Habitat quality and biological community responses to innovative hydropower plant installations at transverse in-stream structures

Ecological assessments of the effects of hydropower plants (HPPs) are
often limited to aspects of entrainment, mortality, injuries, and passage
of fish, whereas the effects on riverine habitats and biological
communities in proximity to these structures are hardly documented. In
this study, aquatic communities comprising fish, macroinvertebrates,
macrophytes, and periphyton as well as physical and hydromorphological
parameters were investigated in upstream and downstream river sections at
five transverse structures at different seasons before and after the
installation of an innovative HPP. At all study sites, significant
differences in the aquatic community composition between the assessed
upstream and downstream sections were found after HPP construction,
indicating distinct serial discontinuity. Raising the damming target at
the sites Großweil and Au deteriorated the habitat conditions in the
upstream area close to the weir and presumably influenced in particular
the macroinvertebrate community, where a significant decrease in the
density of rheophilic mayfly, stonefly, and caddisfly larvae was observed
after HPP construction. Synthesis and applications: The installation of
different types of innovative HPPs has not improved the habitat conditions
for rheophilic species, contrary to the promises raised by the developers
of these concepts. Conversely, retrofitting existing weirs accompanied by
further damming even significantly increased the effects of serial
discontinuity and deteriorated the habitat conditions for rheophilic
species in upstream sections. As evident from the findings of this study,
habitat and biological community effects resulting from serial
discontinuity should become better integrated into ecological assessments
of HPP developments.