The Effects Of Riverbank Stabilization Through Rock Riprapping On Fish Density And Diversity In Streams Impacted By Agricultural Activities

Rock riprapping revetment is a form of riverbank stabilization that is commonly used to protect road and bridge infrastructures from fluvial erosion. However, little is known about how these may affect habitat selection by riverine fish in streams impacted by multiple stressors stemming from agricultural activities. Nine streams in Southern Quebec (Canada) served as study sites, where fish surveys and habitats attributes were measured. Nested linear mixed-models using percent cover of rock, wetted stream width, water depth, and flow velocity as fixed effects, and spatio-temporal variables as random effects, were conducted to assess the ecological effects of rock riprapping revetment across agricultural streams. Results indicated that overall fish density was significantly explained by fixed effects (R-2 = 35.7% : Marginal) and by random effects (R-2 = 24.2) which lead to a model explaining 59.9% (R-2 : Conditional). Nested linear mixed-models was assessed by cross-validation (jackknife leave-one-out procedure) and showed an (RCV)-C-2 of 57%. An interaction between rock riprapping revetment and wetted stream width on fish densities was also observed (p-value = 0.0195). These findings suggest that the rock riprapping revetment zones had greater fish densities if water depths were maintained, as these zones contributed to stream habitat complexities, providing suitable fish habitats that were not available elsewhere in these streams. The knowledge gained here may further improve on existing riprap zone designs implemented by the Ministsre des Transports du Quebec (Quebec Ministry of Transportation).