Effects of Stream Crossing Type on Fish Assemblages and Stream Ecosystem Conditions

Abstract:

Culverts are used as road crossings to connect the upstream and downstream reaches of a stream, but they can severely alter habitat characteristics and species assemblages. Many culvert features impede fish biodiversity, movement, and survival. Restorations can be completed to help address these ecological problems. Paired Upstream-Downstream assessments were completed to determine the effects of restoration of old culverts and to determine the success of newly replaced culverts. Looking at stream orders from 1st through 3rd, we sampled 11 streams in the French Creek Watershed to evaluate the influence of road crossing types. Three sites will contain old, to be replaced culverts scheduled to be replaced in 2023, four sites will contain recently replaced/new culverts, and the last four sites will be bridges as our reference sample. We determined passability scores for three different stream crossing classifications, determined if restoration increases the similarity between upstream and downstream fish assemblages, and determined whether newly replaced crossings have restored biotic integrity relative to bridges and old crossings. Findings from NAACC passability tests show that to be replaced crossings had the lowest passability scores from 0.03 – 0.597 on a scale of 0 to 1. Restorations had new, positive effects on creating a more similar upstream and downstream connection. Outlet drop had the biggest impact on the passability score. To ensure longitudinal connectivity, restorations can be beneficial.