Dredge tailings on the red river narrows channel restoration project: weed sites and the effectiveness of restorations

Abstract

The success of river restoration is contingent on revegetation to stabilize river banks, yet few restoration projects complete any kind of long-term monitoring. Common challenges at river restoration projects include mining dredge tailings which create challenges for the establishment and retention of healthy, native plant populations. These challenges are evident within the Red River Narrows channel restoration project near Elk City, Idaho, where leveling or removal of all the dredge tailings was not completed between 2008 and 2012. These restoration methods have resulted in an environment with inadequate conditions for native species to reestablish due to the presence of bare tailing materials, exposed substrate from tailing removal, and potential mineral leaching in the area, allowing invasive species to establish and persist. Therefore, I used GIS and remote sensing techniques to assess various vegetation changes within the Red River Narrows restoration project area between 1984 and 2023. I used unsupervised classification to estimate overlap between areas dominated by invasive species, such as spotted knapweed (Centaurea maculosa auct. non Lam.) and yellow toadflax (Linaria vulgaris Mill.), and those with dredge tailings and exposed substrate and completed a change detection analysis to demonstrate vegetation changes pre- and post-restoration. I also discuss broader implications for restoration planning and completion, long-term monitoring, invasive species, and herbicide treatments. My results indicate there are more weed species in areas with dredge tailings and exposed substrate, and vegetation changes pre- and post-restoration have only recently begun to return to pre-restoration levels of vegetation health, as measured by NDVI. My study echoes the importance of other restoration literature and the importance of long-term monitoring, given that revegetation is crucial to determine restoration success. Future development of remote sensing techniques to measure how a restoration project is progressing may be an essential part of future restorations, considering the lack of long-term monitoring in nearly all ecological restorations.