River restoration should be directed at moderately impaired regions

River restoration costs millions of dollars. Yet, the literature is full of case studies that demonstrate its failure in achieving the desired biological outcome. Much of river restoration over the past few decades has focused on fixing up habitat (hydromorphological restoration) in the hope that species will reappear through time. This approach was termed the ‘field of dreams hypothesis’ following the idea from the classic baseball movie that “if you build it, they will come.” However, this approach has been shown to be flawed in many cases largely through lack of consideration of regional species pools. So there is a need to plan restoration projects appropriately to ensure such large expenditures don’t go to waste.

In a recent paper published in the journal Science of the Total Environment here, we demonstrate that for river restoration to be most effective, it should be directed at regions that are moderately impaired, rather than pristine or heavily impaired. In regions of intermediate habitat quality, stream invertebrate communities responded to local habitat quality the strongest. In contrast, at high or low regional habitat quality, community quality was independent of local habitat quality. These results suggest that directing local habitat restoration efforts at sites within these moderately impaired regions will lead to the best bang-for-your-buck.

These ideas are centered around the fundamental importance of dispersal from the regional species pool on successful restoration outcomes. We demonstrated this in a study published in Freshwater Biology here in 2014, where the regularity of occurrence of species in the regional pool and distance to the nearest source overrode any local habitat restoration measures.

What we can take from this is that restoration efforts require careful spatial planning for them to be worthwhile and cost effective.


These papers can be found at my website jdtonkin.github.io on the publications page.

References

Stoll, S., P. Breyer, J. D. Tonkin, D. Früh, and P. Haase. 2016. Scale-dependent effects of river habitat quality on benthic invertebrate communities — implications for stream restoration practice. Science of the Total Environment 553:495–503.

Tonkin, J. D., S. Stoll, A. Sundermann, and P. Haase. 2014. Dispersal distance and the pool of taxa, but not barriers, determine the colonisation of restored river reaches by benthic invertebrates. Freshwater Biology 59:1843–1855.