Sediment bypass tunnels and biodiversity
October 11, 2018,
Eawag scientists, in collaboration with Japanese colleagues, have now investigated the effects of sediment bypass tunnels (SBTs) on macroinvertebrates (e.g. insect larvae or amphipods). In the study, analysis of DNA metabarcoding data was used for species identification. This method is less time‑consuming and more precise than morphology-based assessments of macroinvertebrates.
Positive influence on biodiversity
The scientists assessed macroinvertebrate communities in three dam-fragmented rivers with SBTs (Reuss/Pfaffensprung, Rabiusa/Egschi and Albula/Solis) in comparison with two free-flowing rivers and two dam-fragmented rivers without SBTs. Overall, they collected almost 7000 larvae from 16 sampling sites and analysed 2.3 million gene sequences, which were assigned to 131 species.
Comparison of upstream and downstream communities showed that SBTs have a positive influence on macroinvertebrate diversity: species composition at downstream sites becomes increasingly similar to upstream sites the longer a tunnel has been in operation and the more frequently it is operated. In contrast, if no sediment is transported to residual reaches, marked dissimilarities are observed between upstream and downstream communities.
The results of the genetic analysis correlated well with the morphological assessments carried out in parallel. The scientists thus demonstrated that DNA metabarcoding is a suitable method for obtaining quantitative estimates of diversity.
Publication (open access)
Stonefly larva, family Perlidae. Typical for this family are the gills on the underside of the thorax.
(Photo: Silvana Käser, Eawag)