of the parts. Theecological engineer is nature’s tinker.

5. What we do now

We are approaching an age of diminishing re-sources, the growth of the human population is


continuing, and we have not yet found means to solvelocal, regional, and global pollution and renewableresource shortage problems properly. When the firstgreen wave appeared in the mid and late sixties, itwas considered a feasible task to solve the pollutionproblems. The visible problems were mostly limitedto point sources and a comprehensive “end of thepipe technology” (=environmental technology) wasavailable. It was even seriously discussed in the USthat what was called “zero discharge” to the nation’swaterways could be attained by 1985. In fact, theUS Congress decreed in the 1970s that the streamsand rivers of the country needed to be fishable andswimmable by 1983. When that date came, a sig-nificant percentage of those streams and rivers washardly ready for swimming or fishing.

It became clear in the early 1970s that zero dis-charge would be too expensive, and that we shouldalso rely on the self-purification ability of ecosystems.That called for the development of environmentaland ecological models to assess the self-purificationcapacity of ecosystems and to set up emission stan-dards considering the relationship between impactsand effects in the ecosystems. Meanwhile, we foundthat the environmental crisis was much more com-plex than we initially thought. We could for instanceremove heavy metals from wastewater but whereshould we dispose the sludge containing the heavymetals? Resource management pointed towards recy-cling to replace removal. Non-point sources of toxicsubstances and nutrients, chiefly originating fromagriculture, emerged as new, threatening environmen-tal problems in the late seventies. It was revealed thatwe use as much as about 100,000 chemicals that maythreaten the environment due to their more or lesstoxic effects on plants, animals, humans and entireecosystems. In most industrialized countries com-prehensive environmental legislation was introducedto regulate the wide spectrum of different pollutionsources. The focus on global environmental problemssuch as the greenhouse effect and the decomposi-tion of the ozone layer added to the complexity.Trillions of dollars have been invested in pollutionabatement on a global scale, but it seems that twoor more new problems emerge for each problem thatwe solve. Our society does not seem geared to en-vironmental problems—or is there perhaps anotherexplanation?

Environmental technology offers a wide spectrumof methods that are able to remove pollutants from wa-ter, air and soil. These methods are particularly appli-cable to cope with point sources. We have, for instance,many environmental technological methods for cop-ing with different wastewater problems. To select theright method (or most often the right combination ofmethods), a profound knowledge of the applicabilityof the methods and of the processes and characteristicsof the ecosystem receiving the emission is necessary.

Clean technology, while not in our definition of eco-logical engineering explicitly, explores the possibili-ties of recycling byproducts or the final waste productsor attempting to change the entire production technol-ogy to obtain a reduced emission. It attempts to an-swer the pertinent question: couldn’t we produce ourproduct by a more environmentally friendly method.It will to a great extent be based on environmental riskassessment, LCA and environmental auditing. Some-times it is referred to asindustrial ecology.

Sustainability has become another of the buzzwords of our time. It is used again and again inthe environmental debate—sometimes in a wrongcontext. It is therefore important to give a clear defi-nition to avoid misunderstandings later. The Brundt-land report (World Commission on Environment andDevelopment, 1987) produced the following defini-tion: sustainable development is development thatmeets the needs of the present without compromisingthe ability of future generations to meet their ownneeds. Note, however, that this definition includesno reference to environmental quality, biologicalintegrity, ecosystem health, or biodiversity. Conser-vation philosophy, which portends to seek a sus-tainable society, has been divided into two schools:resourcism and preservationism. They are understoodrespectively as seeking maximum sustained yield ofrenewable resources and excluding human inhabita-tion and economic exploitation from remaining areasof undeveloped nature. These two philosophies ofconservation are mutually incompatible. They areboth reductive and ignore non-resources, and seemnot to give an answer to the core issue—how toachieve sustainable development—although preserva-tionism has been retooled and adapted to conservationbiology. Taken as a whole, conservation ecology can-not provide all the answers to a sustainable societyeither.


6. The new approach—ecological engineering

The state of our environment, combined with adwindling of non-renewable natural resources avail-able to solve environmental problems, suggests thatthe time has come for yet a new paradigm in engi-neering that involves ecosystem and landscape scalequestions and solutions. There are a great number ofenvironmental and resource problems that need anecosystem approach, not just a standard technologi-cal solution or even clean technology development.We have finally recognized that we cannot achievethe complete elimination of pollutants owing to anumber of factors and that we need new approachesbetter in tune with our natural ecosystems. In ourattempts to control our own environment, we havealso seen that we have tried to control nature toomuch at times, with disastrous consequences, such asenormous floods, invasive species, and air and waterpollution being transported hundreds and thousandsof kilometers instead of tens of kilometers. But whynow and why do we offer this new field to engineers,whom many blame for the difficult situation in whichwe find ourselves?

Ecological engineering is needed because we onlyhave limited nonrenewable resources too solve all ofour environmental problems, because we now justmove pollutants around in a kind-of shell game, andbecause secondary effect of technological fixes areother pollution problems at a larger scale.

6.1. Limited resources

We have a finite quantity of resources to address tothe problems of pollution control and natural resourcedisappearance. This is particularly true for developingcountries that wish to have the standard of living andtechnologies of developed countries but currently mustdeal with pollution problems often more serious thatthose in the developed world.

The limited resources and the high and increasinghuman population force us to find a trade-off betweenthe two extremes of pollution and totally unaffectedecosystems. We cannot and we must not accept a situa-tion of no environmental control, but we cannot affordzero-discharge policies either, knowing that we do notprovide one-third of the world’s population with suf-ficient food and housing.

6.2. The shell game

When we control pollution through technologicalmeans, we are often playing a shell game with the pol-lution. Toxic substances present in municipal wastew-ater cannot be biodegraded in a mechanical-biologicalwastewater treatment plant but will, depending on thewater solubility, be found either in the treated water orin the sludge. If the sludge is used as soil conditionerin agriculture the toxic substance will contaminatedthe soil—or if the sludge is incinerated it may causeair pollution or be found in the ash. We may use scrub-bers to prevent sulfur emissions from power plants andthen be faced with enormous solid waste storage prob-lems from the sludge left behind. We build solid wastefacilities and water pollution control systems and at-mospheric emissions of the greenhouse gas methaneresult. We use industrial wastewater treatment meth-ods to remove heavy metals from a factory and thenmust dispose of metal-rich sludge. We burn sludge andsolid wastes and we create air pollution problems. Weare moving materials around in a shell game—if it isnot under one shell, it is under another.

6.3. Climate change, bigeochemical pollution, andthe secondary pollution effect

We are now faced with the fact that even seeminglyinert CO2 is considered a pollutant. It is the chiefatmospheric gas thought to be causing changes inour climate and international efforts through treatiessuch as the Kyoto Treaty are attempting to limit theburning of fossil fuels to minimize future climatechanges. If expensive environmental technology is be-ing used to solve a pollution problem, we are solvinga problem of one type and may probably be caus-ing global emissions of CO2 to increase at the sametime.

Problems of excessive buildup of chemicals in thebiosphere are not limited to CO2. It has been estimatedthat we match the amount of nitrogen that nature fixesthroughout the biosphere, (Fig. 5). We are fixing nitro-gen to produce fertilizer, we are fixing nitrogen fromN2 and O2 in the atmosphere and N stored in fos-sil fuels through high-temperature combustion of fos-sil fuels, particularly by the automobile, and we areplanting crops that fix additional nitrogen from the at-mosphere. We have doubled the inflow of nitrogen to


100

80

60

40

20

01900 1920 1940

Year

Atmospheric CO2

Global Nitrogen Fixation

1960 1980 2000

Fig. 5. Pattern of increase in atmospheric carbon and increase inbioavailable nitrogen in the 20th century (modified fromVitouseket al., 1997; from Mitsch and Jørgensen, 2004, reprinted withpermission, Wiley).

the biosphere, in contrast to the net increase of 20%of carbon in the atmosphere since 1900 (Fig. 5).

We have undoubtedly used a great amount of fossilfuel in the economy to develop the technology that issolving some of our pollution problems. The amountof energy used is generally proportional to the costof the technology, and the carbon dioxide emission isproportional to the amount of fossil fuel used. The useof soft technologies, low-cost technologies whereverpossible, such as those afforded in ecologically en-gineered systems, are therefore more important thanever in pollution abatement that does not, in an indi-rect way, cause more increases of CO2 and nitrogen.

7. Ecological engineering—an overdue alliance

Engineering and ecology are ripe for integrationinto one field, not separate approaches that are of-ten adversarial. Ecology as a science is not routinelyintegrated in engineering curricula, even in environ-mental engineering programs. Engineers are missingthe one science that could help them the most in envi-ronmental matters. Likewise, environmental scientistsand managers are missing a crucial need in theirprofession—problem solving. While tremendouslycompetent at describing problems and maybe even

managing ecosystems one species at a time, ecolo-gists are not well versed in prescribing solutions toproblems. The basic science of ecological engineer-ing is ecology, a field that has now matured to thepoint where it needs to have a prescriptive—ratherthan just a descriptive—aspect.Matlock et al. (2001)describe an interesting course curriculum for US uni-versities for ecological engineering that would havecourses in quantitative ecology (population, com-munity, ecosystems), restoration ecology, as well asmodeling, economics, and engineering.

Ecological engineering is now, in effect, beingpracticed by many professions under a great variety ofnames, including ecotechnology, ecosystem restora-tion, artificial ecology, biomanipulation, ecosystemrehabilitation, nature engineering (in Holland), hy-droecology (in eastern Europe) and bioengineering(originated in Germany) but with very little theoryto back the practices. Engineers are building wet-lands, lakes, and rivers with little understanding ofthe biological integrity of these systems. Ecologistsand landscape architects who now design ecosystemswith home-spun methodologies that must be relearnedeach time. Engineers who design ecosystems relearnthe approaches each time and do not generally pub-lish their successes in the open literature. The theoryhas not yet connected with the practice.

Some of the ecotechnological methods are not newand, in fact, some have been practiced for centuries,particularly in China. In earlier times, these methodswere considered as good, empirical approaches. To-day, ecology has developed sufficiently to understandthe scientific background of ecological engineering, toformalize usage of these approaches, and to developnew ones. We must understand not only how we caninfluence the processes in the ecosystem and how theecosystem components are linked together, but alsohow changes in one ecosystem can produce changesin neighboring ecosystems.

We must acknowledge that there are two billionmore people on earth and that the non-renewable re-sources are more limited today than 20 years ago(Fig. 6). We therefore need to find new ways. Wehave attempted to solve the problem by use of avail-able technology. It has partially failed. Therefore wemust think more ecologically and consider additionalmeans. Ecological engineering, if properly applied,is based on ecological considerations and attempts to


21002000190018000

2

4

6

8

10

Human population,billions

Fig. 6. Change in population, 1805–1999. For the period1999–2050, an optimistic prognosis predicts that the populationgrowth will level off after the year 2015. In the period 1805–1975,the growth was been more than exponential (fromMitsch andJørgensen, 2004, reprinted with permission, Wiley).

optimize ecosystems (including limited resources) andman-made systems for the benefit of both. It shouldtherefore afford additional opportunities to solve thecrisis. We have had several energy crises during thepast 30 years and we know that new crises will ap-pear in the future. Therefore we have to rely more onsolar-based ecosystems, which are the bases for eco-logical engineering.

In the short term, ecological engineering could bringimmediate attention to the importance of “designing,building and restoring ecosystems” as a logical exten-sion of the field of ecology. In the long term, it willprovide the basic and applied scientific results neededby environmental regulators and managers to controlsome types of pollution while reconstructing the land-scape in an ecologically sound way. The formalizationof the idea that natural ecosystems have values for hu-mans, other than directly commercial ones, is also abenefit of ecotechnology and will go a long way to-ward enhancing even further a global ecological con-servation ethic.

Our experience with the formal field of ecologicalengineering and its possibilities is limited today. Wehave had one decade of formal peer-reviewed experi-ence in the journalEcological Engineeringand a fewacademic settings in the world where the field is only

beginning to be taught. Although the results we dohave look very promising, we need to integrate theapplication of ecological engineering much more inour educational systems in the future. This will re-quire a much deeper understanding of the reactions ofnature to our activities. This will therefore require acontinuous development of ecology, systems ecology,applied ecology, ecological modeling, and ecologicalengineering. Ecological engineering offers us a veryuseful tool for better planning in the future. It will be areal challenge to humankind to use this tool properly.

Acknowledgements

We appreciate the useful comments provided byextramural reviewers. We particularly want to notethat one of those reviewers—obvious by his style, bigtypeset, and extraordinary insight—was H.T. Odumwho soon afterwards was diagnosed with incurablebrain cancer. H.T. died on 11 September 2002. We feelpriviledged to have among his last words on ecologicalengineering. Paper 03-xxx of the Olentangy RiverWetland Research Park.

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