Ecology is the study of interactions between living organism and their environment. In every ecosystem, species composition and abundance at every level, from primary producers to top consumers to decomposers, are regulated by environmental conditions. Compared to most aquatic ecosystems, stream environments are more dynamic and are characterized by nonequilibrium conditions. However, compared to small streams, larger streams and rivers are typically more stable in regard to discharge, chemical composition, and community structure. Fundamental ecological interactions among components are very important because knowing how ecosystems are likely to respond to each management action is critical to the success of a management program.
Ecological stream management focuses on the physical, chemical, and biological constraints on developing stream communities that are predictable, and uses these relationships as a starting point to design a management strategy. There are, however, many uncontrollable variables that may alter interactions, including stream size, precipitation intensity and frequency, and ambient temperature.
Following is a list of the major physical, chemical, and biological components of stream ecosystems. Included with each factor are anthropogenic actions that alter the components, and some basic, direct consequences of their alterations on stream ecosystem structure and function. This is by no means a complete list of components or consequences, as many of the basic, interacting, and synergistic effects of stream ecosystem alterations are not well known or understood.
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