Impacts of bank stabilization on fish habitat in two contrasted environments
Impacts of bank stabilization on fish habitat in two contrasted environments
Previously Published Material: An earlier iteration of these finding were presented at the American Fisheries Society (AFS) annual symposium at Québec city on August 15. Finding will soon be under review. Submission is planned to Earth Surface Processes and Landforms in the month of February.
Abstract ID#: 34002
English Abstract:
Riprap is a form of riverbank stabilization that has a standardized design based on local hydraulic conditions and is commonly used for protecting and repairing road and bridge structures. However, little is known about how streams adjust to such perturbation or how this can affect fish habitat in different fluvial environments. The objective of this study is to assess impacts of riprap on fish habitat quantity and quality through a pairwise comparison of stabilized and non-stabilized stream reaches in two physiographic regions, the St. Lawrence Lowlands and the Appalachian highlands of Montérégie-Est (Quebec). For each stream reach high-resolution measurements of depth and velocity were taken to determine zones of fast, slow, shallow and deep flow, as well as to calculate a hydro-morphological index of diversity (HMID). The reach area proportions of in-stream cover (woody debris, overhanging vegetation, undercut banks, aquatic macrophytes) and habitat units (pools, riffles, runs, glides) were also documented, longitudinally. Fish habitat quality was also assessed holistically, using a Qualitative Habitat Evaluation Index (QHEI). Results demonstrated a significant (p<0.05) decrease in the median proportion of woody debris and overhanging vegetation at stabilized reaches in both Lowland and Appalachian environments. Riprapped reaches in the Lowlands also showed significantly lower proportions of pool/glide habitats and higher proportions of riffle/run habitat as well as higher HMID scores. QHEI scores were found to be significantly lower at stabilized reaches for Appalachian streams and higher quality Lowland streams, while stabilized reaches for extremely degraded (straightened) Lowland streams showed higher scores. These results indicate that riprap can significantly alter fish habitat in ways that reduce fish habitat quality and the availability of specific habitat types but also improve habitat quality and diversity in streams which were already degraded.