Ecological engineering incorporates contemporary environmental engineering practices with ecological principles to attain ecologically driven goals. Ecological engineering is defined as the design, restoration, or creation of ecosystems, with a strong emphasis on ecosystem self-design and self-organization. When using ecological engineering to restore a system, often less effort is needed, or desired, to begin ecosystem recovery due to the self-designing qualities of this approach. Stream conditions are designed to mimic the predisturbance environment and incorporate not only physical parameters such as channel dimensions and hydrologic variation, but also include species composition manipulation and water quality. Once these initial conditions are implemented, the system is left to organize itself. The basis for this approach is that the biotic component will organize itself through community interactions such as competition, predation, etc., to establish the most stable and energy-efficient system for the environmental conditions in the stream. Essentially, if the abiotic template is restored, conditions under which the native community evolved will exist and native organisms will be favored to dominate the system without input of additional effort. See Stream Management for further information on the basic principles of ecological engineering.
The focus of ecological engineering and ecological restoration is similar. Both strive for ecosystem functioning and biotic resilience from disturbances comparable to the historic conditions through the creation of the most natural system obtainable. Resilience is the ability to return to the original state after a disturbance. In streams, disturbances are a natural part of the ecosystem, as floods and droughts shape the physical aspects of the channel and the development of native communities. Thus, native species abundances often quickly return after a natural disturbance and are said to be very resilient. However, recovery from anthropogenic disturbances such as channelization, chemical contamination, or cultural eutrophication often provides a different starting point for native species recovery. Instead ofnative species colonizing a 'bare' system, recovery occurs with a shift in dominance from pollution-tolerant species to pollution-sensitive species. The distinction between resilience to natural and anthropogenic disturbances is important because a pollution-tolerant community may be more resilient to a natural disturbance in the presence of human-caused disturbances, which may be the reason these pollution-tolerant species have taken over.
In addition, both ecological engineering and ecological restoration stress on minimal human maintenance and continued interference. To correctly identify the best ecological engineering approach to use for a given restoration situation, is it imperative to understand the ecology of the stream.
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