Habitat Alteration and Loss

Because southern Appalachian rivers were not exposed to Pleistocene glaciation, native aquatic organisms have had a long evolutionary history, and possess adaptations to the environmental conditions that prevail in mountain rivers and streams. These conditions reflect the natural forest cover of landscapes in the region, and include:

• Extensive physical structure as provided by rocky stream beds and large woody debris.
• Clear, pure water with low concentrations of dissolved nutrients and suspended material.
• Cool to cold water depending on elevation.

Most impacts to aquatic ecosystems indirectly affect organisms by altering their habitat (Allan and Flecker 1993). The most harmful impacts can render the habitat unlivable for sensitive species. Habitat alteration may include any combination of the following:

• Modification of natural flow regimes by dams, diversions, and watershed land uses.
• Changes in water quality due to point and nonpoint source pollution.
• Woody debris inputs to streams are diminished or lost as a result of reduced forest cover along waterways.

The combined, possibly synergistic, effect of these changes in the physical and chemical environment amounts to a deterioration in the quality of habitat for native taxa. Species tolerant of environmental change dominate biological communities, while native species decline.  Endemic species, whose distribution is often limited to a single watershed, appear to be particularly sensitive to environmental changes, disappearing where habitats have been altered extensively (Morse and others 1993, Scott and Helfman 2001). Endemics are often disproportionately listed as threatened or endangered.

As habitat continues to be degraded under the socioeconomic pressures of development, the threats to the well-being of native organisms and ecosystems mount. Loss of endemic species and concomitant invasion of tolerant, generalist species from outside the region erode the unique faunal diversity of the region. This trend toward homogenization points to a simplified, ecologically bleak future if actions are not taken to reverse the process.

Proper stream habitat management and best management practices in streamside zones can help protect and restore aquatic ecosystems.