Linking Channel Stability and Bed Sediment Characteristics to Biological Integrity in Tennessee Ridge and Valley Streams

Streambed sedimentation has plagued waterways since the beginning of civilization, whether as a natural flow process or human disturbances on the landscape in more recent times. Due to the continual degradation in the quantity and diversity of aquatic organisms within streams, the issue has finally surfaced as a significant concern. The need to develop better Total Maximum Daily Load (TMDL) assessment tools to link sediment impairment to biological integrity was the driving force behind this study.

Within the Ridge and Valley Ecoregion, 76 stream reaches were analyzed to investigate the impacts of stability issues and bed sediment characteristics on stream biological integrity. The field data were correlated and related to benthic macroinvertebrate indices of biological integrity through non-parametric statistical procedures. It was found that the presence of larger sediment size classes was more significant, in a positive relationship, than the negative association of the finer particles. Medium to fine silt, channel stability, channel slope, and the percent below 2-mm from a modified Wolman pebble count, were also found to be significant parameters in their relationship to biological integrity scores.

The analyses revealed the importance of the larger bed materials and heterogeneity of bed sediment along the riffles. The significance of these results indicates that habitat heterogeneity from larger bed substrate material may be more relevant to the biological integrity than the weaker effects of fine sediment. The negative impact from fine sediments were observed and found to be mostly in the size range of medium to fine silt. Overall, the processes from the Rapid Geomorphic Assessment, including channel stability, and slope, were found to have good correlations to biological integrity.