Design Principles

S Bolton, University of Washington, Seattle, WA, USA © 2008 Elsevier B.V. All rights reserved.

Common Steps for Ecological Engineering Design Further Reading

Introduction Overarching Principles


Engineering is the application of science through design to create systems to benefit humans. Design is the essence of engineering. Engineering has its basis in math and physics, but subfields are based on a particular science. For example, chemical engineering is based on chemistry, mechanical engineering on mechanics, and electrical engineering on electricity. The concepts of ecological engineering were introduced in the United States in the 1960s by H. T. Odum. Ecological engineering, as the name implies, is an engineering subfield that is based on ecology. Ecology includes aspects of all of the sciences that study living or nonliving components in an ecosys tem, for example, biology, botany, geology, hydrology, soil science, zoology, and specifically addresses the inter actions among the living and nonliving components ofthe ecosystem. Historically ecologists have viewed many engineering projects as destructive of natural systems making ecological engineering a contradiction in terms. Likewise, engineers often have little appreciation for eco logical knowledge, which is usually less precise and mathematical than traditional engineering science.

Ecology is the study of the interrelationships between biotic (living or previously living, e.g., plants, animals, carcasses) and abiotic (never living, e.g., water, sediment, chemicals, temperature) components of the environment. Ecological engineering incorporates elements of the sciences used in ecology to create engineered designs that reflect and incorporate ecological processes. The goal is to provide for human welfare with engineering projects while also protecting the goods and services that are provided by a natural environment. These goods and services include production of oxygen, air and water purification, carbon storage, flood control, regeneration of soil and soil fertility, pollination of food crops, waste decomposition, and protection from ultraviolet rays. Recognizing that all social and economic systems depend on a functioning ecological system implies that ecological engineers acknowledge the values of sustainability and protection of natural systems even as they design systems for the benefit of humans. These concepts define an engineering discipline based on ecological science with an explicit recognition that the values of sustainability and protection of natural systems are incorporated in designs for the benefit of humans and the environment.

Increasingly, natural scientists with no training in design methods are engaged in applied science as they address and try to solve environmental problems such as wetland loss, river and water quality degradation, and soil contamina tion. Engineers are addressing similar questions with more formal design procedures but with little training in the relevant scientific areas. This can create a variety of unin tended consequences that can diminish the ecosystem's ability to provide the goods and services upon which all life on Earth depends. Ecological engineering uses ecolo gical knowledge and theory and standard engineering design procedures to address environmental problems. Standard design procedures allow for the collection of information on which design criteria are successful and which are not. Documentation of the design process allows for others to learn from either design errors or less than perfect designs and contributes to improved future designs. Numerous authors have discussed design principles for ecological engineering all of which derive from the over arching principles of thermodynamics and evolution.

Overarching Principles

Thermodynamics and Conservation of Mass and Energy

Ecological engineering principles are constrained by the laws of conservation of mass and energy and the laws of thermodynamics, just as chemical, mechanical, or electri cal engineering principles are constrained by these laws. Ecosystems are open systems that require a continual input of energy to maintain their structure and function. Two of the most inviolable principles of ecological science can be described as energy flow and material recycling.

Energy flow

Energy inputs, driven by solar radiation, are required to maintain structure and function in the face of the physical tendency toward disorder (the increase of entropy). Traditionally engineered systems use human and hydrocarbon based energy to maintain order (keep the system intact and functioning). Ecosystems use photo synthesis, driven by solar energy, as their energy source. Biological energy flow can be measured by rates of pro duction (biomass accumulation) and respiration (energy used for production). Physical energy flow can be measured by the mobilization, transport, and deposition of organic and inorganic materials by the kinetic and potential energy of fluids or solids such as water, wind, and sediment. Both biological energy and physical energy are constrained by conservation of mass and energy laws. Ecology as the interaction of biotic and abiotic processes looks at the interactions of both types of energy. Some energy is lost at each transformation so while total entropy increases in accordance with the second law of thermodynamics, order is locally increased. This has been described as the self organization feature of ecosystems or exergy.

Emergy, an accounting system developed by H. T. Odum, can be used to put all natural and human produc tion into common units based on solar radiation. Emergy measures the inputs to make a product or service. It is a measure of energy used in the past and thus is different from a measure of current energy use. This provides a way to evaluate the costs of ecological goods and services in the same units as the costs of human production of goods and services. Ecological engineering designs seek to maximize the use of renewable energy (e.g., solar radiation) and minimize the use of nonrenewable energy.

Material recycling

Nutrient and material (re)cycling is another major ecolo gical principle. Material is conserved by the continual reuse of materials and the transfer of those materials between organic and inorganic states through biogeo chemical cycles. Organic and inorganic materials cycle through the system appearing in different locations and forms through time. Waste disposal is seldom an issue in a functioning ecosystem as the output from one system is used as input to another. Natural biogeochemical cycles mobilize, transport, and store material in the atmosphere, biosphere, hydrosphere, and lithosphere. Producers, con sumers, and decomposers transfer organic matter and nutrients among themselves and the storage compart ments. Many traditional human engineering designs lead to the accumulation of waste materials that cannot be reused by the original process and can contaminate other processes. Ecological engineering designs seek to minimize waste production and to utilize wastes (material not related to the primary function ofthe design) as inputs for other processes. One example of this is using ecologi cal processes to clean up waste products such as using wetlands to treat wastewater or phytoremediation to clean up soil contamination.

Natural Selection and Evolution Self-organization

In traditional engineering design, one seeks to maintain the independence of functional requirements. Functional requirements are the specific functions that the design feature is to provide. The engineer selects specific physical elements (design features) to meet each func tional requirement. In the final design, each functional requirement has one solution and does not rely on other design features; that is, modification of any one design parameter affects only one functional requirement. There is no interaction or coupling of design features to multiple functional requirements. This is exempli fied by the concept of modularity in software design where individual modules can be swapped in and out of programs without affecting program stability or performance.

Engineering designs seek tight tolerances and rigid, stable systems that do not change. Nothing is left to nature; everything is preplanned. In the event of system or component failure, identical back up systems or com ponents may be built to provide redundancy. The traditional engineering approach of maintaining indepen dence between subsystems ignores the interrelationships and complexity of ecosystems.

Nature does not build things the way humans do. There is no external plan, design engineer, or architect that creates steps to achieve an envisioned final product. It is the flow of energy and material through an open system that allows for self organization. Ecosystems are complexly coupled, that is, everything is connected to everything else. Ecosystem structure and function can be maintained through many different pathways that can operate under varying conditions, that is, wide tolerances. For example, accumulation of biomass can be accom plished by a wide array of plant and animal species. The actual species that live in a given ecosystem are adapted to the abiotic and biotic environment of the system. The loss of one species, either through succession or extinc tion, does not destroy the ecosystem. Other species continue the flow of energy and the cycling of nutrients and materials. In other words, there is redundancy of function but not necessarily of structure.

One measure of self organization is the amount of information that is required to predict the final outcome. Higher levels of self organization require large amounts of information to predict the final composition. To pre dict what an office building will look like when finished requires the blueprint and some drawings; to predict which organisms will provide structure and function to an ecosystem at any given time is almost impossible except in general terms. Self organization also gives eco systems properties of robustness, persistence, the ability to self repair, and flexibility in the face of changing envir onmental conditions. Because of the interactions among system components, biotic and abiotic, changes in one component can ripple through the system and change many other components.

Self organization is visible as an ecosystem goes through successional stages. It derives from the overarching actions of natural selection and evolution through which organisms have adapted to certain physi cal, chemical, and biological environments over time. For example, bare rock exposed by glacial retreat will pass through a series of plant and animal communities com posed of different combinations of species over time as it develops into a forest. The general progress of this succession is understood, but predicting the exact com position of each step and the duration of each step is not. The exact composition is an emergent property of the interaction between the biotic and abiotic components of the ecosystem.

This ability of self organization is taken advantage of by ecological engineers. Ecological engineering designs work with nature and allow nature to do some of the 'engineering'; that is, rather than fully proscribing only one satisfactory end result, the ecological engineered design recognizes that more than one final state may meet the functional requirements of the design. Engineering designs that ignore the self organization properties of ecosystems require continued inputs of human based energy and dollars (to buy materials and energy) to keep the system in the designed state (the desired, predicted outcome). Allowing nature to finalize the outcome of the design uses solar energy to organize the system and ensures some flexibility in the face of changing conditions.

Ecological engineers can take advantage of ecosystem self organization in various ways. For example, a wetland or streambank restoration project may plant a variety of species that are water tolerant. But rather than insisting that the original mix is the best and inputting labor and energy to maintain the original composition of species, the system is allowed to mature without interference, resulting in a set of species that is most suited to the conditions at a given site. The species most able to survive and reproduce in that particular environment will spread and grow. In a stream restoration effort, material neces sary to create lost habitat complexity and diversity, such as large organic debris or sediment, can be provided to the system and then be distributed by natural stream forces to distribute rather than anchoring it in place. By incorpor ating natural process into ecological engineering designs, ecological engineers reduce the use of nonrenewable energy and nonrecyclable material input and allow the self organization capacity of the ecosystem to determine what is most suitable in a given location using natural goods and services.

Disturbance and thresholds

Ecosystems have a history of disturbance that influences the current composition of the ecosystem. Self organization capacity in concert with natural selection and evolution results in an ecosystem that reflects past conditions and disturbances. Some organisms are more successful in relative stable conditions; some can only compete successfully in dynamic and ever changing con ditions. Disturbances (e.g., fires, floods, tides, seasons, and plate tectonics) periodically introduce forces that reset ecosystem structure at varying temporal and spatial scales. If a disturbance occurs that creates a large change in the abiotic or biotic environment, an ecosystem can cross a threshold which makes it unable to recover to its previous state. Examples include loss of soil fertility that cannot be restored, changes in water table levels that lead to desertification or wetland development, loss of a key stone species, and introduction of new diseases or species.

Human managed systems typically lose structural and functional diversity (fewer species providing fewer goods and services) and become more spatially uniform over time, for example, agricultural fields, managed forests, and urbanization. The alteration of natural disturbance cycles (e.g., fire suppression and flood control) disrupts the patch dynamics of ecosystems and generally reduces habitat complexity and thus biodiversity. As uniformity increases, resistance to disturbances decreases. For exam ple, spatially extensive monocrops, whether mountain forests, urban trees, or agricultural crops, can be destroyed by a single virulent disease vector. Monocrops tend to be genetically similar, do not have the variability to resist diseases, and diseases spread rapidly to adjacent identical, susceptible plants.

This homogenization of human managed systems highlights the differences between engineering resilience and ecological resilience. Designing for traditional engi neering resilience seeks stability and permanence; systems with high engineering resilience return to a stable equilibrium point quickly after a disturbance. Ecosystems do not exist around a stationary equilibrium point. Ecological resilience is a measure of how large a distur bance an ecosystem can absorb and maintain its original structure and function. Major disturbances, whether chronic or instantaneous, such as volcanic eruptions, gla cial advances or retreats, overfishing, or sea level rises and falls, may cause an ecosystem to cross a threshold. The ecological resilience of ecosystems can be exceeded by a major disturbance. This typically results in a dra matic change in species composition and the start of a new self organization process perhaps with different abiotic conditions.

Ecological engineering recognizes the stochastic nat ure (unpredictability) of disturbances in space and time and seeks designs that tolerate multiple states while still meeting the design purpose, thus benefiting humans and protecting the environment. Ecological engineers recog nize the hubris in the thinking that ecosystems need to be managed constantly or extensively to provide goods and services. Ecological engineering designs take into account the variability in time and space of processes and species composition across the landscape.

Traditional engineering design incorporates factors of safety in design parameters. Risk analysis estimates the probability of failure of the design, and energy and mate rial are used to enable the structure to resist failure that can result in harm to humans or infrastructure. This is called fail safe design. The risks are known and are more or less predictable. Efficiency, constancy, and predict ability are guiding principles for traditional engineering. Ecological engineers recognize that over time the forces of nature can overcome any affordable design. Persistence, change, and unpredictability are hallmarks of ecological theory. Ecosystems are complex systems with many variables and risk may come more from unknown (or unrecognized) sources than from known sources; that is, the probability of occurrence of the risk is unknown or in some cases, the risk itself is unknown. For this reason, ecological engineering strives for safe fail design, that is, when the design fails, the failure takes place such that extensive harm to humans, infrastructure, and the ecosystem is minimized. When considering design alternatives, ecological engineers choose the one that has the best worst case outcome.

Common Steps for Ecological Engineering Design

There is no cookbook available for ecological engineering design. The emergent properties of ecosystems do not lend themselves to a constant set of variables such as exists for chemistry (periodic table of elements) or mechanics (design table properties for steel or concrete). Each setting for ecological engineering design will have a unique history and set of interactions.

Ecological engineers are aware of and take advan tage of the processes that are active in natural systems. This awareness comes from a thorough understanding of ecological theories that describe the ecosystem of interest to the designer. The naturally occurring eco system processes are partners in design, not obstacles to overcome and dominate. Important aspects of eco systems that need to be accounted for in design include disturbance, diversity, heterogeneity, change, and self organization at multiple scales in space and time. Using a standard design procedure allows for the documentation of responses and allows ecological engineering to be used to test ecological theories. Importance of the following components and depth of analyses will vary by environment and design objectives.

Table 1 Concepts and characteristics of traditional versus ecological engineering designs

Traditional engineering

Efficiency of function

Seeks stability

Resists disturbance

One equilibrium point

Redundancy of structure

Single acceptable outcome

Spatially and temporally uniform

Tries to control natural forces



Tight tolerances

Heavy reliance on nonrenewable energy and material

Rigid boundaries and edges

Unconcerned by production of waste materials from the design Deductive

Engineering resilience

Ecological engineering

Persistence of function

Accepts inevitability of change

Absorbs and recovers from disturbance

Multiple, nonstable equilibria

Redundancy of function

More than one acceptable outcome

Spatially and temporally diverse

Works with natural forces



Wide tolerances

Maximum use of renewable energy and energy and material Flexible boundaries and edges

Minimizes production of waste and seeks to use the waste in another design or process Inductive

Ecological resilience

Following the steps below provides the relevant ecological information that is needed to create an ecologically engineered design. The final design, grounded in the information gathered below, adheres to the traits listed in Table 1 under ecological engineering.

1. Identify the biotic and abiotic factors that drive the ecosystem of interest.

(a) Climate affects site potential and the presence and absence of biota.

(b) Site history of physical, chemical, and biological components should be investigated as historic con ditions can affect current site conditions and site potential.

(c) Current biotic and abiotic factors control organ isms and pathways through which energy flows and materials cycle.

(d) The design should be compatible with existing con ditions and enhance or sustain organisms and pathways through which energy flows and materials cycle.

2. Identify the types of disturbance, whether chronic or intermittent, biotic or abiotic, that are present in the system.

(a) The design should be ecologically resilient to these disturbances.

(b) The design should be safe fail.

(c) The design should maintain spatial and temporal heterogeneity in the system.

3. Identify the goods and services being produced by the ecosystem.

(a) Production of goods and services should be main tained or enhanced.

(b) Inputs of human produced materials should not exceed assimilation capacity.

(c) Any wastes that are produced should be usable in another design.

(d) Energy needs of the design should minimize the use of nonrenewable sources.

(e) Extraction of renewable resources should be less than the rate of renewal.

4. Use the naturally occurring forces of nature to help with design and maintenance.

(a) Working at cross purposes with nature is frustrat ing and expensive in the best case and disastrous and counterproductive in the worst case.

5. Recognize that implementation of any design will cre ate some disturbance to the preexisting conditions.

(a) No design is perfect. Accurate appraisal of poten tial problems allows for minimization and/or mitigation of the impacts.

(b) Where possible, connectivity to adjacent ecosys tems should be maintained or enhanced through use of corridors and ecological networks.

6. Keep complete and accurate documentation of design process, parameters, and outcome.

(a) Documentation of preexisting conditions, design process, and monitoring of outcome provides the means to improve designs in the future.

Ecological engineering designs can be applied to a variety of ecosystem problems, such as

• Phytoremediation and wastewater treatment wetlands can be used to reduce or solve pollution problems. In this case, the design seeks to replicate or take advantage of ecosystem properties.

Forest restoration or wetland mitigation can be used to reduce resource problems. Here the design seeks to copy or reproduce ecosystem structure and function. Mine land restoration or lake restoration seeks to has ten the recovery of an ecosystem following major disturbance. Here the design seeks to use the self organization properties of ecosystems to recreate the predisturbance system. The design is mindful that some disturbances, such as fires and hurricanes are natural, and ecosystems have recovered from them before human management or intervention was possible or even considered.

Extraction or use of ecosystem goods and services are done such that production of those goods and services is not decreased. Here the design seeks to meet sustain ability criteria and decrease the use of nonrenewable energy.

Further Reading

Bergen SD, Bolton SM, and Fridley JL (2001) Design principles for ecological engineering. Ecological Engineering 18: 201 210.

Brown MT and Ulgiati S (1999) Emergy evaluation of natural capital and biosphere services. AMBIO 28(6): 486 493.

Hollings CS (1996) Engineering resilience versus ecological resilience. In: Schulze PC (ed.) Engineering Within Ecological Constraints, pp. 31 43. Washington, DC: National Academy of Engineering.

Kangas PC (2004) Ecological Engineering: Principles and Practice. Boca Raton, FL: Lewis Publishers.

Krotscheck C and Narodoslawsky M (1996) The sustainable process index: A new dimension in ecological evaluation. Ecological Engineering 6: 241 258.

Mitsch WJ and J0rgensen SE (2004) Ecological Engineering and Ecosystem Restoration. Hoboken, NJ: Wiley.

Odum HT (1996) Environmental Accounting: Emergy and Environmental Decision Making. New York: Wiley.

Suh NP (1990) The Principles of Design. New York: Oxford University Press.

Todd J and Josephson B (1996) The design of living technologies for waste treatment. Ecological Engineering 6: 109 136.

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