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A Coopemtive Role
the Planetary upport System
s resources, both renewable and nonrenewable, are diminished worldwide, environmental problems are becoming more complex a n d less “solvable” by conventional technological means (I, 2: see box). In the past we have built technological solutions that solve one type of pollution only to find that they create another type of pollution. We now consider the ultimate degradation product, CO,, to be a global
,
pollutant. Now many third world countries aspire to imitate current fossil-fuel based food production practices in developed countries just as we are finding such practices ecologically threatening and energy intensive. An effort is under way in ecological research and practice that focuses on designing and reconstructing ecosystems that serve human needs and are sustainable in times of diminishing resources. Called ecological engineering, this approach was first described by Odum
“As the resources of the world becomt increasingly limiting to the expansion OJ the human economy, the management OJ e planet must turn more and more to G cooperative role with the planetary lifc support system, sometimes called the stew. ardship of nature. The pattern of humanio and nature that prevails is symbiotic b e cause two coupled svstems have highei
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W I L L I A M J. M I T S C H The Ohio State University Columbus, OH43210
in the early 1960s as “those cases in which the energy supplied by man is small relative to the natural sources, but sufficient to produce large effects in the resulting patterns and processes” (3), and as “environmental manipulation by man using small amounts of supplementary energy to control systems in which the main energy drives are still coming from natural sources” (4). Ecotechnology, a synonym for ecological engineering, was described in Eastern Europe as “the use of technological means for ecosystem management, based on deep ecological understanding, to minimize the costs of measures and their harm to the environment” ( 5 , 6). Mitsch and Jsrgensen (7)defined ecological engineering as “the design of human society with its natural environment for the benefit of both.” The late S. Ma, known as the “father of ecological engineering in China,” defined ecological engineering as . a specially designed system of production process in which the principles of the species symbiosis and the cycling and regeneration of substances in an ecological system are applied. . . .” ( 8 ) . Ecological engineering, or the building of sustainable and selfdesigned ecosystems, is becoming a useful paradigm in ecology for deal‘I.
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0013-936X/93/0927-438$04.00/0 0 1993 American Chemical Society
ioms synon ms or subsets if ecologica engineering or
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cotechnology Synthetic ecology Restoration ecdogY Bioenalneerina Sustai;laMe
agmecolcgy
Habitat reconstruction
Ecosystem rehabilitation * Biomanbulation * River *
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restoration Wetland
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Reclamation ecdcgy
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ing with environmental issues such as preventing and mitigating the destruction of wetlands; adapting to global warming, increased sea levels, and acidic deposition: controlling nonpoint source pollution from agriculture and mined lands; protecting clean lakes and reservoirs and restoring those that are polluted adapting ecosystems to environmental improvements, such as river and lake cleanups, that are a result of past environmental regulations; and cleaning up and stabilizing wastewater, septage, and hazardous waste sites. But many questions remain. Can wetlands be properly constructed for wastewater treatment, mine drainage control, or mitigation of the loss of another wetland? Can coastline ecosystems and agroecosystems be designed to adapt to the effects of C0,-induced climate change? Can forests be made less susceptible to atmospheric pollutMtS? As rivers and streams recover from pollution or are stressed by more pollution ( % T I ) , what are the desirable ecological communities, and how much “control” do humans have over them? Can sustainable agriculture diminish the problems of nonpoint source water pollution?
Goals and features The goals of ecological engineering are as follows: the restoration of ecosystems that have been substantially disturbed by human activities such as environmental p o l l u t i o n , climate change, or land disturbance: the development of new sustainable ecosystems that have human and ecological value: and the identification of the life support value of ecosystems to ultimately lead to their conservation (11. Several new ecological fields, such as ecotoxicology and landscape ecology, are dedicated to the 440 Envimn. %I. Technol., Vol. 27, No. 3, I S 3
lescription of humanity’s effects on he environment. But description is lot enough to deal with many of tolay’s environmental issues (2).Our seemingly intractable problems require prescriptive ecological approaches ranging from constructing new ecosystems for solving environmental problems to ecologically sound harvesting of existing ecosystems (see box). Ecological engineering combines basic and applied science for the restor a t i o n , design and constructioi of aquatic and teI restrial ecosystems. Self-design and s u s t a i n ability. Ecotechnology depends on the self-designing capability of ecosystems. When changes occur, natural systems shift, species are substituted for one another, and food chains reorganize. As individual species shift and adapt, a new system ultimately emerges that is well suited to the environment that is superimposed on it. Ecological engineers participate in the ecosystem design by providing choices of initial species as well as the starting physical conditions: nature does the rest. The multiple seeding of species into ecologically engineered systems is one way to speed the selection process in this selforganization or self-design (13). Once a n ecosystem is designed and constructed or restored, it must sustain itself indefinitely through self-design with only a modest amount of human intervention. This means, for example, that an ecosystem running on solar energy or the products of solar energy does not depend on technological energies as much as would a
traditional technological solution to the same problem. If the ecosystem does not sustain itself in its originally designed conditions, it does not mean that the ecosystem has failed (its behavior is ultimately predictable). It means that the ecological engineer has not facilitated the proper interface between the ecosystem and its environment or has not allowed for natural processes, such as succession or competition, in the design. $ Ecosystem conservation. Ecological engineering is not biological conservation, per se; rather, it leads to biological conservation. It involves identifying the biological systems that are most adaptable to human needs and the human needs that are most adap table to existing ecosystems. This means that ecological engineers have in their toolboxes all of the ecosystems, communities, populations, and organisms that the world offers. Therefore a direct consequence of ecological engineering is a conservation ethic; simply stated, it would be counterproductive to throw away any of the parts. For example, when wetlands were recognized for their ecosystem values of flood control and water quality enhancement through ecological engineering experimentation and observation, wetland protection efforts gained a much wider degree of acceptance and even enthusiasm than they had before, despite the long-understood values of wetlands as a habitat for fish and wildlife (14).In short, recognition of ecosystem values conserves ecosystems.
The acid test. Ecological engineering will be the ultimate test of many of our ecological theories. Restoration ecologists have suggested the tie between basic research and ecosystem restoration by making an analogy: The best way to understand a system, whether a car, a watch, or an ecosystem, is to “attempt to reassemble it, to repair it, and to adjust it so that it works properly” (1.5).Cairns describes the idea in a more direct way (16):“One of the most compelling reasons for the failure of theoretical ecologists to spend more time on restoration ecology is the exposure of serious weaknesses in many of the widely accepted theories and concepts of ecology.” Bradshaw [ I 7),who describes the restoration of a disturbed ecosystem as the “acid test of our understanding of that system,” has stated that although we cannot prove an ecological theory with a restored ecosystem, we will “learn more from our failures than from our successes since a failure clearly reveals the inadequacies in an idea, while a success can only corroborate and support, and can never absolutely confirm, an assertion.” Comparisons with existing fields Applied ecology. The integration of ecology and engineering into a formal application is beginning to progress rapidly, perhaps more so in Europe and China than in the United States. Most ecologists remain low on the learning curve compared with engineers when confronted after formal education with real-life issues such as wetland construction, river restoration, habitat reconstruction, or mine land rehabilitation. They often rise to the occasion quickly with homespun ecotechnology a n d novel a p proaches, but the integration is not there, the theory does not support the technique, and techniques are relearned each time. Although the ecological theory may be mentioned, it has usually not been integrated into a framework within ecology that ecological engineering could provide. Ecological engineering has its roots in ecology, just as chemical engineering is close to chemistry and biochemical engineering is close to biochemistry. It extends the usual concept of applied ecology, often limited to monitoring and assessing environmental impacts or managing natural resources. Figure 1shows that both basic and applied ecology provide fundamentals to
FIGURE 1
Relationships among theoretical ecology, applied ecology, and 11eng ring
ecological engineering but do not define it completely. Ecological engineering, in turn, feeds back ecological theory and management practices to the theoretical and applied ecology (f]. Because of the unique research approach taken by scientists when reconstructing ecosystems, there is a high probability that ecological engineering will advance the understanding of ecological systems. Environmental engineering. Ecological engineering is not the same as environmental engineering. Environmental engineers are certainly involved in the application of scientific principles to solve pollution problems, but the concepts usually involve energy- and resource-intensive operations such as settling tanks, scrubbers, filters, and chemical precipitators. As Mitsch and J0rgensen stated (7):“[Ecological engineering] is engineering in the sense
that it involves the design of this natural environment using quantitative approaches and basing our approaches on basic science. It is technology with the primary tool being self-designing ecosystems. The components are all of the biological species of the world.” This focus on, and utilization of biological species, communities, and ecosystems, as well as the reliance on self-design,are what distinguish ecotechnology from the traditional environmental engineering technologies, which rely on devices and facilities to remove, transform, or contain pollutants but which do not often consider direct manipulation of ecosystems. Biotechnology. Ecological engineering and its synonym, ecotechnology, also should not be confused with biotechnology, which involves genetic manipulation to produce new strains and organisms to carry Environ. Sci. Technol.. Vol. 27, No. 3, 1993 441
described as “environmentally responsible technology [which] would provide little or no sludge, generate useful byproducts, use no hazardous chemicals in the process chain and remove synthetic chemicals from the wastewater” (26). All of these applications use ecosystems for treatment of wastewater with an emphasis on solving problems instead of simply shifting them to another medium (28). The systems typically involve a series of tanks in which aquatic food chains and diversity are actively encouraged. They can contain microbiota, floating and suspended aquatic plants, crustaceans, and fish. Used in greenhouses, they allow reliable :lassification and examples of ecotechnology according to ty wintertime functioning in northern ,f applications climes. Walter Adey and his colleagues at LppllcBtlon Exampla the Smithsonian Institution have :cos sterns are usea 10 reddce or so ve a Wastewater recycling in wellanas; slbdge advanced the field of building ecorecycilng gl!ulion problem Inat othenvise would logical mesocosms as an extension harmfulto other ecosvstems. of attempts to replicate nature in aquaria (29). Two of his Adey’s large-scale mesocosms are located in Washington, DC: greenhousescale replications of the Florida EvBiomanipulatlon of tish in reservoirs I Existing ecosystems are modified in an erglades and the Chesapeake Bay. ecologically sound way to solve an environmental problem. Adey was also involved in designsurce: Reference 12. ing the aquatic ecosystems in what many believe to be the most ambitious ecologically engineered system yet-Biosphere 2 ( 3 0 ) . These out specific functions. Some of the deals with terrestrial ecology, based mesocosm projects demonstrate the differences between ecotechnology on the pioneering work of Aldo enormous complexity of nature and and biotechnology relate to their ba- Leopold more than 50 years ago the difficulty we face in trying to sic principles, control, design, and (25). The ecotechnology approach replicate it. Ecosystem scale. Ecological engiultimate possible costs to society also has been applied to river and (Table 1). A comparison can be stream restoration (24) and to agri- neering in the United States has fomade, however, between the devel- culture as agroecosystems ( 2 5 ) . cused on forming a partnership opment of ecotechnology and that Some of these approaches seem to with nature and has been investiof biotechnology. Ecotechnalogy is ignore one or both of the major com- gated with experimental ecosysalmost at the stage where biotech- ponents of ecological engineering, tems, primarily aquatic systems nology was 20 years ago. Molecular namely, the self-designing ability of such as shallow ponds and wetbiology was just beginning to estab- the ecosystem or the importance of lands. Odum (23, 33) reported on lish the basic science and tech- a theoretical ecology base, rather one of the first studies, done in the 1960% that was described then as an niques for the yet unborn field of than sheer empiricism. experiment in ecological engineerbiotechnology. Today, ecology is ing. Estuarine ponds were built in recognized as a fundamental sci- Examples of ecological engineering Some e x a m p l e s of projects coastal North Carolina to investience and is now developing the ecosystem-level tools to develop the throughout the world have been gate ecological changes as t h e called ecological engineering (Table ponds received secondarily treated field of ecotechnology. Restoration fields. Several fields 2). They have been categorized by municipal wastewater mixed with that are equivalent to or are subsets scale-mesocosm, ecosystem, and salt water. Formally, the question of ecological engineering have de- landscape-and are briefly dis- being asked was “whether the selforganization process [of species arveloped somewhat independently, cussed below. Mesocosm scale. Mesocosm ap- rangements] occurs readily there and all appear to have the design of ecosystems as their theme (see box). proaches are used to replicate or en- with new conditions from wastewaEarly work in Europe used the con- hance, in time or space, ecological ter influence and how much time is cept of bioengineering, or using processes. Ecological engineering required” (23). One of the first experiments to inplants as engineering materials (28). approaches have been developed More recently, much has been writ- for a number of years by John Todd vestigate the idea of wastewater and ten on the recently described fields and his associates for the treatment wetlands was conducted in the of restoration ecology (25,29-22) and recycling of sewage wastes and early 1970s in Florida by Odum, and ecosystem rehabilitation (22, septage, usually in greenhouses Ewel, and colleagues (34-36). 23).A large portion of this literature (26-28).Here the applications are Whole ecosystem experiments run I
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for several years demonstrated that forested wetlands could be used to remove nutrients from wastewater with a minimum application of expensive fossil-energy-consuming technology. It is now common to see ecological engineering concepts applied to the treatment of domestic wastewater in constructed wetlands (37-38).
In Europe and in a few applications in the United States, root-zone wetlands have been used for treating wastewater (38-40). Wetlands also have been used with varying degrees of success for pollution control of coal mine-drainage in the eastern United States (38, 41-43) and are now being investigated for controlling nonpoint source pollution (44). In contrast, ecological engineering in China has been applied to a wider variety of natural resource and environmental problems, ranging from fisheries and agriculture to wastewater control and coastline protection (8, 45-47). The emphasis in the Chinese systems has been on applications rather than experimentation and on the production of food and fiber rather than on environmental protection (48). It has been suggested (49) that “the objective of ecological research [in China] is be-
ing transformed from systems analysis to system design and construction.” For example, a 3-ha riverine water hyacinth (Eichhornia cmssipes) mat was investigated for its role as a water pollution control system in a series of experiments on a section of
Landscape scale. The restoration of entire landscapes is a more difficult task. One ecological engineering project on the Des Plaines River north of Chicago in Lake County, IL, involves restoration of a length of a river flood plain and establishing experimental wetland basins on the flood plain where the dynamics of sediment and nutrient control can be determined (50). On the entire 182-ha site, nonnative woody and scrub vegetation has been replanted with native prairie species. Abandoned quarry lakes are connected directly to the river as sediment traps and backwater habitats for fish and shore birds. Preliminary results (51, 52) suggest that the riparian wetlands are removing a high percentage of the sediments, phosphorus, and nitrogen from the inflowing river. On a similar scale, the restoration of a forested wetland-upland complex in central Florida is described by Brown et al. (53). Here, ecosystem design and hydrological conditions were closely matched in an effort to reconstruct the landscape after phosphate mining. Integration of food production with landscape approaches has been used at several sites in China. Ma (8)suggested that there were
M/e cannot solve all of our environmental problems with high technology solutions alone. the Fumen River in eastern suburb of Suzhou, China (47).The benefits of this system include the partial reclamation of polluted river water, particularly for nutrients, organic matter, and heavy metals, and the production of green fodder for fish, ducks, pigs, and oxen. After the experiment was completed, the local townspeople continued to grow and harvest the water hyacinths to feed to their animals.
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about 500 agroecological engineering trial sites in more than 20 Chinese provinces. For example, the Lake Go Reed Wetland and Fish Farm, located in Yixing County, China, integrates a freshwater marsh with fisheries production. Water levels are controlled in such a way as to maximize production of herbivorous grass carp (Ctenopharyngodon idella) and Wuchang fish (Megalobrama amblycephola) as well as harvest of the reed grass (Phragmites sp.) for various uses, including fuel. This application of ecological engineering is accomplished primarily through water level manipulation, synchronized with fish growing seasons and harvesting schedules, and a series of deeper channels for fish overwintering (48). In another example (54), production of the “three materials” of fertilizer, forage, and fuel at a small village produced 89% of the energy needed for the village with only 11% coming from industrial energy (no energy quality ratios used in the calculation). Furthermore, 88% of the total organic production is consumed in the village: only 12% is exported (54). Salt marsh restoration has been a commonly practiced approach to landscape ecological engineering around the world (55-60). For example, salt marshes, dominated principally by Spartina anglica and S. alterniflora, have been constructed along the east coast of China to stabilize the coastline; to accelerate accretion of sediments for reclamation of tidal land for agricultural or industrial development; to produce green manure, foodstuff and fuel; and to control stream siltation and pollution (6063). The Spartina grass increased aeration and organic content and decreased the salt content of the soil in addition to dissipating wave energy and slowing currents. The newly created salt marshes also were used as a habitat for migratory birds, waterfowl, domestic fowl, nereids (worms), and crabs and as a pasture for cattle and pigs. The grass also is harvested as a source of animal fodder, as an effective “green manure’’ for rice fields, as a source of fuel, and as a source of marsh gas (methane) for cooking and illumination (63). A future for ecological engineering Because ecological engineering may be the beginning of a new paradigm in ecology, serious consider444 Environ. Sci. Technol., VoI. 27,No. 3, 1993
ation needs to be given to its scope, its theory, and its applications. In the short term, ecological engineering will bring immediate attention to the importance of “designing and building ecosystems” as a logical extension of the field of ecology as it applies directly to solving environmental problems. In the long term, the new field could provide the basic and applied scientific results needed by environmental regulators and managers to control some types of pollution while reconstructing the landscape in an ecologically sound and sustainable way. Ecological engineering will aid its sister field of ecological economics (64) in the formalization and quantification of the idea that natural ecosystems have both direct and indirect values for humans. It will lead to preserving biodiversity and promoting an environmental conservation ethic. Specifically, ecotechnology could contribute to an improved environment in the long term in several ways: We will continue to be faced with climate changes, disappearing wetlands, degraded forests, and polluted lakes and coastal waters. Adaptation as well as prevention may be the most appropriate choices for dealing with some of these conditions. Ecotechnology will provide environmental managers with the tools needed to help natural and human systems adapt to these change; Drainine wetlands and surface mining conGnue to alter watersheds forcing agencies to consider how to repair or replace the landscape. Wetland mitigation and surface mine reclamation are generally approached on an empirical basis, with littlebridgeto the theoryofecosystem function. An emphasis on the fundamental principles of ecological engineering will contribute to the formulation of ecological theow to support current empirical approaches. There is also the need for ecotechnology as environmental agencies begin to show progress in their mission to clean up the environment. Restoring solid and hazardous waste dumps and replacing them with sustainable ecosystems; reintroducting fish and other aquatic organisms to recently improved streams, rivers, lakes, and reservoirs: and recovering forests by lessening acid precipitation are all important adjuncts to dealing with the effects of pollution on ecosystems.
Ecotechnology will play a significant role in a sustainable society. Because we cannot solve all of our environmental problems with high technology solutions alone and our energy future is quite clouded, we need to investigate alternative means of cleaning the environment. Because ecological engineering is, by definition, a combination of basic and applied research, it requires interdisciplinary teams for its proper application. The development of such an interdiscipline and its methodologies and principles will require cooperative efforts from many fields, especially ecology and engineering. The fruitful integration of these efforts may need the formal establishment of a multidiscipline open to both ecologists who design ecosystems and engineers who know ecology. It may need the formal recognition of the field in government, private, and accrediting sectors. It may also require a new administrative and academic structure in universities and research laboratories to stimulate the crossfertilization required for this field to prosper. The need for the paradigm is clear: its implementation is still before us. Acknowledgments I wish particular1 to thank H. T. Odum for his initial see&ng and continued encouragement of this work. Collaboration
William I. Mitsch is professor ofNatural Resources and also holds faculty appointments in the Graduate Program in Environmental Science and in the Department of Civil Engineering at The Ohio State University. He has o Ph.D. in environmental engineering sciences from the University of Florida and is a certified senior ecologist with the Ecological Society of America, past president of the North American chapter of the International Society for Ecologicol Modelling, and editor-in-chief of Ecological Engineering-The Journal of Ecotechnology.His research andgmduate teaching have focused on wetland ecology and biogeochemistry, ecotechnology, and ecosystem modelling.
with Sven Erik J ~ r g e n s e nwas very helpful in focusing some of the ideas and case studies. Useful reviews of this manuscript and the concepts were provided by Ann Mari Jansson, Bob Knight, Charlie Hall, Dennis Knight, and several anonymous reviewers,
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