This article was first published in The Canadian Civil Engineer, vol. 17. pages 11-13. 2000.
Many aspects of engineering seek to fulfill the needs of society by modifying the landscape, designing water conveyance structures, constructing transportation networks, and assembling the very structures that house society. Unfortunately, much of the tradition has been destructive and against the forces of nature. The environmental movement of the 1960s and 1970s made it increasingly clear that the needs and practices of humanity were taking a toll on the natural environment. Engineering designs needed to be more in harmony with nature and efforts made to correct past mistakes by restoring nature. However, to accomplish the change required a greater understanding of how nature works and an appreciation for the ecological interactions of natural systems and the organisms comprising them. This realization led to the relatively recent emergence of a new sub-discipline of environmental engineering, which combines both engineering and ecology.
What is Ecological Engineering?
Ecological engineering, also referred to as ecotechnology, can be defined as the design of human society with its natural environment for the benefit of both (Mitch and Jorgensen 1989). Barrett (1999) provides a more literal definition: "the design, construction, operation, and management (that is, engineering) of landscape/aquatic structures and associated plant and animal communities (that is, ecosystems) to benefit humanity and, often, nature." Ecological engineering has its roots in ecology and is practiced within an engineering context. Although there are some similarities, ecological engineering is not to be confused with environmental engineering as we have come to know it, wherein the focus is on solving problems of pollution using advanced technologies, which are heavily dependent on fossil resources.
Traditional engineering relies mainly on human control processes occurring in human-created, "hard" structures, and it is reliant upon fossil resources, including both energy and materials. In contrast, ecological engineering attempts to utilize natural processes occurring in natural land- and waterscapes (i.e., "soft" structures), which are driven primarily by natural energy (solar and gravity). Some of the differences between ecological engineering and traditional engineering are summarized in Table 1.
Ecological engineering is more than a set of structures and techniques. It requires a philosophical shift, which values engineering structures that look and function more naturally in the landscape and ecosystem and which values the diverse and multiple benefits of a healthy and beautiful environment. It is often outside the scope of a traditional engineering approach. Moreover, some large-scale problems, such as agricultural non-point source runoff treatment, are beyond the scope of concrete and steel structures. In such cases, landscape-scale structures are necessary.
Table 1. Some differences between ecological engineering and traditional engineering (modified from Barrett 1999).
|
Category/
characteristic
|
Traditional |
Ecological |
|
Project goal
|
Single purpose |
Multiple benefits |
|
Benefits to the ecosystem
|
Low priority |
High priority |
|
Structures
|
Concrete, steel, human-made, “hard” |
Landscape/aquatic features, natural, “soft” |
|
Energy source
|
Fossil fuel combustion, electricity |
Solar, gravity, plants, animals |
|
Material movement mechanisms
|
Pumps, blowers, conveyors |
Convection/gravity, plant/microbial processes |
|
Processes |
Human-driven, human-regulated |
Natural, self-regulated |
|
Climate and landscape setting
|
Relatively unimportant |
Critical |
|
Useful lifespan
|
Relatively short |
Relatively long |
|
Performance
|
Controlled |
More variable |
|
Performance
|
Controlled |
More variable |
|
Robustness
|
Often low |
Usually high |
|
Land requirements
|
Low |
High |
Principles of Ecological Engineering
There are four guiding principles, which may be used to describe ecological engineering and which provide a relatively sound basis for evaluating the ecological engineering merits of a project. These principles are as follows (Mitsch and Jorgensen 1989; Mitsch 1997):
- A part of, not apart from, nature. Ecological engineering planning, design and monitoring should be founded within the framework of natural systems. In essence, it involves using nature as our guide and moves us toward a symbiotic relationship between human society and the natural environment. Ecological engineering has been dubbed "green technology" because it relies on photosynthetic plants and natural biological systems, which are user and environmentally friendly. Moreover, systems with living plants are often both aesthetically and economically appealing. Property values may increase because of the cost-effectiveness and fuel savings, aesthetics and novelty of an ecologically designed project.
- Self-design and self-regulation. Self-design and self-regulation comprise the basic premise behind ecologically engineered systems. There are natural adjustments in food chains and shifts in species within populations and communities. In fact, a considerable degree of resiliency is inherent in self-organization, which allows ecosystems to adapt to both natural and human-induced changes. Within this framework, engineers participate as a choice generator and as a facilitator of matching environment with ecosystem, but nature does the rest of the engineering. In this way, nature is a collaborator.
- Solar basis and sustainability. Ecological engineering is based on a solar energy philosophy. It does not depend on fossil fuels and other potentially damaging energy sources. Furthermore, greenhouse gas emissions are minimized by the possible sequestration of carbon in the biomass of the organisms comprising the ecosystem. Once a system is designed and put in place, it sustains itself indefinitely with only a modest amount of human intervention. Moreover, most projects have direct and indirect, expected and unexpected, spin-off benefits.
- Ecosystem conservation. A consequence of an ecologically engineered system is preservation of ecosystems. In part, this effect occurs in response to increased recognition of the value of ecosystems. For example, when the abiotic values of wetlands were recognized for flood control and water quality enhancement in addition to the provision of habitat for fish and wildlife, then the protection of natural wetlands and construction of artificial wetlands increased dramatically.
Applications of Ecological Engineering
A systems approach is required when undertaking ecologically engineered designs. Ecosystems are characterized by the intimate linkages between physical, geochemical/biochemical, hydrological, and biotic processes, which must be incorporated into engineering designs. To do so requires a multi-disciplinary team approach with the team members being drawn from the physical and life sciences and engineering. Moreover, an ecologically engineered system should be designed to serve several purposes, such as wastewater treatment, enhancement of wildlife habitat and improved landscape aesthetics. Such an approach has both ecological and economic advantages. However, the approach to design requires more in-depth understanding of ecological processes and engineering design principles, including economic cost-benefit analysis (van Ierland, E.C. and Man 1996).
Applications of ecological engineering can be classified or grouped in several ways (Table 2). A brief discussion is given of a few representative examples of applications of ecological engineering, with particular attention to Canada.
Table 2. Applications of ecological engineering (modified from Mitsch and Jorgensen 1989).
|
Ecosystems are used to reduce or solve a pollution problem
|
Sludge management |
|
Ecosystems are imitated or copied to reduce or solve a pollution problem
|
Wetlands |
|
Ecosystems are created or restored after major disturbance
|
Mine tailings reclamation |
|
Ecosystems are used for the harvest of products without destroying them
|
Fish or timber harvesting (aquaculture) |
|
Ecosystems are used to provide health benefits
|
Indoor air quality improvement |
|
Ecosystems are created to improve aesthetic values
|
Artificial landscapes |
Wetland Technology: German botanist, K. Seidel, in 1953 first pointed out the ability of aquatic macrophytes to transform contaminants in polluted waters and advocated the controlled use of aquatic macrophytes for improving water quality in lakes, rivers and wetlands (Tourbier and Pierson 1976). This discovery led to engineering designs of controlled wetland systems supporting aquatic macrophytes, commonly referred to as treatment wetlands, for the purpose of improving water quality (e.g., Reed et al. 1995; Kadlec and Knight 1996; Verhoeven and Meuleman 1999). In Canada, some of the first, notable treatment wetlands were constructed in the 1970s (e.g., Lakshman, 1979; Wile et al. 1985). Today, there are hundreds of sites in all provinces and territories that are in place, including full-scale operational systems, pilot projects, and abandoned or destroyed systems. Both free surface flow (Figure 1) and subsurface flow (Figure 2) designs are used. Contaminants contained in the water undergo biochemical/geochemical transformations in both oxygen-rich and oxygen-poor compartments of the wetland and are removed by diverse microbial communities living on the plants leaves, stems and roots, by plant uptake or by volatilization.
Figure 1. Cross-Section of a Free Surface Flow Constructed Wetland System.
Figure 2. Cross-Section of a Subsurface Flow Constructed Wetland System.
Wetland creation and restoration is another application of wetland technology. Ducks Unlimited Canada is the lead agency responsible for this application of wetland technology, largely for the conservation of natural habitat in an attempt to reverse historical losses of natural wetland (Leitsch 1978). They have been responsible for 4500 projects involving the creation and restoration of more than 1.4 million hectares of wetland during their 60-year history (Murkin 2000).
Walls of aquatic plants for use indoors represent one of the most imaginative and complex designs within the wetland technology spectrum. Rather than have the plant bed lie horizontal, these designs have the plant bed on the vertical, wherein water is allowed to run from top to bottom by gravity through the rooting zone. Although they are not generally thought of as wetlands, their principles of design and operation do mimic wetlands.
Poplar Tree Technology: Terrestrial vegetation communities have been found to be effective in the phytoremediation of mildly to severely contaminated soils. Poplar and cottonwood (Populus spp.) trees have been found to be especially effective in a variety of applications, but other trees such as willow (Salix spp.), locust (Gleditsia sp.) and sycamore (Platanus occidentalis) have been used (Freeman 1997). Poplar tree technology has been applied for a number of years in the United States, but it is only in the last few years that there has been interest in Canada, with a few sites now existing in Ontario. Remediation occurs largely through plant uptake of contaminants, through rhizosphere oxygenation and by enhancement of soil microbes that reside on the roots and within the root region. The trees are tolerant of saturated conditions. They can remediate contaminated groundwater by producing deep taproots capable of penetrating into the phreatic zone.
Soil Bioengineering. Soil bioengineering, in its most common usage, is an approach to erosion control and bank stabilization using living plants and other organic products as the basic construction materials. In a broader context, it can also be considered to include remediation of contaminated soil with microorganisms. With respect to erosion control, soil bioengineering techniques include contour wattling, trench packing, brush matting, planting of live cuttings, prevegetated mats and interplanting stone riprap. Advantages of such an approach are fast and reliable bank stabilization, habitat enhancement, purification and filtration of overland runoff, contribution of organic matter and aesthetic improvement. Soil bioengineering techniques should, in many instances, be considered in conjunction with more conventional approaches such as riprap, articulated block systems, geogrids, geotextiles, gabions and cellular confinement systems (Sotir 1998).
Other Applications. There are many other applications of ecological engineering. Nature-like fishways, which simulate a natural channel, are intended to provide suitable passage conditions and habitat for a wide variety of fish species (Katopodis 1995). They generally adhere to the several guiding principles of ecological engineering, in which anthropogenic works are made to function in harmony with nature (Kells et al. 2000). Urban rooftop gardens and rain barrel catchment systems have also been promoted as a means of "recycling" rainwater. These systems serve to both reduce stormwater runoff flows and demands on the water treatment, distribution and collection systems.
Concluding Remarks
The future of ecological engineering in Canada is bright. Many of the applications of ecological engineering offer new alternatives that compliment and add to the wide range of more mainstream applications. The environmental friendliness, cost effectiveness, and greater aesthetic appeal are proving to favor the widespread use of ecotechnology.
Unfortunately, the science of the technology has not been able to keep up with the rate at which ecotechnology has been applied and used in the marketplace. Most designs remain to be verified or calibrated with credible data. Questions remain as to the long-term endurance of specific designs and maintenance requirements. One thing is certain. Ecotechnology is a business where customized designs are required, each and every one of which require calibration to realize their full market potential.
References
Barrett, K.R. 1999. Ecological engineering in water resources: The benefit of collaborating with nature. Water International, 24(3):182-188.
Freeman, H. 1997. The standard handbook of hazardous waste treatment and disposal. 2nd edition, McGraw Hill, New York, 628 p.
Jorgensen, S.E. and Mitsch, W.J. 1989. Classification and examples of ecological engineering. In: Ecological Engineering, Edited by: W.J. Mitsch and S.E. Jorgensen, J. Wiley & Sons, New York, pp. 13-19.
Kadlec, R.H. and Knight, R.L. 1996. Treatment wetlands. CRC Press, Boca Raton, 893 p.
Katopodis, C. 1995. Recent fishway design problems in Canadian rivers. Proceedings, International Symposium on Fishways '95 (guest lecture), Gifu, Japan, October 24-26, 8 p.
Kells, J.A., Acharya, M. and Katopodis, C. 2000. Design of nature-like fishways for small dam projects. Proceedings, Annual Conference of the Canadian Dam Association, Regina, SK, Sept. 16-21.
Lakshman, G. 1979. An ecosystem approach to the treatment of wastewaters. Journal of Environmental Quality, 8:353-361.
Leitch, W.G. 1978. Ducks and men. Ducks Unlimited Canada, Winnipeg, 268 p.
Mitsch, W.J. 1997. Ecological engineering: The roots and rationale of a new ecological paradigm. In: Ecological engineering for wastewater treatment, Edited by C. Etnier and B. Guterstam, 2nd edition, pp. 1-20.
Mitsch, W.J. and Jorgensen, S.E. 1989. Introduction to ecological engineering. In: Ecological Engineering, Edited by: W.J. Mitsch and S.E. Jorgensen, J. Wiley & Sons, New York, pp. 3-12.
Murkin, H.H. 2000. Personal communication. Senior Scientist (Ph.D.), Institute for Wetland and Waterfowl Research, Ducks Unlimited Canada.
Reed, S.C., Crites, R.W., and Middlebrooks, E.J. 1995. Natural systems for waste management and treatment. 2nd edition, McGraw Hill, Inc., New York.
Sotir, R.B. 1998. Soil bioengineering takes root. Civil Engineering, ASCE, July, pp. 50-53.
Tourbier, J. and Pierson, R.W. 1976. Biological control of water pollution. University of Pennsylvania Press Inc., Philadelphia.
van Ierland, E.C. and Man, N.Y.H. 1996. Ecological engineering: First steps towards economic analysis. Ecological Engineering, 7:351-371.
Verhoeven, J.T.A. and Meuleman, A.F.M. 1999. Wetlands for wastewater treatment: Opportunities and limitations. Ecological Engineering 12:5-12.
Wile, I., Miller, G. and Black, S. 1985. Design and use of artificial wetlands. In: Ecological considerations in wetland treatment of municipal wastewaters, Edited by P.J. Godfrey, E.R. Kaynor, S. Pelczarski and J. Benforado, Van Nostrand Reinhold Co., New York, pp. 26-37.
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