Abstract:
Removal of dams is increasingly being used to restore fragmented rivers and streams. The incentive is often to give migrating fish access to upstream spawning habitats, but dam removal may also bring other benefits, such as recovery of riparian vegetation and a more heterogeneous environment for aquatic invertebrates. Dam removal may also act as a disturbance on the system, releasing trapped sediments to downstream reaches. Depending on the amount of sediments in the former reservoir this disturbance may be transient or act over a longer time period. Whether dam removal is beneficial or not to the ecosystem may therefore depend on the type of organism. We have studied the effect of dam removal on riparian vegetation and benthic invertebrates in two Swedish streams over a period of 3 and 5 years respectively, and found that riparian vegetation generally benefitted from removal. Species richness increased, and species composition became more similar to a reference situation within a three year period. In contrast, benthic invertebrates seemed to be negatively affected by dam removal. While we saw no effects on community composition of benthic invertebrates, taxon richness decreased continuously over a five year period and total densities decreased initially but showed weak signs of recovery over the five year period. Our results also indicate that the response varies between invertebrate taxa
