Replacement of culvert styles has minimal impact on benthic macroinvertebrates in forested, mountainous streams of Northern California

Culvert styles are being replaced on many road-stream crossings to provide long-term (>2 years) benefits, but these projects may result in short-term (0-2 years) biological impacts. We quantified the short-term effects of replacing steel-pipe culverts with open-arch structures on the benthic-macroinvertebrate communities of 6 streams in the Klamath National Forest of Northern California USA. Physical habitat showed notable site-specific effects in channel form and sedimentation, but no significant change among sites. In contrast, we observed small though significant impacts of the culvert style replacement on benthic macroinvertebrates among sites, including a statistically significant reduction in both taxa richness (p = 0.012) and abundance of intolerant taxa (p = 0.004). Moreover, there was also modest evidence of slightly elevated variability in the benthic-macroinvertebrate communities downstream following the replacement of culvert style. The long-term benefits of culvert style replacement that have been observed in other studies may outweigh the minor, short-term biological impacts observed in these streams.