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Habitat Assessment

Habitat Monitoring

The Cobb County Stream Monitoring program performs habitat assessments at 24 biological monitoring stations located throughout the county. Primary instream physical characteristics such as epifaunal substrate/available cover, embeddedness, velocity/depth regime, and pool/substrate variability directly affect the biological community. Secondary parameters relate to channel morphology and include channel alteration, sediment deposition, channel flow status, frequency of riffles, and channel sinuosity. Tertiary parameters such as bank stability, bank vegetative protection, and the riparian vegetative zone indirectly affect the amount of sediment input and habitat availability within the stream. All parameters are evaluated over the designated area (100 meters) of a stream.

Ten habitat parameters are given a condition category rating of Optimal, Suboptimal, Marginal, or Poor. Scoring individual parameters enables comparison of the variability of habitat characteristics from year to year and stream to stream. These 10 parameters are then tallied to determine a habitat assessment score for the monitoring station. Habitat Assessment scores give insight as to what may be affecting biological populations. Parameters that score poorly may not provide the required habitat necessary to support certain organisms; therefore, habitat assessment scores, particularly individual parameters, may help explain the presence or absence of some aquatic species.

Important information such as date, season, assessor, parameter score and overall score are recorded and stored in a database for evaluation. Changes over time may indicate trends in the availability and/or stability of habitat accessibility to aquatic organisms. Combined with observed changes in chemical and biological data over time, there may be a correlation of impacts of external changes or significant events impacting stream health in a particular watershed.

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picture of hands holding a clipboard doing an assessment

Habitat is the physical environment where an organism lives. Individual aquatic species have evolved to thrive in different niches of the stream but ultimately, a suitable habitat must be stable and provide food, shelter, and protection from prey. The habitat assessment process involves 2 or more trained individuals rating ten stream parameters. The habitat parameters evaluated are related to overall aquatic life use and habitat absence or impairment may serve as a limitation for the aquatic biota.

Habitat Parameter Definitions

  • Bank Stability - Measures the existence of, or the potential for, detachment of soil from the upper and lower stream banks and its movement into the stream.
  • Bank Vegetative Protection - Measures the amount of the stream bank covered by vegetation which helps resist erosion and shade the stream.
  • Channel Alteration - Measurement of large-scale alteration of instream habitat that affects stream sinuosity and causes scouring. Examples of channel alteration are: artificial embankments, riprap, and other forms of artificial bank stabilization or structures, channelization of the stream, or presence of dams or bridges.
  • Channel Flow Status - The degree to which the channel is filled with water during base or average annual flow periods, judged by the vegetation line on the lower bank. A decrease in water will wet smaller portions of the streambed, thus decreasing available habitat for aquatic organisms.
  • Embeddedness  -The degree to which cobble, boulders, and other rock substrate are surrounded by fine sediment.
  • Epifaunal substrate/available cover - Physical features such as woody debris, root mats, leaf packs, and riffles that are available as shelter, feeding, spawning & nursery areas for aquatic organisms.
  • Frequency of Riffles - Estimates the frequency or occurrence of riffles which are a high-quality habitat supporting diverse populations of aquatic organisms.
  • Pool - A segment of the stream with little velocity. Commonly with water deeper than surrounding areas.
  • Riffle - A shallow part of the stream where water flows swiftly over substrate (cobble/gravel rock or woody debris) to produce turbulence. A riffle area is characterized by three components: (1) a change in elevation, (2) oxygenation of the water, and (3) the riffle area is audible.
  • Riparian Vegetation Zone Width - Measures the width of natural vegetation from the edge of the upper stream bank out through the floodplain. The Riparian Vegetation Zone serves as a buffer to pollutants entering a stream from runoff, controls erosion, and provides stream habitat and nutrient input into the stream.
  • Run - A relatively shallow part of a stream with moderate velocity and little or no surface turbulence. A run usually connects a riffle and pool area.
  • Sediment deposition - Sediment influx from within the watershed and bank erosion may accumulate and cause an increase in the formation of islands and point bars, resulting in the filling of pools. High levels of sediment deposition create an unstable and continually changing environment that becomes unsuitable for many organisms.
  • Velocity/depth regime - High quality riffle/run prevalent streams are comprised of four combinations of velocity and depth: slow-deep, slow-shallow, fast-deep, and fast shallow.