Ecological Engineering and Streams

First introduced by H. T. Odum in 1957 as 'community' engineering, ecological engineering has the goal of attain ing sustainable ecosystems that integrate human society with the natural environment for the benefit of both. One of the key aspects that separates this approach from con ventional environmental engineering is a strong emphasis on ecosystem self design and self organization. In other words, the designer makes available the necessary components and conditions, and then natural processes arrange the components to create the most functional and efficient ecosystem. Another defining characteristic of ecological engineering is that it has both empirical and theoretical bases. The approach not only uses data col lected on the cause and effect relationships through many decades of ecological and mechanical research, but also incorporates predicted outcomes of ecological reactions

Table 1 Relative physical differences between large rivers and small streams that affect ecosystem structure and function

Large rivers

Small streams

Catchment area

High

Low

Average discharge

High

Low

Flood frequency

Low

High

Channel dimensions

High

Low

Water contact with bottom

Low

High

Slope

Low

High

Dilution potential

High

Low

Substrata heterogeneity

Low (fine)

High (coarse)

Temperature stability

High

Low

Light availability

Low (turbidity)

Low (canopy cover)/high (open channel)

to environmental changes based on simulation modeling and extrapolated theories. Since it is a form of engineer ing, there is an explicit preplanned purpose for the 'constructed' ecosystem. In the case of stream manage ment, the purpose is to achieve a physical, chemical, and biological state that is in accordance with predisposed human goals, but is self sustainable. Specific intended outcomes are determined by the goals of the managing entity, and are often devised to increase aspects such as sustained resources, economic worth, or the intrinsic value of the system. Specifically, the focus of ecological engineering is to create the most natural system possible, given the current stream conditions.

Ecological engineering is well suited to ecological stream management because the self organization process it uses fills the voids in our current knowledge of stream ecosystems. Ecological engineering uses nature to engi neer aspects of the ecosystem that humans cannot. Furthermore, it can be very cost effective to rely upon natural processes that require little monetary input as opposed to those that require continuous or repeated human intervention. For example, the self purification (natural reduction of a pollutant as it travels downstream) characteristic of lotic systems, which is often a manage ment emphasis, is essentially a longitudinal self organization process whereby the system adjusts itself in changing conditions to maximize energy flow and eco system stability. For example, using an artificial wetland to purify waste before it enters the stream may be much more effective than chemical treatment in an industrial setting. Thus, the manager's goal is to create conditions that will maximize a stream's ability to cleanse itself naturally, and perform a defined task efficiently, such as reducing water nutrient concentrations, supporting tradi tional native and/or sport fisheries, or generating power.

The tools available to the manager are based in both ecology and engineering. In addition to conventional engineering stream management practices, biotic organ isms are essentially tools designed by evolution, which can be used to create a network of energy flow that human engineering cannot replicate. In this sense, native species diversity can be the key to successful management because it may allow for the most efficient organizational endpoint with the highest degree of ecosystem stability. Ecological stream management through ecological engi neering therefore minimizes maintenance of the system, while preserving natural ecosystems.

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